My very own Quick Change toolpost

It would be much more confusing and against the nature of this forum if it didn't go haring off in quite unexpected directions!

For myself, I'm going to follow through on my idea. Not so much because it's better as because it's mine!

I expect it will take a few weeks to get round to completing it. If it succeeds even marginally I shall boast unreservedly. If not..... (silence is golden ...).

iain

Well good on you Iain for having the courage of your own convictions. Shall expect to hear great sounds of boasting from your direction in due course,

all the best, Chris

DOH!

I should have looked at my drawings and not worked from memory.

The piston is turned from 5/8" brass to be 0.500" diameter with a 9/16" flange on the end.

The flange is milled or filed off top and bottom. This means the piston seats fully in the cam, but can't rotate which stops the spring wire getting out of line. The flange also stops the piston dropping out should the spring go astray or if you leave it out.

In my defence, the web page does explain the flanges!

Neil

Edited By Neil Wyatt on 27/09/2017 09:37:38

Many thanks Neil - all is now clear! I must admit also that I did not study the web pages closely. merely skipped through them to look at the drawings - sorry - and so missed the flange. I saw a 9/16" piston reduced to 1/2" for the last 1/32", not the other way round. Your sketch all makes sense of it all now! I do like the concept of this QCTP.

Chris

Hi Iain

A couple of constructive comments if I may ....

Personally, I do like the Dovetail principle, pulling the holder into a known and repeatable position and I would argue that the piston design is not as accurate. Your design is not quite as stiff as a Dickson type, but hey, practically on our class of lathe, it should be rigid enough.

One thing to consider though is that pulling the dovetail upwards (in your first drawing), there will be big bending and side forces on the screw against the corresponding hole when you clamp it up. This is not the most rigid method because of that, may wear quickly and may also suffer from a wedging effect, where undoing the nut does not release the wedge very easily.

I have seen some designs where a screw or a cam pulls the wedge in a direction 90 degrees to yours, ie the bolt is horizontal in your drawing, pulling the wedge in the same direction as the clamping force, without any side force on the bolt.

But enjoy making it and, of course, there's always the option of a sharp tap with a mallet if it wedges

Cheers - Peter

Hi Iain, if you can do the milling drilling and turning for a dovetail toolpost it is very likely you could make a ring and pin one like I showed. If you break the bits down into their indvidual shapes there is nothing complex about it. The pins for example on the tightening ring do not need to be cut as part of it, they could be screwed or welded or silver soldered onto the tightening ring. Tightening rings could be cut from solid or could be bent to shape after heating to red heat. High precision is not required for most of the tightening rings - if you get the pins at the right location and square to the eccentric tightening cam hole, that's all you need - the rest could be all over the road. The central post could use 90 degree V slots made with an endmill if need be, or could even be drillings to accept a slightly larger dia pin on each toolholder. The eccentric tightening cam could be done with packing one jaw of the 3 jaw chuck if you don't have a 4 jaw. All manner of tricks you could employ to make a really good toolpost designed to good basic tooling principles, and without dovetails. Dovetails are far from easy to make well.

Again, just food for thought. Good luck whatever you build.