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Member postings for John Slater 1

Here is a list of all the postings John Slater 1 has made in our forums. Click on a thread name to jump to the thread.

Thread: Four Index Thread Indicator
10/02/2022 13:44:37

I recall an aged turner many years ago recounting screwcutting with out the use of a thread indicator. His explanation centred on what he called chalk marks. Apparently if my aged memory serves the procedure was to mark the bed where the carriage was located establishing a start point. The lead screw was also marked along its length against a static part of the bed. On a Myford say the tailstock end leadscrew bearing so the point at which the half nuts were engaged was indicated. Thus a start point for the leadscrew and a corresponding start point for the carriage were established. The marks enabled the turner to return to the same start point relationship after each cut.

I've not tried the method but am not able to see why it wouldn't work and on the face of it should work for any pitch.

Or am I way off?

Maybe one of the ancient tomes on lathework might have a description although I'm unable to recall seeing it described in print.

John

Thread: HELP
01/12/2020 20:17:49

Hello David

I suggest you will find the details you are after in a series of articles titled "Making Tracks" by Denis Monk that were published in Model Engineer beginning in volume 161 for 1988 and concluding in 1990.

Best wishes

John

Thread: Thread Depth vs Strength
13/01/2011 09:21:18
This case of a thread stripping is a complex stress system that is not well understood.
 
Factors involved include the material of the nut and male thread and how they each respond to loads, the quality of the thread both male and female( ie how well they fit together and the surface finish) and the nature of the load applied.
 
In the UK, professionally guidance would be sought from British Standards as they are supposed to embody whatis considered by the great and the good to be "best practise".
 
Have a look at BS3580 "Guide to design considerations on The strength of Screw Threads" for further information, particularly appendix A where equations are given to enable a "length oif engagement" to be determined. You should be able to access a copy through a town library or local technical college library.
 
Sorry if this reads as a "cop out" but if you are designing something critical it could have serious consequences.
 
Practical rules of thumb generally indicate that a length of engagement equivalent to the thread diameter would give failure in tension rather than stripping, however don't forget that chamfers on the male and female threads reduce the effective engagement.
 
The late Professor Chaddock published some data on bolted joints through the Design Council that might be useful too.
 
Best wishes
John
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