Heavy Duty Plasma - Ball Screws

BigJohnT wrote:
Do you know how they preload the pinions?

John[/quote]

I took a few pictures of one about six years ago as I was thinking of copying it. Of course I have no idea where the pictures went. IIRC they used a third gear to drive the two that rode the rack. By careful consideration of the geometry they ran with some interference. There was still some spring preload to the rack.

Single spring preloaded pinions are also common. The involute path of a rack gear is a straight line so it is possible to increase the depth of engagement to full contact without ill effects.

Large machines typically use rack in easily replaceable 4-6 foot sections. Ours (60 feet long) had the rails and rack bolted to the concrete on adjustable supports, about a foot high.

Doug

Iv seen a few plasma and alot more laser machines that use ball screws. messer makes lasers with ball screws and shop saber makes plasma/router machines with ball screws. Shop saber tells me they reach 700ipm with servos. I looked at one that was a router table ran 400 ipm no problem hogging threw alot of material. As for accuracy of the plasma, the curf vary about 4 thousands with hyperthem 1000 finecut (powermax 65 now). Has anyone seen a company using the preload rack and pinion ? I would be interested in getting a price quote.

ShopSaber Y Axis

Apart from all the engineering pro & con, one need to factor-in the actual working environment, unless you cut in submerge water, plasma cutting environment is just too dirty for a happy ball screw. This is the area where rack & pinion shines. Belt should be able to handle the dust too, since pitch will not be affected by dust...

My opinion is that a rack and pinion should be used. You also have high quality rack and pinion, like:

www.atlantadrives.com/systems1.htm

Ballscrews are good in a clean environment and with smallest travels. Of course, if money is not a problem, then you can also build it with ballscrews, but you would need to rethink how to cover them, and this solution is not easy.

Much more important than having the best ballscrew or rack and pinion is their seats... How will you machine the length of your table? Because there is no sense in having a good rack an pinion if the place where it will fit is not straight

Well we bought a shopsabre its been pretty good. accuracy is right there. Had to do some modifications of how it sense the sheet tho.