thread dial

Hi all.

Can some one tell me if a 8TPI leadscrew, Dial Indicator Pick-up chart, will be the same for a 4TPI leadscrew chart. ??

Thanks. Chubbs.

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Just bumping this one for the attention of the experts.

My understanding is that the 8tpi chart would have more entries than the 4tpi chart, but would include all of the 4tpi ones. ... Someone will surely be able to express that better than me !!

MichaelG.

The thread dial indicates movement of the carriage relative to the leadscrew. With the leadscrew not rotating move the carriage along the bed the distance required to turn the dial one revolution. I would expect this to be 2" but it may be 1".

This distance is divided up by the marks on the thread dial. If you have 2" of travel and 8 marks then each mark is 1/4" of relative motion. If it is marked 1 to 4 with the intermediate marks not numbered then the numbers show 1/2" of relative motion.

This works as follows.

Any even numbered TPI value can be engaged at any numbered position. Eg 2TPI, 4TPI, 6TPI etc.

Any TPI value that is divisible by 4 can be engaged at any numbered or un-numbered mark. Eg 4TPI, 8TPI 12TPI etc.

Odd numbered TPI values should only be engaged at opposite marks on the dial eg 1 and 3 or 2 and 4.

Very odd threads with a 1/2 on the end such as 11.5TPI should only be engaged at the same point on the dial through the threading process for example the indication marked 1.

For a beginner it is easiest to stay safe by only using the line marked 1 until you are happy you know what you are doing.

Martin

This link to something I wrote on this subject may work but it is to a Yahoo Group and it might be closed to non-members.

https://xa.yimg.com/df/smart_and_brown_lathes/Understanding+the+threading+dial+.pdf?token=b8UcLiy8FkHOFeZ59SP-GnG0_mV9-cUnqX-c7yGn0WjmuZc28fruhLfSA8qxVftXll7vY5LlmOlGDXuXl9f1uYcBb0wnthFS43C7RuTnpt3GsNIdfi4kTggDe52ntCBjG7ZySNfVJN58m6eE&type=download

Edited By Martin Connelly on 21/11/2017 13:34:09

It can depend too on what numbers and lines you have on your dial, and on how many teeth the gear that engages with the 4tpi leadscrew has. What make and model of lathe is it on? Someone on here may well have an original handbook for it.

Edited By Hopper on 22/11/2017 10:18:01

This may help understand it or may confuse you further:

I have converted the PDF file mentioned in my earlier post into jpg format. It may help understanding of how to use the dial.

Thanks Martin!

Hi all.

Have all the info i need now, thanks for your reply s , all is clear now. just need to try it out.

Chubbs.