Follow-up tap question

[thewishman]

I have a cap tube - 13.9mm interior size and want to make a centerband. A 14x1 tap and die would give me an interior wall of .9mm in the cap and the body tenon would be 14mm.

Did I get the math right?

 

[mredburn]

The interior should be 13.2 for the hole and the body tenon 13.9 For the interior threads, (drilled hole) take the diameter of the tap and subtract the pitch. (rule of thumb) 14-1=13. because the taps and dies dont cut 100 percent make it 13.2 or what ever is closest. You also need to keep in mind when measuring that wall thickness left after subtracting has to be divided in half. If you have a 15mm outside diameter and you tap it for 14 x 1 threads you have 1mm divided by two or .5mm wall thickness left(.019+/-)

 

[thewishman]

Ahh. I thought I was forgetting something - wall thickness is divided by 2. Thanks for saving me again.:redface:

 

[thewishman]

So a 14 x 1.25 would give me approximately .625 interior cap walls and a 14 x 1.5 would be about .75 walls?

 

[mredburn]

that is thread depth not necessarily wall thickness. It would be considered part of the wall thickness. In some smaller parts I make the thread depth has t be considered on both the out and inner threads. Like the 10 x.75 outer and 8.4 .75 inner threaded pieces for rollerballs or fountain pen front sections.