MadModder
The Shop => Tools => Topic started by: Rick O Shea on November 04, 2016, 04:42:17 AM
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Hi All I know that most imperial micrometers have a 40tpi thread but what is the thread form? can any one offer any advice.
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Hi All I know that most imperial micrometers have a 40tpi thread but what is the thread form? can any one offer any advice.
Mike,
I don't know what the exact thread angle is but it's a very simple v with pointed roots and flats on the crests. According to the handbook the gaps formed between the male and female parts are to give a space for dirt to accumulate. I scanned a picture from a Moore & Wright micrometer handbook and measured the angle by importing the picture into Autocad. I got 57.16 degrees. The picture may not have been drawn exactly.
Photobucket is down at the moment so I've attached the scan.
Phil.
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I scanned a picture from a Moore & Wright micrometer handbook and measured the angle by importing the picture into Autocad. I got 57.16 degrees.
When you measured the angle, did you measure the enlarged view or the main picture? Try both and see if they differ.
Before you measure the angle, you might have to scale the scan in X and Y to make sure it is proportionally correct (to compensate for distortion in the scanning process).
This may not be as simple as it first looks. In the X-direction, you need 40 crests per unit (inch). In the Y-direction I think you would need to measure across the crests of an existing micrometer, use that value and scale Y to suit.
We know that all the bodies use 40 tpi. What I do not know is if all bodies are the same diameter.
If the ratio of the X and Y scale factors you eventually use is significantly different from unity, something has gone wrong - scanners are not too bad.
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ME thread is Whitworth 55 degrees , tap or thread guage should show if they are 60 gegrees .
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Here is a 40 tpi whitworth from the resourse section.
http://www.watchman.dsl.pipex.com/thread.html
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Thanks for the comments so far , I am moving to the idea that is is a special fine whitworth 40tpi thread? but I am still searching for authoritative confirmation.
any more information would be very welcome.
Mike
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Mike - if you haven't already, it might be worth searching the patent & reg. design databases in case it is mentioned there?
Dave
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:proj:
Hi All I know that most imperial micrometers have a 40tpi thread but what is the thread form? can any one offer any advice.
Curious.
What are you up to?
Going into the micrometer repair or manufacture business?
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I suppost I have become a bit fascinated by them, they don't need batteries are very accurate and are pretty cheap. I quite like working on old precision equipment. I am a clockmaker but also repair old speedometers as my day job, and so a possible adjunct to my day job might well be the restoration and repair of micrometers. However I am also interested in making and as I can't find a vertical micrometer or and instrument makers micrometer I am planning to have a go at making one or more....
does that make it any clearer?
best wishes
Mike
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I've just checked the thread on one of my Imperial micrometers. It is definitely a Whitworth thread form.
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I suppost I have become a bit fascinated by them, they don't need batteries are very accurate and are pretty cheap. I quite like working on old precision equipment. I am a clockmaker but also repair old speedometers as my day job, and so a possible adjunct to my day job might well be the restoration and repair of micrometers. However I am also interested in making and as I can't find a vertical micrometer or and instrument makers micrometer I am planning to have a go at making one or more....
does that make it any clearer?
best wishes
Mike
Thanks.
Sounds interesting.
Keep us posted.