Thanks Don!
Next on the list are the Collets. These will, of course, have a taper matching that of the spindle.
I'll be making quite a few collets, but this post will cover my first one, which I chose to make 3/8". This seemed like a nice middle size so I just went for it.
Using a length of 7/8" round 12L14 bar I drilled a center hole just over 2" deep. The size of the hole was selected for a 10-32 tap, which is what will be used for the draw bar.
Next I drilled about 1.5" deep to a size just under 3/8". I wanted to leave some room to bore the hole straight, then use a 3/8" reamer for final size. Here I'm skimming the hole with my smallest boring bar. This will be a complication for smaller collets, not sure I'll be able to bore them, I may just have to assume the drill went straight...
Then reamed it to 3/8".
Using that nice hole, I supported the piece with the tail stock and turned it down to the maximum diameter of the tapered part, then started cutting the taper:
Here is the taper, completed:
Next I turned the rest of the length down to where it would fit inside the spindle. I wasn't able to test fit this part, so I measured the inside bore of the spindle carefully, and turned this to about 1/2 thou under the spindle bore, hoping that was about right. The problem is, if I get this size wrong, I won't know it till after I cut the part off the parent stock. And I don't know how to hold it for additional turning after that! So I measured VERY carefully! Several Times!
Using the parting tool, I marked the beginning and ending of the waist of the collet. This is to give the collet the ability to more easily in order to clamp the part.
I used the parting tool to make successive cuts to remove the bulk of the material.
Then cleaned it up to the right diameter with right and left hand tools.
Finally, part it off from the parent stock.
After this, I checked the fit of the collet in the spindle and was a nice fit. Maybe a touch snug, but I can clean that up if needed. At least it wasn't sloppy loose! That would have been worse
One of the final operations for the collet is to cut the slits so that it can clamp down during tightening. I did this on the mill using a hex 5C-collet block. Again, my problem with the 5C collets came up. The diameter I'm trying to hold (18mm=0.709") is about 10 thousandths smaller than a standard 23/32" collet (23/32"=0.719". My solution was to use a piece of 0.004" brass shim stock and wrap that around the collet where I want to hold it. This worked out wonderfully giving a nice snug fit even before tightening! You can see the shim in the 5C collet in my setup shot here:
I needed (wanted?) to bring the slit all the way back to the base of the collet. Unfortunately, the slitting saw I have is 3" in diameter, and I couldn't get in any closer that this without damaging the far side of the collet (the one I'm making).
This probably would have been enough of a slit, but I wanted it to go all the way back. My solution was to use a 1/16" mill and mill the remainder of the slot. I'd considered using the mill for the whole slit, but the front of the collet is too thick for the 1/16" bit. So ended up doing both. You can also see that I had to mount the hex collet block 30 degrees off from the way it was when I used the slitting saw. But that wasn't too hard to figure out.
And here we are with all three slits completed:
And this shows what it looks like in the spindle, holding a 3/8" item in the collet. I used a random 10-32 bolt for the draw bar and it held that drill bit tight! How cool is that?!
Now I'm going to make a half dozen more collets - all the eighth-inch increments and maybe some select sixteenth increments too.
Kim