I think one that size should have two. Our 2x4 with 125 lb. gantry has two and I can't see one as large as yours getting by with only one motor. Racking issues aside, I just think it needs two.
David
David
Dual Y ballscrews or not?
I'm building a nearly 4x8 foot CNC. I'm figuring to use double ballscrews on the Y axis, but how bad a mistake would it be to use a single in the center instead? Would I get a lot of racking? Or is it just too much work on the one motor and ballscrew? I'm using NEMA 34 with 20mm rods.
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Do you mean 20mm screws?I'm using NEMA 34 with 20mm rods.
I'd use two 2525 ballscrews (25mm diameter, 25mm lead). 20mm is not big enough for that length.
I'd drive them with pulleys and a 1:2 ratio.
You'd really be better off with rack and pinion on a 4x8 machine.
I would worry about screw whip even using 25mm screws at that length. I agree with Gerry on using Rack and Pinion instead of the screws for the Y axis.
Thanks for this insight! So I guess the next question is: Where can I find a rack and pinion that size?
No, I meant the linear rods that the bearing blocks travel on. Sorry for not being more clear. The boss was wanting to leave early, so I had to post like NOW. :grin:Do you mean 20mm screws?
Bah! My order for the 20mm linear rods and bearing blocks was cancelled. Something about not being able to ship such a long package due to covid restrictions.
They don't have to be that long. You can butt shorter sections against each other to form one continuous rack. Just make sure they're straight.Thanks for this insight! So I guess the next question is: Where can I find a rack and pinion that size?
David
Yes, you use a small piece of rack, teeth to teeth to align two pieces of rack with the correct spacing.
I bought my rack and pinion from McMaster Carr. 20 pitch, 20° Pressure angle It’s available in 6’ length. I have seen a 4’ x 8’ with a singe center screw, a DMS Patriot machine. The screw was probably 3” in diameter and the servo driving it was the size of my tablesaw motor. DMS makes nice machines in Colorado Springs.
Thanks for this insight! So I guess the next question is: Where can I find a rack and pinion that size?
Almost everyone uses the rack and pinion drives from AVID CNC.
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