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.

 

[Jon Leary]

Don't worry about it. Clean up the "chicken groove" when the thtead fits.

 

[ChristianSilver]

If I have close tolerances on a chicken grove I run the other way.
Use internal thread tool, cut from grove to end of thread in reverse..

 

[Lucky Shooter]

I was taught by a very fine machinist to use an indicator and to simultaneously
raise the half nut and back out the cross slide. This was good and dependable
when my reflexes were younger and sharper but I eventually started depending on the groove.

I tied a different method for the groove and think I like it----too soon to tell.
I listen to tool tip sing as it cuts and when the singing stops, raise the half nut.
This seems to be easier than eyeballing the tool tip through accumulated chips
and lube.

This method might also eliminate the need to set up an indicator.

A. Weldy

 

[Will Henry]

I have to confess, when I first saw the title of this thread, the first thing that came to mind was the Chicken Ranch. Maybe it's just me.
For a few years, I worked at a shop where I built a lot of hydraulic cylinders. I cut a mile of threads. Inside, outside, vee threads, square threads, Acme threads, buttress threads, standard and metric. A radiused relief groove at the end of most threads was SOP. This radiused groove reduced the tendency of some rods to fail at the end of the piston threads on the tenon.
Rifle barrel threads aren't subjected to anything like the same stresses so it's not such a big deal, but it looks nice. WH

 

[JFrank]

I was wondering what that area was referred to, now I know..

 

[Fuj]

Here is what I do quite a bit and even yesterday. I use the eyeball method,
but......I have a can full of o-rings. If threading to a shoulder, I slip on an
o-ring against the shoulder, and cut to that. I used to just mark that area
with Dykem. I don't cut a groove unless it's specified on a drawing.

 

[Will Henry]

Here is what I do quite a bit and even yesterday. I use the eyeball method,
but......I have a can full of o-rings. If threading to a shoulder, I slip on an
o-ring against the shoulder, and cut to that. I used to just mark that area
with Dykem. I don't cut a groove unless it's specified on a drawing.

That's pretty clever.

 

[JFrank]

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

I’m hearing you say it doesn’t have to be at the thread minor ?

 

[Will Henry]

I’m hearing you say it doesn’t have to be at the thread minor ?

That's right. It's just a mark. Now, I will often cut a radiused relief at the end of the thread, down to minor diameter, just to get rid of the sharp cut. This after the thread is cut. I like a radius on the corner of the shoulder/tenon as well. Just not as large a radius. I can't say this is best practice, or even good practice, but it is mine; at least it is for now! I have changed my technique over the years. WH

 

[tobnpr]

That's right. It's just a mark. Now, I will often cut a radiused relief at the end of the thread, down to minor diameter, just to get rid of the sharp cut. This after the thread is cut. I like a radius on the corner of the shoulder/tenon as well. Just not as large a radius. I can't say this is best practice, or even good practice, but it is mine; at least it is for now! I have changed my technique over the years. WH

This is true- but again, ONE of the parts needs thread relief. Can't work otherwise.

 

[Sniperhandle]

This is true- but again, ONE of the parts needs thread relief. Can't work otherwise.

Yes, Either the brake/mount or Receiver needs a counterbore or the tenon thread needs a relief cut. Either way there needs to be clearances. I don't know why people have to resort to calling them "Chicken Grooves" Not "Groves" by the way. Many prints and mfg calls for a relief cut including Bat Machine.

If some of you want to white knuckle every cut you make, Knock yer self up, It is not necessary.

 

[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

View attachment 1747925

Unless specified on the drawing not to make a thread relief cut. Or the thread relief cut is dimensioned on the drawing. The accepted standard as defined by various Standards Comities for external threads Is:

Depth: .015” (.03” diameter) below minor diameter.

Width: 1-3 times thread pitch with 1.5 times being most common.

A 45 deg exit into the groove is recommend to reduce burrs.

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

 

[JFrank]

@Skedaddle Shooter
Thanks for posting this topic Joe, and thanks to all those contributing and sharing their knowledge .
I’m learning more everyday and looking forward to chambering my own barrels.
Jim