Looking to build another cnc specificially for solid surface carving

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.

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.

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?

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.

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.

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.

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Originally Posted by marbles

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

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

[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