Myford VMC Spindle Advice Please.

[Michael GilliganParticipant @michaelgilligan61133]

I hesitate to even mention the possibility, but here goes:

Is it feasible that the previous owner suffered a “crash” which ever-so- slightly bent  the quill ?

… that would explain a lot.

MichaelG.

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Graham.

I will examine the quill’s fit and movement carefully. I’ll turn the top on its side as you suggest to make this easier.

I’ve not seen any sign of damage, and the quill was always stiff but seems to have worsened lately. It would not move under its own weight with the pinion, lock and depth-stop all removed. I saw the edge of the interpenetration between the quill and lock bores was very sharp, and I eased that a touch with a fine file.

One edge I examined carefully is the top of the quill, for any sign of burring or bruising. There wasn’t any.

Err, you can’t readily refer back up-thread once on a new page, but someone asked if a previous owner had managed to bend the quill. That would have to be a hefty crash! There is no evidence for that, nor of over-enthusiastic lock-tightening. Doing that would more likely break the lock itself, perhaps snap its small handle, than harm the major components. No sign of damage to the rack and pinion teeth.

The quill has no external lubrication point, so could well be stuck on glue that was once grease. I’ll clean everything thoroughly with white spirit before trying the quill back in the head.

 

I succeeded in removing the lower bearing, with the aid of a hide mallet, but more to the point having chilled the spindle using a plumber’s pipe-freezing kit. The blurb says it will cool down to -50ºC: I can’t vouch for that but it certainly created an impressive frost halo on the steel.

The worn-out locating-pin turned out to be a tiny grub-screw. Identifying it was hard but it seems to be 6-32 or 6-40 ANC. I was surprised because the spindle is all to nice tidy millimetre measurements, I found when I measured the bearing and shaft. Metric screws don’t fit properly; 4BA fits rather sloppily.

The spindle appears unhardened and it may be feasible to convert the pin to the slightly larger M4, easier to obtain and compatible with its metric home. An M4 screw does nestle in a collet’s keyway. I’d wondered about even moving it to above the bearings; though hopefully once the machine’s back in action that will become my executor’s problem!

The bearing is an SKF, its number partly illegible, but I will contact Townsend Bearings about a replacement, and take it with me so we are sure. It seems to have a very slight rough point but I probably damaged it trying to remove it. Had I been unable to remove it at all I would have found an engineering-services company (possibly Townsend) or HGV garage able to carry out the work.

The thrust bearing is fine: that is not held tightly to the shaft so comes off easily, and shows no sign of harm. The top bearing similarly turns smoothly.

 

I’ve wondered why the pin / grub-screw became so mangled. My guess is insufficient draw-bar tighting so the pin became a drive key rather than to aid tightening the bar; and once it started to wear the problem worsened. It still seems a curiously weak detail. I’d expected a rectangular key held by a small screw.

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