My first screw

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Both will work with Thunderbird 2.

Either use a thread chasing dial, or never disengage from the feed screw

- return the slide by reversing the feed instead.

You would normally undercut where the thread ends and either move very quickly when the tool enters the undercut or use a lathe that automatically disengages the feed when the cross-slide hits a stop. The latter requires a thread chasing dial.

Any engineers' supplier.

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Colin Bignell

Fnarr! Fnarr!

Yes, a very good point. I didn't draw the plans. However, I had plenty of plated M16 nuts, and no plated Whitworth or UNC nuts (which are too coarse), and no UNF 5/8 nuts at all.

I remember being taught to use the top slide rather than the cross slide fo= r screw cutting, rotating it round until the tool movement is in line with = the right hand edge of the cutting tool point. The result of this is that a= s you make successive cuts the bulk of the work is done by the tool edge cl= oser to the headstock. You can then get the rake angles right for that edge= without having to worry about what that does to the angles on the other ed= ge. The consensus among most of the people I spoke to was that it was best to w= ind the tool out (to avoid problems with backlash in the lead screw) and th= en put the lathe into reverse, rather than disengage from the lead screw, e= ven if you did have a thread chasing dial, unless you were very sure of the= accuracy of the lathe you were using.

screw cutting, rotating it round until the tool movement is in line with the right hand edge of the cutting tool point. The result of this is that as you make successive cuts the bulk of the work is done by the tool edge closer to the headstock. You can then get the rake angles right for that edge without having to worry about what that does to the angles on the other edge.

the tool out (to avoid problems with backlash in the lead screw) and then put the lathe into reverse, rather than disengage from the lead screw, even if you did have a thread chasing dial, unless you were very sure of the accuracy of the lathe you were using.

If you are doing it as a hobby, you probably do have time to reverse the lead screw. For production work, time is money, so the lathe better be in good enough condition to allow you to disengage from the lead screw and wind back quickly.

Colin Bignell

e for screw cutting, rotating it round until the tool movement is in line w= ith the right hand edge of the cutting tool point. The result of this is th= at as you make successive cuts the bulk of the work is done by the tool edg= e closer to the headstock. You can then get the rake angles right for that = edge without having to worry about what that does to the angles on the othe= r edge.

to wind the tool out (to avoid problems with backlash in the lead screw) an= d then put the lathe into reverse, rather than disengage from the lead scre= w, even if you did have a thread chasing dial, unless you were very sure of= the accuracy of the lathe you were using.

I found there was very little difference for the relatively short lengths o= f screw that I was cutting. The actual act of moving the cutter back to the= start of the thread was only a very small part of the total time taken.

Incidentally, the people who I asked about this were instructors at the Wor= ks training schoool in Derby Loco Works and at a local technical college.

I suspect that even then the propotion of screws cut on general purpose lat= hes rather than automatic screwcutting lathes and capstan lathes was quite = small. These days most of that would be done on an NC machine, which would = be programmed with the most efficient way of cutting the threads, and may w= ell use tools which can cut a full depth thread in a single pass.

screw cutting, rotating it round until the tool movement is in line with the right hand edge of the cutting tool point. The result of this is that as you make successive cuts the bulk of the work is done by the tool edge closer to the headstock. You can then get the rake angles right for that edge without having to worry about what that does to the angles on the other edge.

wind the tool out (to avoid problems with backlash in the lead screw) and then put the lathe into reverse, rather than disengage from the lead screw, even if you did have a thread chasing dial, unless you were very sure of the accuracy of the lathe you were using.

screw that I was cutting. The actual act of moving the cutter back to the start of the thread was only a very small part of the total time taken.

At £36 per hour charge out rate, which is rather low, but makes the maths easy, 1 second longer on the job increases the price of the product by 1p.

training schoool in Derby Loco Works and at a local technical college.

I am not surprised. The job of instructors is to teach how to do the best job, not the most profitable, which requires the ability to balance quality against cost of manufacture.

rather than automatic screwcutting lathes and capstan lathes was quite small. These days most of that would be done on an NC machine, which would be programmed with the most efficient way of cutting the threads, and may well use tools which can cut a full depth thread in a single pass.

I think you will find there are a lot more manual lathes out there than you think. Large companies may invest in CNC equipment, but there are plenty of small one and two man engineering businesses that do things the old way.

Colin Bignell

The cost really. Most of the time only a few parts are needed to be made on the lathe. It's used maybe a few times per week.

screw cutting, rotating it round until the tool movement is in line with the right hand edge of the cutting tool point. The result of this is that as you make successive cuts the bulk of the work is done by the tool edge closer to the headstock. You can then get the rake angles right for that edge without having to worry about what that does to the angles on the other edge.

Yep, the best way, and just as quick as using the cross slide. It also avoids tearing or digging in so that you end up with a thread of the correct depth without the sharp crest.

A runout groove at the headstock end also helps ease any stress for the operator.

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