Replacing thrust bearings yourself?

[SRT Mike]

How hard is it to replace the X and Y axis thrust bearings on a 12x18 VMC? It's a Leadwell MCV-0P and it started making bearing noise on X movements of the table. I figure its easier just to replace the Y at the same time.

Should I get the bearings from Leadwell or are same-size replacements from McMaster suitable? Any special tools or procedures I need to follow?

[HuFlungDung]

Gosh, I do so want to be a troll and post a reply that will get NCCams in here

Did you slide back the way covers and have a look yet, Mike? If they are bad, there is little choice but to tackle it. I would remove the originals carefully, noting orientation, shims etc, and look for the bearing numbers. I'd go to a bearing supply house, rather than getting "original" parts from anywhere, if possible, but sometimes you might have trouble getting bearings of a certain spec from a general supplier.

[SRT Mike]

Originally Posted by HuFlungDung Gosh, I do so want to be a troll and post a reply that will get NCCams in here Did you slide back the way covers and have a look yet, Mike? If they are bad, there is little choice but to tackle it. I would remove the originals carefully, noting orientation, shims etc, and look for the bearing numbers. I'd go to a bearing supply house, rather than getting "original" parts from anywhere, if possible, but sometimes you might have trouble getting bearings of a certain spec from a general supplier.

Feel free to troll my thread, NC's response would be good Should I just bore the bearing holes out 10 thou and use loctite to fill in the gap? hehehe

Anyway, i pulled the way covers but there isn't much to see - I can't hear much because the machine noise overwhelms the bearing noise. The guy I got the machine from told me when I got it that the X thrust bearing was making some noise, now it's really noisy/grinding.

I figure my options are to call the manufacturer and have their guy come out and probably pay a couple grand or more. Or to call an independent repair guy and probably pay a hair less, or do it myself and probably pay $50 in parts.

I assume it's just a bearing block with a cap on the end supporting the end of the leadscrew? I don't know if I'm talking about taking the table off and doing a whole lot of work or just something I could do while leaving the screws on the machine and jogging the table all the way to the side to do one, then back the other way to do the other end of that screw, then do the same on the Y?

Also not sure if the bearings need greased before install and if so is it a special kind of grease? I have the manual on the mill but it doesn't get into things like replacing bearings.

[Tailwheel]

Originally Posted by SRT Mike How hard is it to replace the X and Y axis thrust bearings on a 12x18 VMC? It's a Leadwell MCV-0P and it started making bearing noise on X movements of the table. I figure its easier just to replace the Y at the same time. Should I get the bearings from Leadwell or are same-size replacements from McMaster suitable? Any special tools or procedures I need to follow?

I know the Taiwan machines well cuz I worked in Taiwan for 8 years and designed and manufactured my own machinery for many years. Paul Chang, the president of Leadwell was a good friend of mine when I lived there.

It's pretty easy to replace the bearings. They are probably combination radial/thrust bearings and should be bought from a bearing house that sells precision bearings.

First, remove the old bearings and get the bearing numbers. You will have to remove the ballscrew support on the other end of the table and then by rotating the ball screw, you should be able to jack the ballscrew free on the end that supports the drive. You may also want to replace the support bearing as well. It is an ordinary ball bearing. You will not want to place any lubricant on the replacement bearings as they should be lubricated by the pump that supplys oil to the ballscrew. It's a no-sweat job, but will probably take you a full day if your lucky and the bearings are in stock.

When you reassemble the drive, put a 10's indicator on the end of the ballscrew and check for backlash. You may have to shim the INNER bearing race to remove any lash.

I'll keep an eye on this thread and if you have any questions, I'll try to answer. Incidentally, leadwell has been out of business for about 15 years or so now.

[NC Cams]

TRUE ball screw support bearings are NOT the same as "generic A/C bearings". YOu might be able to determine the size using the numbers off the bearing but do not necessarily expect the EXACT replacement using this "identification" method.

Many "custom" bearings were made from generic "cores" with all sorts of trickery inside. Sort of like saying the Chevy in your drive way is the same as the ones they race at Daytona - not f'ing hardly. For this same reason, generic replacements often suck when it comes to duplicating OEM performance.

Ball screw bearings are typicaly heavily preloaded and have a very high (roughly 60 deg)internal contact angle to make them stiff so that axial deflection is low and position accuracy is high. Regular spindle bearings don't have these features thus they fall short in performance in ball screw supports.

Chances are you'r going to either have a duplex or quadriplex bearing in the ball screw thrust/support position. A duplex ABEC 7 that is essentialy a tricked up pair of 6204's will run about $825 PER bearing set (20TAC47 is basic NSK part number). There are other sizes and configs so don't quote me on that price or size - that is just a size I'm familiar with.

Some screws are "stretched" between dual thrust bearings on either end and some are fixed thrust on one end and float on the other - which do you have?????

A quad setup will probably be a multiple cost of that. Bigger bearings or special sized ones are more costly - economies of scale are quite critical to bearing pricing and availability.

It is hard to say what you need until/unless you provide size and/or design information. Use extreme care in taking the thing appart - the bearings ARE probably quite position and/or direction sensitive, especially when you reassemble them!!!

Some bearings are lubed for life with grease - some are oil lubed via a pump, depends on the machine design. I'm not familiar with the specifics of your machine but it will be one way or the other.

EDIT: YOU CAN NOT ALWAYS REPLACE ANY SHIMS THAT ARE USED INBETWEEN BEARING SETS ON AN END AS IS.

Why? Because in some instances, the OEM used unequal custom width shims and NON PRELOADED bearings to create a custom preloaded bearing.

If you buy preloaded bearings you have to grind the shims to an equal common width and rely on the built in bearing preload for stiffness and bearing accuracy. THIS IS NOT COMMONLY KNOW BY BEARING HOUSES and by very few aftermarket machine tool bearing engineers. You may have heard it here first.

And people wonder why bearings replaced in service don't always replicate OEM performance????

BTW, trolls are good for green leafy plant life as they do make good carbon dioxide generators but one can argue that they are not necessarily good for much else.

END EDIT.