Conventional method is to machine first, then split, why can’t you do this, as you mention splitting before machining in your post, I’m not sure if super glue will cut the mustard? Also what machine tools have you?

Tony

HI James

 

You need a gap between the surfaces so that the object in the middle is gripped well. I would surface finish two bits of rectangular material and glue then with a bit of thin metal separating them. The thin metal shim is equal to the required gap for generating the clamping action. As you can mic up the parts you can easily find the required gap as this will have a circular outside diameter when held apart by an appropriate distance. Glue or use double sided tape if handling during centering is an issue for you.

 

Turning the part from a single piece and slitting with a slitting saw is the best way if you have the equipment.

 

The important thing would probably be keeping the bore concentric with the outer diameter and taper.

 

Regards – Pat

James, splitting the collet after turning will not make anything elliptical! All diameters, threads and lengths will not change in the splitting process. The turned diameters will still be true cylinders. If you haven’t got a stub arbor and suitable slitting saw avaliable, careful use of a junior hacksaw should be ok to make the split.

Tony

Hi James

 

You need to replicate the existing collet. That is why I suggested that you measure the existing collet to see what the gap is. Do this by measuring the outside diameter of the lip on the front face with the two parts held together at right angles to the slit and let us call this measurement one. Measure the width across the lip of each part of the collet and call this measurement two. Subtract the measurement one from two and this will be the first approximation to the slit width. Repeat using a shim of any hard material equal in thickness to the gap you have just established. Check that holding the two parts of the collet together with the established shim pack in the gap that the collet is round by measuring at several points round the circumference – I suggest you use the maximum OD and check against the measurements from the step. If the collet is circular with the gap filled with the shims then this is the gap you need between the two rectangular bits of stock.

 

The gap is not that critical as it will be very difficult if not impossible to collapse the brake tube as these are a peculiar alloy which I think is called Bundy tubing. Even soft copper tube will be difficult to reduce in diameter by clamping in a collet with a gap that is excessive – after all the tube has to be very firmly gripped to permit the end to be flared and belled over.  Also the bore of a flaring collet should not be too smooth so that the pipe is gripped properly.

 

 

Hope this helps clear up why the gap is necessary and why it is not that critical.

 

Regards – Pat