Rolled Ballscrews

[georgebarr]

This site is selling some Rolled Ball Screws with Nut at a pretty good price:
http://www.homeshopcnc.com/page2.html

They are 5/8" diameter screws. My CNC table travel length is approximately 45". My question is will these screws bend, whiplash, or cause any problems when using screws as long as 45"? After all, the diameter is only 5/8" as compared with other screws that are > 1" diameter. Also, how much accuracy difference is there between Rolled and Ground screws? Any comments?

[Al_The_Man]

Mostly the difference between ground and rolled is the accuracy with ground being usually .0001/ft and rolled .001/ft error. also ground tend to come with pre-loaded ball nut, rolled generally not, and have a bit of inherent backlash.
Whip occurs on small dia like 5/8" when you run them at high feed rate.
Al.

[space_case]

I don't know. Got a little bit of a sticker shock there, but I think I need to get used to that if I want to build a sizable CNC router. 6' long 1" dia was $211. The 12' version was $404!!!

I geuss I am making these comparisons to the 1/4" rods I built my CNC foam with. These were only a few dollars at Lowes. Looks like I am in a whole new league now!

[ViperTX]

Originally Posted by georgebarr This site is selling some Rolled Ball Screws with Nut at a pretty good price: http://www.homeshopcnc.com/page2.html They are 5/8" diameter screws. My CNC table travel length is approximately 45". My question is will these screws bend, whiplash, or cause any problems when using screws as long as 45"? After all, the diameter is only 5/8" as compared with other screws that are > 1" diameter. Also, how much accuracy difference is there between Rolled and Ground screws? Any comments?

George,

Since you're building a custom machine....I would recommend that you just order from McMaster Carr......get the larger ones....

[ger21]

You might be better off going with rack and pinion or belt drive.

[WayneHill]

Use bearing blocks on both ends of the ballscrew to reduce the whip.

[2muchstuff]

Acording to Nook Industries and their calculator, you can run a 5/8" by 45" long screw with double bearings on each end at 2833 RPM. With a .200" lead that would come out to be 566.6" per minute or 9.443" per second or 45" in 4.765 seconds---WOW--- thats movin. At a .500" lead, that comes out to be 1416.5" per minute, 23.6" per second, 45" in 1.9 seconds---greased lightning.
From those figures I think a 5/8" screw would be ok since running steppers/ ballscrews at those speeds (RPM's) would be impractical.