Hollow mill ?

[Bent]

This looks like a great alternative to use if you don't have a 4-jaw chuck. I know, chucks are horribly expensive and the more ideas for alternatives we can get, the better.

[Bill Ford]

Scott,
I had completely forgotten about those,(slapping forehead). But if you have a Jackobs chuck for your lathe, you probably already know of these collets.Some have internal, some external threads as per mfg. type of chuck. I prefer this over what I posted, unless there is a "one use" job involved, or you already have this type chuck it's not worth the expense. You may want to think about a slipring affair to replace the clamp for better clamping in a 3 jaw.

Bill

[Scott Howard]

Bill , what kind of slip ring ?

I am a total idiot when it comes to buying stuff for the mill or lathe . I always end up buying the wrong thing the first time. I originally bought a 4 jaw chuck but it doesn't fit my lathe. I then bought the collet but it doesn't fit my lathe properly. So I modified it. I just have a regular 3 jaw chuck .

I just ordered another wrong part for my mill and luckily a freind wanted the wrong item so I am only out the shipping.

Any good books on basic machine shop ?

[burt]

I have had good results holding square bar in a 3 jaw chuck in my regular job as a toolmaker/maintenance man/getusoutoftheshitman/etc.

Assuming the square cross-shafts are 3/8" across the flats, that works out at 17/32" across the corners.

Mount a piece of mild steel round bar (about 3 inches long and 3/4" diameter) in the lathe, centerdrill it, then drill it just under 17/32", (say 1/2").

Get the 17/32" drill, (or ideally a reamer) and slowly drill the hole out to size.

The reason for not drilling 17/32" immediately after the centerdrill is that it might cut oversize.

Mark a line in between two of the chuck jaws with a marker pen, and mark the chuck also so that when you put the collet (for that is the word for this thing that you are making) back in the chuck, it will go back in its original position.

Remove the collet from the chuck, and hacksaw completely down the length of it, on the aforementioned mask.

Insert the square shaft into the collet (making sure that no corners of the shaft are in the hacksaw slot), with only the minimum sticking out (so that when it is being turned, it is as close to the chuck jaws as possible), put the collet back in the lathe chuck, then tighten the chuck.

Hopefully now the square shaft should be running concentric, and you can turn the ends down the required size.

Don't be greedy and try to turn the end down with one cut, as the collet might slip.

It's a matter of 'slowly slowly catchee monkey'

[Bill Ford]

Scott,
Make a bushing of sorts with the inside diameter the size of where the clamp is on your collet, the wall thickness needs to be at least 1/8", cut a slit on the bushing(all the way through as per my dwg on page one) cut another slit on the inside at 120deg for expansion (not all the way through) so it will expand over the larger dia of the collet you have, being careful that the cuts on the bushing don't line up with any of the slits on the square fixture, which are at 90deg.

burt, Look at my dwg and pic on page one...great minds do think alike !!!
Bill