Collet inserts for square stock

[mklotz]

Soon after getting a lathe I built a 5C collet chuck for it. Early on, I bought only round collets, planning on adding other types as needed. Before I could get a set of square collets, an engine I was building required turning on some small square stock.

So I made these two split collets to hold 3/16 and 1/4" stock in a 1/2" round 5C collet.

While these look pretty simple, care is required in making them. There are undoubtedly numerous ways to make them but I'll describe what I did.

1/2" stock was held in a round collet in a square collet block in the mill vise and exactly half the diameter was milled away for a length a bit more than twice the finished collet length. The collet block was then held in a V-block so the milled section was 45 degrees to the horizontal. A conventional end mill then milled out the V-groove in the collets. The resulting piece was then split into two collets and the ends finished.

As can be seen from the picture, the two halves fit together nicely into a cylinder with a neatly centered square hole in the middle.

Bonus hint:

This is also a nice way to produce a square hole for a wrench or similar. Simply make the collets as described and silver braze the two pieces together.