Chuck seating on headstock spindle problems; Chuck minimum runout

ONE - I have been restoring a 10L tool room lathe. It is mostly up and running, but I noticed that the chuck that came with it is .015" out of center. I bought a face plate and an old Buck 4 jaw for it and got a spindle adapter made so I can use a Jacobs 58 for really small jobs. THE PROBLEM. Only the face plate seats against the spindle shoulder, the others hang up on the unthreaded portion of the spindle, I'll call it the spindle shank. I've seen many comments about how important seating on the shoulder is as well as suggestions that the various face plates be cut out a little so they clear the "spindle shank." NOTE: SWARF, CLEANLINESS AND LUBE ARE NOT THE ISSUES.

My thought is this: This is a beater lathe, the ways are marginal. Why not just take a couple of thou off the spindle shank. Then everything fits, the fix was fast and the next thing I buy will fit as well. I'm looking for more experienced folks than me to weigh in on this and the potential unintended consequences.

TWO - Once shoulder alignment is settled, shouldn't I face off the face plate and even 3 & 4 jaw chucks (after removing the jaws) to minimize runout when seating material against the face of the chuck. I recognize that the jaw faces would be slightly non-orthogonal to the chuck body.

Why not do what is really needed??? Measure things before cutting anything..

Most likely you will need to open up minor diameter of the screw cut chuck backplate threads, a few thousandths.

The spindle threads were thread milled, they do not have the sharp v shaped thread root of a single point cut thread. Most chuck backplates have been single point threaded...

ALWAYS modify cheapest, easiest to replace part..

Your method will result in a chuck/backplate that still does not fit on spindle all the way..

Well it will, after you remove all the threads...

And yes I had to open up minor ID of threads, on all the non SB chucks I fit to my spindle..

Sometimes counter bore at spindle end of chuck, needs to be deepened.. The threads on spindle simply do not get close enough to spindle shoulder before stopping..

abarnsley said:

Why not do what is really needed??? Measure things before cutting anything..

Most likely you will need to open up minor diameter of the screw cut chuck backplate threads, a few thousandths.

The spindle threads were thread milled, they do not have the sharp v shaped thread root of a single point cut thread. Most chuck backplates have been single point threaded...

ALWAYS modify cheapest, easiest to replace part..

Your method will result in a chuck/backplate that still does not fit on spindle all the way..

Well it will, after you remove all the threads...

And yes I had to open up minor ID of threads, on all the non SB chucks I fit to my spindle..

Sometimes counter bore at spindle end of chuck, needs to be deepened.. The threads on spindle simply do not get close enough to spindle shoulder before stopping..

Click to expand...

WHAT HE SAID!!!

Pete

abarnsley said:

Sometimes counter bore at spindle end of chuck, needs to be deepened.. The threads on spindle simply do not get close enough to spindle shoulder before stopping..

Click to expand...

I just did this to a backplate last week. Modifying the spindle would never have occurred to me because it would be hard to do and easy to screw up a spindle I can't replace.

Try installing it backwards to see if it threads down all the way. If it does, then your threads are the correct pitch diameter and it's the counterbore. If it does not, then it's the minor diameter.

Steve

If that's the case (register diameter wrong or too short) then you can fabricate a spacer ring,
put the spacer ring under the backplate when it's threaded on backwards.

This presents the register diameter at the front so you can machine it.

yes, to above.

a simple slip fitting ring that is wide enough to cover the spindle register
slip it on,screw plate on backwards, and bore out the register.

No fuss. Dead easy.

jim rozen said:

If that's the case (register diameter wrong or too short) then you can fabricate a spacer ring,
put the spacer ring under the backplate when it's threaded on backwards.

This presents the register diameter at the front so you can machine it.

Click to expand...

Use a milling arbor spacer. Hardened and ground accurate and parallel. I used one to do just that.

Note that you don't need one the exact size - it just has to sit flat on the spindle register and the face, so if your spindle is something odd like 1-5/8", you can use 1-3/4.

Steve

There was not any problem with the threads. Just as I stated, my spindle shank is on the big size. But, I bow to the experience and knowledge on the forum. It took about 5 hours to go through all my various chucks and remove the back plates, then enlarge the counter bores. I also did some chuck maintenance while I was at it.

For one, I had to use a wooden spacer (hole & band sawing) to get the back plate out far enough. Now the runout is 5 mils or less on all the chucks and 3 is typical. Thanks for the help.

PS. In a small way, I did get to experience some of the thrill of the industrial revolution. The first one was hard, it started way off center. After I re-assembled the first one, I was able to use the newly accurate chuck to hold the next one much more accurately.

South bend literature shows the register to be over sized I think nine thousandths. Some of them are more. Look at tooling dimensions chart in HTRAL.