Am I well wee'd off with this? Logged in, wrote a long thread, went to post it and guess what, a clever note saying I had to be logged in to use this facility. I WAS logged in or else I couldn't have written the thread. Why hasn't this been sorted by now? Moderators/web chiefs, please note. It is seriously annoying as well as a complete waste of the threadwriters time.
Rant over, now:
Anyway, what I was asking was HELP! Could someone please point me in the right direction and advise where I am going wrong.
I am trying to set up my lathe to turn parallel as well as then making one of Harold Hall's cylinder squares, but am getting nowhere fast.
My lathe is a German made Weiler lathe, about 35-40 years old. OK, it is a bit worn but quite OK within the area in which I work, very manageable. The lathe sits on a very robust welded mild steel bench made by Weiler, and is held down by four holding down bolts, one at each corner, of the headstock, and by another four at each corner of the tailstock. When I first set the lathe on the bench I set out to minimise the twist as far as possible with 6thou shims under the holding down bolts, as that was all I had at the time, being guided by a reasonably accurate level.
Today I set out to make it turn parallel and make a cylinder square in the process. I set a length of 30mm diameter bar with about 30mm in the chuck and a tad over 90mm as turned length. As originally set up, I got an out of parallel of 0.05mm, being larger at the outer end. In this case the manual says to harden down the headstock front right bolt, followed by the tailstock rear left bolt if necessary. As all bolts were already hardened down I thought again. Using another 6mm shim which was already cut to fit, I inserted it under the rear right headstock bolts and tried again with another cut. This time I got out of parallel of 0.04mm, but this time the other way round, the chuck end was bigger.
Simples I thought, substiture the 6thou shim for a 3thou shim and she'd be right. Wrong! Now it was out 0.02mm.
The lathe speed is about 300rpm, a very slow feed is being used, the tool is HSS ground on an off-hand grinder and honed with a diamond hone, it's 1/4in square and protudes from the tool post about 15mm, the tool is like a knife tool with a bit of approach rake (forget the correct term!).
I played with bit of different shim all afternoon getting nowhere, then I noticed an oddity which baffled me. My practice was to take a 2thou cut down to the chuck, and without touching anything bar reverse the feed, cut back out again. I noticed that on the cut towards the tailstock the tool was taking a progressively heavier cut, heavier being a relative term given the original depth of cut.
So I took another cut towards the chuck and stopped the lathe when the tool reached the chuck, and micrometered the bar. It was 0.09mm larger at the tailstock end. So I just reversed the feed and cut back out again, and remeasured after that cut. Still out, but now down to 0.035mm.
All this has, as I say, me baffled, the little grey cells are getting ever older! My thought process have seem to have been driven down a dead-end and have just given up tonight.
So can anyone, please please, tell me what I am doing wrong, why/how is the lathe cutting like that, and what I need to do to get back on track – I need pointing in the right direction!
Chris
PS, this damned website only wanted me logged in AGAIN, even though I was. Had copied what I had wrote this time but….
Edited By ChrisH on 09/04/2013 21:50:07