Chicken Grove

[Skedaddle Shooter]

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

 

[X Count]

Tool tip radius might be the issue. If your tool has a smaller radius it is essentially longer which would require a deeper chicken groove.

 

[Will Henry]

I do usually cut a groove but I don't cut it to full depth. It is only a visual reference to let me know it's time to disengage and/or back out. I always try to avoid any sharp corners. WH

 

[tobnpr]

I am measuring the minor diameter with a thread mic.

Thread mike measures pitch diameter- not minor diameter.
Apples and oranges.
You need a relief groove on either the tenon, or the part being screwed onto it.
I work off a chart showing minor diameter for the class of thread I'm cutting, then I go five thou deeper than that if the part I'm fitting-such as a brake or receiver doesn't have a thread relied cut. If it does, then depth is immaterial as mentioned, so long as the thread relief in the part is longer than that in the tenon.
I used to try to keep the thread relief grooves "tight" dimension wise, only to find out that the part wouldn't thread in fully; no reason to try to cut the groove to the exact minor diameter, make sure you've got plenty of clearance (within reason, natch) so you don't need to go back a re-cut it.

 

[LVLAaron]

Eyeball it. It's not an aerospace part.

 

[DShortt]

Eyeball it. It's not an aerospace part.

True. But. There's no harm in treating it like it is if one is so inclined.

 

[Skedaddle Shooter]

Thread mike measures pitch diameter- not minor diameter.
Apples and oranges.
You need a relief groove on either the tenon, or the part being screwed onto it.
I work off a chart showing minor diameter for the class of thread I'm cutting, then I go five thou deeper than that if the part I'm fitting-such as a brake or receiver doesn't have a thread relied cut. If it does, then depth is immaterial as mentioned, so long as the thread relief in the part is longer than that in the tenon.
I used to try to keep the thread relief grooves "tight" dimension wise, only to find out that the part wouldn't thread in fully; no reason to try to cut the groove to the exact minor diameter, make sure you've got plenty of clearance (within reason, natch) so you don't need to go back a re-cut it.

Thanks. I appreciate the advice.