The task is to make end mill holders for my "Eklind" vertical mill head, that uses collets similar to a Bridgeport B3 (sort of a shrunk R8).
A sketch of a collet that would fit can be seen here:
My material is 12L14 bar, about 4" long. The lathe is a SB 9 Mod C., without a toolpost grinder. I will be using a B3 collet as the template for the draw angle.
What order of operations will maintain concentricity as I drill, turn, bore and ream?
Thanks,
Kevin Gallimore
Long term, the material choice isn't very good, but it will machine beautifully and yield good finishes. It's desirable for collets to be heat treated for longevity.
Be certain to set your compound angle before embarking on the process----so you don't have to remove the collet from your chuck once you've started machining it. Make certain that your indicator is in the same plain (on center) as the cutting tool if you choose to set the angle that way, otherwise the angle the machine yields won't be the same as the one you want. The collet would be made with the holding end out, even if you have to do a second operation on the back side for the thread. That isn't critical to the function, so even if you're slightly eccentric, no big deal.
Regards process, the one thing you should do is rough all features (except for the slots) before thinking about finishing any of them. That way you'll have relieved, as much as possible, all the stress inherent in the material from the rolling process. Leave somewhere between .03"/.05" on the diameter for finish cuts. Sequence isn't as important as the roughing and finish cuts are. Drill your hole undersized and bore for concentricity---and turn all features inside and out that are possible in the same setup. By having roughed first, then finishing without removing the collet, everything should come out as true as your machine. Cut your slots last, after you've tapped the thread. Any changes at that point will be self correcting when the collet is in use. Deburr the slots well, naturally. Does this make sense? Need more info?
Harold
Except he said end mill holder, so he won't need the slots. Substitute drill and tap setscrew holes last. I've got the same job when I get my M-head with B3 collets up and running. Also 5C end mill holders for the TM.
Pete Keillor
Pete sez: "> Except he said end mill holder, so he won't need the slots. Substitute
Yeah but, the drop box pix looked like a collet. Maybe he is using the terminology. . interchangeably.
BTW, Pete - do you plan to heat treat the ones you are going to make? If so, how will you handle the "internal stress" problems alluded to by Harold? Will you grind?
Bob Swinney
The steel I would use in this application, if heat treatment were not part of the job, is C1144 for preference, or 4140 heat treated and stress relieved.
Both have a yield strength in excess of 100,000 PSI, and the C1144 is also quite hard and reasonably wear resistant, while a pleasure to machine.
I use C1144 also to machine crank shafts from the solid, but that's another story.
Wolfgang
Thanks, Pete. Nothing like having your head in a dark place, eh?
Harold
Thanks, Harold.
Pete
That's a no-brainer. Stressproof.
Harold
Welcome! You'll love how it machines. It works better with HSS (positive rake with chip breaker) than it does with carbide. Wonderful finishes and great chip control.
Harold
Thank you gentlemen. I agree that 1144 is a better material for this application. I am a small quantity user. I could not find drops of 1144, and 12L14 bar ends are available on Ebay for a reasonable price. This is my first experience with 12L14, and for me 1144 machines better. I'm sure this says more about my lack of skill than the qualities of the metal.
Kevin Gallimore
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