I'm in the process of replacing the lubrication pipes for the table of my Elliot Sturdimill; I have had to remove the table to do this and I am wondering how to set the preload on the leadscrew bearings when I refit the table. The bearings are angular contact ball bearings at each end with a locking nut / thrust pad at one end which appears to be used to set the bearing preload. Do I just tighten it sufficiently to remove the axial play? TIA, Martin.
That sounds about right to me.
I did something like this on a mill spindle a while back.
Had one of those nuts with slots in (turret nuts?) and you had to bend a tab to set the nut in place.
I just set it so that it was one stop looser than too tight.
DOC
Talk to your friendly local bearing supplier. Mention the application and the bearing numbers if possible. This should get you the straight goods without guesswork.
Ken.
Do you have one bearing at each end of the shaft? Are they 7000 series (single row)? If so, you should probably check with the equipment mfg. to see what they recommend. Most angular contacts are ground to clamp together with the proper preload but if you have one at each end of the shaft you can easily have too much or too little preload. Also, make sure you install them in the proper direction (face to face or back to back as they may separate if facing in the same direction without something on the other end to accept thrust in the opposite direction. If they are double row (5000 series) then removing axial play should be sufficient and other problems do not apply.
Generally, pairs aren't used at the opposite ends of any long shaft....instead, if support is needed at the opposite end, then a standard radial bearing is used there, this because unequal thermal expansion rates would make setting and maintaining preload near to impossible.
Right - that's why I was not sure about his statement "The bearings are angular contact ball bearings at each end with a locking nut / thrust pad at one end which appears to be used to set the bearing preload." and wondered if he had one angular contact at each end (or pairs) which would be difficult to set and virtually impossible to maintain or double rows. You're right about a pair at one end and a standard deep groove radial at the other but this is not consistent with his comment of "angular contacts at each end". Sorry but I'm just in my constant state of confusion.
The bearings appear to be 7000 series (7305B) going by their dimensions; of course they're mounted with the markings on the inside of the housing so I can't get the full number and verify the preload class. This table DOES have
1 angular contact bearing at each end of the table, mounted in opposing directions as you would expect. I have a manual for the mill, but there is no mention of removing or adjusting these bearings. Elliot went out of business years ago, so there's no chance of getting advice from the manufacturer :-( I would think thermal expansion wouldn't be a major problem as the leadscrew and table are made of similar, if not identical, materials, so, provided the room temperature only changes slowly, the parts should all be expanding at the same rate; of course I could be totally wrong ;-) Martin
Call NTN Bearing Corp at 1-800-323-2358 and ask for aftermarket engineering. They may have info on Elliot or if not, can lead you in the right direction. Good luck.
The leadscrew can often heat up more quickly than the table, which typically has coolant being sloshed all over it--this especially true with cnc.
You might try these guys for purchasing the bearings :
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