Quote Originally Posted by Clive S View Post
This is the guy to follow with lathe work this is part three but worth watching https://www.youtube.com/watch?v=mAzCVDF304o
Thanks Clive. I know Keith's channel well, he does some great work.

For info he held the tool in the 3 jaw, which will have some run out, but as this is a single point tool it does not matter as such because it will still cut a circle. What it does mean though is measurements of the cutting bit (made with a mic or calipers between the tool tip and back of the bar) can only be judged relative to the last cut, not absolute. So if the cut needs another 0.25 mm taking off then that is the increment of the tool.
However, using between centres (effectively no run out) allows absolute measurements of tool stickout because it is revolving about the true centre of the bar, assuming the bar is straight. So if you want an 80 mm diameter cut you can set the tool to that distance before the cut. Of course you would still check the bore of the last cut as you proceed to be sure. Either way works.
Also I had to make a lathe carrier (to transmit the rotation) because couldn't find a commercial one that big (bar is 50 mm). I'm sure they exist, just didn't see one on a quick search and I made mine in the time it would take the postman to send one, plus it was 'free' from scrap material.