How to cut/grind new sub-spindle chuck jaws

tome9999 · Feb 2, 2020

I bought new chuck jaws for a 3-jaw chuck in a lathe with a main and sub-spindle. These are hardened chuck jaws for the sub-spindle. After installing them and lining them up for a work piece I noticed that the workpiece was not running true. There is a slight but visible wobble. The workpiece I used happened to be turned down on the main spindle. So, I guess the new jaws need to be trued up in relation to the main spindle? I have seen videos on grinding jaws with tool post grinders etc. but wondering what people typically do on a two spindle machine? Is there some way to put a grinding wheel on (very!) straight shank into the main and grind the jaws in the sub...? Or can they be hard turned with a boring bar?
-Tom

Milland · Feb 2, 2020

The basics, adjust for your needs:

YouTube

YouTube

Scruffy887 · Feb 2, 2020

tome9999 said:
I bought new chuck jaws for a 3-jaw chuck in a lathe with a main and sub-spindle. These are hardened chuck jaws for the sub-spindle. After installing them and lining them up for a work piece I noticed that the workpiece was not running true. There is a slight but visible wobble. The workpiece I used happened to be turned down on the main spindle. So, I guess the new jaws need to be trued up in relation to the main spindle? I have seen videos on grinding jaws with tool post grinders etc. but wondering what people typically do on a two spindle machine? Is there some way to put a grinding wheel on (very!) straight shank into the main and grind the jaws in the sub...? Or can they be hard turned with a boring bar?
-Tom

I have always turned soft jaws for Main and Sub spindle. Some day may buy hard jaws for the Main spindle. Someday. May send back if they wobble. I think hard jaws for the main spindle are for very low volume or
"one of" parts. If transferring to the sub spindle you are not looking at "one of" parts. Bore the jaws and at some point you will have a library assortment of good jaws.

tome9999 · Feb 2, 2020

Milland said:
The basics, adjust for your needs:

YouTube

YouTube

I saw these videos but these are for soft jaws. The jaws I have are hardened. So what do I do for these?
-Tom

jhearons · Feb 2, 2020

If you insist on using hard jaws in the sub, just use a stout boring bar and take a dust cut on the clamping surfaces.

Milland · Feb 2, 2020

jhearons said:
If you insist on using hard jaws in the sub, just use a stout boring bar and take a dust cut on the clamping surfaces.

Or kluge a die grinder so that it's mounted to the carriage, take light cuts with a good wheel.

tome9999 · Feb 2, 2020

Milland said:
Or kluge a die grinder so that it's mounted to the carriage, take light cuts with a good wheel.

That made me realize I can put a grinding wheel on an arbor into a live tool holder facing the sub-spindle and grind it that way.
Thanks,
-Tom

13engines · Feb 2, 2020

jhearons said:
If you insist on using hard jaws in the sub, just use a stout boring bar and take a dust cut on the clamping surfaces.

Like this person said. Just use a carbide or carbide tipped boring bar. Even insert drills make a good boring bar.

People drill out taps all the time using carbide, so why not hard jaws. There is no need for a grinder.

Hardplates · Feb 3, 2020

CBN or ceramic. In a day and age where hard turning has replaced most grinding OPS its not difficult to get the correct tooling.

D.D.Machine · Feb 3, 2020

There normally not that hard ,, low to mid 50`s RC and you can just take a light cut on them ,, I have done it a lot over the years to true them up ,,

Orange Vise · Feb 3, 2020

Standard carbide will not last cutting case-hardened chuck jaws.

But in an application like this, where you're just truing up one set of jaws, they don't need to last.

Expect the first edge to be toast roughing out the high spots, and the second edge should make it through the finish cut.

tome9999 · Feb 14, 2020

I ended up using a stout boring bar and carbide insert. Worked great and didn’t seem to mind the hardened jaws in the least. Thanks for the suggestions.
-Tom

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