Have a mini-lathe, am making a gadget to pun on the toolpost so I can use the lathe chuck as an indexing head and mill sections/slots whatever.
All my mills have a 3/8" shank with a flat.
Is a 3/8 hole bored in the spindle and a set-screw good enough?
Or should I make some sort of collet and holder?
If I make a collet, what keeps the mill from slipping - just friction, or is there supposed to be some sort of method involving that flat?
Bear in mind there's not a lot of room...
jt:
I'm pretty sure the flat on the shank of the mill is for the set screw - as in an end mill holder. The flat would resolve any issues that would come up with scoring the shank.
After years of following this newsgroup, it seems that an end mill holder has an edge over a collet for milling. I just made some 3/8" end mill holders for my CNC mill using 23/64" drill & 3/8" reamer.
The "not a lot of room" was the bugger for me. I modified an Atlas milling attachment for my SB10k and managed to mill a couple of pieces. Fixturing and rigidity were a constant problem. The lowest of the low end mill/drill's was a gigantic leap forward.
Should I use an exact 3/8 reamer, or one that's oversize?
Or could I just plunge a 3/8 endmill into a 23/64 hole?
I'd use a 3/8" reamer, not over or under.
Failing that, I'd bore it out, which is not unlike plunging the endmill. However I'm not sure what size hole you'd end up with. Nothing is perfect, but most of the end mill holders I have are close enough to give a bit of resistance (compressing the air) when inserting the mill.
The commercial units are hardened, then ground true. Maybe using the reamer would work, though. The shanks are generally .0005" to .001" undersize. Mike a few of your shanks to see what size they are. If you have something you can set up as a toolpost grinder, you might ream first, and if the shanks are too tight, then you can do a very light ID grind on it. Otherwise, you could make up a barrel lap and lap the ID slightly larger.
Jon
Don't do that. It'll be oversize. Bore it or ream it.
Gary
That's what I thunk, but thanks for confirming...
The chip load per tooth in milling steel with hss is only a few thousands, so if the hole is off center by just a few or the hole is on center but oversized (mill will then be pushed to one side by the set screw) a multi flute mill will not mill with all flutes.(not the end of the world if you don't need max mill life, speed or accuracy of size). If you are using a single flute mill like an indexable one then it isn't as important. Having the hole dead center is probaly first concern, if oversize you may be able to wrap the endmill in shim stock but this can be a pain especially if you don't have shim stock.
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