How did they do it? (Fit a tailstock key)?

[graham-xrf]

I just have to wonder how the 3/16" wide tailstock anti-rotation key was fitted into the casting of South Bend 9" lathes.
I must stress that at this point, I ask entirely from curiosity. Messing with something like that is not really where I want to go!

I happen to have the 9A tailstock apart for other reasons, not least of which includes a cleanup + paint job. Key evidence of a more "relaxed standard" paint job is where some daubs made it onto the quill clamp lever. Rusty too! The key has a couple of small burrs which do scratch on the quill slot. I think I can take care of that - even working down the hole.


Hmm.. Let's set the picture sideways? You can see the little fella down there.
The original circumferential boring marks remain along where the quill keyway would be, and everywhere else has been rubbed axial.
There is a sort of slight oval depression around where it fits. The part number is 286, or 286NR1.

I know it is a separate item, but it has so become one with the tailstock casting, it looks like it was cut free out of the Universe!
Just suppose (shudder), the bore was so messed, someone chose to bore it out again. How would they ever get it out?

 

[darkzero]

Not sure on SBs but on some tail stocks I hear there is a hole drilled through the TS. Can see the hole when removing the bottom half of the TS to drive the key out.

I had to make a new one for my import lathe but mine was not pressed in/tight, I was able to just lift it out with tweezers.

 

[graham-xrf]

My thanks darkzero.
Going on what you said, and given that the paint job was to be stripped down to metal anyway, I scraped some of the paint away from the outside of the casting - and there it was! Some kind of slant drilled insert.



This one does not look like it would simply "lift out" anytime soon.

I am so much resisting "getting further down the rabbit hole", as you folk have warned, but I am now thinking now it may be more than just curiosity. I have in mind that since the new quill has to be made anyway, I would not simply make it the same size as the old one. I would try to "fit" it, hoping to take up any wear. This may not be such a good plan if the wear is uneven, or mainly around the MT2 taper end. There may come a point where I have to consider pulling out the key.

I thought about "how much wear should we care about"? Being the type I am, I have now measured the wear.
With the quill extended to the 2" maximum on the markings, the waggle is 0.012".
This remains so, even with the benefit if having the ACME screw and thrust nut in place.
It would drive me crazy trying to get a centre-drill to start it's hole at the centre without it getting dragged around in little 12 thou circles!

I am hoping I can improve things back to "nice" just from the new quill, without having to straighten up the bore in the tailstock casting as well.
Now THAT would be a novel problem for one like me!

There is a YouTube video of where someone made up a trick boring bar that could slide up the middle of a keyed adapter in the chuck, but I lost the link. Maybe I won't look for it unless all else fails. Dang! 0.012" sideways is a whole 0.3mm. Way too much!

 

[graham-xrf]

Not sure on SBs but on some tail stocks I hear there is a hole drilled through the TS. Can see the hole when removing the bottom half of the TS to drive the key out.

I had to make a new one for my import lathe but mine was not pressed in/tight, I was able to just lift it out with tweezers.

When you say "drive the key out", was that "drive out into the bore", or drive out the other direction, out of the tailstock casting?
OK - so yours just lifted out, and was not SB anyway.
I have searched for information on this, and so far struck out. This may be one of the few places on the Planet where SB tailstock key removal will end up fully described!

 

[darkzero]

When you say "drive the key out", was that "drive out into the bore", or drive out the other direction, out of the tailstock casting?
OK - so yours just lifted out, and was not SB anyway.
I have searched for information on this, and so far struck out. This may be one of the few places on the Planet where SB tailstock key removal will end up fully described!

Yes I would think it would drive out into the bore. Again I don't know about SBs but that's how I've seen them come out on other lathes also.

May not help much at all since I have a modern import but here's what mine looked like.

 

[SLK001]

Are you sure that it is "slant drilled"? It's probably just a straight in key that is ground to match the contour of the shell. It will probably just push out - I doubt that it is anything other than a light press fit.

If you are going to change the bore, look into line boring, which can be set up on your lathe. Have a look at this post over on practicalmachinist. The OP goes thru his reboring of his H10 tailstock. Pretty interesting read.

 

[MrWhoopee]

It would drive me crazy trying to get a centre-drill to start it's hole at the centre without it getting dragged around in little 12 thou circles!

If you're center (centre) drilling with the quill fully extended, you deserve to have it dance around. No worries, apply a little pressure, it will find the spot.

 

[graham-xrf]

If you're center (centre) drilling with the quill fully extended, you deserve to have it dance around. No worries, apply a little pressure, it will find the spot.

You are right, and for me, long quill centering has never happened, partly because of instinct, and partly because I have simply not been at machines long enough to do much centre drills. I got the 9C properly rotating in 2018, and I have not actually been using it much. Maybe playing snooker in my teens taught me why long shots with too much cue sticking out are harder to do.

Still, from what you said, I went back to the measure, this time with the quill extended only about 6mm (1/4").
The play is, or course, much less, but it does not decrease to near zero!
I get it somewhere between 0.003", and 0.0036".

The measure set-up is, I admit, a bit ad-hoc, just being done on a tile, using the measure arm of a height gauge.
I bias the quill upward, and set the gauge down to just graze it. I use my multimeter resistance continuity beeper to tell the contact. Then I slightly press the quill downwards, and use some feeler gauge shims.
0.09mm makes it through with the little "feel".

So maybe the centres it finds by itself, "with a little pressure" will be entirely good enough. Even so, if I get the chance to help it a bit, I would probably try.

 

[graham-xrf]

Are you sure that it is "slant drilled"? It's probably just a straight in key that is ground to match the contour of the shell. It will probably just push out - I doubt that it is anything other than a light press fit.

If you are going to change the bore, look into line boring, which can be set up on your lathe. Have a look at this post over on practical machinist. The OP goes thru his reboring of his H10 tailstock. Pretty interesting read.

Just looking at the outside, and where it arrives on the inside, it is not a hole perpendicular to the bore.
It looks to be at a 45° slant. Confirming this, in the picture, the hole is going through a casting fillet and the hole seems square-on to the fillet. The hole shape outside seems round except for the narrow curve of the fillet. The shape of the key entry into the bore looks oval, and the long part is the way you would expect from a slant entry.
I am definitely going to give it a tap this way or that, and see if it moves.

Thanks much for the link on line boring.

 

[RobertB]

Just looking at the outside, and where it arrives on the inside, it is not a hole perpendicular to the bore.
It looks to be at a 45° slant.

This is the line drawing from a 1935 SB parts list:



The key bore is indeed at an angle