Hello Bob,

The angle doesn't really matter, something in the order of 45 degrees will do perfectly well. The lock works by the camming action of the two taper faces being pulled together within a hole bored to contain them and reaction forces resisting the outward thrust from the tapers does the job of jamming and therefore holding the head locked to the pillar

In your design, include a short compression spring between them to help the two haves of the clamp release when the clamping bolt if freed off.

Regards Brian

5/16 will work fine and allow a little room for a release spring.

From what i've seen normal British practice was to make the bolt pretty much as large as would fit in the space and not use a release spring. Common to need a quick donk to release. Especially if the last guy to lock it was channeling their inner gorilla!

The angle on the end determines the force distribution. Following Alains' photo steeper angles push more force outwards to the main casting and shallower ones put more force along the clamp thread. With steeper angles you really don't want to do things up any tighter than needed as the outward force rapidly becomes enough to jam everything up solid.

It is said that shallower angles aren't as effective.

But I've never seen any sensible engineering explanation.

I imagine its like everything else in engineering. So long as the basic concept is workable the effectiveness in practice is down to how well the details have been handled. Careful engineering oif a theoretically not so good concept beats slap dash implementation of a theoretically better way every time. Good enuf is good enuf.

Clive

Hello Bob I confirm that on my drill it is 3/8" BSF see pictures.

Edited By Alain Foote on 24/10/2022 16:16:19