Boring chuck bore

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SteveM
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Boring chuck bore

Post by SteveM »

I have a collection of chucks from my prior lathe, a 12x36 Atlas.

I now have a South Bend 9a, which has the same spindle threads. Saved me a bundle not having to buy a bunch of chucks.

When I went to thread on my Union 4-jaw, which has an integral mount and not a separate backplate, the chuck jammed as it got to the unthreaded portion of the spindle.

I measured the bore of the chuck and the diameter of the spindle and the chuck is about 10 thou under.

Trying to figure the best way to set this up.

I put a morse taper toolholder in the spindle and using the jaws was able to get the perimeter of the chuck to within a thou, but the perimeter isn't an important surface.

I'm thinking that I should indicate on the original bore, but I have no guarantee that that bore is correctly located. It's a few thou off right now as it sits.

The face of the chuck shows 6 thou of wobble.

I'm thinking that good thing to have done would have been to machine the rear surface of the rim while chucked up in my old lathe, which would have made that a reference surface.

The toolholder is out by a little over a thou.

I have a long MT2 extension I could use with an MT2-3 adapter and support with a live center on the other end, but that leaves very little room to get a tool in there (actually, whatever is holding that tool will be more of a problem than the actual tool).

Any suggestions?

I'm probably going to have to do this with several chucks. Some have backplates, so I can use a different approach.

Steve
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Bill Shields
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Re: Boring chuck bore

Post by Bill Shields »

I would consider holding the chuck body by a larger chuck in a bigger lathe.

What you have there is not so rigid and likely to cause problems once you start cutting .

Or clamp it face down on a milling table and shove a boring bar into it.

Send it here..will do it but shipping costs...

ALTERNATELY... If you have a chuck for the lathe that you can use to hold a big slug of material, then clamp the new chuck on it ...

Find a friend....

Yes, I would take a light truing cut on the back flange face at the same time
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SteveM
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Re: Boring chuck bore

Post by SteveM »

Bill Shields wrote: Tue Jan 10, 2023 6:49 pm ALTERNATELY... If you have a chuck for the lathe that you can use to hold a big slug of material, then clamp the new chuck on it ...
Turning a slug in place is a good idea.

Only problem is that THAT chuck suffers from the same issue.

I could start with the backplate for the 3-jaw. Put a milling spacer on the spindle, put the backplate on backwards, bore and then reinstall on the chuck.

Then use THAT chuck to fix the four jaw.

Then use the 4-jaw to fix the original problem, which is boring something to remove it from a tool where it is jammed.

Steve
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Bill Shields
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Re: Boring chuck bore

Post by Bill Shields »

Or put the back plate that you have on the spindle, then clamp the 4 jaw on it backwards.

You to not care if the back plate runs true ..you only care if the chuck onto which you are going to clamp to it runs true.

Careful adjusting and tapping with rubber mallet can get anything where you need it

Or did you already say that? :mrgreen:

We're it me I would clamp it down on a milling table...but then that is me.
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SteveM
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Re: Boring chuck bore

Post by SteveM »

Bill Shields wrote: Tue Jan 10, 2023 7:22 pm We're it me I would clamp it down on a milling table...but then that is me.
My milling machine is still in storage.

Steve
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Bill Shields
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Re: Boring chuck bore

Post by Bill Shields »

Good place for it..... :mrgreen:
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Re: Boring chuck bore

Post by Bill Shields »

Do you have a faceplate that fits spindle?
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SteveM
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Re: Boring chuck bore

Post by SteveM »

Bill Shields wrote: Tue Jan 10, 2023 9:32 pm Do you have a faceplate that fits spindle?
Yes.

Hadn't thought of that, even though it's sitting in the drawer right next to me, and I can see it staring back at me, as the drawer is cracked about 2".

That would just be clamping and bumping to get it centered, correct?

Steve
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Bill Shields
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Re: Boring chuck bore

Post by Bill Shields »

Yes. I would clean up the face of the chuck with a draw file to remove any high spots.
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Re: Boring chuck bore

Post by Rich_Carlstedt »

Careful there Steve !
The bored area of the chuck which hits the spindle shoulder means nothing , you can open it up ,020" to give you clearance.
But do not cut the face adjacent to the bore ! that goes against the face area of the spindle and that face was cut at the same time as the threads
were made and is perfectly perpendicular to the thread and it's pitch center. It's important to not mess with it !
Using the faceplate for mounting is a wonderful idea.. even if the new c'bored area is not concentric to the OD, it does not matter

Rich
Cleaning the front face first as Bill mentioned is a good idea before mounting on the face plate
SteveM
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Re: Boring chuck bore

Post by SteveM »

There are people who say that the bore is what centers the chuck, there are others that say it's the threads. Not sure who is right or wrong; maybe a bit of both.

If you put some spotting paste on the face of your spindle and put the chuck on, you may find that it's only contacting on a small portion of the face. The problem I see with that is that with such a small contact, it will wear and the chuck will go on at a different rotation from where it originally was when you machined it, so it might be off.

When I fit a new backplate to a chuck, I did that and scraped the surface until it made full contact. The angular change from doing that was probably infinitesimal, but when I put that chuck on it makes a solid thump. That, of course, was before machining the face and register of the backplate, which is not something I can do in this case because there is no backplate.

Steve
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Bill Shields
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Re: Boring chuck bore

Post by Bill Shields »

I have always assumed that the combined bore / spindle shoulder -> face contact area is what centers the chuck...and treated these surfaces accordingly.

in your quest:

I would recommend that you do your very best to get the bore concentric and maybe shim with paper as needed to get the contact shoulder / face area runout to as small a number as possible...since the face of the faceplate may not have zero runout (which in reality is not that difficult to correct)

keep in mind that most lathes (esp these old SB 9's with the sleeve bearings)...may also have some axial runout that you need to worry about as you take measurements -> it is not like you have tapered bearings on the spindle...
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