From Left-Overs

[machineitright]

Hi everyone,
New to the forum and really like all the experience and know-how on here, would like to have your help on my build.

I have started the build with a torsion table out of some Advantech osb board that I had left over from a remodeling project, a cnc router seemed like a great way to use it up and get a new toy in the process. The osb seems to have a high strength to weight ratio, the table I have built setting on 2 saw horses with nothing between only flexes about .004 in the middle.

Here are some pictures of what I have so far and would like your thoughts.










Used plenty of this!!!

I will be building the rest of the router along the same design as the Black-Toe that I found online with a few deviations because of the materials and electronics that I already have. They were actually purchased to cnc my PM25MV mill but I have decided to try all this out on the router first.

Looking for any suggestions or help ya'll are willing to provide.

[dkirtley]

Looks really nice. The OSB is much stronger than MDF.

I am not as much a fan of the Polyurethane glues, but if you have good fit and clamping, it should be fine.

What kind of drive system and linear motion bearings you planning on?

[machineitright]

Thanks for the reply. So far I have had great luck with the Gorilla glue on stuff like the osb because of the open structure along the edges, when the stuff expands it really gets in the cracks and crevasses, usually use plain wood glue on anything else.

Linear motion will be v-groove bearings running along 3/4 x 1/8 aluminum angle, not original by no means but seemed like a good way to keep the cost down.

I was planning on going with ball screws and drive the X-axis underneath the table which is 6' long to get the 4' cutting length that I want, oh the dims on this router are 2'x4' cutting area and would like to have 6" z. I have looked at r&p, acme screws(multi-lead), and ball screws all seem to be about the same cost when you look at extra motors and drives for driving both sides of the x-axis to eliminate racking. Has anyone tried to add skate bearings running perpendicular to the rails on both sides to control racking and just drive from one side?

The motors and drives that I have are from Keling and were purchased for a metal cutting mill as I said in my first post, there are 2-570 oz in and 1-906 oz in which was to drive the heavy head on the mill. I am limited to 1/2 and 1/8 stepping on the drives for the 570's but more flexible with the 906 drive.

I would like to stay with 5 pitch screws if possible because that was what the drives were optimized for. I will be changing to more appropriate motors and drives when the budget allows for the router.

Sorry about the long post but looking forward to your input!

[dkirtley]

This is from a thread here (I think titled rock solid gantry)

It is a technique that has been used for many years on drafting tables to keep the ruler parallel to the table.

cockrum.net

I totally went away from Gorilla Glue once I got used to working with epoxy. It is cheaper, stronger , doesn't require as much clamping force, has a lot longer open time, and fills gaps much better.

[machineitright]

That is pretty cool cabling, what kind of resolution and accuracy you think?

Looks like he used the same kind of linear rail design that I am going to use. Are there any draw backs to it that I need to be aware of?

Thanks for the heads-up on the epoxy, do you use a particular kind? Would like to use it on the rest of the build if it is that much better.

I routed the edges of my table today to get them trued up and smooth, didn't get any pics but at least got something done. I also cut out my gantry uprights and hope my layout works, I will take some pictures tomorrow and get them posted. I thought I would get everything cut out and assembled on the wood side before I tackle the metal work.

I am still wanting to try ball screws and pretty sure I can build a zero back-lash ball nut assembly which should help with any whip in the 6' x-axis screw. I was thinking a 5/8 screw would be big enough am I wrong? Should I go bigger?

[dkirtley]

For general gluing, I like System 3 GelMagic. It is pre-thickened (a little bit thinner than vaseline) You just mix 2 parts to 1 of the resin and the hardener.

They also sell it in a cool caulking tube that can mix in the tip (or just measure out proper mixture for small batches) The tube is more expensive though. I am cheap and bought a 2 qt or so kit. I just use little medicine measuring cups.

There are some other mixtures for doing things like filleting and filling. Easy Fillet and Easy Fair. You can get the plain resins and mix in your own fillers but that is messy and a pain the rear unless you are doing lots. You also use the plain resin for laminating (fiberglass or carbon fiber)

That cabling just keeps the other end of the gantry square. I have only come across it on drafting tables. It works well there.

[DIYaholic]

That cabling just keeps the other end of the gantry square. I have only come across it on drafting tables. It works well there.

If you search for "Moving Knot" you will find several threads discussing it's implementation on CNC machines. ex: http://www.cnczone.com/forums/diy-cn...ock_solid.html

Randy,

[machineitright]

Thanks for the links, read through them last night and will probably be incorporating that into my build.

Is there a ratio for the gantry hieght to table width that helps? I want to get 6" of usable Z. I cut my gantry supports 24" X 12" with a angle cut from 6" wide at top down to about the 10" mark. The way I have it figured I will need my Y axis to be about 9" wide so when the Z is working on thin material and close to the 6" projection it will be supported.

Am I headed in the right direction?

[dave22]

Thanks for the links, read through them last night and will probably be incorporating that into my build.

Is there a ratio for the gantry height to table width that helps? I want to get 6" of usable Z. I cut my gantry supports 24" X 12" with a angle cut from 6" wide at top down to about the 10" mark. The way I have it figured I will need my Y axis to be about 9" wide so when the Z is working on thin material and close to the 6" projection it will be supported.

Am I headed in the right direction?

Check this link: Do it yourself CNC router: Design Considerations, the Gantry

Excellent diagrams showing the geometry and forces involved with the design of a gantry style router table.

Hope this helps and Good Luck with your build.

[machineitright]

Thanks dave22

I have been reading what they have on that site and was how I arrived at what I have so far, just wanted to see if I read it right.

I have been re-thinking the x-axis drive and would like to know what you think of the chain drive system, pros and cons. Trying to keep the costs down as much as possible on this first build. Any dirt cheap suggestions on drive?

After reading more builds and posts on the forums I think I may back off wanting to cut aluminum with this router and just use it for wood and plastics. This is just going to be a hobby machine and if it really takes off I will probably want to build a better machine.

[dave22]

Thanks dave22

I have been re-thinking the x-axis drive and would like to know what you think of the chain drive system, pros and cons. Trying to keep the costs down as much as possible on this first build. Any dirt cheap suggestions on drive?

Here is a link that describes precisely why I would never use chain and sprocket for a CNC motion drive system, see the animation near the bottom of the page:Report on CNC Linear Drive Mechanics

Ballscrew, Timing Belt, Acme leadscrew,and Rack&Pinion would all be acceptable choices.

Price the required components for each type of motion drive system and see which one best fits your budget. Also consider how this will effect your design, ease of assembly, operation and maintenance.


Hope this Helps and Good Luck with your build.

[dkirtley]

Just to be fair, that flash animation is pretty biased and contrived to steer people away by exaggerating the issues. Where would you even find a 6 tooth sprocket to make the effect that bad? As the circumference of the sprocket goes up, that jumpiness goes down. The real problems with chain are the same ones that go along with rack and pinion. They are basically a very coarse tooth rack and pinon with a bit of elongation issues as they wear. The minor fluttering in speed would be a challenge to measure in most cases.

All positioning systems have their drawbacks.