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Micrometer thread form
Rick O Shea:
Hi All I know that most imperial micrometers have a 40tpi thread but what is the thread form? can any one offer any advice.
philf:
--- Quote from: Rick O Shea on November 04, 2016, 04:42:17 AM ---Hi All I know that most imperial micrometers have a 40tpi thread but what is the thread form? can any one offer any advice.
--- End quote ---
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.
djc:
--- Quote from: philf on November 04, 2016, 07:31:15 AM ---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.
--- End quote ---
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.
chipenter:
ME thread is Whitworth 55 degrees , tap or thread guage should show if they are 60 gegrees .
tom osselton:
Here is a 40 tpi whitworth from the resourse section.
http://www.watchman.dsl.pipex.com/thread.html
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