[VegasRhino]

Hi all, I have stepped up to the plate and have been bug bitten to build my own desktop sized C framed mill. I'm having the good folks at Castinite company build my mold and pour the frame in epoxy granite. I have already purchased some thk - C0 20mm ground ball screws, and some hiwyn linear rails and am now getting the cad drawings happening. I'm looking for travels of around x20,y10,z15. The X axis casting will be stationary and only the table will move right/left. The goal is to fit the machine in an enclosure that I already have that houses a small Minitech mill.
To maximize travels, im requesting input on the pros and cons of direct vs timing belt mounting of the step motors. My thought is if timing belts have no drawbacks, it would allow the motors to be thoughtfully mounted as to allow the frame to be made as large as the enclosure allows without the step motors eating away valuable real estate. I'm going all in on this build and really want a high precision/ high rigidity machine. This is a first attempt and I sure hope with your input it is a successful conclusion! Thanks for the suggestions!

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[awerby]

I don't think it makes any difference, as long as you aren't changing the pulley ratios. On the one hand, you have the expense of getting all those pulleys and belts, but on the other, you avoid having to provide flexible couplings. If you figure it's going to save you some travel to use the belts and pulleys, then it sounds like a good idea. But if you're doing that anyway, you might consider using servo motors instead of steppers. Servos don't do so well if directly mounted, since they run best at fairly high speeds, but since you're using timing belts, you can change the pulley ratio to trade extra speed you don't need for extra torque that might come in handy.

Andrew Werby
www.computersculpture.com

[mactec54]

vegasRino

If the Timing Belt drive will help you with your design, then you should use it, the best timing belt to use is the (Gates) GT2-5mm or 8mm pitch pulley/belts

Your Ballscrews C0 grade is way over kill, most machining centers run C5 grade, some use a C3 grade, C0 grade is usually for inspection/Grinding machines

[VegasRhino]

Thanks for the good recommendations from both of you. Pictured is the current mill with a few of the ball screws on the table. Yes, C0 grade is overkill, as is 20mm size, but that's eBay, if the deal is too good to pass on, roll with it. I am somewhat torn on going servo system from cnc4pc.com or the hybrid closed loop stepper system featuring encoders. From my reading, the stepper route is much easier to plug and play. I think the gates belts are a good point, for this enclosure it's really the only way to go it seems. My spindle selection is a sherline collet.com setup with tapered roller bearings in an er32 collet and will crank 10,000rpm using a DC servo motor, has 3x the power as a sherline DC motor. By the end of my little adventure should be just shy the price of a good used Fadal vmc. But try fitting one of those in a hobby room. Thanks again for thought provoking opinions fellas.

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[mactec54]

vegasRhino

Ebay can be your friend for things like this, I thought by your post you had brought them from THK, the 20mm diameter is good, bigger the better, if you can fit them in

Take a look at the AC servos from Dmm, they are the easiest to set up & you have a large Encoder count which is what you want for a build like yours

DMM TECHNOLOGY CORP.