Chicken Grove

[59FLH]

So I have a question for you experienced guys. In looking at this diagram from my “Machining Fundamentals “ text book, one would assume the the chicken grove would only need to be a few thousands deeper than the minor diameter of the thread to avoid having a grove from the threading tool in the chicken grove once you disengage the half nut. That doesn’t seem to be my experience so far and I’m not sure why? I know you can back off the cross slide just as you get there, but what if you’re late on a pass, or if you are threading the Joe Pie method, starting in the chicken grove and threading away from the chuck? I am measuring the minor diameter with a thread mic. I cut the chicken grove with a carbide parting tool. I touch off the parting tool on the major diameter once I hit that number and input it into my DRO. I also rough check the depth with calipers. None of my mic’s will fit in the grove for a more accurate measurement.
Thanks,
Joe

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As was pointed out in tobnpr's post thread mikes measure pitch diameter and pitch diameter only, not minor diameter nor should they they be used as an outside micrometer in you application.

Here is a quick and dirty math formula to determine minor diameter with out looking it up. The result will be the drill size in decimals for the internal thread equivalent (aka tap drill size), you can use that value as the minor diameter of an external sharp v thread and add your clearance to it for the diameter of your relief cut. Its close and should work until you develop your own method(s).

(1.29904 x % Full Thread) / # of threads per inch.
Subtract that result from your Basic Major Diameter.

Example for an 80% thread (Rem 700) 1.0625” - 16

1.29904 x .8 = 1.039232

1.039232 / 16TPI = .064952

1.0625” – .064952” = .997584”

.997584” – your desired clearance = diameter of relief cut.

I hope this information is helpful, but by all means do what works for you.