3-jaw vs. 6 jaw chucks for round stock?

[wquiles]

Main question: Besides the higher price for the 6-jaw, why not "always" use a 6-jaw everywhere I use a 3-jaw today?

Secondary question: I have been exclusively using a 4-jaw, independently adjustable chuck in my lathe. I noted that you can also buy a "micro-adjustable" 3-jaw celf-centered chuck (also available on 6-jaw type) - are these any good? Again, ignoring the higher price, are these worth using instead of the slower but tried and true 4-jaw independent jaw chucks?

Will

 

[Anglepoise]

I always understood that the 6 jaw was used where great clamping pressure
was required or for maximum contact area when gripping very thin wall items.
Where possible, IMHO, collets are the way to go with thin wall stuff.

For normal everyday use, a good 3 jaw will be fine.

If you want repeatability and accuracy in a 3 jaw chuck, be prepared to pay for it. I just got a quote from my supplier to replace my 'Kitigawa' 5 inch, 25 year old chuck. I was informed by the factory that they no longer make a 5 inch but their suggested 6 inch replacement would be $2,537.00.

Their chucks have always been very, very good and when mine was new, it was accurate to 0.0005" at the 3/4" setting. Amazing.

However since all good chucks are expensive and not usually owned by hobbyists, we now see lots of 'Set True' style chucks that allow the user to shift the chuck around a little to get best concentricity. People that have these I am told are very happy with the results.

Another method I have heard works well is to machine the backplate one thou under and then rely on the retaining bolt friction for final positioning. Concentricity then can be set with gentle taps and held by snugging the bolts.

 

[PhotonFanatic]

Will,

I would think that your four-jaw should be fine for 99.9% of what you might make. Sure, it does take some time to set up, but I find that I can now do that in less than two minutes, to the point where the runout is down to .01mm. That's good enough for my work.

 

[wquiles]

Where possible, IMHO, collets are the way to go with thin wall stuff.

I could not agree more, and I recently got an ER-40 collet set for my mini-lathe and mini-mill, but, this only goes to about 1 inch dia. I should have pointed out above that my question was specifically for a 6" dia chuck

For normal everyday use, a good 3 jaw will be fine.

If you want repeatability and accuracy in a 3 jaw chuck, be prepared to pay for it. I just got a quote from my supplier to replace my 'Kitigawa' 5 inch, 25 year old chuck. I was informed by the factory that they no longer make a 5 inch but their suggested 6 inch replacement would be $2,537.00.

Their chucks have always been very, very good and when mine was new, it was accurate to 0.0005" at the 3/4" setting. Amazing.

However since all good chucks are expensive and not usually owned by hobbyists, we now see lots of 'Set True' style chucks that allow the user to shift the chuck around a little to get best concentricity. People that have these I am told are very happy with the results.

Another method I have heard works well is to machine the backplate one thou under and then rely on the retaining bolt friction for final positioning. Concentricity then can be set with gentle taps and held by snugging the bolts.

Thanks so much for the long, detailed answer. That was awesome, and I had no idea some chucks were so expensive!!!. It sounds like the "set true" ckucks, might be something to read more about

Will

 

[will]

I always found that the standard 3 jaw chuck will not repeat exactly each time somthing is taken out and put back in. Collets do a much better job. Sometimes the jaws can be bored out to make them fit better, sometimes taking out the jaws and cleaning everything helps. It really gets down to 'how exact do you have to be?'

 

[modamag]

David you sure have all those exotics. First the tool holder, now this chuck. I'm in envy.

Will, IHMO the "Set True" chucks are overhyped. I have a set it take FOREVER to set them true. There is simply too much variable at play when you got a hobbiest lathe. Mounting plate --- Adapter plate --- Chuck body --- Jaws --- Part

For the price of a 6J chuck you can "almost" get yourself a collet chuck which will help grip those with little surface area (eg bezel ring, & small CR2 lights).

If you're dealing with the same part all the time (eg MiniMags) then make yourself a sleeve out of delrin it will get you 95% there.
1. Mark the position of where the jaws meet the plastic so you can return it to the same position on every mount.
2. Bore the ID to be slightly smaller (0.001-0.003" ID)
3. Slit it along the X-axis to provide relief.

 

[TranquillityBase]

Main question: Besides the higher price for the 6-jaw, why not "always" use a 6-jaw everywhere I use a 3-jaw today?

Secondary question: I have been exclusively using a 4-jaw, independently adjustable chuck in my lathe. I noted that you can also buy a "micro-adjustable" 3-jaw celf-centered chuck (also available on 6-jaw type) - are these any good? Again, ignoring the higher price, are these worth using instead of the slower but tried and true 4-jaw independent jaw chucks?

Will

Will, you're gonna love this link...

http://warhammer.mcc.virginia.edu/ty/7x10/5c-chuck.html

Make the chuck...spend the $$$ on top-of-the-line collets, in the sizes you'll use most...

That would be a awesome project.

TB

 

[Anglepoise]

David you sure have all those exotics. First the tool holder, now this chuck. I'm in envy.

.

That's just the way lathes were sold 25 years ago. Both the 'Kitigawa' and the 'MultiFix' were standard equipment back then on the lathe I purchased.

Suddenly I feel rather old..........

 

[gadget_lover]

According to what I've read, the set-tru chucks are great if you are doing a production run of the same size and and not mounting/unmounting the chuck frequently.

I've heard of three variations on the poor man's set tru (PMST) chuck as mentioned by David in post #2.

The second method uses an under sized shoulder (by only a few thou) on the lathe spindle. You drill and tap through the body of the chuck so you can use set screws pressing against the shoulder to adjust the chuck a few thou in each direction.

The third method uses a backplate that has a lip that extends over the spindle's flange. Set screws are again used to offset the backplate by pressing against the flange. There's a great writeup at Ty's website that's well worth looking at. He got TIR to under 0.0001. I think about building this one once in a while.

Daniel

 

[McGizmo]

The 3 jaw on my old Craftsman (Atlas) was well used when I got it. A guy I knew who rebuilt machines for a living suggested I make a ring that the jaws would clamp internally with an opening resulting in the jaws corresponding with the OD of material I usually worked on. I went for a 1" OD. I then set up a die grinder on the tool post and with a grinding stone, took a bit off the inside surface of each of the jaws. This presumably equalized the wear on each jaw relative to its backlash. I recall an improvement afterwards.

My new lathe has collets and I use brass emergency collets often which have been turned specific to the part. I am spoiled!

 

[modamag]

Those emergency collets are great. Considering the cost of the lathe they're cheap.

 

[scott.cr]

Another method I have heard works well is to machine the backplate one thou under and then rely on the retaining bolt friction for final positioning. Concentricity then can be set with gentle taps and held by snugging the bolts.

I've used this method for a few years now and it's decent, except with my Chinese-made 3-inch chuck, the backplate is .010" under!!

As a result, I normally go with a Bison brand four-jaw... I'm pretty fast at getting .001" repeatibility.

 

[wquiles]

The third method uses a backplate that has a lip that extends over the spindle's flange. Set screws are again used to offset the backplate by pressing against the flange. There's a great writeup at Ty's website that's well worth looking at. He got TIR to under 0.0001. I think about building this one once in a while.

Daniel

That was in fact a great read - thanks

Will

 

[gadget_lover]

The rest of that web site has good info too. The "vault" is the repository for the uploads to the yahoo group for the minilathe. ( http://groups.yahoo.com/group/7x10minilathe/ )

There are many projects, mods and improvements on that website.

I'm up to message #20535 of 167702 in the yahoo group. That's Jan 22, 2001

Daniel