Thread calculations 1

[spider80]

Is it right to say :
minimum dia of the internal thd. = (major dia. of internal thd.) -(5/8 *pitch * cos30)
for an UNC or UNS thd?
Thanks

 

[spider80]

To rephrase my question, how can I calculate minor dia of internal thread? I was referring to MH and couldnt work out numbers based on the thread profile dwg (on pg 1793). I need to cut 2B thd of dia 11.625.
What I calculated was for a UN, height of a thread is basically 5/8 times its sharp thread height (with the crest and trough flattened or rounded for engagement) so that comes out to .0169in, to get minor dia, I would sub two times of this from the major and end up with 11.591.
Is this correct? I believe this might be directly mentioned in the ANSI/ASME B 1.1-1989 standards (for threads over 4in in dia) but I dont have that.
Thanks

 

[HemiBuell]

I think you need to invest in a Machinery's Handbook.

 

[spider80]

I was referring to MH (Machinery's Handbook). I would just like to verify the numbers with the ANSI standards or calculations.

 

[Screwman]

Get a copy of ASME B1.1 for the formulas for the limits of size for inch threads.

Dick

 

[diamondjim]

If you find a chart with the tap drill
size, that plus the amount of oversize
that drill might make would give you
the actual rather than the theoretical
size which is probably more important.

 

[rob768]

When will you guys join the rest of the world in using international standards, I wonder

 

[spider80]

I wish I could rob768. Believe me am a mm guy.

 

[bobc]

simplistic formula for tap drill diameter is: major diameter
-1/number of threads.

example 1" 8 thread = 1"- 1/8 = 7/8" drill.

this is very close for all thread sizes. don't kmow if it is close enough for your needs.
bobc