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Can you true up lathe chuck jaws on a mill?

jools

Aluminum
Joined
Mar 28, 2017
Hi all: me again :-)

I have my new Haas mini mill installed in the old garage now and am happily making big lumps of plastic turn into smaller lumps of plastic quite well :-) A lot of my big lumps of plastic are circular in profile so I quite often (90% of the time) hold them in a standard lathe 3 jaw chuck.

The problem with this method is my chuck is of dubious quality and the faces/points (bits that contact the workpiece) are not perpendicular to the table so if doing two op's part alignment can be dubious. If I had a lathe with a toolpost grinder I could sort this problem out, but I don't. So is there a way of doing something on the mill, without screwing over my fine new Haas investment with loads of grinding dust, that will help me with my alignment problem?

As an aside I had thought about flattening off the top of some soft jaws and making a set of pie jaws to bolt on, or making some soft jaws in the vice for the smaller bits (40mm diameter aka 1.5") . If I were to do this do you cut your soft jaws slightly undersize, if so how under size, or just bang on?

Cheers all

Jools
 
Mount a dremel tool in shank that can be clamped in the QCTP. Cover everything in aluminum foil to catch the grit.
Not nearly as accurate as a real grinder but sounds like it will make things good enough for your needs now. After it is done I would take the chuck apart and wash it out. Or will that ruin the ground in accuracy?
Bill D.

Idea to get you started. I would weld two pieces together.
Lathe’s Tool Holder Holds A Rotary Tool | Hackaday
 
Mount a dremel tool in shank that can be clamped in the QCTP. Cover everything in aluminum foil to catch the grit.
Not nearly as accurate as a real grinder but sounds like it will make things good enough for your needs now. After it is done I would take the chuck apart and wash it out. Or will that ruin the ground in accuracy?
Bill D.

Idea to get you started. I would weld two pieces together.
Lathe’s Tool Holder Holds A Rotary Tool | Hackaday

I don't have a working lathe :(
 
It sounds like you don't own a lathe yet so mounting anything in the QCTP is going to be an issue. There have been quite a few discussions about what you are attempting. Aside from all the other issues the main problem is that if the scroll is worn, then grinding the jaws only works on one diameter. There is really no way to fix a worn scroll. If your jaws are belled out and the scroll is still good you could probably improve the chuck by grinding. With the equipment you have you may be able to improve your chuck using your mill but it will take some thinking on your part. Since you do have a mill, you should be able to locate the chuck in the center of the spindle fairly accurately and fixture it to your mill table. At that point you could try a cast iron lap chucked up in your mill with a course abrasive to start with and tighten the jaws ever so slightly on the lap. Cover your ways with aluminum foil to keep the crud where it should be. I have some diamond coated rounds that would probably do the job but I can't say for sure where I got them since I've had them for over thirty years.
 
I’d do the soft jaws. Buy (or make) a set.
Clamp something in them to take up the backlash and mill the diameter you want.

Mark the jaws to match the master they were machined on and use the same spot to chuck and unchuck. You should be able to swap them off and on and get pretty good repeatability.

Eventually you’ll have a good assortment. I usually bore them a little big. Like .001
so the slug just slides in.
 
How are you holding this chuck on your mill? I'm asking
because how do you know the chuck is sitting flat?

If the chuck is shot balls, a new chuck is damn near free on E-bay.
If its a cheapy chinese chuck, just get a new one, don't waste your
time

You could also buy a stick of aluminum and make a stack of soft jaws
for your vise.


The good thing about a 3 jaw on the mill. Even if its out by a mile, as
long as its still perpendicular, it doesn't matter, you just dial it in
for the diameter you are running. If its 1/2" off center its not a big
deal, it will always be a half inch off center.

And don't tell anybody I told you this, but I have a 3 jaw I use on the mill,
its 12 years old, its a POS and it has a lot of miles on it. Its sprung
from abuse. Mainly from grabbing short stuff that barely goes into the jaws.
This also makes holding longer things problematic, they shift since the
jaws are bell mouthed. I wrap a piece of high temp masking tape around the part,
the stuff is maybe .002 or .003 thick and will squish, fixes that problem right
quick.

Just get a new chuck.
 
Buys Haas mini mill and can’t afford a Chinese chuck? Get another cheap 6” chuck with 2 piece jaws, I have a couple of Gator ones at home that are fine. Unless I’m mistaken and you have a 12” chuck on the table, then I might try and fix it.
 
There's a well respected tool grinder on this board that very frequently uses a Haas with diamond wheel to grind carbide tools, and he has for many years to no apparent detriment.

I posit that if you stuck a grinding rock in the spindle and wound it up with helical ramp you could touch up your jaws quite nicely. Flood coolant to keep the dust suppressed, then a thorough cleaning afterward.

Sent via CNC 88HS
 
It sounds like you don't own a lathe yet so mounting anything in the QCTP is going to be an issue. There have been quite a few discussions about what you are attempting. Aside from all the other issues the main problem is that if the scroll is worn, then grinding the jaws only works on one diameter. There is really no way to fix a worn scroll. If your jaws are belled out and the scroll is still good you could probably improve the chuck by grinding. With the equipment you have you may be able to improve your chuck using your mill but it will take some thinking on your part. Since you do have a mill, you should be able to locate the chuck in the center of the spindle fairly accurately and fixture it to your mill table. At that point you could try a cast iron lap chucked up in your mill with a course abrasive to start with and tighten the jaws ever so slightly on the lap. Cover your ways with aluminum foil to keep the crud where it should be. I have some diamond coated rounds that would probably do the job but I can't say for sure where I got them since I've had them for over thirty years.

Yeah it's more the belling that I'm worried about than the scroll accuracy. I can indicate to find the center everytime if need be as am low volume high profit stuff.

I thought about a centralised grinder/lap but couldn't find them in the UK (a lap that is) so maybe a cylindrical grinding wheel gently tightened would be a good place to start.

Jools
 
How are you holding this chuck on your mill? I'm asking
because how do you know the chuck is sitting flat?

If the chuck is shot balls, a new chuck is damn near free on E-bay.
If its a cheapy chinese chuck, just get a new one, don't waste your
time

You could also buy a stick of aluminum and make a stack of soft jaws
for your vise.


The good thing about a 3 jaw on the mill. Even if its out by a mile, as
long as its still perpendicular, it doesn't matter, you just dial it in
for the diameter you are running. If its 1/2" off center its not a big
deal, it will always be a half inch off center.

And don't tell anybody I told you this, but I have a 3 jaw I use on the mill,
its 12 years old, its a POS and it has a lot of miles on it. Its sprung
from abuse. Mainly from grabbing short stuff that barely goes into the jaws.
This also makes holding longer things problematic, they shift since the
jaws are bell mouthed. I wrap a piece of high temp masking tape around the part,
the stuff is maybe .002 or .003 thick and will squish, fixes that problem right
quick.

Just get a new chuck.

Its a front mounted chuck that bolts onto the Tee-Nuts.

It's pretty much new but the belling is an issue in what I do, not bothered about anything else on it. Just want to get it to hold a machined workpiece perpendicular to the table nicely.

ATB
Jools
 
Buys Haas mini mill and can’t afford a Chinese chuck? Get another cheap 6” chuck with 2 piece jaws, I have a couple of Gator ones at home that are fine. Unless I’m mistaken and you have a 12” chuck on the table, then I might try and fix it.

Buys Haas Mini Mill. Can afford any chuck he wants. Just wants to see if this one can be made good first rather than creating waste.

ATB
Jools
 
I've ground Kitigawa hard jaws on the surface grinder after documenting the taper and adding a bit for flex. I've hard turned them in place. Don't see any reason they couldn't be hard milled with a ring on them with something like a 3/4" dia long endmill.

When I've done stuff like this, it was cause it was a rush job that couldn't wait on tooling. 99% of the time it's more profitable to just buy the correct tool.
 
Its a front mounted chuck that bolts onto the Tee-Nuts.

It's pretty much new but the belling is an issue in what I do, not bothered about anything else on it. Just want to get it to hold a machined workpiece perpendicular to the table nicely.

If you don't want to buy a new chuck because front mounted chucks always go for a premium
and are harder to fine... There are ways around that.

Many moons ago, I needed a front mount chuck for my 4th. Over $300 for a POS, a non front
mount, same damn thing was about $100.

My 3 jaw that I use on the mill. Its mounted to a rectangular plate, and I just grab
the plate in a vise. No front mounting needed.

Just in the past 6 months, my chuck on my lathe crapped out, blew a seal.. I already
had a manual 4 jaw that I could mount on the front of the big 3jaw, so I just did the same
thing with the 3 jaw off my 4th. On the second cut I took, the chuck cracked.

So. Grab another 3 jaw POS that I had kicking around and put some holes in her and front
mounted her. Not a lot of clearance in there, but it worked for what I needed that day, and
then right after that a job came up that I needed a bigger through hole. Just bought a
cheapy 8" 3 jaw, and drilled some holes and face mounted that one also. Just cheap chinese
crap, about $100 with shipping. It'll get me by until I tackle the seal for the real chuck.

50397665007_5c63979197_c.jpg
 
Whats all this about grinding in the mill? Why not buy a decent (MA Ford, Garr, etc) carbide endmill and mill them? But as mentioned, if the scroll is worn it will only work *well* for the diamter you are cutting. Get soft jaws and mill them to size and be done with it, oh and label them as someone else said so they go back the same.
 
Whats all this about grinding in the mill? Why not buy a decent (MA Ford, Garr, etc) carbide endmill and mill them? But as mentioned, if the scroll is worn it will only work *well* for the diamter you are cutting. Get soft jaws and mill them to size and be done with it, oh and label them as someone else said so they go back the same.

Some chucks only have 1pc jaws.
 








 
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