Looking to build another cnc specificially for solid surface carving

[marbles]

Hi there,

I have already built two cnc machines from scratch using advice from here but I’d like a smaller machine able to machine a workpiece dimensions of 600mm x 300mm x 40mm. The machine is specifically for milling lots of parts for museum display in Corian type solid surface.

Critically due to the duration of some of these machining jobs I want be make a soundproof box to enclose the machine to keep the sound to a minimum. Having a dedicated smaller machine is therefore easier to build an enclosure for that the bigger machines.

I’ve been getting some prices from China to import a 6090 however with the import costs and my previous experience i’m pretty confident I would put together a decent machine well under the door to door prices I’m being quoted.

I would have thought a short gantry in 6mm wall steel box, all 20mm linear rail, twin ballscrew Y axis, closed loop setup would be the way forward. Saying all that I do have a Gecko540 controller, mach 3 pc and all the cabling and Nema 24 motors all ready to go so as a first port of call I really should look at reusing that.

Questions

Q. If using ballscrew on all axis should I be looking to use a gear drive with the motors?

Q. What size and pitch of c7 ballscrew on each axis?

Q. Where can I source a T-slot bed or t-slot sections to make a nice rigid bed surface?

Q. Should I be considering using a water cooled spindle with better lower end torque. One of the four or 6 pole 18,000rpm spindle?

Q. If I fabricate most of the frame from 6mm wall box and 12mm laser cut plate what profile size alu extrusion should I use for the gantry?

Thanks in advance.

[routerdriver]

I would suggest that the first two questions are asking the same thing in a roundabout way.It comes down to how many steps per mm and a finer pitch with no gears will move the same distance as a coarser pitch with a gear reduction interposed.So perhaps check the prices of a couple of thread pitches for the lengths you require and of sufficient diameter and use this as a basis for your decision.

[JohnHaine]

Do you mean gears? Using ballscrews the last thing you want is backlash in gears. But reduction using toothed belt would be fine. For precision better to use a bit more mechanical reduction than higher microstep ratio.

I machine Corian a lot, wonderful stuff. I only have 5k rpm max spindle and I find I can take deep and fast cuts quite happily using standard milling cutters. So maybe you don't need a very high speed spindle which could reduce your noise level?

[routerdriver]

Good gear selection would minimise the backlash and a few months of use will quite likely introduce some wear to a toothed belt system. My choice would be a finer pitch leadscrew with direct drive and microstepping that isn't too fine.Lets not forget that lots of machines use rack and pinion drive.

[JohnHaine]

The toothed belts on my Novamill have no signs of wear-induced backlash after 20 odd years. Timing belts are much easier to fit than gears too. But I agree that finer pitch ballscrew and direct drive would be superior, but finer than 5mm I think get expensive - over £200 a metre £100 for the nut?

But actually a 5mm pitch ballscrew would give plenty of resolution with modest microstepping - say 5/(200 x 8) = 3.125 micron which would be significantly smaller than the remanent backlash and probably as accurate as the screw itself.

[marbles]

I've built a rack and pinion and a HTD belt drive cnc before but have wanted to build a ballscrew system for a while. Especially as its small the parts should be less expencive. I'd have thought RM1605 ballscrew which seems very common would be fine given that the Y axis travel is only 700mm however RM2005 might be better or just overkill. Also do I need two ballscrews on the Y or could I use just one?

Yes your right about the backlash, it'd need to be very low ARC sec gearboxes (expencive) or 5:1 belt reduction which I use on the rack and pinion.

Good to hear you machine corian at 5k, now that is slow. I guess its a fairly high torque spindle/machine.

[JohnHaine]

........

Good to hear you machine corian at 5k, now that is slow. I guess its a fairly high torque spindle/machine.

Not particularly I think. Half-horsepower (375W) dc motor running at spindle speed.

[m.marino]

[QUOTE=marbles;132289

Questions

Q. If using ballscrew on all axis should I be looking to use a gear drive with the motors?

Q. What size and pitch of c7 ballscrew on each axis?

Q. Where can I source a T-slot bed or t-slot sections to make a nice rigid bed surface?

Q. Should I be considering using a water cooled spindle with better lower end torque. One of the four or 6 pole 18,000rpm spindle?

Q. If I fabricate most of the frame from 6mm wall box and 12mm laser cut plate what profile size alu extrusion should I use for the gantry?

Thanks in advance.[/QUOTE]

As someone who has a "smaller machine" which was built with the aid of Jazz. I can tell you with years of experience that Yes you can most likely build a much better machine than what China is selling. Also I have done a lot of cutting on solid surfaces and one item you will need is high quality dust extraction. You don't want to be breathing the dust at all. Yes, I know what Corian's research says and they were very creative in how they did their safety research. Now one to your questions.

Look up th design I did as it is still here on the forums and fits well within what you are shooting for.

Q1: I use a belt drive on the X (gantry axis) and the Z axis. That is both for space saving in the design and also the benefits that going to a belt drive gives. Y axis is two ballscrews driven independently.

Q2: Given that the prices on C5 ballscrews have come down a reasonable amount I would strongly suggest going with 1605 (same as on my machine currently).

Q3: If you have a good quality machine at present you might be able to mill them yourself and mill spacers to allow for being set into the bed in a way that will best benefit your requirements and what options you will need.

Q4: Solid Surfaces don't need a large amount of torque when cutting them. They easy to machine and once done very stable. It is just that machining that produces some really nasty dust. I have machined Corian to high level of finish with an FME 1050-1 and very reasonable cutting time. I would suggest going with a minimum of a 2.2kw spindle though as it does allow for some additional cutting depth at speed that lighter motor won't give you.

Q5: You could use box section for the gantry as well though it does add a bit of weight. Really that depends on what you have or are comfortable with. I would not use anything below 40 series, but that is just me.

Hope these answers help and seriously from what you asking take a look at the build I did as it should help you a lot in the direction you are heading.

Michael