threading help please

[Investigator]

I need to understand cutting threads on an non-standard diameter. For example, (making up numbers) if I had a 1.133"OD and wanted to cut threads at 20tpi (or any other pitch) how deep do I need to cut them? I understand looking up major and minor diameters for standard sizes, but what about one offs?

 

[Holescreek]

Looks to be .0307" external.

 

[Investigator]

Wow where do you find that calculator? I just made up the diameter for discussion

 

[ThinWoodsman]

On a Windows 3.1 machine, by the look of it

 

[Ed ke6bnl]

Got the same result on (thread Calc) android app

 

[Bi11Hudson]

Then the diameter minus the pitch works well enough for tap drills. Just invert where needed. And never worry about fresh batteries again.

 

[Tinkertoy1941]

Bi11Hudson has the correct answer

 

[Holescreek]

I do a lot of oddball thread stuff in SAE (at home) and metric at work. I measure threads at work and the numbers have to be perfect with regard to JIS standards for metric threads. I started using a program called "ME Threadpal" a long time ago when the program designer first made it available. It has features that allow me to make threads up that I really like. I couldn't tell you if the program is even still available since it's been so long.

I realize that there are lots of ways to get close to the answer you're asking for, this was just one of them.

 

[Tinkertoy1941]

I would be interested in finding another way to calculate odd ball threads.
I do a lot of Amish Sawmill repair and some is beyond repair but you have to use what not broke up.
Most all shafts are fractional in 1/16 2 7/16 1 5/16
They do not have a answer only that's it's the way it has always been.

 

[dpb]

For standard 60° threads, the tpi determines the depth of the thread, not the diameter of the piece being threaded. In other words, a 20 tpi thread is always cut to the same depth range, regardless of work piece diameter.