Bloomers and cock ups learning to cut thread on the lathe

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Stilldrillin:
Is it Me? :scratch:

I was taught to screwcut in the apprentice school, 1960. Then, spent a lifetime machining.

I have NEVER have seen an angled compound, for screwcutting purposes......

David D

vtsteam:
Debate about this has appeared in the model engineering press for a long time. Not really debate, I guess, maybe more like discussion.

Anyway, I'll hazard a guess about why. Small lightly built and homemade lathes, like my Gingery lathe in its original form have low bed, spindle, and carriage stiffness and mass. Avoiding chatter in machining operations becomes a priority by comparison with manufactured cast iron hobbyist lathes, not to mention commercial and industrial practice. It means taking very light cuts, and a long time to do some things, and any procedure that can increase that cut depth or reduce that time is a boon.

Straight plunge cuts to any depth with form tools are often out of the question. So, methods become popular that reduce the contact cutting surface in plunge cutting. I'm guessing that's why the compound set over method was developed. It wouldn't be so important for a heavier lathe, and I can understand why commercial screw cutting machines and industrial lathes just cut straight on.

unc1esteve:
Perhaps I should have worded my post differently, not sounding as if I was criticizing.
I have seen incorrect, sometimes unsafe advice given on machining sites. Usually to novices. I think we would all be served if we encouraged each other to learn the traditional (I do not want to say 'proper') manual machining methods first. Then, when one feels that he has learned and is comfortable, make whatever changes he chooses. I believe Bangkok Mick would benefit from at least reading instructions on 'how to cut a thread on a lathe'. I suppose I have a problem with 'been there done that' advice as it does not exchange knowledge.

I was taught and do the opposite of Stilldriling concerning cutting screw threads on a manual lathe.

One thing I do differently is to grind the cutting tool with a top and back rake. It makes a much cleaner cut with a better finish.

DavidA:
It does seem to come down to the way you were taught. Where I worked there were three other machinists. Non of them had even heard to the idea of setting over the topslide. I had never heard of it until I started with my own lathe and began reading the hobby journals.

I suppose it is a case of whatever works for you. you use.

Dave.

Bangkok Mick:

--- Quote from: unc1esteve on July 02, 2013, 10:43:21 AM ---Perhaps I should have worded my post differently, not sounding as if I was criticizing.
I have seen incorrect, sometimes unsafe advice given on machining sites. Usually to novices. I think we would all be served if we encouraged each other to learn the traditional (I do not want to say 'proper') manual machining methods first. Then, when one feels that he has learned and is comfortable, make whatever changes he chooses. I believe Bangkok Mick would benefit from at least reading instructions on 'how to cut a thread on a lathe'. I suppose I have a problem with 'been there done that' advice as it does not exchange knowledge.

I was taught and do the opposite of Stilldriling concerning cutting screw threads on a manual lathe.

One thing I do differently is to grind the cutting tool with a top and back rake. It makes a much cleaner cut with a better finish.

--- End quote ---

Just for clarity I am also reading up on and researching the internet as I go and trying to apply each different method to see what works best including safety.
I have tried setting the compound at 60deg. And this was a successful exercise but as I am cutting soft material such as aluminum and brass a parallel compound is also working out, still it is good to practice each way for future reference.

Thanks for all the feed back to this thread.

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