3 jaw chuck

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ALCOSTEAM
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Re: 3 jaw chuck

Post by ALCOSTEAM » Sun Dec 08, 2019 10:53 am

When I bought my first lathe almost 30 years ago I got the "best" lowest grade chucks the guy was willing to let go of. In hindsight it would have been far better to of negotiated a better price and left the old wore out chucks and bought the best new I could afford at the time. I finally bought new Bison 3 and 4 jaw chucks, and even a nice used Buck 3 jaw adjust tru. Once fitted and tweaked even being a threaded spindle life was so much better not fighting wore out junk.
Precision is so much improved and easier to achieve once you get past the threaded spindle lathes.

justinp61
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Re: 3 jaw chuck

Post by justinp61 » Mon Dec 09, 2019 10:25 am

hoppercar wrote:
Fri Nov 15, 2019 9:12 pm
My 3 jaw chuck on my south bend lathe does not run concentric very well. This is a non adjustable three jaw that is threaded directly to the spindle. The jaws screw into the chuck scroll plate, is there any way to regrind these jaws to get them to run true again ?
I had the same issue on a South Bend 9A that my Uncle gave me about 15 years ago. I took the chuck apart, cleaned it good and put it back together and it still had .007" run out. Tiring of trying to use a shim every time I wanted to use the machine I ordered a new cast steel 3 jaw chuck and mounting plate from Shars. The description stated that the mounting plate would require no facing but mine did, it had a spot that was .004" out. The new chuck runs nice with just under .002" runout.

John Hasler
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Re: 3 jaw chuck

Post by John Hasler » Mon Dec 09, 2019 11:08 pm

Runout in a three-jaw is a much less serious problem than is bellmouthing. When I need something accurately centered I use a four-jaw.

reubenT
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Re: 3 jaw chuck

Post by reubenT » Tue Dec 10, 2019 10:37 pm

When I got my ancient FE Reed lathe it had a cracked and very inaccurate 3 jaw scroll chuck. (and of course the 4 jaw independent and face plate and a bunch of tooling.) But I needed accurate scroll chuck, so I found in the grizzly catalog an 8" universal bolt on 6 jaw scroll chuck with reversible jaws and it had provision for alignment. So I got that and made an adapter back plate for it from 3/4" plate steel with steel ring welded to it and turned just right for the adjuster screws to work off of. It would go on the back piece of the old chuck. A screw on with bolt flange. It works nice, I can make fine adjustments to it and get it down to inside .001" accuracy when needed. The lathe isn't perfect, when I need to do something really precise with it I usually find the thing off center just a hair and have to realign it with gauge riding on a round milling bit in the chuck.

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liveaboard
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Re: 3 jaw chuck

Post by liveaboard » Wed Dec 11, 2019 3:15 pm

A trick I found; I mark the position of work before taking it out of the chuck.
If put back in the same position, it's usually close to where it was during the previous cuts.

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NP317
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Re: 3 jaw chuck

Post by NP317 » Wed Dec 11, 2019 9:22 pm

Same here.
RussN

John Hasler
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Re: 3 jaw chuck

Post by John Hasler » Thu Dec 12, 2019 12:13 am

When I'm using a three-jaw I just don't take the part out of the chuck until I'm done. I sometimes take the chuck off with the part still in it, do something else, and the put the chuck back on, though.

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liveaboard
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Re: 3 jaw chuck

Post by liveaboard » Thu Dec 12, 2019 2:38 am

When you can, that's best.
For instance, yesterday I had to bore a collar, then press a bushing into it, then make the final bore on the bushing.
The accuracy required for the whole thing is fairly casual. It could have been done by calculation, but it was easier to just take the part out of the lathe and then put it back in the same position.

Harold_V
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Re: 3 jaw chuck

Post by Harold_V » Thu Dec 12, 2019 2:45 am

Soft jaws. They solve all those problems.

H
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SteveM
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Re: 3 jaw chuck

Post by SteveM » Thu Dec 12, 2019 9:54 am

Harold_V wrote:
Thu Dec 12, 2019 2:45 am
Soft jaws. They solve all those problems.
Harold made me a convert years ago:

I bought a chuck with 2-piece jaws missing the tops and made my own soft jaws:
SoftJaws1.jpg
SoftJaws1.jpg (37.46 KiB) Viewed 670 times
I have since found that US Shop Tools has soft jaws for cheap and have bought a few more sets.

I find that even without machining the jaws for each use, they are pretty well centered, and the jaws are always parallel to the spindle bore with no bellmouthing.

If you don't have a chuck with 2-piece jaws, you can make a set of shoes that go on your existing jaws:
SoftJaws2.jpg
SoftJaws2.jpg (25.77 KiB) Viewed 670 times
The shoes are good for larger pieces, like the wheels you see in the picture.

The other advantage is that if you machine a shoulder, the depth of your workpiece is consistent and it is always perpendicular to the spindle.

I had to drill a hole in a bunch of metal caps for a friend. We machined the jaws with a shoulder and were able to drill each cap in a matter of seconds because we just slapped the part in and it was exactly where we needed it with no fiddling.

Steve

John Hasler
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Re: 3 jaw chuck

Post by John Hasler » Thu Dec 12, 2019 10:57 am

It occurs to me that one could make shoes that are drilled and tapped for seperate jaw pieces. This would convert a chuck such as my small three-jaw into a poor man's two piece jaw chuck.

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SteveM
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Re: 3 jaw chuck

Post by SteveM » Thu Dec 12, 2019 2:31 pm

John Hasler wrote:
Thu Dec 12, 2019 10:57 am
It occurs to me that one could make shoes that are drilled and tapped for seperate jaw pieces. This would convert a chuck such as my small three-jaw into a poor man's two piece jaw chuck.
Chucks missing the jaw tops can be had for quite cheap (the one above was $60) because the only thing people think when looking at them is that a new set of hard jaws costs $300.

Steve

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