Two Piece Lathe Jaw procedures snd jaw sizing ?

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jcfx
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Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby jcfx » Sat Aug 12, 2017 2:59 pm

From the start I've always used solid jaw chucks on my lathe ( it's what came with my 1st lathe )
having acquired a second lathe a while ago which came with a two piece jaw chuck which are new to me,
I look at the two pieced jaw chuck with dread, since the jaws stick out so much compared to solid jaws.
It does have some advantage since the jaws are so deep there's a little more gripping surface
than solid jaws, but it's a chore to flip them for outside gripping.

Which leads to my questions -
When the jaw inserts ( for lack of a better term ) on a two piece jaw are removed and replaced
should they seat back to registration or should they be preloaded so the jaws are even ?
I seem to need to either preload them or close them all the way with the allen screws just snugged
and check that the jaws are in contact then tighten the screws.

And do the jaw inserts have a standard sizing ? The removable jaws on the chuck look pretty worn and
I was thinking of replacing them

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SteveHGraham
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby SteveHGraham » Sat Aug 12, 2017 3:13 pm

Two-piece jaws allow you to use soft jaws and pie jaws, and you can also remove the tops of the jaws and just use the bases for holding certain things.

I never preloaded mine when putting them back. Not sure how you would do that. They register just fine.

Unless you have a weird chuck, you should have standard-sized jaws that can be replaced easily.
Don't trigger me, bro!

Harold_V
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby Harold_V » Sat Aug 12, 2017 3:57 pm

The typical design for two piece jaws includes registers that properly locate the top jaws. Considering the fact that there is typically far more error in the scroll/chuck relationship than clearance for the fit of the jaws, there is little to be gained by preloading the top jaws when they are installed. My practice is to hand load each one in the same direction it will be loaded in use, then I tighten the screws. If you preload using the scroll, you may overwhelm your ability to properly tighten the mounting screws.

When jaws are installed, they rarely return to the identical location from which they came (in spite of registers). You can see evidence of that when you machine previously used soft jaws. They will be close, but rarely correct. It is for that reason that one uses soft jaws, as they permit correction of any errors.

H
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jcfx
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Re: Two Piece Lathe Jaw procedures and jaw sizing ?

Postby jcfx » Sat Aug 12, 2017 10:59 pm

Steve, Harold, thanks for chiming in, the chuck is an old polish made chuck ( PUTm brand ) that came with my Maximat V10P
so I guess you could consider it a 'weird' chuck, the jaw inserts don't look like anything thats available.
Luckily the spindle thread is the same as my V7 so I've been using that solid jaw chuck on the V10P.
By preload i mean I'm lightly tightening the jaws so that the screws don't bind, and make sure all three jaws touch
before tightening the screws, I haven't tried it but I don't think I could tighten the jaws to the point where the screws wouldn't
tighten up, the jaw inserts have a rather massive register compared to offering out there now.
IMG_4800.jpg

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spro
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby spro » Sun Aug 13, 2017 1:23 am

Those Polish PUT m are generally well thought of. They are heavy, quite accurate but I agree that the top jaws may not be the same dimensions as a later standard. Remember this was Poland before the wall came down and they were very good at making chucks for Soviet machinery. These same factories evolved into Bison. I had never heard about those chucks on a Maximat but am not surprised either. Emco Lux chucks are a thing of beauty but I never saw one that large and my Emco has the separate outside jaws.

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NP317
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby NP317 » Sun Aug 13, 2017 9:31 am

When flipping those removable jaws around, I always swap them one at a time, and return them to their original location, after thoroughly cleaning the jaws and their seating areas.
I use tooth brushes and a clean cloth to clean them. Every time.
And I never expect perfection in location.
~RN

spro
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby spro » Sun Aug 13, 2017 11:17 am

A little clarification: The Enco lathe came with the PUT m ZD-6 chuck with reversible top jaws. It has a large spindle. My South Bend 9A has an Emco chuck and not nearly as heavy for it has separate jaws for holding larger diameters.
Another chuck, PUT m ZD-8 is an 8" chuck but the master and top jaws are 1 1/8" wide. The masters grip 1 1/8" themselves. The top jaws grip another 1 1/2" in normal configuration.
In all cases, everything is numbered, relieved and ground to a tight fit.

spro
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby spro » Sun Aug 13, 2017 2:51 pm

I want somebody to tell me what is Bad about these chucks. I can handle it and don't want to spread false information. Maybe I got lucky and maybe they wear over a time period unreached. These chucks come or came up on ebay. Most the time, the sellers didn't know anything about them. Tell me horror stories about them for otherwise, they are heavy peaches.

jcfx
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby jcfx » Sun Aug 13, 2017 4:44 pm

Don't have any horror stories about PUTm chucks, they seem well made with proprietary jaw insert registers ( keys as I would call them )
which makes it hard to find and buy new replacements. Lathe chucks for threaded spindles are universal to me, all you need is a corresponding threaded
back plate for your spindle thread and a truing cut to fit whatever flavor chuck. So an Atlas could have a Schaublin chuck.

spro
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby spro » Sun Aug 13, 2017 4:59 pm

Have you noticed there are six bolt holes to secure the custom backplate to the incuse register of the chuck. Then did you notice three more? If you turn a backplate for these, drill those three holes too. They adjust the scroll, although I hadn't needed to do that.

spro
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Re: Two Piece Lathe Jaw procedures snd jaw sizing ?

Postby spro » Mon Aug 14, 2017 4:36 am

Sorry, jcfx. I went right over your reply talking about Polish chucks. I never had one smaller than ZD-6 and they are heavy. Bison does make smaller and lighter ones these days. They could provide the same momentum closer to the head, altogether better.
There is something else. Bison or another inserted a brass emblem into the chuck face. I have seen these deliberately carved out. We still know it is a good chuck and it was made in Poland but there was a time when either it didn't meet expectations or the sheer hatred of a Bison within a gear. Those gears changed the world.


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