DIY 5C collet chuck question

AllThumbs · May 27, 2008

I would like to build a collet chuck for my 8x12 lathe. It will bolt on the existing face plate/chuck adaptor. 2 questions:

1) I would like to build it to incorperate a big nut on the front to tighten against the collets so no draw bar. This will enable long stock to be machined. Is this an acceptable method? I see some E3 collet chucks made this way.

2) If I do the above, it will look similar to the image below, but with an external thread on the end. I plan on using cast iron for the chuck (since this is what I have around). Will the cast threads be ok? I will probably make the nut from bronze material and it will likely be knurled and holes for a tommy bar.

Thanks for any input.

Eric

Bogstandard · May 27, 2008

I think you will have great problems doing it the way you suggest.

Because you will always have to have clearance around the collet for it to fit into the hole it sits in (like size will never fit in like size), it will kick over on the nose area and won't keep straight register. It is the draw nut on the back, pulling it into the taper, that keeps it straight.

On collets that use a nut as you suggest, they usually lock into the nut first (ER collet system), or have a shaped nose that registers into the nut, then gets pushed back into the taper to close. So it is the nut that then keeps it central.

So somehow you would have to modify the nose of the 5C collet to allow the nut to keep it in central register.

John

AllThumbs · May 27, 2008

Thanks John,

Maybe I didn't explain very well. The 5C collets are tapered, and I plan to make the same taper inside the chuck, so the nut would merely push the collet into the taper, much the same way a draw bar would pull the collet into the taper. Removing the nut, I would still need to pop the collet out of the chuck with some kind of bar from inside the spindle....

Eric

Bogstandard · May 27, 2008

Eric,

I was explaining it as if it had a taper in the nose. Because you have to have a certain clearance around the collet for it to enter into the chuck, when you push on the nose, the collet will take a random course until one part of its circumference hits the inner wall, then it will start to tighten, but not guaranteed to be totally central and straight.

John

BobWarfield · May 28, 2008

Eric, you can make a collet closer that's hollow without too much trouble. Not sure the advantage of the nut in that case. I think that's going to be the better route. I will also point out that the cheap chucks such as you have pictured can be made to work extremely well. With some effort, I got mine repeatable to maybe 3 or 4 tenths. This was the el cheapo $150 model, not a $300-400 Bison. You can also make your own set-tru setup for your chuck and go that route.

I'd be tempted to go one of those two tried and true paths rather than the nut arrangement you describe. I agree with Bog's remarks and would add that the nose of the 5C is curved. That just strikes me as likely to stress the collet in odd ways that won't behave well if you drive a nut down onto it.

If you're ambitious, I've seen a gorgeous collet chuck made that used a planetary gear set from an automatic transmission to tighten the threads.

Cheers,

BW