Here is an 'oops' with a difference. The difference being that a useful idea came out of it.
As some of you may know, I retired about four years ago but occasionally get hauled back in to work if some one is off. Well, one of the lads managed to break his leg. so I'm back for a couple of month. I only work half days (mornings) and this suits me fine. It also means that I can use the 'big' machines during the lunch break before I leave to do any jobs I have for myself.
After all the discussion on half-angle thread cutting over on the other thread I decided to have a go at it. On Monday I had made a dummy 8 tpi mandrel nose to assist in making bits to fit my lathe. So today (Tuesday) I thought it would be interesting to make another but this time set over the top slide to half the angle and do it the approved way.
So, it's all set up. Lathe running, just touch the tip to the job (30 mm EN8 bar), zero the cross slide. Zero the top slide. So far so good.
Set a slow speed (45 rpm) engage the feed and away we go.
I'm only cutting about 3/4 " long, and have machined a run-out groove for the tip to stop in.
I keep the feed engaged all the time, reversing to get back to the start.
All goes well. But there is a potential problem. The lathe, and old Colchester Triumph 2000, has a lot of backlash in the cross slide wheel.Almost half a turn.
After about eight cuts I am into a rhythm. return to the start, wind in to zero on the cross slide, add a few thou on the top slide, make the cut, wind out the cross slide a full turn and reverse back for the next cut.
Then somehow I lost concentration. On the next cut there was a bang and the tip went to meet it's maker.
I worked out that, due to the excess play in the cross slide wheel, I had wound it in two turns. I actually realised that the tip was too far in just as it was about to touch, but it was too late to stop it.
So, my own fault. But how to avoid this happening again ?
In future I would fix a stop on the cross slide once I had zeroed it so that I could not wind in any further than the one required turn. I could remove the stop for the last 'cleaning up' cut using the cross slide.
Of course, I could simply go back to the old 'straight in' method that I have always used.