Thread Pitch & Major Diameters
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Posted by: knuyenly

03/27/2006, 17:13:52

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Hello,
Can sonmeone please help me out how to get the Pitch & Major diameters of a M37 x 0.75 external thread?
Thank you very much







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Re: Thread Pitch & Major Diameters
Re: Thread Pitch & Major Diameters -- knuyenly Post Reply Top of thread Forum
Posted by: randykimball

03/27/2006, 23:41:22

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Sure, I'd be happy to.. and I'll explain how I do it.

Let's take a known thread from the Machinery's Handbook and extrapolate it out.

Doing internal first.

An M4.5x.75mm internal thread has:
Major diameter of 4.5mm
Minor diameter of 3.838 to 3.688
Effective diameter of 4.108 to 4.013

If we take 37mm and subtract the 4.5 we get 32.5mm.

the major dia. + 32.5mm becomes 37mm
the minor dia. + 32.5mm becomes 36.338 to 36.188
effective dia. + same becomes 36.608 to 36.513


Now let's do your external.

An M4.5x.75mm external thread has:
Major diameter of 4.5 to 4.410
Minor diameter of 3.580 to 3.470
Effective diameter of 4.013 to 3.953

Same process....

the major dia. + 32.5mm becomes 37.000 to 36.91
the minor dia. + 32.5mm becomes 36.080 to 35.97
effective dia. + same becomes 36.513 to 36.453

metric Effective Diameter = our Pitch Diameter

No matter the diameter, the thread pitch still effects it the same way. However, the thread form and roundness of the part become more critical with diameter increases.

Also, I would tend to run some on the loose side with a larger diameter (smaller end of the external and larger end of the internal tolerances).

I need to state, although I'm quoting from the book, I have a bit of a problem with the internal and external major diameters being allowed to both tolerance into the same 4.5mm. I recommend that you DO NOT allow the external thread major diameter ever actually reach 4.5mm (or 37mm).

Be sure to check my work.... wink..

/←randy→/





The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.

Modified by randykimball at Tue, Mar 28, 2006, 00:08:51


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Re: Thread Pitch & Major Diameters Smile
Re: Re: Thread Pitch & Major Diameters -- randykimball Post Reply Top of thread Forum
Posted by: knuyenly

03/28/2006, 12:06:31

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Thank you very much!
That was clearly help.







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