Reamer Print Spec's??

[Nvreloader]

Hey Guys,

I am having a new reamer ground/made by PTG,
7mm Imp/06 using the 280 Imp spec's, shortened for 26/06, 270 and 30/06 case lengths,
which will be changed to my spec's etc.

On the reamer print, it shows the neck, body and other tapers spec's as given TPI" per 20".

Why is the spec's given this way?,

How do you figure this taper out?

What are the formulas needed to work the tapers out for 20" ?

This 20 tpi taper has me baffled at this time, as nothing I have tried works etc.

I can figure taper per in/foot etc, with NO problems.

Tia,
Don

 

[Roeder]

I took a PTG print for a .280 Remington that specs TPI in 20 inches at .145. The Body Specs .471 at the Bolt Face and .442 at the junction of the body and the shoulder. Using .471 - .442 = .029 / 1.992 = .1455. Looked at another way, .145 / 20 = .00725 (TPI) The body tapers .029 over 1.992 inches which is .01455 over 1 inch.

I am going out on a limb here, but I think the 20 inch spec is to convert the taper to a number that can be used to adjust a grinder. some cylindrical grinders have a table with a center pivot and if an indicator takes a reading 20 inches from the pivot point it would read taper in 20 inches. The taper is expressed from the centerline, not included.

I do have some experience operating cylindrical grinders, but I don't have one close by, so this answer is somewhat speculative.