[lagfish]

I don't understand why some choose to replace the stock thrust bearings with angular contact bearings? As far as I can tell, there is no radial force on the bearings. Any radial force is supported by the dovetail ways. The precision thrust bearing on mcmaster that looks similar to the stock ones on the x3 (6681K12) says they have a max dynamic rating of 2110lbs. This is more than enough to withstand the cutting forces.

[cncuser1]

The reason why angular contact bearings are preferd on the roller ball lead screws has been explained in detial in prevoius posts ( try a search) but the short answer is that by squeezing two of them you take up axizl play in the bearings, thereby gettinng much less backlash.

Two angular contact bearinngs would be used on a machine that also has two ball nuts on one screw. the ball nuts are separated by bellville washers.

Like i said try a search, it has all been talked about bbefore.

[lagfish]

I already did a search on thrust bearings. Couldn't find anything.
Yes, by squeezing them together you are preloading them to avoid axial play. This can be, and is done with the STOCK thrust bearings on the stock X3.
Now my original question was, why is it better to replace the stock THRUST bearings with ANGULAR CONTACT bearings?

[LongRat]

I wondered that myself. I can only assume that the stiffness of the preloaded angular contact pair is greater than that of preloaded axial thrust bearings. When I converted my X2 to CNC, I used preloaded axial thrust bearings, thinking that if it was insufficient, I had lost very little as they are so much cheaper than angular contacts. 2 years down the line, I am still running all the same bearings and still have absolutely zero end float, so I am not complaining.

[skmetal7]

I guess its up to you and your willingness to mount angular contacts. I'm using a/c bearings on my x2 mini mill, I guess I thought that it would be better in the long run and easier to fit on the axes. check out my conversion here (a work in progress): http://www.cnczone.com/forums/showthread.php?t=36403

You can get nice sized ones for 5/8" ballscrews from vxb.com or their ebay store for like $9.00 a set, so they aren't too expensive.

[lagfish]

I checked out the vxb site. I couldn't find any info on loading capacity or contact angle.

ABEC-7, 12mm ID, 15 deg, A/C contact bearings on McMaster states max radial load of 1243 lbs. If we assume axial to radial load capacity is proportional to the contact angle (I don't know if this is right, but it makes sense intuitively), then in theory the max axial load should be 1243 * 15 / 85 = 220 lbs. This is probably not enough.

If the VXB bearings have a higher contact angle than the mcmaster carr ones - say 40 deg, then it should work. Has anyone contacted them about their bearing specs?

If the bearings don't have to support radial loads, then going with A/C bearings is actually a compromise over thrust bearings.

[lagfish]

I just talked to vxb.com, the 7201 bearings have 40 deg contact angle.