Materials for new CNC machine

[aarongough]

Hey all!

I'm working on the design and construction of a new fixed gantry CNC router. I already have a Fireball V90 so accurate construction of the parts is not a problem.

Right now the main problem I have is selecting materials. Initially I tried MDF, but I am not overly happy with it as a construction material. It's a pain to finish, it's extremely sensitive to humidity and is not really all that stiff.

I was planning to use good quality birch ply, but I just noticed one piece of birch ply I cut about 6 months ago has bowed noticeably, it's probably about 1/8" bowed over 2'... This is good quality 12 ply birch that I has assumed would be relatively immune to bowing.

So my question now is: what next? Should I be looking at aluminum for all the construction? How about some sort of composite like mircata or G10?

Ideally I want a material that is relatively easy to cut using my V90, which is why I'm shying away from aluminum a little. But I'm definitely open to suggestions here...

Thanks in advance for your feedback! -A

[JerryBurks]

Maybe not for everybody, but I am building a new machine with bamboo plywood.

Nor sure about the long term bending tendency but that can be mitigated by multiple layers and varnishing. Otherwise it is stronger and a bit more rigid than Birch, also somewhat more expensive and maybe more difficult to find (I have a wholesaler around the corner).

There is also construction grade woven bamboo that is much cheaper but not locally available to me.

It does machine exceptionally well with little dust (but very noisy). Even using a pretty flimsy CNC machine I can cut parts with an 1/8" single flute cutter to 2/1000 accuracy. No fuzzy edges or splintering.

Obviously I do not have practical performance results yet since I am still building.

[kbisswanger]

You might consider MDO (medium density overlay). I haven't used it, but it looks like it would be stable and it is water resistant. The commercial sign guys use it alot.

Biss

[ger21]

It's not so much what material you use, but how you use it. You can build a bad machine out of any material, but you can also build a good machine out of a lot of different materials.

I was planning to use good quality birch ply, but I just noticed one piece of birch ply I cut about 6 months ago has bowed noticeably, it's probably about 1/8" bowed over 2'... This is good quality 12 ply birch that I has assumed would be relatively immune to bowing.

No wood is immune to warping. Wood usually warps due to changes in moisture content. Thorough sealing can really help to minimize movement due to moisture.
As far as plywood goes, good quality plywood is getting harder and harder to find. And even if you have good quality plywood, it's very important to store it flat. Leaning it against the wall is almost a guarantee that it will warp.

If you plan on building a machine out of large pieces of single layer plywood, then rigidity will be a problem.
You get around that problem by building box structures, and laminating multiple pieces together. 3 layers of 1/4" MDF is much stiffer and more stable than 3/4" MDF.
And a torsion box can be incredibly strong and rigid.

I'm building a 4'x6' two spindle machine that will be mostly wood. A lot of baltic birch, with laminated beams for the gantry and frame. The linear rails will be bolted to phenolic plates bonded to the plywood, and the the bearing blocks will be bolted to aluminum plates screwed and bonded in place.

All wood is sealed with epoxy before painting, so moisture isn't really an issue.

Everything in the first image here will be made of baltic birch. (except aluminum plates)
The second pic is one of a pair of prototype carriages I made to test a V bearing system.
I'm switching to linear bearings, but the new carriages will be almost exactly the same, except for an aluminum back plate to allow bolting the bearings to.

[aarongough]

Originally Posted by ger21 It's not so much what material you use, but how you use it. You can build a bad machine out of any material, but you can also build a good machine out of a lot of different materials. No wood is immune to warping. Wood usually warps due to changes in moisture content. Thorough sealing can really help to minimize movement due to moisture. As far as plywood goes, good quality plywood is getting harder and harder to find. And even if you have good quality plywood, it's very important to store it flat. Leaning it against the wall is almost a guarantee that it will warp. If you plan on building a machine out of large pieces of single layer plywood, then rigidity will be a problem. You get around that problem by building box structures, and laminating multiple pieces together. 3 layers of 1/4" MDF is much stiffer and more stable than 3/4" MDF. And a torsion box can be incredibly strong and rigid. I'm building a 4'x6' two spindle machine that will be mostly wood. A lot of baltic birch, with laminated beams for the gantry and frame. The linear rails will be bolted to phenolic plates bonded to the plywood, and the the bearing blocks will be bolted to aluminum plates screwed and bonded in place. All wood is sealed with epoxy before painting, so moisture isn't really an issue. Everything in the first image here will be made of baltic birch. (except aluminum plates) The second pic is one of a pair of prototype carriages I made to test a V bearing system. I'm switching to linear bearings, but the new carriages will be almost exactly the same, except for an aluminum back plate to allow bolting the bearings to.

Thanks everyone for your responses!

I went and checked some of my newer stock of russian birch and it's all dead flat. It's possible that the storage was the thing that bowed the other pieces.

I'll keep in mind what you said Ger about laminating the plywood. So in your mind it's better to build a piece out of three layers of 1/2" rather than two layers of 3/4"?

In the design I'm working on only very small spans are made out of a single layer, most of the spans are doubled up 3/4" or are backed by another piece at right angles... Sounds like I'm on the right track there.

[jm82792]

Originally Posted by JerryBurks Maybe not for everybody, but I am building a new machine with bamboo plywood. Nor sure about the long term bending tendency but that can be mitigated by multiple layers and varnishing. Otherwise it is stronger and a bit more rigid than Birch, also somewhat more expensive and maybe more difficult to find (I have a wholesaler around the corner). There is also construction grade woven bamboo that is much cheaper but not locally available to me. It does machine exceptionally well with little dust (but very noisy). Even using a pretty flimsy CNC machine I can cut parts with an 1/8" single flute cutter to 2/1000 accuracy. No fuzzy edges or splintering. Obviously I do not have practical performance results yet since I am still building.

From my experience bamboo is really volatile, it grows and shrinks like mad.
I've seen tons of the bamboo floors warp since people aren't into expansion gaps...
I'd try to coat it with something....

[JerryBurks]

Originally Posted by jm82792 From my experience bamboo is really volatile, it grows and shrinks like mad. I've seen tons of the bamboo floors warp since people aren't into expansion gaps... I'd try to coat it with something....

I will surely coat it. But from my research (I know it is all Internet so inherently questionable) the dimensional change coefficient for Bamboo is only 0.00144 while most hardwoods including Birch (0.0038)have much higher expansion due to humidity.

I guess I will find out....

[jm82792]

That's weird, my father has been a licensed hardwood flooring contracter for 30 years and he says it more volatile then anythign else he has done yet(then again it seems many weird thing happen with natural stuff ) I've seen it happen to a lot of bamboo clicks(solid? I don't have a clue how they turn bamboo into a solid). I like the concept, it looks great, it is rock hard, and it's also cool because it contains silica unlike wood does.

[awerby]

go ahead and use the bamboo - it'll make a great post here on the Zone, even if it turns out to work poorly or not at all. But if you mainly want to build something that actually works pretty well, use aluminum for the parts that have to move, and steel for the rest.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[JerryBurks]

Originally Posted by awerby go ahead and use the bamboo - it'll make a great post here on the Zone, even if it turns out to work poorly or not at all. But if you mainly want to build something that actually works pretty well, use aluminum for the parts that have to move, and steel for the rest.

Sure, will do and there is already a log on the build log sub-forum, look for the "Big Bamboo" thread. Right now I am about 30% done. I am not concerned it won't work at all but the difference to other plywood may be just nominal. My intent was rather to design something that will match the rigidity of a typical aluminum machine with material I can actually cut on my existing equipment and the bamboo is just fabulous to work with. Let's see if the result works out....

Apologies to the thread starter that the discussion got somewhat bamboo-heavy.

JB

[jm82792]

Originally Posted by JerryBurks Sure, will do and there is already a log on the build log sub-forum, look for the "Big Bamboo" thread. Right now I am about 30% done. I am not concerned it won't work at all but the difference to other plywood may be just nominal. My intent was rather to design something that will match the rigidity of a typical aluminum machine with material I can actually cut on my existing equipment and the bamboo is just fabulous to work with. Let's see if the result works out.... Apologies to the thread starter that the discussion got somewhat bamboo-heavy. JB

Perhaps it would be an applicable platform for small machines?
Then you could mass produce tiny ones with ease?