Hand machined mechanical pencils

Split clamp for holding work in the lathe (20/02/15)

Expanding mandrels are very useful for accurately holding hollow cylindrical parts on the lathe. Once set up (by chucking and centering in a 4-jaw), they're also highly repeatable. However, I haven't really seen much use made of the "inverse" - a split clamp/collet for holding cylindrical work, so thought I'd share a few examples.

It's simply a turned/drilled/bored (whatever's relevant) piece of stock which is split with a saw cut after machining. The cut only goes as far as the thickness of the shaft collar, which is then used to clamp the two halves together, tightly gripping whatever part is present. The photos below show clamps for both 4mm diameter rod and a tapered part with 1° per side angle. Both grip very strongly and are highly repeatable.

These have one major advantage over a traditional collet + drawbar - stock of any length can be held.

Instead of using a separate shaft collar for clamping, it's possible to use the chuck itself and simply split the clamp along its entire length. However, this requires careful adjustment of the chuck when loosening - it has to be loosened just enough to release the grip on the part, but not too much that the clamp falls out and alignment is lost! It's far better to use the shaft collar instead.

Clamp for 4mm rod

Clamp for 1° taper

Quick video: