Zach's Homebrew CNC Mill

[Zach_G]

Well after years of inspiration, figured I should give back to the community by documenting my own build. The plan is to end up with a vertical mill that mills aluminum and some steel. Overall work volume should be about 19x10x14 inches X Y Z with future 4th axis. I had been considering gantries and other nonstandard layouts but finally decided on C frame for manufacturing simplicity.

Spindle is a mini mill run by a 1.5 HP treadmill motor. I feel this to be the weak link so far, but it's what I have on hand presently and in the future could be switched out.

Ballscrews are from our favorite Chinese manufacturer of cheap rolled precision ballscrews. For some reason there's alot of drag on them (like hard to rotate the nut and screw by hand) I'm attributing to tight rubber seals that hopefully loosen up since they spin fine without em. Linear guides for Y and Z are 2 each NSK 35mm 4 way contact long blocks with high preload, and 25mm THK on X.

Main structure is 8x8x3/8 and 5x5x1/4 steel tubing with an E/G sandwich between to help dampen vibrations. Total weight should be around 700lbs, lightweight for the work volume but hopefully the choice of materials and FEA simulations will keep things stiff. Using surplus flat ground 3/4 steel waterjetted for various mating plates, and then epoxy/metal powder to level the way surfaces on the steel tube. Still trying to find an answer on how necessary stress relieving is on these A500 steel shapes. Id like to weld em together but again, stress relieving on such an ungainly structure may be costly. The table is a replacement from a 8x28 HF mill, only like $130 to my door, not too shabby. Overall trying to avoid milling parts since access to machinery is limited, at worst there is a pay per personal use shop nearby (I'm in Dayton Ohio).

Controls provided by Mach3 and parallel port (I hear that's the most reliable Mach setup) I spent the last 2 weekends wiring up the enclosure and got my motors to spin! Zeta4 drives will push about 400W through some Nema 34 steppers from Lin Engineering and compumotor (love not having a giant transformer). Kinda a waste having such high quality motors attached to high quality drivers, the anti resonance driver settings seems to overlap the Lin's superb rotor design, didn't need any of the damping settings which were necessary for the old compumotor stepper, but hey they were all cheap ebay buys so it's all good =p

Oh yeah, and I'm pretty commited now since the steel and ballscrews are cut to length, we'll see how fast progress is.

Enough chitchat, here's some eyecandy:

[Eson]

I like it! Are you buying the linear guides new?

[Zach_G]

Its all mostly ebay/surplus so far, except for the ballscrews and structure. The 35's for the Y and Z are new in box, but the X was a pull from a scrapped machine. The whole thing has been designed around components I could scrounge.

Bit of a status update, hit a big setback when I blew up my control computer trying to get mach to control spindle speeds. Managed to connect -60V through the parallel port ground and fried the motherboard and the non-optoisolated breakout board. Thought I was smart enough but guess we all get our daily value of stupid. Hopefully a new $50 motherboard, some replacement chips for the breakout board and Im back to where I started a few weeks ago.

Ill start doing mechanical stuff once I get set up in a machine shop at work later this week.

Here's some pictures of the allmighty pile-o-parts and a nice render I put together. For some reason linearmotionbearings2008 cut the ballscrews a good bit longer than i specified. Guess I get to machine them to length, sucks because i paid for end machining too =\ Theyre also really tight in the bearing blocks which appears to be the rubber seals that will hopefully wear in.

[T.W.O.]

I Like the idea of 2 concentric square tubes.
Do you think that the tubes are straight/flat enough to bolt your linear guides on or are you going to mill/grind them first?

greetings & good luck with the build

[johnohara]

Zach~

May I suggest reading Dr. Eberhard Bamberg's "Principles of Rapid Machine Design" before you go ahead with the E/G sandwich?

Beginning on page 90, he discusses the concept of "Constrained Layer Damping" and addresses segmenting the inner sandwich to improve the dampening characteristics.

Although his discussion involves concrete inside circular tubing, his conclusions are very informative and relevant to your build. (Thank you Dr. Bamberg.)

http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf

Have you decided on an E/G formula?

~John

[TarHeelTom]

Excuse my ignorance. What is an "E/G" sandwich?

[johnohara]

What's a peanut butter and jelly sandwich? Peanut butter and jelly between two pieces of bread.

What's an E/G sandwich? Epoxy-Granite between two pieces of steel.

~John

[TarHeelTom]

What's a peanut butter and jelly sandwich? Peanut butter and jelly between two pieces of bread.

What's an E/G sandwich? Epoxy-Granite between two pieces of steel.

~John

Thanks. Although I used to work for a company that made sinks and bathtubs out of similar material, I'd never heard it called E/G. Actually, I think we used polyester resin and granite.

Tom

[jsheerin]

Looks cool.

I read someone's post recently (I think in the diy router forum) where they mentioned they took apart the bearing blocks from linearmotionbearings2008 and found that the rubber seals were what the screw and nut were hitting (instead of the little metal spacers), that the inner geometry of the block was messed up and no preload was being applied to the bearings, and that there was no lube on the bearings. So they made some new spacers and added some oil, I believe. Anyway, you might want to check that out. I have parts from him as well that I need to take a look at before I put them on my router.

[pete from TN]

This is almost exactly what I am considering building. If I do actually build it I will go for more travels and make the parts larger but other than that I am right there with you on this. What are your thoughts on mounting the linear rails on the tubing, Do you intend to weld the column to the base or make some bracketry to bolt it all together for adjustability once it is working? Do you have any way to weigh those two main tubes you bought for the column and base? I will be following this thread with close interest. I have a friend who has some steel tubing like that who lives nearby and he said I could buy it pretty cheap. Do you have an idea what you are paying for the linear rails and ballscrews? Peace

Pete

[Zach_G]

To answer questions/comments:

Im 99% positive that trying to mount the rails directly to the tube will result in terrible accuracy/binding. I plan to level the surfaces by mixing up some epoxy and steel powder (kinda my own moglice formulation) and coat the tube then press a well waxed surface plate against it to transfer its flatness into the tube. As for joining the Y and Z columns, Ive considered welding them but worry about stresses causing shifting (need to stress relieve the tubes still as well). The option Im leaning toward would be to weld some flanges to the tubes, stress relieve, epoxy level the linear bearing surfaces, then align using leveling screws or maybe a big right angle plate and inject epoxy between the flanges. Tighten with screws once its all set up. That way I have stable, disassembleable fabrication.

Johnohara, I actually read through Bambergs paper and designed my structure to meet his recommended machine tool stiffness. The inner tube is part of the structure, Im banking on the E/G to provide damping and transfer sheer loads like a composite sandwich. Could fill with sand for more damping effect as well. The E/G mix will be play sand, gravel and epoxy.

Hi Jsheerin, hope your design is coming to fruition. I got antsy and started building before going through all the calculations, hope it still pays off.

Pete, Id love larger travels too but this thing is pushing 700lbs which is topping out my weight (has to be moved next year) and budget. The tubes weigh 94 91 40 38 lbs. So far Ive invested about $1800 with probably another $1000 to go. Ballscrews and bearing blocks were $334 and linear bearings usually can be had for ~$130 a pair on ebay.

[johnohara]

Zach~

I recommend adding some Aluminum Oxide abrasive to your E/G mix. 220 grit (or 320 if you can find it) at 10% by weight will work well.

Some reasons:
1. The Al Oxide will fill in nicely with the sand and gravel.
2. The Al Oxide is a little heavier and will add more weight.
3. You'll find the Al Oxide easy to work with vs. sand.

I suggest mixing the Al Oxide with the sand before mixing with the epoxy.

Another suggestion, if I may. Use pea gravel. It's cheap and has a nice
range of small sizes that will work well with the Al Oxide/sand mix.

Some links:
2 Lbs. 220 Grit White Aluminum Oxide Abrasive
Epoxy :*Epoxy Resins and Hardeners with #556 hardener.

~John