Bearings for screw drives

[futura]

I'm building a CNC machine and will be using large diameter ballscrews for vertical and horizontal movements, what types of bearings at each end of the shafts should be used to get the best performance? Roller? Thrust? combinations?

Also, any tips on designing high-quality shaft end seats/mounts for these bearings.

Any help is greatly appreciated.

Thanks!

Larry

[sdantonio]

I asked a similar question in another thread recently.

Most of the people I have seen make their own bearings using a skate bearing (or something similar) seated in a MDF or HDPE housing. These are usually trapped by nuts to hold the lead screw in place (see thread by joe2000che regarding his 2007 machine for pictures).

I was asking about the use of flange bearings:

Has anyone tried using flange bearings (similar to pillow blocks) http://www.wttool.com/c/40410009p to anchor the leadscrews, or are they to stiff? I've used then in a number of aplications (non-cnc stuff like polishing wheels and customized sanding wheels) and they seem to be pretty good. They may be a bit stiffer and heavier than the home made things with the skate bearings. But they also have the locking allen screws to trap the leadscrew tightly and may decrease the whipping problem.

This seemed to have met with at least one aproval.

Steven

[ViperTX]

Check out misumiusa.com. I'm using a single bearing 6001ZZ (U-BASA 6001ZZ) on the un-driven end and a dual bearing setup on the driven end (u-BASB6001ZZ)...my idea is to preload the driven end. Also they are having a 50% discount until Feb 2006, so the parts are great deals.

[Billyum]

Go to 5 bears website, he explaines the type of bearings & details on mounting.

[Billyum]

Go to the 5 bears website. He explaines how to mount the right kind of bearings beatifully.

[futura]

Thanks to each of you for your help. I will do a little more research using the information you have provided.

Billyum, do you know the url for 5 bears website?

[ger21]

http://www.5bears.com/

More specifically, http://www.5bears.com/cnc04.htm

[futura]

I've just looked over the 5bears site not only is it informative it uses great photography, has excellent step by step continuity and the writing is clear and concise. An A+ without hesistation. I'm headiing back for more!

Thanks again for the direction.

[jimbo]

another thread I liked, that shows how to make some bearing supports if you have the tools to do it
New milling machine project

vipertx, how does one get the 50% discount at misumi?

[runswithscissor]

I am working with my local bearing store, who recommended a sealed bearing flange mounted. I have installed them, but was a little reticent due to the resistance. I can turn the shaft by hand and move the z axis carriage along the y axis. I intentionally oversized my stepper for that reason. The bearing store said that if I did not seal whatever bearing I used, that I would have trouble. Frankly, I am still worried about the resistance. Has anyone tried sealed bearings, and did it overheat the stepper? If I had the tools, I would fabricate like 5bears. If anyone has a source, let me know and I will see if I can afford.

[futura]

Hello again,

You may be interested in a request for information I posted in the Bridgeport Mill forum regarding bearing selection and block designs for the Brigdeport type ballscrews I am using in my design.

Jimbo, I just looked over the thread you suggested, thanks!

[NC Cams]

How accurate and how repeatable do you want to get and how much do you want to spend???

An ABEC 7 true ball screw bearing (IE 24TAC47...) will be deadly accurate, have minimal axial runout and be very stiff due to precise and high preloading and inherent stiffness (IE; 60 deg internal contact angle). It will spin as smooth as glass and last a long time.

A deep groove ball bearing (IE 6204 shimmed to preload) will not be as stiff as the above, be MUCh cheaper and spin like a cement mixer at a fraction of the preload of the 24TAC47. It will last OK but not as long as the above TAC at the same preload is a 6204 is designed to be loaded at high axial loads as a true ball screw bearing

Check out the prices for a pair of NSK 6204's (or anybody's) and then check the price (and accuracy specs) of 24TAC47( ) ball screw bearings or anybody's equivalent. ( ) denotes more data but can't recall it off hand.

Simply put, you get what you pay for.