New thread micrometer uncovers a problem with theoretical machinist data?? maybe

Brento said:
Gotcha. Thank you. I have a job coming up where i need to cut 3/8-26 and 1/4-26. Some sort of specialty threads for older bikes i guess. I need to figure out how to get a pitch diameter so i can measure them as i thread them.
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Probably Theoretical as I think it still works. I am now not sure about the use of Machinery's if it lists the 0.1697 and boom. my head exploded.
 
All classes ( 1-4 ) have upper and lower limits and they are different . They are listed in the handbook . The upper limit of the bolt has to be smaller than the lower limit of the hole . If not , it wouldn't work , and dat's da law . They are denoted as A and B , like belly buttons , innies and outies . :grin: Just figure out the nominal PD and stay within .001 , you'll be fine even with a GH1 tap .
 
Brento said:
Gotcha. Thank you. I have a job coming up where i need to cut 3/8-26 and 1/4-26. Some sort of specialty threads for older bikes i guess. I need to figure out how to get a pitch diameter so i can measure them as i thread them.
Click to expand...
There are very easy formulas to figure PDs for any size thread . Look in the handbook . The formulas are there . :encourage:
 
This is the formula i found online:


Pitch diameter of external thread = Major diameter of external thread-(0.650*Pitch)
dp = d-(0.650*P)
 
You da man ! :grin: The handbook may dig into it deeper if you're interested in learning that kind of stuff . These days .........................I'm not ! :big grin:
 
Or , just plug in your numbers here . :)
www.omnicalculator.com

Pitch Diameter Calculator

Use this pitch diameter calculator to find the basic, maximum, and minimum pitch diameter of ISO metric screw threads.
www.omnicalculator.com www.omnicalculator.com
 
I will make a separate thread on my questions. I dont want to hijack woodchucker’s thread more then i did.
 
woodchucker said:
So I think I found part of my error. I am reading the wrong part of the chart. I read thread plug gauge, which is probably for internal threads.. I think I need to read the ring gauge?
I just noticed the 2b 3b, which is internal. and looking over the right side I found 2a, 3a.
But still not sure then what Machinery's is saying by saying that's the basic pitch diameter.
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Are the sizes on the chart for making gauges or threads? Gauges will have different unilateral limits depending on plug or ring.
 
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