The next instalment of “Teach the New Guy”: Thread Micrometer.

The #210 is only used for comparative measurements and is faster to use, the 575 series is used to measure pitch diameter, but is fairly fussy to use resulting in more time used up. If I was making a thread gauge, I would be using the 575, if I was threading most other work, I'd be getting close to finish and be using a nut or gauge for the final fit unless specs were called out for a pitch diameter.
 
All the input is greatly appreciated. Last question then. What is the difference between pitch diameter and minor diameter?


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Look at this diagram:

thread nomenclature.jpg

On the right, see major, minor and pitch diameters? The pitch diameter is halfway between the major and minor diameters. You will not use the minor diameter when cutting threads except for cutting thread reliefs. Thread reliefs are the space we make for the cutter to run into and they are typically 0.003 - 0.005" deeper than the minor diameter and 2-3 thread widths wide when we have enough room.
 
Unless you need to make a thread to meet a spec, minor diameter is not so important but it is important.

Depending on your threading tool, if your using a tool that your ground on your own, the minor diameter will vary depening on the tip radius you grind on your tool if at all (sharp V). Same with partial profile inserts (cuts a range of pitches), they have a sharp point. Full profile inserts wil have the correct form to cut the root but full profile inserts can only cut one single pitch. You would need a different full profile insert for every thread pitch. So a thread cut with a full profile insert should have a stronger thread than a sharp V tool since there will be a radius at the root of the thread.

I say not important but important cause if you have too much of a radius ground on your tool, it will not cut enough clearance at the root of the thread for the crest of the mating thread to fit.
 
mikey said:
Okay, Will has a prettier picture!
Click to expand...

Actually I like yours better. The one I posted was just the very first one that popped up on google images. :)
 
You guys are rockstars. I do understand what you have been trying to get across to me. What’s more is that I appreciate that I can ask a legitimate question, get some positive feedback and come away from the experience better because of it. Thanks guys!! Dinners over and I’m heading to the shop to put this into practice. Cheers. My respect and thanks to all who took the time to help me through this.


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Pitch diameter of a typical Vee thread is the diameter where thread thickness is equal to groove width, that is, where both thicknesses are equal to 1/2 of the thread pitch. It’s halfway between major and minor diameters only when the roots and crests are mirror images of each other, as in a 60 degree Vee thread where the crests and roots are actually Vee shaped.

Tom

1575350434680.png
 
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