Myford VM-B mill

[Martin CusdenParticipant @martincusden44107]

After 15 years the locating pin for the arbour, R8, has become worn. I see that it is an Allen screw, but only half the key access is visible. Having undone the rubber gaitor all appears tight. Has something moved?

[Martin CusdenParticipant @martincusden44107]

[Douglas JohnstonParticipant @douglasjohnston98463]

My VMB is exactly the same so looks like a complete strip down would be needed to replace the locating pin.

Doug

[BazParticipant @baz89810]

Exactly the same problem with mine, happened last summer. I have done without it up until now and wonder if I really need to repair it or just carry on with it as it is.

[Clive FosterParticipant @clivefoster55965]

In the Bridgeport user world there is a significant school of thought claiming the locking pin to be, in practice, an unnecessary refinement which can be done without if sheared or too damaged to work as designed. Some of the folk who advocate this have skills and knowledge of the very highest order so its certainly a viable viewpoint albeit one with which I personally disagree feeling that if it wasn't needed Bridgeport wouldn't have designed it in.

To my mind the more important question is what casued the wear. After all the only thing the pin does is to restrain the arbour or collet against rotation whilst being spun up or down the drawbar thread. So far as I can see there is always a bit of oil floating around there and restraint forces against a free running thread will be minimal. As soon as things begin to tighten up the taper engages absorbing most of the twisting forces. So it ought to last pretty much forever.

In the Bridgeport world shearing is much more reported than wear. Presumably due to something highly loaded and inadequately tightened, so the taper cannot supply all the drive force needed, hammering against the pin until it breaks. Flycutters or the larger variety of face-mills being obvious suspects. May be worth checking the mutual fit of your R8 tooling and spindle to ensure you don't have potential problems of that sort.

Clive.

[KWILParticipant @kwil]

I have done without one on a Bridgeport for some time, it is probably more useful if you tighten the drawbar by hand, because it will draw in slowly. I use a power draw and hence it is faster and snaps home the R8 with no rotation as I hold the arbor.tooling by hand as well.

[Max FranceyParticipant @maxfrancey87566]

I have the same issue with my Myford VM-B, and am just looking at replacing the grub screw which provides the register. I think the damage was caused when I inserted an R8 arbour for a slitting saw. The arbour was tight and fooled me into thinking the draw bar had properly seated it. When the saw touched the metal I was cutting, the arbour spun in the spindle. Fortunately the spindle still seems OK, but obviously the register is no longer there. It looks like removal of the oil seal will not allow proper access of the grub screw, so I would need to loosen the elastic stop nuts at the top of the upper roller bearing and lower the spindle 4mm or so to give access. I'm loathe to do this as I'm unsure of the process to pre-load the bearings.

So, the question is, do I put up with lack of register (seems ok from the posts above), or do I plunge in and lower the spindle. What do folks think?

[Chris Evans 6Participant @chrisevans6]

It is not a big job on a Bridgeport to replace the location screw, I can not comment on the Myford. I have not had a screw in my Bridgeport for many years now and it works OK, just my idleness as I even have the 1/4" 32 tpi die to make a new screw.

[Roy MParticipant @roym]

I have worked professionally on Bridgeport machines for probably the best part of 40 years, lastly on E-Ztrak. Usually what happens is that the key shears, you order one from Bridgeport, you use the machine while waiting for the key, weeks later the key arrives, having not noticed any detriment to operating without said key. Then you fit the key. Two weeks later, the key shears, you order one from Bridgeport, then when it arrives, you put it in your toolbox forever.

Roy M.

[Max FranceyParticipant @maxfrancey87566]

Conclusion then: The key does very little, and since the VM-B requires a strip down to fit a new one, its not worth bothering.

Thanks for the inputs folks

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