making a collet or sub collet

[ptheys]

I have a 7×12 lathe and can make a 8mm collet to fit my jeweles lathe. Sawing ultra thin slots for holding the parts is the challenge .I was also thinking for the real small sizes to make sub-collets. again how to cut the slots.Dremel wheels don’t last long.How did they do it why back?

[Bob Tascione]

Hi Paul,
My guess is that they just used very thin slitting saws in a mill or milling attachment back then.
Enjoy,
Bob

[david pierce]

Paul,
There are some tricks to making collets. The hole should be marked for the center with a small center drill or a graver, then drilled under size, This is importent because a drill will not drill a round hole. The hole then needs to be bored with a single lip cutter (boreing bar) then reamed to size. Next, the collet needs to be put on centers and turned to the final outside diameter. Do not try to finish the outside diameter first and then drill, bore and ream the hole second. To slot the collets you need to make an indexing fixture attached to an indexing head. The head of the collet must be longer than the final collet to provide stability during the slitting operation. The saw must not cut through this end. The slitting operation will cut through the fixture and the collet on each index. Make sure you have a brass pin weged into the collet hole during this operation. The last operation is to chuck the collet into a lathe with the brass pin and machine the head to the final size.
david

[ptheys]

Not really understanding the part about using a boring bar and reaming it. We’re talking very fine holes. My smallest boring bar is about 1/4″.I have a wide range of jewelers drill bits.I was thinking of making blank collets on my larger lathe and drilling on my moseley. First I’d like to see how sub collets will work.I’ve found some slot cutting blades at .03 thickness. For cutting I took square key stock and tapped a hole for the collet(also a brass ended set screw). The key stock bolts into my lathe tool holder.I can feed it in slow and perfect 90 deg angles.I’ve tried it using a dremel cut off disk. Now if work would quit interupting my fun I could do something.

[david pierce]

Paul,
Commercially made end mill cutters can be purchased from tool supply houses as small as .010″ in diameter. if you hone away one side of the end mill you will have a single lip cutter that can be used as a boreing bar. It will only be able to take very tiny cuts and you will need to mount dial indicators to your tool slides in order to avoid taking too heavy of a cut. High precision collets are expensive but there are many steps involved in making them with enough precision to warrant their existence.
david

[ptheys]

Thanks for the info.

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