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Greolt
03-19-2007, 12:35 AM
My CNC router is pretty much up and going. (just gotta get a better spindle)

However you pretty soon realise that securing material to the table is a whole new can of worms.

Screw it down. Clamps don't reach far from the edge. Double sided tape. There has to be a better way. (nuts)

I'm going to have a go at making a vacuum hold down thingy.

I had a piece of acrylic (I think that's what it's called) 20mm thick that someone gave me. A bit beaten up but OK.

Got some quarter inch rubber stuff. Sort of foam rubber with an external skin.

Drew up a grid pattern in my cad program. 30mm squares with 3mm radius on the corners. 5.25mm channels in between.

Generated a toolpath in sheetcam. Didn't know how hard to push the 1/8th endmill I had.

So I went 1000mm per min. RPM? About half speed on the cheapy little router that is my temp spindle. Sounds like it's about to explode if I go faster. :eek:

1mm depth of cut. Could have gone deeper I think but I did not want to break the only little end mill I had seeing it was the weekend and couldn't get another. :)

Set my machine going and went and watched TV. Took about 90 mins.

Greolt
03-19-2007, 12:56 AM
Drilled an inlet. Maybe that should be called an outlet. :D

Fitted a quick release air coupling.

Have no vacuum pump yet. I want to see how well this works before splashing out the hard earned on one of those. :)

So I pressed the little shop compressor into service. Connected up the hose to the inlet side just to see what will happen. :rolleyes:

Well it worked @#&%* brilliantly. :banana: No way that piece of board was going anywhere.

Sucked it down like you wouldn't believe. Well a lot of you would of course as you've had plenty of experience with vacuum tables. :)

Now where am I going to get one of those nifty little vacuum pumps like they have in the US ?????

.

Geof
03-19-2007, 01:12 AM
...So I pressed the little shop compressor into service. Connected up the hose to the inlet side just to see what will happen. :rolleyes:

Well it worked @#&%* brilliantly. :banana: No way that piece of board was going anywhere....

Now where am I going to get one of those nifty little vacuum pumps like they have in the US ?????

.

Why not keep on using a little compressor? I was planning on experimenting with one sometime but I would be happy to learn from your experience.:)

Greolt
03-19-2007, 01:37 AM
Yeah I am thinking about that Geof.

They can be had quite cheaply here. I thought I could reverse the head and hook it up permanently that way.

Have to replace the presure switch with a vacuum type and guage as well.

Then you would have a all in one unit with a good size reservoir.

Don't see why it would not last just as well as when it is compressing.

It's real noisy though. :mad:

A silencer on the air out port would maybe help a little bit.

Greg

sailfl
03-19-2007, 04:00 AM
You are aware of this site?

http://www.joewoodworker.com/veneering/welcome.htm

He has a whole thing about vacuum press and pumps you build.

Greolt
03-19-2007, 04:17 AM
Had a look at that Sailfl. Good site. Lots of info.

Unfortunately the most important or at least the most expensive part is the pump.

We have different voltage here in Aus.

And changing our dollars to yours then paying freight makes things very pricey. :eek:

sailfl
03-19-2007, 04:23 AM
I completely understand about the cost thing. But I thought you might like to look at the information. That is part of the price you pay for living down under.

ger21
03-19-2007, 07:20 AM
Not sure what the shipping would be, but you can get a 220V pump from www.surpluscenter.com for $89 US. I just got one the other day.

Geof
03-19-2007, 09:34 AM
In the days when all car engines were carburetted with vacuum operated winshield wipers you could just run a tube out to the vacuum connection on the intake manifold and leaving it idling in the driveway.

Greolt
03-19-2007, 05:26 PM
Not sure what the shipping would be, but you can get a 220V pump from www.surpluscenter.com (http://www.surpluscenter.com) for $89 US. I just got one the other day.
Hey thanks for that Gerry. I have requested a shipping price.

What are you using it for? Do you think it will keep up with vacuum clamping as above?


In the days when all car engines were carburetted with vacuum operated winshield wipers you could just run a tube out to the vacuum connection on the intake manifold and leaving it idling in the driveway.
We're showing our age now aren't we Geof. :D

I remember they used to slow to a crawl when you put your foot down and go like the clappers as you eased off. :)

Geof
03-19-2007, 05:36 PM
Hey thanks for that Gerry. I have requested a shipping price...

Make sure you are sitting down when you get the shipping price. That is if they will give you one. We ship metal parts to Sydney (Allambie Heights) and it costs a few penneis.

ger21
03-19-2007, 06:02 PM
It was $17 to ship to Detroit, probably at least $75 to ship to you. I should also mention that although they are advertised as new, mine was a bit banged up. Consider them "unused". They are not in any factory packaging, so may be dented a little. Mine does work fine, though.

Anyway, I'm going to use it for both veneering and a hold down system, whenever I finally get my router done. I was already using a Joe Woodworker venturi setup, but it puts a strain on my compressor. I'm going to set it up just like the JoeWoodworker system.

I hooked up the Gast pump to my reservoir in place of the venturi, and it pulled 26"Hg pretty quickly. If you get a very good seal, it should work just fine. The Joewoodworker site has a small section on clamping, and he uses the same system as for veneering. http://www.joewoodworker.com/veneering/vacuumclamping.htm

At work today I was making a new set of vacuum pods for our router. If I get a chance this week, I'll try to make a small clamping jig to try with the new pump.

For good quality gasket material, check out www.allstaradhesives.com

Geof
03-19-2007, 06:48 PM
I just went online to UPS and got a shipping quote for 50lbs from Chicago to Sydney. Around $400 so now you know what the upper limit should be.

ger21
03-19-2007, 06:54 PM
It says 31 lbs I think, but I don't think it's that heavy.

Geof
03-19-2007, 07:00 PM
Yikes!! I also looked up US Postal Service rate; $340. Which surprises me.

epineh
03-19-2007, 08:29 PM
Here is a crazy thought (yes I am full of them :D))

If by chance you had access to a working CNC router :stickpoke

You could possibly cut out a simple multi bladed impeller design similiar to a standard vacuum cleaner's, make a matching housing, keeping things simple, 2D outlines, and hook up a motor, something like one of those small fan motors they use on coldroom's you MAY be in business... might be worth a try.

Of course you would have to find someone who had a CNC router heh

Russell.

Geof
03-19-2007, 08:35 PM
Here is a crazy thought (yes I am full of them :D))

If by chance you had access to a working CNC router :stickpoke

You could possibly cut out a simple multi bladed impeller design similiar to a standard vacuum cleaner's, make a matching housing, keeping things simple, 2D outlines, and hook up a motor, something like one of those small fan motors they use on coldroom's you MAY be in business... might be worth a try.

Of course you would have to find someone who had a CNC router heh

Russell.

You will not get enough vacuum. A really good multistage centrifugal fan will pull a static negative pressure of maybe 1/3 of an atmosphere. This is not really adequate for vacuum holddown unless you are working with large intact areas.

Greolt
03-19-2007, 10:29 PM
Eloid you posted a PM to me with a question but I am unable to answer via PM because your inbox is full.

So I will respond here. :)

Look at the pic in the post,

http://www.cnczone.com/forums/showpost.php?p=273499&postcount=2

You can see that I have temporarily hooked my hose to the side of the compressor head that usually sucks the air in.

It normaly just has a filter on there.

And I also temporarily disconnected the side that goes on to the tank or pushes the air out.

Hope that is clear.

Greg

Greolt
03-20-2007, 06:26 PM
The Surplus Center have said approx shipping cost is $160

So all up it would be about $335 of our Aussie dollars. I think I will keep looking for a second hand one here.

But for now I am going to get one of these cheap air compressors and turn it into a "joe woodworker" style of unit.

I won a cheap vacuum switch on ebay so the rest should be easy. I'll let you know how I get on. :wave:

Greg

Greolt
03-22-2007, 04:07 AM
Well I got myself a 2 hp compressor, direct drive, 30 liter tank for $50.

Brand new, the plastic shroud over the motor / compressor had been cracked in shipping.

Repaired and good as new. :) Well it doesn't look as good as new but....:rolleyes:

Directly attaching a fitting to the head (the suck side) works like a dream.

Got a gauge. vacuum switch, check valve and a couple of other bits coming from an ebay purchase and from JoeWoodworker.

Can't see why it won't work to make it cycle on and off using the air tank to hold the vacuum.

So we'll see. Just gotta wait on that international post. :p

crocky
03-22-2007, 08:34 PM
Well done, it sounds like you are well on the way now and you should have a nice vacuum system when the rest of it turns up :)

You did really good getting a compressor for that much :)

epineh
03-31-2007, 05:53 AM
Funny coincidence, this week I was working at a hospital and noticed a medical vacuum pump sitting in the dungeons of maintenance section, asked a few questions about its future, and now it sits under my router :)

I don't know if it will be any good for a large table, but it definately sucks !!!

The guage goes from zero to 760mm Hg(I'm guessing mercury), don't know what that translates to for CNC apps but it has a little knob that lets you adjust the vacuum totally in that range. It is nice and quiet as well, not that you can hear much over the noise of the router. I will post pics as soon as my wife gets back with the camera tomorrow.

Russell.

epineh
03-31-2007, 05:59 AM
Just did some research (googling :)) and it seems 760mm Hg is one atmosphere, wonder if this is enough ?

Russell.

ger21
03-31-2007, 07:42 AM
and it seems 760mm Hg is one atmosphere, wonder if this is enough ?


I hope so, because it's impossible to get any more. :) You just need to make sure you have a very good seal. And remeber, vacuum force is based on area, so, the smaller the part, the less force you have. But at max vacuum, a 100mm square should be able to pull with over 200lbs of force.

epineh
03-31-2007, 08:22 AM
Are you saying that 1 atmosphere is a total vacuum ? Or is that the limitation of most pumps...never mind, I just worked out what you mean, at sea level 1 atmosphere is all the pressure there is to "push" against a vacuum.

I especially liked how you used mm for the hole size :cheers: at least this Aussie knows what you mean, although you used lbs for the force, lucky that we still use lbs as a measurement of fish weight (never worked out why that is so, also we still use feet to measure boat length, so much for SI units!!!)

And how do pounds get changed to lbs ?

Russell

ger21
03-31-2007, 08:26 AM
And how do pounds get changed to lbs ?


As long as you understood what I meant, it really doesn't matter (I don't know) :)

It's too early for me to figure out Kilograms or Newtons, so lbs it is. Our router at work uses mm's, so I'm somewhat fluent in both inches and mm's.

ger21
03-31-2007, 08:29 AM
Actually, you don't need a hole that size. Just the size of the perimeter of your seal. You want a small channel just inside the seal, and connect this channel with a grid of channels to distribute the vacuum to the entire part. And you're actual vacuum hole can come into this grid of channels anywhere, but doesn't need to be very big. A 6mm hose should work fine

epineh
03-31-2007, 08:34 AM
As long as you understood what I meant, it really doesn't matter (I don't know) :)

It's too early for me to figure out Kilograms or Newtons, so lbs it is. Our router at work uses mm's, so I'm somewhat fluent in both inches and mm's.

To be honest I only thought of it when I read your post - how we get lbs from pounds, and I will use a similiar excuse to yours, it is too late here to convert ANYTHING.

I can understand pounds (and lbs) but those inches are crazy talk :stickpoke

epineh
03-31-2007, 08:39 AM
Actually, you don't need a hole that size. Just the size of the perimeter of your seal. You want a small channel just inside the seal, and connect this channel with a grid of channels to distribute the vacuum to the entire part. And you're actual vacuum hole can come into this grid of channels anywhere, but doesn't need to be very big. A 6mm hose should work fine

Ah, you have just answered a couple of things I was wondering about, for a reasonably large pump, it had a small hose, I wasn't sure it would work for hold down purposes, and also explained why the vacuum tables have that network of "slots" forming a grid of sorts.

So long as I can seal the parts to be cut it sounds like it should be apples :)

Russell.

ger21
03-31-2007, 09:38 AM
With a small pump, you need a very good seal. Big commercial machines use huge pumps that draw lots of volume, but can't pull as much vacuum, which makes up for leakage, but they actually can't hold as strong as a smaller pump with a good seal.

Geof
03-31-2007, 05:05 PM
Russell; with a small capacity but high vacuum pump like than you may find a large reservoir tank useful.

When you first apply the vacuum your parts will nearly always leak a bit around the seal and the small capacity never overcomes the initial leakage so you never get a seal.

With a reservoir connected through a large diameter ball valve you can pump the reservoir down to a good vacuum and then apply this rapidly to the part hold down and there is enough initial flow to pull everything down and form a seal.

I would also go with vacuum lines as large as possible on the ball valve side. Try sucking hard through a long piece of 6mm ID plastic tube and compare it with 10 or 20mm. Your pump or vacuum tank, has a similar problem with the smaller size.

ger21
04-01-2007, 12:16 AM
Try sucking hard through a long piece of 6mm ID plastic tube and compare it with 10 or 20mm. Your pump or vacuum tank, has a similar problem with the smaller size.

Geof, if the pump inlet is 1/4" (6mm) would the 10-20mm hose still help, or are you limited by the inlet size? Or does the larger hose act like a small reservoir?

Russel, if you haven't already, look at the www.joewoodworker.com articles on vacuum pump reservoir setups.

Madclicker
04-01-2007, 12:47 AM
Geof, if the pump inlet is 1/4" (6mm) would the 10-20mm hose still help, or are you limited by the inlet size? Or does the larger hose act like a small reservoir?

Russel, if you haven't already, look at the www.joewoodworker.com articles on vacuum pump reservoir setups.

Any volume acts as storage reservoir. The more the better and the closer it is to the application the better.

I use 2 methods of vacuum clamping:

High volume, low quality....works very well with larger panels.

High quality, low volume....works well with smaller, not-so-porous parts. Works poorly with larger wood parts that bleed the vacuum.


I love vacuum clamping. I save an enormous amount of work using it.

Greolt
04-01-2007, 12:48 AM
Russell

You lucky %#@*#. I wish I could stumble on a vac pump like that. :D

I reckon it would work most adequately with a similar devise like I started this thread with.

Because the seal can easily be made pretty good, it does not need much volume capacity.

You just gently press down on the material and the seal works and the vacuum takes over straight away.

Get a bit of some sort of stable non porous material and machine up a grid to fit some gasket type material.

No need to spend more than a few bucks.

You're a "Give it a go" sort of bloke. So get going. :stickpoke

Greg

Greolt
04-01-2007, 12:57 AM
Hey Madclicker/Steve

You posted while I was typing. One finger. :p

I would love to read more about your methods and systems.

Is there existing threads I could read back on?

If not maybe you could start one with some pics and wisdom to dispense. :D

I reckon this is an area more homebuilt type blokes (or sheilas :)) should be getting into.

Greg

Madclicker
04-01-2007, 02:06 AM
Hey Madclicker/Steve

You posted while I was typing. One finger. :p

I would love to read more about your methods and systems.

Is there existing threads I could read back on?

If not maybe you could start one with some pics and wisdom to dispense. :D

I reckon this is an area more homebuilt type blokes (or sheilas :)) should be getting into.

Greg

My first build log keeps going farther back. I post things like the vacuum table, but it never gets much interest. Big deal to me!

http://www.cnczone.com/forums/showthread.php?t=14863&page=11

Don't have any pics on my lab grade vacuum setup yet.

epineh
04-01-2007, 06:35 AM
Thanks for the tips guys, I am planning to make a reservoir, I was going to use something like that as a type of filter anyway, now I will just make it bigger and include some valves to control operation, as Geof mentioned set it up so a vacuum is formed initially then "opened" to quickly grab the piece to be machined. I also noticed vacuum filters on the Joe Woodworker site, that will be on the list as well.

Geez this would have been handy while I was milling PCB's ah well I still have those pesky dinosaur skeletons to make for the kids, hopefully they will get them THIS christmas.


Russell

You lucky %#@*#.


Ha, I thought the same thing once I found out I got it for free :)

Geof
04-01-2007, 10:23 AM
Geof, if the pump inlet is 1/4" (6mm) would the 10-20mm hose still help, or are you limited by the inlet size? Or does the larger hose act like a small reservoir?...

I wasn't totally clear in my phrasing; when I said on the ball valve side I meant between the reservoir tank and the work hold down. You want unobstructed rapid flow here to overcome initial leakage. On the pump side just keep the line as short possible to the tank.

Greolt
04-06-2007, 04:00 AM
The bits I was waiting on arrived so time to finnish this little project off.

Made the connection from the "suck" side of the compressor head to the tank.

I reused the existing check valve at the tank end of the connection.

Just reversed it. Works OK. Maybe a little high on the "crack" pressure. (yes that's the proper term :) )

Fitted up the gauge, pressure switch and outlet fitting.

I had the on/off switch in my junk box. Was able to fit the vacuum switch inside the switch box which made things neat.

Tried it out and it pulls about 22"hg. Not too bad.

When I tried the gauge direct to the hose coming off the compressor I had 26"hg

So I've lost a little bit. I think it is the check valve which could be bit lighter on the crack pressure.

Remember it was not designed to be used in a vacuum setup.

Anyhow it works great for what I am doing. Cycles on for about 15 seconds and off for about a minute when used on the vacuum hold down thingy.

Does not even get warm. Should be able to do that for years. Not bad for $50 plus gauge and vacuum switch. :)

Here is some video. EDIT: YouTube was not so good so here is a better link

http://web.aanet.com.au/greolt/Vacuum.wmv

.

epineh
04-06-2007, 04:41 AM
Nice work (as always) Greg, I especially like the demo piece :)

Youtube does its own compression thing so the video shown will be a lower quality than what you uploaded, no matter, we can see what is going on.

Cheers.

Russell.

Kipper
04-06-2007, 03:24 PM
Nice "KISS" solution :salute: At work we use vacuum priming systems on our pumps 1bar or 29"hg and we have the industrial 2bar flavour rotary vane compressors....You just gave me an idea :beer:

Vac-Clamp
05-01-2007, 07:29 PM
Have a look at V-Clamp (http://www.vac-clamp.com/)vacuum hold downs.
They run on compressed air and they work. An inexpensive, and complete, solution for holding you work piece.
CNC application information on this page (http://www.vac-clamp.com/vc%20cnc.htm)

Geof
05-01-2007, 07:34 PM
Have a look at V-Clamp (http://www.vac-clamp.com/)vacuum hold downs.
They run on compressed air and they work. An inexpensive, and complete, solution for holding you work piece.
CNC application information on this page (http://www.vac-clamp.com/vc%20cnc.htm)

Maybe not inexpensive when you take into account the cost of the compressor.

And be careful about just hooking them up to the shop air that supplies all the other machines. They all start flashing red lights when the compressed air vacuum hold down steals all the air and the central compressor cannot keep up.

Vac-Clamp
05-01-2007, 07:46 PM
Hi Geof,
It sounds like you are having problems with your Vac-Clamp.

Could you please advise what air pressure you are running them at?
Are you using a VC4 or VC5?
How many are you using at one time?
Lastly what is the size of your compressor?

A VC4 at a supply pressure of 80 psi uses 1cfm. A double sided VC5 uses 2cfm at the same pressure.
We have a display unit that we use at trade shows, that has a total of 4 clamps (3 VC4's and one Double sided VC5) the compressor is a $99.00 (Australian dollars) 2 horsepower item. It keeps up.

Greolt
05-01-2007, 08:03 PM
Have a look at V-Clamp (http://www.vac-clamp.com/)vacuum hold downs.

Yeah I think they are fine and probably a good product for bench top use.

But my point is that a lot of users on this forum already have a machine easily capable of

making their own vac hold down device of a very similar type.

Also whatever size they want.

Providing the vacuum to use it is another matter.

My cheap compressor mod is working great so far. :)

Greg

Geof
05-01-2007, 08:18 PM
Hi Geof,
It sounds like you are having problems with your Vac-Clamp.


Sorry I did not realise you were touting your products in a thread.

I read it quickly and thought you were referring to generic compressed air vacuum generators. My experience is that to get any type of decent volume flow to compensate for leakage the compressed air consumption is large. Yor product is designed for non-porous materials which may mean low air consumption but it also means conditions have to be ideal to have a zero leak situation.

Vac-Clamp
05-01-2007, 09:00 PM
I put forward the V-Clamps in this discussion because they work, they are cost effective and they are an alternative. They are configurable to a range of applications and machines.

We have more than a few people using our Vacuum hold downs on CNC machinery, with excellent results.

About the only material that we have a problem holding is raw MDF. Coated MDF negates this problem.

Sizing of the pad meant that we could work with low porosity materials as well as non-porous ones as well.
We looked at the flow of low porositiy materials for a given surface area. The surface area of the pad has been matched to the vacuum generator to provide more than useful holding power on materials such as chipboard/ particleboard.

The vacuum generator is built into the pads so you don't have to modifiy your compressor. Indeed you can chain them together to build them to whatever configuration you need.

I simply wanted to make people aware that such an item existed, rather than them "re-inventing the wheel"

If your system works that's great.

Vac-Clamp

Greolt
05-01-2007, 10:17 PM
About the only material that we have a problem holding is raw MDF. Coated MDF negates this problem.

Yeah it's unreal how much air raw MDF lets through isn't it.

I put a piece of 18mm MDF on and can feel the air getting sucked through just by putting the flat of my palm on it.

That makes my modified compressor run all the time and not cycle on and off. :)

Still holds it good though.

Greg

Greolt
05-01-2007, 10:35 PM
....................... so you don't have to modifiy your compressor.

.....................rather than them "re-inventing the wheel"

There is no doubt that will appeal to a lot of your users.

However on this forum we are sharing ideas among the type of people many of whom have built their own CNC controlled router.

Taught themselves to use Cad / Cam software and cut all sorts of things on their machines.

These people tend very often to like to make their own devices and have the skills to do it.

I personally wish you every success with your product and have no problem at all with you talking about it on this forum. (especially being an Aussie product :))

Greg

Vac-Clamp
05-01-2007, 10:37 PM
Hi Greolt,
If you want to get a better hold with MDF us a sanding sealer or watered down PVA adhesive on one side, and allow it to dry. Put this side on your vacuum pucks.
You will find the increase in holding force will give you a better finish on the edge.

I also had a look at the modified compressor that you have used. Nice job.
I assume that the receiver is now the "reservoir". Have you had a chance to put a filter in-line?
BTW, the compressor that you have modified is pretty much identical to the one we have used on the trade display, without the modification of course.

Vac-Clamp

Greolt
05-01-2007, 10:45 PM
Vac-Clamp

Do you think I need a filter? I spose long term it might be an issue.

The air comes into the reservoir at a different point to where the copresssor "sucks"

The thing to bear in mind here is that the compressor cost me $50 so unless there is a real cheap way of installing a filter. Who cares. :D

Greg

Vac-Clamp
05-01-2007, 11:11 PM
Greolt,
Might be worth having smaller reservoir before the main reservoir made from pvc pressure pipe fittings. Have the inlet and outlet at the top, and have a screw off fitting at the bottom.
That way when you have some rubbish get into the vacuum line it will fall out in the primary (palstic) reservoir, which can be cleaned out, rather than the steel one that can't.
Your setup might have cost $50.00, but how much to replace.

I built my first CNC machine some six years ago, and faced the same problem as a lot of builders face... how do I hold the workpiece down. The first hold down that I made was "loaned" to a friend. It is still on loan, and is still being used frequently.
This is why I have put in the occaisional posting on this forum.
Vac-Clamp

Greolt
05-01-2007, 11:46 PM
Your setup might have cost $50.00, but how much to replace.
Your point is quite valid however I'm not much concerned.

When I bought the compressor I was not at all sure it would work well in the configuration it is now.

My thinking was the reservoir with wheels and all would make an exellent (and cheap) base to mount a proper vac pump.

It would cost me more in materials alone to construct a reservoir out of plumbing fittings etc. JoeWoodworker style.

Over the next few years or whatever that this setup lasts, I will keep my eyes open for a cheap second hand vac pump to mount on top of it.

So money spent on the tank, vac gauge and vac switch will still be good.

The way I look at it the motor/compressor unit on top is just a free bonus. :)

Greg

mhasting2004
05-22-2007, 01:18 PM
Hi Greg

Just reading through your build...nice. Must get off my butt and get mine going.
I'm also one of those lucky ******** that has a nice big Gast pump (along with most of the other pieces to build my gantry router) and would highly recommend you put some filtering in between the hold down and the pump. Its not the dust getting into your tank you need worry about but it going through the pump. It will stuff it up rather quickly I would wager.


Cheers
Mark
Central Coast NSW

catsam
06-10-2007, 04:26 PM
wow this looks a good idea i might make one off the for my mill when i finish makeing it do you have any more pics of it

Greolt
06-11-2007, 07:47 AM
wow this looks a good idea i might make one off the for my mill when i finish makeing it do you have any more pics of it
There is really not much more to show. Pretty simple really. :)

But if there is particular detail you're interested in let me know and I'll take a pic.

Greg

DrewSmith007
06-12-2007, 10:46 AM
I didn't take the time to read the whole thing, so someone may have already said this, but i read somewhere the other day you can use a refridgerator compressor in reverse, like you did with your compressor, as a vacuum pump. I just don't know how strong they are. You shouldn't have any trouble finding one of those in Austrailia, I would think.

epineh
06-12-2007, 08:13 PM
I didn't take the time to read the whole thing, so someone may have already said this, but i read somewhere the other day you can use a refridgerator compressor in reverse, like you did with your compressor, as a vacuum pump. I just don't know how strong they are. You shouldn't have any trouble finding one of those in Austrailia, I would think.

They are all in use... keeping beer cold :D

Geof
06-12-2007, 08:42 PM
They are all in use... keeping beer cold :D

Go on, since when were Aussies civilized enough to keep their beer cold?:D

johnmac
06-12-2007, 10:30 PM
The compressor in reverse will work better than a refrigerator compressor as it pumps a larger volume of air, thus overcoming small leaks around the work piece. Keep watch on the oil, as some may suck up past the rings.

Greolt
06-12-2007, 11:55 PM
Keep watch on the oil, as some may suck up past the rings.

Good point. I'll keep that in mind. :)

Greg

epineh
06-13-2007, 12:22 AM
Go on, since when were Aussies civilized enough to keep their beer cold?:D

Ha, well it needs to be cold to help cool down after a long day of bare handed crocodile wrestling :p

dodgy74
07-07-2007, 02:33 PM
I've been doing vacuum forming for a couple of years and the best pump I've used has been the refrigerator compressor. I can pull a vacuum of 28.5 in hg. (which out does the small commercial pumps I've spent hundreds on) It's virtually silent, the only noise is from the fan I use to keep them cool, and they're free. I'm lucky enough to live in an area where people like dumping trash in the middle of no where (refrigerators included) so I have access to as many pumps as I want for virtually no cost.

Here's the link to what got me started...
http://www.dream-models.com/eco/vacuumpump.html

These work so well that I doubt that I will ever use anything else and are so cheap to set up that I have one at ever layup station.

I've yet to try using one for clamping but they do perform better than the actual pump that I purchased for material clamping so I'm assuming it would work quite well. If I ever try it for clamping material I'll be sure to post the results.

Regards,
David

epineh
07-07-2007, 08:21 PM
Great link David !

I have bookmarked it and will definately keep it for 'Ron

Cheers.

Russell.

thesaent14
08-02-2007, 12:58 AM
really nice work man is there a way any one can tell me how the vacum should work and one more Q? what happens if i have to cut trow the pis i will like to make me one to cut acrylic can any of you guys help me i have search and look around for the actual concept but only pictures not the real meaning on how work for a cnc machine

btw
i will like to make one for my hall table is this possible

thanks

manny

Greolt
08-02-2007, 02:40 AM
The vacuum plenum I made for the router is so usefull I knocked one up for the X3 mill.

Uses the same 1/4" round rubber as a gasket. Acrylic again. Another piece I had lying around.:)

It is machined on the back and has locating runners that fit snug in the tee slots so that makes it dead square without even thinking.

Bolts down with tee nuts. Has a shoulder at 0,0 or lower left so material is always square.

And works a treat. :)

Greg

.

Greolt
08-02-2007, 05:43 AM
A little video of it in action :)

http://www.youtube.com/watch?v=U9rqj96b4XE

Greg

crocky
08-02-2007, 06:46 AM
You have been busy again :)

I won't say anything about the spelling :rolleyes: either!

Bob

zoltan
08-02-2007, 12:37 PM
Greg,

Could you provide some drawings of your reversed compressor's connections and of the vacuum clamp?

Thank you.

Zoltan

Greolt
08-03-2007, 07:09 PM
Sorry Zoltan I don't have drawings. You'll have to look at the photos.

Any specific questions and I will try to help.

Greg

thesaent14
08-03-2007, 10:40 PM
what happens if you cut trow the material

Greolt
08-04-2007, 12:05 AM
This setup is not suitable for operations that cut "trow" the material.

It could be adapted by sealing off zones that will not be cut through. However I do not wish to mark the plenum as would happen in that case.

The biggest hurdle is obtaining a vacuum source. The making of the plenum is actualy the easiest part.

So other plenum styles could be made and would be a better way to go if that is what you need.

I keep calling it a plenum but I don't think that is correct. :)

Greg

Geof
08-04-2007, 12:20 AM
.....I keep calling it a plenum but I don't think that is correct. :)

Greg

plenum

Pronunciation: 'ple-n&m, 'plE-
Function: noun
Etymology: New Latin, from Latin, neuter of plenus
1 a : a space or all space every part of which is full of matter b : an air-filled space in a structure; especially : one that receives air from a blower for distribution (as in a ventilation system)
2 : a general assembly of all members especially of a legislative body
3 : the quality or state of being full


Taking into account that you are taking air out and it is a vacuum, i.e. less than full, perhaps you should be calling it a "munelp" :D

Seriously, I think your terminology is quite correct.

Greolt
08-04-2007, 12:41 AM
G'day Geof

Yeah I did a little search and No. 2 made me think it was wrong.:)

n. pl. ple·nums or ple·na (plhttp://img.tfd.com/hm/GIF/emacr.gifhttp://img.tfd.com/hm/GIF/prime.gifnhttp://img.tfd.com/hm/GIF/schwa.gif, plhttp://img.tfd.com/hm/GIF/ebreve.gifnhttp://img.tfd.com/hm/GIF/prime.gifhttp://img.tfd.com/hm/GIF/schwa.gif) 1. An assembly or meeting with all members present.
2. A condition, space, or enclosure in which air or other gas is at a pressure greater than that of the outside atmosphere.
3. The condition of being full; fullness.
4. A space completely filled with matter.

Would'nt it be great if that was the biggest worry in life Hey! :D

Greg

Geof
08-04-2007, 12:52 AM
G'day Geof

Would'nt it be great if that was the biggest worry in life Hey! :D

Greg

Right at the moment sitting in front of the computer with a mug of beer in one hand that is the biggest worry of the moment if not the day :) .

Greolt
08-04-2007, 01:11 AM
Enjoy :cheers:

acondit
08-04-2007, 06:21 PM
Greolt,

Maybe its an anti-plenum??? Or maybe who really cares, since it works and we know what you mean?

Alan

Greolt
08-04-2007, 06:35 PM
.............Or maybe who really cares, since it works ............

G'day Alan. That's for sure. We were just having a bit of fun. :)

acondit
08-04-2007, 10:47 PM
G'day Alan. That's for sure. We were just having a bit of fun. :)

I know, but I like using words correctly (when I can). So if you figure out the correct word I would like to know it. It doesn't really seem like a vacuum chamber is the correct term for that plate. It seems to be just exactly the opposite of the definition that was given for "plenum". What about calling it a "vacuum chuck"?

Alan

Geof
08-04-2007, 10:57 PM
It seems to be just exactly the opposite of the definition that was given for "plenum". What about calling it a "vacuum chuck"?

Alan

Okay call it a munelp like I suggested :) .

Plenum seems to be a generally used word to describe a chamber (partially) filled with vacuum.

Manifold is also used so I went looking for a definition; this seems an even worse choice than plenum.

A manifold is a topological space that is locally Euclidean (i.e., around every point, there is a neighborhood that is topologically the same as the open unit ball in ). To illustrate this idea, consider the ancient belief that the Earth was flat as contrasted with the modern evidence that it is round. The discrepancy arises essentially from the fact that on the small scales that we see, the Earth does indeed look flat. In general, any object that is nearly "flat" on small scales is a manifold, and so manifolds constitute a generalization of objects we could live on in which we would encounter the round/flat Earth problem, as first codified by Poincaré.

Greolt
08-04-2007, 10:59 PM
I often just call it a "Vacuum Hold Down Thingy" :)

Geof
08-04-2007, 11:22 PM
I often just call it a "Vacuum Hold Down Thingy" :)

But if you were pedantic and wanted to be technically correct it is really an "atmospheric hold down thingy".

acondit
08-04-2007, 11:29 PM
But if you were pedantic and wanted to be technically correct it is really an "atmospheric hold down thingy".

Geof,

I can live with either one of those as being the technical name for it.

Alan

epineh
08-05-2007, 12:44 AM
What about "Atmospheric differential clamping mechanism" :D

Hey you guys started this...

Russell.

Geof
08-05-2007, 12:47 AM
Gas Enhanced Gravitational Clamping?

Norsksea
08-10-2007, 10:03 AM
The vacuum plenum I made for the router is so usefull I knocked one up for the X3 mill.

Uses the same 1/4" round rubber as a gasket. Acrylic again. Another piece I had lying around.:)

It is machined on the back and has locating runners that fit snug in the tee slots so that makes it dead square without even thinking.

Bolts down with tee nuts. Has a shoulder at 0,0 or lower left so material is always square.

And works a treat. :)

Greg

.

Hi Greg
This is a great little setup you made.
Just got my machine going and I will be making one of these, very nice.
Frank

Cartierusm
09-08-2007, 02:49 PM
I must admit some of you people are very creative. Anyhoo, I'll weigh in with my suggestion. I haven't yet tried it but bought the components a while ago. I will be trying it out today and I'll let everyone know how it's turns out.

So I was cruising the harborfreight.com website and came across a vacuum thing for evacuating A/C systems and it's basically what some of you have a ventrui system that uses an air compressor, but it's cheap. I also figure most of us have air compressors. So I'm going to try it out soon. Here is a link to what I bought.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=3952

Cartierusm
09-08-2007, 04:24 PM
So I just got done testing out the system I built. In all honesty it took since my last post about a 1/2 hour. The rest of the time I was testing it out with various material. Below are some pics. Basically I bought the Harbor Freight Air Vacuum Pump removed it from the housing and replaced the Vacuum input fitting with a Air Compressor Quick Release Fitting. All the fittings on the Vacuum Pump were NPT (National Pipe Thread - American Standard form of thread for pipes). I then put a quick nipple on the air inlet side. Tapped with 1/4-18 NPT Pipe Tap to a hole in a piece of laminated plywood and put some window weatherstripping to hold the piece. It worked like a charm. A small piece didn't seem to move at all. When I put the weatherstripping on to cover the large piece I could move the piece a hair when the vacuum was on, but that was using a lot of force. I had my compressor at 110 PSI, but the directions say I could use the Vacuum pump from 75-180 PSI. This was just a test piece. I figure once I embed the proper gasket material into a piece of plexiglass or the like it will hold like a SOB.

ger21
09-08-2007, 04:28 PM
I use the same HF venturi for veneering. To keep your compressor from running constantly, build a reservoir with a vacuum switch and check valve. Free plans at www.joewoodworker.com

Greolt
09-08-2007, 06:02 PM
Cartierusm

At that price it is certainly cheap enough to experiment with. :)

Is that al block in the pics the innards of the unit? Did you just discard the case?

I was expecting to see the red box thing shown on the HF site.

Greg

Cartierusm
09-08-2007, 06:08 PM
I checked his website out but I don't think my compressor will run out. I have an 80 gallon 5 HP compressor. But you never know.

ger21
09-08-2007, 08:49 PM
Is that al block in the pics the innards of the unit? Did you just discard the case?


Yes, it's just a small aluminum block in the big red case. ;)

They're cheap, but not very efficient. An awful lot of air blows through mine.

Cartierusm
09-08-2007, 09:04 PM
Greolt, yes I just discarded the red box, the aluminum is the actual part. I just cut my first thing ever and it held real tight, no movement at all, oh I all ready incorporated it into my table permanently.

As I said I just cut my first part ever, I have no idea on how to use CAD yet but used a circle program in Mach 3. The circle came out perfect except a slight flat spot at the top and bottom of the circle, along the Y axis. I figure it's either deflection from the Z axis plate holding the router, I was using 1/2" aluminum, maybe I'll switch to 3/4". It could also be backlash, even though I'm using anti-backlash acme nuts. Only on the Y axis could I move the screw about 1/32" before moving the gantry. Maybe I'll try that.

As I built and setup this CNC router from scratch and have no previous experience I am concerned about the Heat of my Keling 425oz. motors. They are pretty hot, is that normal?

Cartierusm
09-09-2007, 01:13 PM
ger21, I think I will build the reservoir on joewoodworker as I have all the parts. I plan on building a vacuum attachment for my router to suck up the dust, but in the mean time I'm going to direct the air coming out of the venturi unit to clear the swarf away during cutting.

Vac-Clamp
09-09-2007, 07:25 PM
I have been reading this forum with a good deal of interest, as this is a target market for our vacuum clamps.
I have been curious to find out why the preference is for building your own as opposed to buying a clamping solution.
Is it a matter of cost, or the satasfaction of building it yourself, or have we not made the virtues of our products readily known throughout the CNC community?
Vac-Clamp

ger21
09-09-2007, 08:13 PM
Is it a matter of cost, or the satasfaction of building it yourself, or have we not made the virtues of our products readily known throughout the CNC community?
Vac-Clamp

Probably a bit of each. You can't really expect someone who's built their own CNC Router to actually buy a hold down system, can you? ;) And after the initial outlay for the vacuum device, making custom vacuum jigs and fixtures that fit ones own machine or workpieces is very inexpensive.

I think those are the main issues. Although I'm sure that a lot of people do not know the virtues of vacuum hold down as well.

Vac-Clamp
09-09-2007, 09:00 PM
Thank you ger21 for your insight.

So a combination of information about the whole field of vacuum clamping, plus the lack of information about our product, are the main reasons in your opinion.
This poses another question. Would it be beneficial to view, via video or similar, a vacuum clamp holding a heavy object to show the holding power of vacuum? The reason for the question is that Woodcraft (http://www.woodcraft.com) stores thoughout the USA have a DVD available to them showing such a demonstration.

Would this be a start?

Vac-Clamp (http://www.vac-clamp.com)

ger21
09-09-2007, 09:14 PM
So a combination of information about the whole field of vacuum clamping, plus the lack of information about our product, are the main reasons in your opinion.


Outside of this forum maybe, but for the members here, I'd say the price and the fact that they can DIY their own are the main factors why you don't see you're product being used here. Just a guess on my part.

Cartierusm
09-09-2007, 09:45 PM
I finished the vacuum clamp system as far as the equipment goes. I still have to figure out a table configuration in terms of: Do I route channels directly into the table top or mount a sacrificial board and then route channels in that then make extra one and just replace when they no longer hold air due to cuts into them?

I went ahead and mounted the vacuum components under the table and made they all nice and strong and out of the way. I decided not to build joewoodworkers system as it needs a $115 part, the pressure switch to turn the system on automatically. I have a huge compressor that will more than suffice. Here's some pics of the finished CNC router, vacuum clamp and soon to be finished vacuum dust collection system. I made a collection skirt for around the router out of some 10 mil plastic and it got sucked up into the vacuum hose. So I taped the individual skirt pieces together and that worked like a charm until the depth of cut got too great and then it got sucked into the vacuum hose too. I don't want to, if I don't have to, build a skirt out of that plastic fiber hairs they use on the dust brush for a vacuum because my clear plastic idea allowed me to watch and keep and eye on the cut. I think I'll remake it with stiffer plastic and then sew it to Velcro so I can take it from around the router when I need to change bits.

I don't know if I mentioned in this thread I was having problems making a perfect circle pocket. I noticed that the 1/4" router bit was chattering and deflecting a bit and I slowed the cut down and that didn't work it just moved the chatter point to a different point in the circle. This time I changed the bit to a 1/2" with 1/4" shank. The circle came out much better, but there is still a slight flat spot on the top and bottom of the circle (along the Y axis).

I always wondered - if the Y axis has to move a 50+ pound gantry and the X only has to move a 12 pound mass and I'm using stepper motors how does the program know to move them in unison? I didn't think Mach 3 got feedback from stepper motors or do the motors receive a signal and how fast to move those steps and the motors adjust torque to meet the signal code for it's speed? Because I'm sure the torques used by the motors are totally different.

sawmiller
09-09-2007, 10:16 PM
for me, vac-clamp, i looked at your system, good writeup of it here.. but
i wanted something that i could vary the size of, and make 3-4 small clamps if needed, and use for vac bagging if i ever decided to. so i bought a vac pump off ebay for $48 including shipping, and built this for about the same price as one of your clamps..
dan
might not be as professional,but it was and is fun.
your clamps are a good deal,i just wanted more flex room

Greolt
09-10-2007, 01:47 AM
I have been reading this forum with a good deal of interest, as this is a target market for our vacuum clamps.
I have been curious to find out why the preference is for building your own as opposed to buying a clamping solution.
Is it a matter of cost, or the satasfaction of building it yourself, or have we not made the virtues of our products readily known throughout the CNC community?
Vac-Clamp

My opinion for what it is worth. :)

Firstly your product to my way of looking at is is aimed at the hobby end of the market rather than the professional CNC user. Nothing wrong with that by the way.

Hobbiest types who make and use their own CNC machine are more inclined to see the Plennum, or whatever you want to call it, as the easy
part to make themselves. Whatever size and shape they need. Probably several of different styles.

The more challenging or expensive side is to provide a suitable supply of vacuum.

Your system provides a venturi vacuum generator which I believe some may see as not ideal.
Not very efficient, noisy and needs a good compressor to keep up. Some jobs can run for several hours. IMHO of course.:rolleyes:

And if they see it as satisfactory then there are options like the HF type seen above cheap.

However I do believe that many more hobby type users having once used vacuum would be very pleased
with it and your product could help to introduce more to it's benefits.

Perhaps you could get some who use your product on a router to post some examples with pics of it being used
with a variety of diferent jobs to show off it's versatility in a CNC environment.

Of course you could always send me a demo and I could use it for a while and post my thoughts. :D:D:D

Greg

epineh
09-10-2007, 02:08 AM
Of course you could always send me a demo and I could use it for a while and post my thoughts. :D:D:D

Greg

Lol didn't see that coming...you don't sell used cars by any chance do you Greg? :D

Russell.

Greolt
09-10-2007, 03:11 AM
Awww....... was I that obvious? :rolleyes:

epineh
09-10-2007, 05:35 AM
Maybe just a little...heh

Vac-Clamp
09-10-2007, 09:50 AM
I have have been reading the input from all, and may I say thank you for the constructive criticism.

A couple of points to clarify however, we have quite a few of the clamps being used on some quite high end CNC machines, Biessie is a notable user here in Australia. We find that some nested based machine owners like the option of being able to do pod type work on a nested machine. Biessie machines are fited with a side drilling attachment which requires the work piece to be lifted off the table, and our clamps are perfect for this application.

The perception still exists that all venturis consume vast amounts of air to provide vacuum. Some do. The main design criteria for us was to provide vacuum with an economical running cost. This meant a trade off. Size of hold versus air flow and consumption.
The VC4 clamps use 1 CFM at 80 psi supply pressure. But they yield a vacuum level to 80% of absolute (about -12psi) but they don't flow a lot of air. This is why MDF is next to useless on the clamps, it is just too porous. The other side to that is that almost anything else is excellent.

I will take on board the suggestion of posting some pictures in this forum, but I would also like to add a method of positioning a workpiece onto vacuum pods (not just ours) on a work table, quickly and efficiently.

The vacuum pump scenario is a fair and valid option, and can understand the satisfaction in building that too.

I also know that the baiting was quite well done, not perfect, just well done and the proposal is not out of the question.

Errol

P.S. I have just had a look at the work of art that is Cartierusm's vacuum table. Very nice. I notice that the top is made from chipboard. Have you coated the inside of the hole into the chipboard? A lot of air can migrate through the edge of chipboard, and reduce the level of vacuum.

Greolt
09-10-2007, 06:54 PM
Errol

I have a question about it that is related to use on a CNC router.

One of the main considerations for me when making my "plennum" was that the material when held must be exactly level or flat.

By that I mean when Z zero is set to the top of material it must be true right accross the extent of the job.

When doing Vcarving if this is 5 or 10 thou out then you might as well not Vcarve. It will show up badly particularly in lettering.

There are many other types of work where this is critical also.

So I had to get the relationship between the Gasket material and groove just right so the the material pulled
down hard against the plennum but the gasket still sealed well.

So my question is if one of your pods is screwed to a true table and a piece of say manufactured board (assumed true) of
apropriate size is held how true will it be to the Z plane?

Does that make sense?

Greg

ger21
09-10-2007, 07:46 PM
The perception still exists that all venturis consume vast amounts of air to provide vacuum.

I was going to mention that after reading Greg's post. Although the unit I have is inefficient, I've seen other units that are actualy ver efficient, although they can cost quite a bit more than the $10 I paid for mine. We have some vacuum workpiece hold down stands at work that seem to draw no air at all, yet hold very, very well.

Cartierusm, all you really need is the vacuum switch from Joewoodworker, for $24.50 and a valve like this.
http://www.surpluscenter.com/item.asp?UID=2007091018355845&item=20-1482&catname=air

It was a few years ago, but I built my system for about $60 for everything. I found a supplier of the switch for $15, but can't remeber where I got it from. Here's the manufacturer.
http://www.air-logic.com/catalogs.cfm?Action=ShowTopCategory&TopCategoryID=2

Vac-Clamp
09-10-2007, 07:57 PM
Thank you for the questions.

We had a chap wanting to use a VC4 on a Bridgeport type "knee" mill. He needed to pocket out smallish (100mm x 150mm) aluminium alloy, with a finish cut to the outside. Mechanical clamps would be in the way and freeze holding was not practical, so vacuum was the answer.
We found that our VC4 was not accurate enough straight out of the box so we suggested that the surface of the clamp should be skim cut after it was bolted down to true up the face.
Two things occurred, firstly the face of the clamp was straight and true, and the height of the clamp was known.


Your question regarding the gasket material is not as easy to answer.
If you work with thin and/or flexible materials, the middle of the workpiece will pull down to the face and will sit high on the seal/gasket. The only way around this is to cut your seal/gasket channel to within 0.75mm to 1.0mm of the height of you seal. In other words it will stick out only a small amount (0.75mm to 1.0mm, 0.03" approx)

To get more rigid materials to pull down against a "true" workface you should use a relatively tall 9.5mm (3/8"), or there abouts, gasket/seal. The channel that it sits in should allow 20% of the seal to compress. The reason for this is that the rubber seal has a rising compression rate. To explain, if you compress the seal 2mm and get 1kg of force pushing back when you compress to 4mm you are likely to get 4 or more times the force pushing back. (These figures are arbitrary and are for example only)

So go for a deeper groove with a taller gasket/seal, and see how that works out.

Errol at Vac-Clamp (http://www.vac-clamp.com)

digital_life
10-05-2007, 11:15 AM
anyone knows how much vacuum do i need at the table? im up to build a 3x2meters router, with 8 zones for vacuum. how much power will i need?

bgriggs
02-08-2008, 02:27 PM
Drilled an inlet. Maybe that should be called an outlet. :D

Fitted a quick release air coupling.

Have no vacuum pump yet. I want to see how well this works before splashing out the hard earned on one of those. :)

So I pressed the little shop compressor into service. Connected up the hose to the inlet side just to see what will happen. :rolleyes:

Well it worked @#&%* brilliantly. :banana: No way that piece of board was going anywhere.

Sucked it down like you wouldn't believe. Well a lot of you would of course as you've had plenty of experience with vacuum tables. :)

Now where am I going to get one of those nifty little vacuum pumps like they have in the US ?????

.

I don't understand how the air is evacuated on your table. You drill a hole through the side of the glass to mount your connector but what is on the other end? I would assume that there is a hole between the top of the plate and the side but I can't see one in the picture. Can you explain.

Bill

Greolt
02-08-2008, 02:51 PM
G'day Bill

Nothing clever or complex about it.

Hole just comes out in the middle.

Not very clear but you can see it in the pic,

Greg

.

bgriggs
02-08-2008, 07:06 PM
G'day Bill

Nothing clever or complex about it.

Hole just comes out in the middle.

Not very clear but you can see it in the pic,

Greg

.

Fantastic! So simple when you point it out...:withstupi

Bill

crocky
04-04-2008, 12:55 AM
Hi Greg,

I know that this vacuum attachment is good :) but for those of us who can't build it and the vac-pump that is needed, http://www.vac-clamp.com/VC4%20cnczone.pdf has a really good write up about the vac-clamp that uses compressed air. Who wrote the cnczone comments?

Mine is on order, should have it Monday.

Cheers,
Bob

Vac-Clamp
04-06-2008, 07:31 PM
Hi Crocky,
The write-up was from ynneb a bit over three years ago.
There have been more tool reviews since then. The most recent ones are new woodworker.com (http://www.newwoodworker.com/reviews/vclamprvu.html) and Tauntons Fine Woodworking (http://www.taunton.com/finewoodworking/ToolGuide/ToolGuideProduct.aspx?id=30644)
I hope this helps you
Errol

ClaudioG
02-24-2009, 07:46 PM
Just wondering if anyone has tried a standalone venturi vacuum generator with a DIY vac table such as this one;

http://cgi.ebay.com.au/Venturi-Vacuum-Generator-Clamp-Chamber-Press-Forming_W0QQitemZ230318371064QQcmdZViewItemQQptZWoodworking?hash=item230318371064

(go here www.WidgetWorksUnlimited.com after the above link expires)

Works out about AU$90 landed.

Do the specs sound as though it would do the job?

Cheers,

Claudio

ger21
02-24-2009, 07:53 PM
You need a large compressor to pull vacuum with that, and you'll need to build some type of reservoir to keep it from running constantly. Look at the Joewoodworker website for plans to build a complete venturi system with automatic vacuum switch.

That venturi looks identical to mine, which is inside this box here for $17.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92475

Greolt
02-24-2009, 08:12 PM
Claudio

If you are going to spend that sort of money get one of these,

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=130286019587&ru=http%3A%2F%2Fshop.ebay.com.au%3A80%2F%3F_from%3DR40%26_trksid%3Dm38.l1313%26_nkw%3D%2B130286019587%26_sacat%3DSee-All-Categories%26_fvi%3D1

Greg

ClaudioG
02-24-2009, 08:25 PM
You need a large compressor to pull vacuum with that, and you'll need to build some type of reservoir to keep it from running constantly. Look at the Joewoodworker website for plans to build a complete venturi system with automatic vacuum switch.

That venturi looks identical to mine, which is inside this box here for $17.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92475

What would be a large compressor? If the material is held down and well sealed, does the compressor keep running?

So did you get the harbor freight unit and not like it?

Cheers,

Claudio

ClaudioG
02-24-2009, 08:27 PM
Claudio

If you are going to spend that sort of money get one of these,

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=130286019587&ru=http%3A%2F%2Fshop.ebay.com.au%3A80%2F%3F_from%3DR40%26_trksid%3Dm38.l1313%26_nkw%3D%2B130286019587%26_sacat%3DSee-All-Categories%26_fvi%3D1

Greg

Greg,

I did like your one I saw in Melbourne and I've seen these go on ebay for around $190 to $220.

What did you end up scoring yours for, so I can work out what price to hold out for?

Cheers,

Claudio

ger21
02-24-2009, 08:49 PM
What would be a large compressor? If the material is held down and well sealed, does the compressor keep running?

So did you get the harbor freight unit and not like it?

Cheers,

Claudio

It uses a lot of air, and when the air stops, you'll lose vacuum. That's why you need a reservoir and switch. Otherwise the compressor would run continuously.

I have the harbor freight unit, but I use it for veneering. I get a very good seal, and the switch only opens the valve to the venturi every 5-10 minuted, for about 15 seconds each time.

I hope to try using it for holding work, but not sure when I'll get around to it.

Geof
02-24-2009, 08:50 PM
Just wondering if anyone has tried a standalone venturi vacuum generator with a DIY vac table such as this one.....

Claudio

I have used a venturi vacuum generator and came to the conclusion they are inadequate. Maybe if you have a big rotary screw compressor you are not using it is worth picking up the venturi units but they consume a lot of air and your compressor will probably run all the time; which is why it needs to be rotary screw.

This thread started with Greolt successfully converting a compressor into a vacuum pump and I have done the same thing which I describe here:

http://www.cnczone.com/forums/showthread.php?t=53796

I think either get a proper vacuum pump or if you can get a cheap compressor convert it. My conversion only required a bit of plumbing work.

Vac-Clamp
02-24-2009, 11:33 PM
I think there have been comments made in this thread subject to conjecture.
1. Not all venturis use a lot of air. The venturi vacuum generators on our VC4 and VC5 clamps use about 1 cfm at 80 psi supply pressure. At 60 psi the usage is about 0.75 cfm per generator. The items on Harbor Freight use about 4 times the quantity of air with similar results.
2. A reservoir for a vacuum is not a useful thing. Being the exact opposite of pressure, a vacuum will be achieved sooner, and more efficiently, with a minimum volume to be evacuated.
3. Most wood and wood products are semi-porous. No matter how good the seal is, air will pass through the wood to reduce vacuum levels. It is for this reason that constant vacuum generation (either mechanical pump or venturi) works well, particularly in CNC applications. Materials such as glass or steel etc are non-porous which makes for a different discussion.

Errol

Geof
02-24-2009, 11:50 PM
I think there have been comments made in this thread subject to conjecture.
1. Not all venturis use a lot of air. The venturi vacuum generators on our VC4 and VC5 clamps use about 1 cfm at 80 psi supply pressure. At 60 psi the usage is about 0.75 cfm per generator. ..Errol

These figures are meaningless until you state what volumes are pumped on the vacuum side and what are the maximum vacuums obtained?

Vac-Clamp
02-25-2009, 12:41 AM
Hi Geof,
A reasonable question. To hand I have air consumption graphs, and vacuum levels achieved for a given air supply pressure.
Air volume being moved (flow rate) is possible to show graphically for a given air supply pressure vs vacuum level. I will forward this when I have it plotted.

Errol

ger21
02-25-2009, 09:14 AM
I think there have been comments made in this thread subject to conjecture.
1. Not all venturis use a lot of air.

No, but cheap ones like the EXACT one he asked about do.

Vac-Clamp
02-25-2009, 04:52 PM
Fair comment Gerry,
Venturis are a useful method of generating vacuum and, as you have pointed out, some are more efficient than others. I think the best way to paraphrase this is "you pay for what you get"

Errol
v-clamp (http://www.vac-clamp.com/)

mediaconvert
05-19-2009, 10:53 PM
I'm looking at using vacuum clamping to hold down sheets of styrene while they are being cut on a cnc router. I'm thinking of this as a 3 layer sandwich.

On the lowest layer, attached to the router bed is a "distribution plate".
Vacuum line attaches here. Feeds a regular grid work of channels. Might have
multiple zones [in case only a portion of the bed is used]. Resilient sealing material can be placed in the channels to create irregular shapes if necessary.

On top of this goes a "spoilboard" which serves multiple purposes. it's customized for the specific job. it has a network of smaller holes that are placed under each separate section of a workpiece. first, it gives the router something to cut into when you want to cut thru your workpiece. second, since cutting thru the workpiece over a distribution plate channel would vent the vacuum, it seals off channels that would be under thru cuts (ie, no holes in those locations). From what I've read here a spoilboard could be something like 1/4 inch hardboard. smooth on both sides.

finally, on top of the spoilboard goes the workpiece. In my case a sheet of styrene to be cut into multiple pieces of varying size.

is this the way a vacuum clamping system is supposed to be used?
anyone have one running that's about 24"x36" that could give me an idea of how much vacuum i'll need to pull? [eg cfm and pressure] to hold down styrene between 1mm and 6mm in thickness?

Frank

hatcat
08-11-2009, 08:02 PM
In the days when all car engines were carburetted with vacuum operated winshield wipers you could just run a tube out to the vacuum connection on the intake manifold and leaving it idling in the driveway.

You can still do exactly the same thing with a modern car if you wish.

tmbg
08-17-2009, 11:30 AM
Frank,

forgive me if i'm off base here, as I haven't experimented with a vacuum hold down system, BUT

Your spoilboard idea probably won't work. The issue with cutting through the workpiece is not that of damaging the plenum, but more an issue of destroying the seal. Once you cut through the workpiece, your vacuum is no longer sealed at that point, and the piece will move. I imagine the second the tool cuts through, all hell will break loose :(

Tde1806
10-29-2009, 08:38 PM
hey what do i need too convert my kompressor to a vacuum pump.

best regards
Tomas



Drilled an inlet. Maybe that should be called an outlet. :D

Fitted a quick release air coupling.

Have no vacuum pump yet. I want to see how well this works before splashing out the hard earned on one of those. :)

So I pressed the little shop compressor into service. Connected up the hose to the inlet side just to see what will happen. :rolleyes:

Well it worked @#&%* brilliantly. :banana: No way that piece of board was going anywhere.

Sucked it down like you wouldn't believe. Well a lot of you would of course as you've had plenty of experience with vacuum tables. :)

Now where am I going to get one of those nifty little vacuum pumps like they have in the US ?????

.

sloppie_1
11-06-2009, 10:36 AM
I work at a plastic machineshop. We use small vaccums I can't remeber the name of right off hand, but we have them run all day. We then use weatherstriping that you use for sealing windows for gasket material. We basicly cut the profile of what we are cutting in the table, then gasket the profile. Regardless we only run plastic but I have run thin alluminum also. We generaly keep a 25psi at all times......

lgalla
11-06-2009, 07:09 PM
Here is a good link.Good info here...http://www.allstaradhesives.com/faq.php
We have a 5X10 router without zones.I has a Busch vacuum pump,model 0630,25HP,490 cfm.Does it work?Yes and no.If the parts are large,no problem.Under 1Sq'we have to tab the parts.
If using gaskets your Z travel will be off by how much your gasket compresses.The problem is the side forces at high IPM.The spoil board is smooth and slipry.If the parts need accuracy a couple of brads does better than a 25grand vacuum pump.Is there some kind of anti-slip coating for the spoil board?
Larry

ger21
11-06-2009, 07:23 PM
Is there some kind of anti-slip coating for the spoil board?
Larry

Try AllStar's Z Grabber tape. It's a thin rubber tape that gives a lot of grip. I made some acrylic pods for our machine and used the Z Grabber, and they worked great.

sloppie_1
11-09-2009, 10:07 AM
Here is a good link.Good info here...http://www.allstaradhesives.com/faq.php
We have a 5X10 router without zones.I has a Busch vacuum pump,model 0630,25HP,490 cfm.Does it work?Yes and no.If the parts are large,no problem.Under 1Sq'we have to tab the parts.
If using gaskets your Z travel will be off by how much your gasket compresses.The problem is the side forces at high IPM.The spoil board is smooth and slipry.If the parts need accuracy a couple of brads does better than a 25grand vacuum pump.Is there some kind of anti-slip coating for the spoil board?
Larry

try leaving a .02 web then use a flush trim router to trim off the web.

lgalla
11-09-2009, 10:15 PM
Sloppie the problem with a .02 web is you still lose some vacuum.Leaving a web or tab seems to be a step backwards as you have to manually finish parts.I thought CNC was to eliminate manual labour.Wish I still had my SCM pin router.
I visited a few shops in my area and here is some reports.
One shop cuts kitchen cabinets at 200ipm on a Holtzer $250,000 with a 25Hp vacuum.They say accuracy is poor at higher feed rates.
Another shop with a Shoda says two pases are necessary to cut 3/4" hardwood plywood.The vacuum is not strong enough to hold accuracy.BTW their vacuum pump is 50Hp.
Another HUGE shop which does furniture for office towers has a million dollar machine and is used only for table tops as they say the vacuum can not resist the side forces.
As I have use of a 5X10'Thermwood with 25Hp Vac and 10Hp spindle,I cut 3/4MDF table top 2'X4' at 600ipm.As I needed the table one and 1/2" thick,we cut 2 pices.You would expect the 2 pieces were exact?Wrong!Out a few thou?Try 1/16".lots of sanding.
Conclusion:Router feed rates or cutting speeds are for cutting paper or air.Wish I still had my SCM pin router

Wolffie
05-26-2013, 10:45 PM
Fair comment Gerry,
Venturis are a useful method of generating vacuum and, as you have pointed out, some are more efficient than others. I think the best way to paraphrase this is "you pay for what you get"

Errol
v-clamp (http://www.vac-clamp.com/)

Or should that be
You get what you pay for?
Cheers
Wolffie