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HomeCNC
04-09-2003, 04:34 PM
Does anyone know anything about building a vacuum hold down setup? I would like to have one for my CNC router I am building. I know I will need a vacuum source. I just got a vacuum pump on Ebay.

Should I add a tank to this so I have a resovoir of, I guess (no air)? How do I build the vacuum plate that will hold the wood?

cncadmin
04-09-2003, 04:48 PM
One way is to make a air tight box that has many 1/16"-1/8" holes in it. Than a very strong vacuum source. You can place tape or alike around the object to provide max suck. A industrial vacuum clearner I belive would work.

balsaman
04-09-2003, 06:12 PM
I have heard you don't need the little holes. Just use a MDF box. The mdf is porus and will hold the part. Use 3/8" or 1/2" MDF on the top. Add supports inside the box to keep the top flat under the suction.

Eric

cncadmin
04-09-2003, 06:14 PM
Originally posted by balsaman
I have heard you don't need the little holes. Just use a MDF box. The mdf is porus and will hold the part. Use 3/8" or 1/2" MDF on the top. Add supports inside the box to keep the top flat under the suction.

Eric

Yes,but that will take alot of vacuum.

Laff Riot
04-09-2003, 07:51 PM
Call a local sign shop. Ask for a piece of Coroplast that is scratched and unsellable. If they try and charge you more than 15 bucks look for another one.

Coroplast is basically plastic cardboard. If you have ever seen a Real estate or Polical sign up close you know what I mean. Coroplast has a series of hollow tube flutes 1/8" that run the length of the material. Block off one end of the coroplast with Duct tape. Grab a shop-vac with the wide pickup nozzle and using a copious amount of duct tape and cardboard seal the other end onto the shop-vac nozzle.

Use your CNC machine to pop a couple hundred holes into the Coroplast tubes for the vac.

You now have independently suctioned tubes. You can block off sections with tape when not in use. Make sure you allow enough air into the shop-vac to not stress out the motor - you can always block off holes again. Block only as many holes as needed to give you hold down. On the plus side you also get dust collection :)

If the coroplast does not have a smooth enough surface for the type of work you want to do ask the signshop for AlumaCore. It is the same thing as coroplast except that it is skinned with .020 aluminum on the face and back and the tubes are about 1/4" thick. Absolutely smooth. About double / triple the cost of corpolast though.

The coroplast is cheaper but IMO go for AlumaCore if you can get it. If you cannot find either locally I can give you a list of suppliers.
Let me know the type of materials you mill - I have several specialty bases that I built to switch out in seconds on my work system. If you need a sketch, gimme a shout.

balsaman
04-09-2003, 08:18 PM
Yes,but that will take alot of vacuume.

He said he bought a vacuum pump, which is perfect for this setup. A vacuum pump is usually low volume, so the holy board doesnt usually suit it. The holy board is better for a shopvac, as you pointed out.

Eric

hardmill
04-09-2003, 09:24 PM
Give me a day and illl sketch something for you.
What size are you looking at.
Not much vacuum is req. Ill let you know what you
need, pretty simple actually.

ger21
04-09-2003, 10:21 PM
I work in a commercial cabinet shop with a large cnc router with a vacuum pod system. We have a VERY large pump and it will draw through MDF a little, but not enough to hold parts still. Most large commercial routers that draw through MDF spoilboards use even larger pumps. I'm not sure exactly how they are rated, but these pumps are larger than the cnc's we're talking about here and VERY expensive. I think I have a better solution. Last year I built a vaccum veneer press with a compressed air powered vacuum generator for under $100. This will draw much more vacuum than a shop vac. Go to http://www.joewoodworker.com for the article on how to build it. Then get a copy of ShopNotes issue 40, which has plans for various hold down jigs and a vacuum table, which should be a good starting point for a cnc vacuum hold down table.
http://www.shopnotes.com/
This is what I plan to use on the router I'm getting ready to start building.

Gerry

HomeCNC
04-10-2003, 10:54 AM
Thanks to everyone for the advice on vacuum clamping. I have also been searching the Internet and have found some information.

Gerry, I have been a subscriber of Shopnotes for about 3 years now. I have that issue and forgot about it!!!

This site has some vacuum plates that they sell. I like the way they use the vacuum tape on plastic plate. Just make one hole and with creative use of the vacuum tape you can open gates or close them to fit your work size.
http://www.qualityvak.com/kaccess.html

HomeCNC
04-30-2003, 03:13 PM
This is my idea for my Vacuum hold down plate. I will start with two plates that are 12" X 24" X 3/8" Alum. (I was going to have a 24" X 24" until I saw the price!!) I cut an o-ring grove in the lower plate (you can get o-ring stock in a roll from McMaster Carr). I drill a cross hole and place a hose barb in it. I make a 1/8" pocket in the upper plate so I have a vacuum chamber inside the two plates. I drill and thread 1/4-20 holes in a 2.25" hole pattern in the top plate. I plug the holes with rubber sealed cap screws. Now I built about 10 or so, small clamping plates that are about 2" square and 1/2" thick Alum. I cut an o-ring grove in both sides and drill a 1/4" hole through the middle of the plate.

To use this thing I just remove a screw and place a clamp plate over the screw hole to receive vacuum. This gives me the ability to create vacuum hold down shapes where I need them.

cncadmin
04-30-2003, 03:27 PM
Very nice that should work very well!

paulried
04-30-2003, 04:56 PM
Here is one I saw while visiting ShopBot in Raleigh, NC. Pretty simple and hooked up to a vacuum cleaner. The plate at the front is what regulate the amount of vacuum. The grooves where sealed with clear varnish bottom and side. The parts are caulked together to avoid vacuum leaks.

Laff Riot
04-30-2003, 09:39 PM
I didn't have a pic the last time I posted on the AlumaCorr product. This is a small piece of a 4x8 sheet. The channels run end to end between the faces.

http://www.nudo.com/nudosign/Alumacorr/defaul4.jpg

http://www.nudo.com/nudosign/Alumacorr/alumacorr.htm

Cost of a 4x8 sheet of this material 5mm thick is 65.00. I run it off a vac. Im sure a sign shop will sell you mini pieces for whatever size table you need for 20 bucks or so. If you need the same function but in a soft plastic that wont bust bits use Coroplast. $7.90 for a 4x8 sheet.

Im not saying my way is the best way by any means. I reposted on this because I think the pic explains a lot of what I tried to get across last time.

HomeCNC
05-15-2003, 02:23 PM
I found a nice web site for the vacuum tape. www.allstaradhesives.com I have ordered two different type of pod tape after talking to the engineer at the company. I will soon have my POD system up and running for my CNC router.

ger21
05-15-2003, 06:00 PM
I've been using their stuff for a few years now on the pods on our point to point at work. I thought you already knew what you were going to use or I would have pointed you that way a few weeks ago. Post some pics and let us know how it works.

Gerry

tsalaf
05-15-2003, 07:58 PM
You might consider attaching the vacuum hose directly to the pods. That way you can have several pods that will stick to any smooth surface. The pods can be permanently attached to a manifold and controlled with simple ball valves. This will also let you dispense with the vacuum box.
If you do decide to build a box, you will need to use braces in the centre as the pressure generated by a properly functioning vacuum pump will easily collapse an unsupported 3/8 aluminum plate.
As an aside, a 2" square pod will generate approx. 40-50 lbs. of holding force (depending on air leaks). This is barely enough for light cutting. To increase the holding force, you have to increase the surface area of the pod, or the number of pods.. Figure on 10-12 psi of holding pressure (allowing for air leaks).

HomeCNC
05-15-2003, 09:57 PM
I did not think of the material under the vacuum chamber bending. I will machine the chamber with islands all over the place to prevent the plate from bending.

Scrit
05-22-2003, 09:47 AM
HomeCNC your vacuum pump won't need a vacuum reservoir unless it is a very low capacity pump. What it will need, however is a vacuum filter on the machine (workbed) side of the pump. This stops the pump from ingesting dust and crud (and thus damaging itself). You will also need a vacuum gauge. This helps to indicate whether you have sufficient vacuum to hold the piece you are about machine. In a real world scenario (I run a CNC router) I find that I need at least 40cm Hg vacuum (that's about 16in) to hold timber/sheet ply/MDF components, although my machine does have a 120 cubic metres/hour pump.

To hold work I currently use a vacuum pod system, with specials and small pieces being held on purpose-made spoilboards bolted onto the pod bars. My spoil boards are normally machined from birch ply with foam rubber gasketing. I have tried MDF, but it tends to swell with age (it absorbs water and has to be remachined once or twice a day in changeable weather) and requires much more sealing. Remember to seal the edges and surfaces of any spoilboard (I use shellac or a thin coating of UF/RF glue, but then again I have them both in plenty). I also surface any spoil board on BOTH sides with a trepanning cutter before use. My purpose-made spoilboards use hard plastic pipe and plastic push-in connectors. Connections onthe underside are screwed into the bottoms of the spoilboards using air tool connectors (1/8 in thread x barbed pipe end) which have had a slot filed at right angles to the threads - this acts as a self-tapping fitting.

HomeCNC
10-13-2003, 01:23 PM
Well I finally had some time to work on my vacuum hold down system. I got the plate finished and built the pluming with the vacuum gauge. I made small rubber washers for all the screws in the plate and sealed them all. With the pump going I read the gauge and it said 29.65.

Its now time to make the pods and use the vacuum tape and try it out on some wood. More to come.

mace
10-17-2003, 12:13 PM
Here is a system i used back in the day on a koma 5'x12' quad head router.
Depending on size of final part it can hold 3" thk al. plate
You can get good ideas or just purchase from them.

http://www.carterproducts.com/product_list.asp?p_id=1&cat_id=9

Scrit
10-20-2003, 06:05 AM
Seen the Carter Flip-Pod system in the USA. Looks good, but does rob quite a bit of Z-axis movement. Also my exerience is that the pods are only availale in multiples of 100 (at multiples of around $1300/$1900)

Nice to see that the range of available pods is now so wide

mace
10-20-2003, 04:00 PM
yes they are salty not really for home setup we spent $10,000 for 5'X12' router and we had 29 HP. (sulair?) rotary vacuum pump.

But it is still good to see if you are thinking of some kind of modular vacuum fixture good ideas can be made from those pics make your own on a 1/4 scale or something.


mace

ger21
10-20-2003, 09:21 PM
Jeff, you might want to look at this.

http://www.m-powertools.com/products/vacuum-holddown.htm

They sell kits or just the individual valves.

Gerry

Woodie1
10-20-2003, 10:36 PM
:p You mite want to check out this site;
http://joewoodworker.com/veneering/welcome.htm
Under part 4-Misc.Info click on Vacuum Clamping.

HomeCNC
10-21-2003, 10:53 AM
Ger21,

Good find for another source for Vacuum tape and stuff.

Vac-Clamp
11-21-2004, 11:26 PM
Without trying to make this sound like a blatant advertisement, the Vac-Clamp (http://vac-clamp.com) website is worth a look to overcome the problems being faced by all the home CNC guys.
Powered by compressed air (venturi) and generating very usable holding force.
Regards,
Errol

cncadmin
11-21-2004, 11:29 PM
Without trying to make this sound like a blatant advertisement, the Vac-Clamp (http://vac-clamp.com) website is worth a look to overcome the problems being faced by all the home CNC guys.
Powered by compressed air (venturi) and generating very usable holding force.
Regards,
Errol


You're products look really good, can they be used for metal work?

Vac-Clamp
11-21-2004, 11:48 PM
No problems with metals. Anything non-porous works very well. Aluminium, stainless, tool steel etc etc. We have a few people using them on CNC mills pocketing aluminium using the appropriate feed rates. When they bolt in a VC4 a skim cut of known height is made and then they zero set from there with the relevant tool offset, and away they go.
Stainless and tool steels can be held but I think that the feed rates might be too slow to be viable, but then again you never know till you try.

Brief tech spec Ambient air pressure 14.7psi. Vac-Clamps generate a holding force of about 12.5 psi (100 psi supply pressure). So more surface area equates to more holding power

Errol

CNC Pro
11-22-2004, 10:19 AM
One thing to keep in mind is surface area! If your running a vacuum system thats low on horse power & CFMs, try to get as much surface area under your workpiece as possible!
I've seen 40hp vacuum systems pull the warp & twist out of 8/4 oak & cherry, and it sounds like a gun shot! But this is on a pieces of material that's 12" wide & 8' long. The same system still has trouble holding on to 4" diameter cut out made of 3/4" ply.

Vac-Clamp
11-22-2004, 07:15 PM
Surface area is indeed the key to a good hold, however Vac-Clamps work a bit differently to "blower" type or "rootes" type vacuum pumps. These types of vacuum pump are very good in nested based cutting on semi porous materials, as they flow a lot of air at quite reasonable levels of vacuum. Think of them as superchaged vacuum cleaners. Vac-Clamps run a built in vacuum generator which is powered by compressed air, they use a flow of air to generate a vacuum.

What limits all vacuum systems is ambient air pressure. At sea level air pressure is about 1 atmosphere or 14.7 psi ( relative to absolute). At the summit of mount Everest the air pressure has dropped to approx 0.37 atm or about 5.4psi. It is this air pressure pushing that will generate the holding force. Even a 40hp vacuum pump flowing 90cfm will not be able to create more force than ambient air pressure will allow.

Vac-Clamps work well with non-porous materials as they create a vacuum between the clamp and the workpiece. Ambient air pressure will push the workpiece onto the clamp. The better the seal the higher the vacuum level this equated to more push or holding force. Our single sided clamp VC4 uses about 1cfm but generates 12.5psi of vacuum.
It doesn't use a lot of air but it doesn't flow a lot of air either. So with very porous materials, such as thin MDF and cardboard, the air gets pulled through, and only a small vauum is created. Small vacuum level less hold.

Referring to the small item (4" round, 3/4" ply) I would guess that it does have a large bed and equally large blower system. To go back to the vacuum cleaner analogy, air is probably being drawn around the workpiece, and a vacuum will not be able to be created. No vacuum, no air pressure to hold the workpiece. The same 4" ply round on a Vac-Clamp would be held on with a force of 73lbs (33.3kg). This is more than enough clamping power. The opening page on our website http://www.vac-clamp.com shows a piece being machined which is 2" x 4".

Vacuum clamping performance is not directly related to lots of horsepower and large cfm rates. It is more a function of air pressure imbalance, and using this to our advantage.

Best Regards,
Errol Weber
Vac-Clamp

ger21
11-22-2004, 07:59 PM
I read in one of the woodworking trade magazines that the large pumps on most big routers only pull around 7 psi, but the large volume makes up for it. And I'm pretty sure the venturi pump I use for veneering would hold better than our big pump at work does, especially on small parts.

Vac-Clamp
11-22-2004, 08:36 PM
The figure of 7 psi vacuum does sound very achievable, and many would pull more than this. The large flow of air allows for losses or leaks.

For example, glass is non-porous and a small plastic suction cup will hold almost indefinitely. The same suction cup will not hold on MDF because it allows a flow of air, it is porous. If we could keep pulling the air out of the cavity between the suction cup and the MDF it will hold, this is why large pumps work well on large tables. They keep up with the leaks very well.

If you work with relatively non-porous materials (eg chipboard, melamine faced board, plexiglass, plastics, aluminum, stainless steel, etc, etc,) a venturi based system will, and does, work very well.
Errol Weber
Vac-Clamp (http://www.vac-clamp.com)

tpworks
11-22-2004, 08:56 PM
I use closed cell foam door insulation from home depot for around $.30 a foot ($3.00 for 10 ft) works really well.
post #9 at this link
http://cnczone.com/forums/showthread.php?t=6001&page=2

Tom

CNC Pro
11-23-2004, 11:20 AM
I agree that a non-porous material does allow for a more complete seal, but that same material usually posses another problem. The hard smooth surface can cause the parts to move or slide even with the neopreme seal.
Both of my routers have the same grid system as your Vac-Clamp, yet I still have issues with small plastic and aluminum pieces moving. I've got 4 vacuum pumps ranging from 3.5-5 hp, pulling 30-40+ CFMs each. And that's on a 5'*8' & 7'*14' tables.

ger21
11-23-2004, 02:40 PM
Both of my routers have the same grid system as your Vac-Clamp, yet I still have issues with small plastic and aluminum pieces moving. I've got 4 vacuum pumps ranging from 3.5-5 hp, pulling 30-40+ CFMs each. And that's on a 5'*8' & 7'*14' tables.

Like I said above, even though your pulling a lot of cfm, the Vac Clamp most likely is pulling more vacuum, giving more holding power. A lot of cfm is good for mdf and large panels, but small parts need more vacuum, and you probably don't have enough.

Vac-Clamp
11-23-2004, 06:05 PM
I think that a vacuum gauge could help CNC Pro with his moving plastic and aluminium problem. It is fairly obvious that there is enough power there, we just need to know how much vacuum (or negative pressure) there is.
An air flow of 30 to 40 cubic feet per minute sounds very usable, but with without the vacuum, small parts will move.

To give an example. A dust extraction system will move huge volumes of air, possibly in the hundreds of cubic feet per minute, but the vacuum level is quite low. Typically these are on the order of 9 to 10 percent of absolute This will only yeild one and a half pounds per square inch of holding force. A 4" disc will be held on with a force of about 12.5lbs in optimum conditions.

The venturi based vacuum clamp that we manufacture flows only about 0.8cfm per pad, but generates a vacuum of better than 80 percent of absolute. Under the same conditions as above the holding force will be more than 157lbs for the same 4" disc. This makes it ideal for smaller items, and works nicely on large items when ganged in groups.

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

CNC Pro
11-23-2004, 07:26 PM
I have to say Errol that Im skeptical that your product would perform better than what I'm currently using, but Im also open to new ideas and Im not opposed to investing in something that works. Do you have one I could try? Being able to tackle small, difficult to hold jobs would have me singing the praises of Vac-Clamp.

Vac-Clamp
11-23-2004, 09:12 PM
This sounds like a good idea CNC Pro. Please go to our website and use the contact email there to pass on your address through there.
We do not usually send product out on approval, but in the spirit of this forum I think that this is an ideal test case.
Our website ishttp://www.vac-clamp.com go to the reseller pages
Alternatively Vac-Clamp Email (sales@vac-clamp.com) will find us

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

eman5oh
11-23-2004, 09:43 PM
This sounds like a good idea CNC Pro. Please go to our website and use the contact email there to pass on your address through there.
We do not usually send product out on approval, but in the spirit of this forum I think that this is an ideal test case.
Our website ishttp://www.vac-clamp.com go to the reseller pages
Alternatively Vac-Clamp Email (sales@vac-clamp.com) will find us

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


CNC Pro I hope you take Vac- Clamp up on this offer and report back with the results.

cncnick
11-24-2004, 09:07 AM
Hi i have used Errols Vac-Clamp it worked very good for me ;but only tested on larger parts look at pics

Vac-Clamp
01-05-2005, 06:37 PM
A product review has been done by an independent product reviewer on the single sided clamp, the VC4.
The pictures within the review show what the clamps are capable of, and I would also guess that even the reviewer was skeptical of the performance of the unit until it was tested.

Click here for the review.
http://www.cnczone.com/forums/showthread.php?p=59052#post59052


Errol

HomeCNC
01-05-2005, 06:47 PM
Saw it. I'm still going to work with my pod design.

SCOJEN
01-07-2005, 04:41 PM
I have set up 2 very large 5 axis machines using a vaccuum hold down systems if you can find a old air compressor tank or several freon tanks to use as a accumulator to give you more volume you will have a vacuum system second to none we currently use 75 gallon tanks one for each table (6'x6') two per machine if you have enough pump 1 hp or better you can use 3/4" mdf boards and pull 23 in/hg as long as you seal the edges of the boards (duct tape works in a pinch) and your work piece to the board.
I am talking about holding down a 4'x4' sheet and moving a cutter thru it at 300 ipm on a initial cut and up to 600 ipm with a precut board on a production basis. On a home cnc rig you should not have any trouble as long as you seal up your work board as described above. If you are making a lot of the different parts it pays to have a seperate board for each part setup with a common 0,0,0 point to work from.

Scott

Salty72
03-25-2006, 07:40 PM
SCOJEN,

Scott, this sound like a very easy thing to do, how did you set it up, do you have any photos, i'm just starting out and would really like to get this style of clamping down pat, i think it would save a lot of programing around clamps and would save re-clamping to cut those areas not accessable due to clamps etc... ebay currently has a few vacuume pumps for auction but non of them say what pressure they produce so I'm not too sure which if any to prurchase.

the other question is can you use a normal compressor and use the inlet as the vacuume suction?

Vac-Clamp
07-19-2006, 08:28 PM
Previously in this forum I had mentioned our compressed air powered vacuum clamps
We now have a couple of new additions that will be of interest to those who need a ready made solution to vacuum hold downs.
Our VC5 clamp will hold itself down to a surface, and then hold a workpiece on top. It has two low consumption vacuum generators built in. The faces can be configured to hold down almost any shape, and no moving parts inside to wear out.
Link http://www.vac-clamp.com/vc5.htm

The other product is a face plug for the VC4 or VC5 vacuum clamp. This is a shim or packer that clips into the face of either clamp. It elevates your workpiece by 3mm to allow you to cut through the workpiece, but not damage the clamp face.
Link http://www.vac-clamp.com/vc%20cnc.htm

Salty72
07-23-2007, 11:54 PM
Can anyone tell me at what is the MAXIMUM rate air can be sucked through a 1"x1" of 16mm MDF and produce a 0"Hg differential....???

Reason I ask is simple - if you can deturmine the airflow through a 1"SQR of 16mm MDF this should be able to tell us what the CFM rate is required for any given size of table (As a LOSS)

then as you inclease the air flow, the diffirential will also increase and thus you have your vacuum - BUT the hard point is finding this flow rate

NOW!! I know all MDF is slightly different so a ball park figuare would be OK

Vac-Clamp
07-24-2007, 12:16 AM
G'Day Salty,
Through experience we have found that all manufacturers of MDF have differing densities. Some even manufacture a "low density fibreboard" which has the porosity equivalent of wire mesh.At the other end of the spectrum, we have used some European MDF which is perfect for our clamps but lousy as a spoil-board.
One of the other variables is when you skim cut the surface a few times the thickness will change the porosity too. You would also have to look at how much coverage you would have of your spoil-board as well.

Great question for debate I think.

jeffygoober
06-08-2014, 10:29 AM
Nice. How big a peice can the VC5 effectively hold? What about wobble on the edges as the router presses down? Or are you saying you need many of these for ,say, a 20" x48" workpiece?