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1236 lathe tail stock shear pin?

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pmason

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#1
Started to play/learn my lathe, the Enco 1236, was drilling a hole, stepping up bits until the finally size and once I got to a 1/2 drill bit it started, then started to spin the tail stock. Now I didn't hear anything break, etc, but clearly it shouldn't be spinning.
Took a part the tail stock and see what was going on. Figuring there was could be a shear pin that goes into the key way. Did find a hole for something just in front of the locking pin hole but there wan't anything in there, (hard to see the photo). Did check the depth of the hole, was about 10mm deep. There is no evidence of the hole on the outside of the tail stock, but guessing they used body filler to hide it.
I was thinking of just creating a brass shear pin to place into the hole to go into the key way.
Thoughts? How tight should the pin fit? The key way is just over 5mm wide.
IMG_20180102_162922.jpg
IMG_20180102_162937.jpg
 

benmychree

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#2
If there was a way for you to do it, I would find a way to cut a keyway inside the tailstock bore and forget about the pin, or whatever it is; using a pin is not good practice for machine building, it is just a cheap way to get the machine out the door.
 

Bob Korves

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#3
From the factory there should be a pin in the front hole to counteract against the torque. Looks like it is broken or missing, or perhaps unscrewed part way. It will work with the sizes of drills you were using, much larger and the pin may fail. benmychree has the correct idea, he also has the tooling and skills to do the work. Most of us do not...
Edit: The pin needs to be hardened steel if you want it to last. Brass will not take the loading, and mild steel might not either.
 

benmychree

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#4
Thanks, Bob for your vote of confidence; my first encounter with this was with my old American High Duty lathe from 1916; the tailstock was worn out in every way; the quill was as sloppy "as a pr-ck a lard bucket", it had a stack of shims between the base and the top part and the key for the quill was worn out both on the quill and the upper body of the tailstock. I threw away all the shims, rescraped the bottom of the tailstock to fit the ways, then linebored the upper part to clean up and made a new quill to fit and milled a keyway in it; to deal with the sloppy keyway in the upper casting, I machined a dovetail keyway with the shaper and made a similar dovetail key that was driven into the keyway; the result was a tailstock with near perfect alignment with the headstock and no slop anywhere.
 

benmychree

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#5
The thing is that a pin has very little bearing area and will last very little time before loosening up and wearing into the quill; a parallel key is the proper cure.
 

mikey

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#6
It's curious that there is no evidence of a broken pin. I would suggest you explore the outside of the tailstock body to see if there is a threaded section in the hole the pin would go in. Most pins have a threaded section and the actual "pin", the part that fits in the slot in the tailstock quill, is a turned down section on the end of that threaded stock. These screws are typically hardened and the pin part of it is a light slip fit in the quill slot. The pin in my Emco Super 11 has a class 3 fit on the threaded part; moves with some effort.

I would agree with benmychree - a key is the best way to do this IF you can modify the tailstock to accept it.
 

francist

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#7
I'm curious now as to how the quill could spin in the tailstock if the locking pin was in place, regardless of what the purpose of the second hole pictured in the bore is? Any chance that the observed spinning was actually between the tapers and not the quill itself?


-frank
 

Tozguy

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#8
It seems to me that a brass shear pin with a T head for aligning the quill is a good idea. Of the possible outcomes of excessive torque on the TS it seems to me that replacing a shear pin is the easiest and least expensive one to fix.
I'd be looking at modifying a brass T bolt (for toilets) to fit the existing hole and slot.
 

pmason

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Thanks for all the input. Yes I don't think there was a pin in there, maybe the previous owner lost it or took it out for some reason. When I was taking it a part I was assuming there had to be some hole for a pin but I couldn't find it until I took the quill all the way out. On the out size you can't see where there is a hole, but assume there is one under the paint and body filler they used, hence I don't think it threads in.
I just assumed it would be brass, but as Bob and Mikey is recommending it should be harden steel. But I do like the idea of a T-bolt but would the head be thick enough, will stop by the hardware store and see what I can find.
 

Tozguy

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I had a look at my TS and can confirm that the 'key' is made of steel. The key is a T shaped pin that just sits in the hole, the head prevents the pin from falling through the hole. The hole is drilled from underneath and is clear, not threaded. Somehow I still feel like a brass one is better.
 

Bob Korves

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#11
My Chinese 13x40 has a threaded hole coming up from the bottom of the tail stock casting and a hardened pin that fits the slot in the quill and is threaded at the bottom. It has a screwdriver slot for adjusting it. The pin is screwed in from the bottom until it bottoms out in the quill key slot, backed off just until it will slide freely the entire travel of the quill, and then a lock nut is tightened to the pin to hold the setting. It is a poor design. Its only redeeming quality is that it will probably fail before something more expensive does.
 

francist

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#12
Most interesting that one can step drill all the way up to half inch with no pin of any kind in there. Bizarre.

-frank
 

pmason

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#13
I went the brass screw route, did pick up a couple of toilet bolts but they seem to have thin head to them.
IMG_20180103_110919.jpg
 

Tozguy

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#14
My Chinese 13x40 has a threaded hole coming up from the bottom of the tail stock casting and a hardened pin that fits the slot in the quill and is threaded at the bottom. It has a screwdriver slot for adjusting it. The pin is screwed in from the bottom until it bottoms out in the quill key slot, backed off just until it will slide freely the entire travel of the quill, and then a lock nut is tightened to the pin to hold the setting. It is a poor design. Its only redeeming quality is that it will probably fail before something more expensive does.
Is it difficult to get a wrench on the lock nut while holding the screw? Sounds similar to some valve lash adjusters on some four stroke motorcycles.
 

Bob Korves

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Is it difficult to get a wrench on the lock nut while holding the screw? Sounds similar to some valve lash adjusters on some four stroke motorcycles.
It is like a valve lash adjuster, but upside down, hex nut locking a screw with a screwdriver slot. In any event, it only is to stop rotation of the quill, so the adjustment is by no means critical, just get as much engagement as you can without bottoming in the groove and stopping or slowing the quill movement.
 
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