How does a CNC machine find the center of a barrel or action ?

[Larryh128]

I'm retired tool and die maker, that loved running manual machines. The problem I see with CNC barrel threading occurs when a tool breaks in the middle of the threading process. I have been retired for 8 years now, so I may be out of date. But picking up existing or partially cut thread is close to impossible.

The new tools aren't single point hand ground. They are inserts and if you break one, you loosen it up rotate it to the next point and start again. You don't loose the thread. The best inserts now also radius the top (point) of the thread. I doubt many running CNC's aren't using inserts.

 

[MDSpencer]

I like the Kennametal top notch.

 

[clowdis]

So, does anyone put a mandrel in the boltway and double indicate it to make sure the machine is running true to the bolt centerline? Just indicating the front of the action doesn't make the bolt centerline straight with the machine axis.

 

[Dusty Stevens]

So, does anyone put a mandrel in the boltway and double indicate it to make sure the machine is running true to the bolt centerline? Just indicating the front of the action doesn't make the bolt centerline straight with the machine axis.

does anybody true actions in a cnc?

 

[rijndael]

does anybody true actions in a cnc?

I believe LRI (Long Rifles Inc.) does.

 

[clowdis]

Looks like the same type of setup would apply to truing an action or chambering a barrel (with the exception that the thread needs to be picked up at the right place on an action). You need to make sure the centerlines are lined up to each other. Does anyone "double indicate" a barrel somewhere on a CNC or do they just indicate the bore and go with it?

 

[STS]

Jackson1

I have 160 308 Win barrels in the shop to chamber and another 250 6.5's and 30 that will be here soon. I don't break inserts I wear them out. I can measure that during the life of the insert with a thread mic with the barrel in the Haas. Also there are some visual clues that indicate it's time to change inserts. I changed one yesterday just from a visual inspection. Have I broken them before? Sure I have when using an aggressive depth of cut on say a 2MM pitch thread. All I do is replace the insert, make sure the inert tip isn't stuck in the barrel, I may or may not change the offset a few thou and run the threading operation again. Not a big deal.

That, my good man, is a LOT of barrels. Makes my back hurt just thinking about it.

 

[Roeder]

Looks like the same type of setup would apply to truing an action or chambering a barrel (with the exception that the thread needs to be picked up at the right place on an action). You need to make sure the centerlines are lined up to each other. Does anyone "double indicate" a barrel somewhere on a CNC or do they just indicate the bore and go with it?

Chad Dixon, the owner of Long Rifles Inc. has explained in depth about how he sets up Remington actions in a stationary chuck mounted on the mill table and then as you say "double indicates" a mandrel in the action to achieve e centerline set up. He also explained how he picked up the existing thread for a thread milling operation. Using CNC, he re-cuts the face and lug abutments and thread mills the threads to the centerline of the action with one set up.
To answer your question: Of course anyone "double indicates" a mandrel or in the case of a barrel, 2 points within the bore to set up for CNC machining.

 

[tobnpr]

"The workpiece gets set up in a CNC machine the same as in a manual machine."

Still lost here. I'm hung up on the fact that there's no 4-jaw or other adjustable fixture, and no truing cut to get the bore centered to the OD.
With the barrel held in a collet, the bore is not running true to the Z axis, assuming the normal concentricity error of the bore to the OD of any barrel.

How can this work be accomplished in a collet- where there is no mechanism (outboard spider) to move the opposite end of the barrel and the barrel is rigidly held in the collet? Which raises another ?...holding a tapered barrel, in a collet??

 

[shortgrass]

"The workpiece gets set up in a CNC machine the same as in a manual machine."

Still lost here. I'm hung up on the fact that there's no 4-jaw or other adjustable fixture, and no truing cut to get the bore centered to the OD.
With the barrel held in a collet, the bore is not running true to the Z axis, assuming the normal concentricity error of the bore to the OD of any barrel.

How can this work be accomplished in a collet- where there is no mechanism (outboard spider) to move the opposite end of the barrel and the barrel is rigidly held in the collet? Which raises another ?...holding a tapered barrel, in a collet??

The SL20 that I run has a 3 jaw power chuck on it and there is a 4 jaw independent , manually operated chuck in the cabinet that fits the spindle. Not all CNC lathes are limited to just collets. Oh! and there's a collet fixture in the cabinet for this machine, also. We run this one as a "chucker". It has no bar feeder/tube on it. While I was in gunsmithing school, 26+ yrs ago, we had a 13" swing South Bend that I did some chambering on. The head stock was too long for an outboard spider. A 'set' of bushings had been made the fit the spindle bore snug was used to support the muzzle end. First, you set the barrel up between centers (driven by a 'dog) and turned the shank to the diameter you wanted. Then, turned it around and turned the part on the muzzle end that you were gonna' cut off. The "bushing" fit snug on the diameter that was turned, or the bushing could be centered by the use of the 4 set screws that were 90* apart, and was then inserted into the spindle bore. Kind crude, but it worked. There is about always some sort of 'work around' if ya' just look for it.

 

[Shrek]

I don’t see it either tobnpr. That appears to me fixed in a collet and don’t see how the CNC lathe is following the bore. If it had a three or four jaw and got dialed in I could understand but I don’t see how the the fixed tool planes are working with a fixed collet to follow the bore. I’m going to assume I just don’t understand but I also wouldn’t send that guy any work until I did.

 

[shortgrass]

I don’t see it either tobnpr. That appears to me fixed in a collet and don’t see how the CNC lathe is following the bore. If it had a three or four jaw and got dialed in I could understand but I don’t see how the the fixed tool planes are working with a fixed collet to follow the bore. I’m going to assume I just don’t understand but I also wouldn’t send that guy any work until I did.

NO one uses collets that chambers using a CNC! They have a chuck mounted on the spindle!

 

[MDSpencer]

The SL20 that I run has a 3 jaw power chuck on it and there is a 4 jaw independent , manually operated chuck in the cabinet that fits the spindle. Not all CNC lathes are limited to just collets. Oh! and there's a collet fixture in the cabinet for this machine, also. We run this one as a "chucker". It has no bar feeder/tube on it. While I was in gunsmithing school, 26+ yrs ago, we had a 13" swing South Bend that I did some chambering on. The head stock was too long for an outboard spider. A 'set' of bushings had been made the fit the spindle bore snug was used to support the muzzle end. First, you set the barrel up between centers (driven by a 'dog) and turned the shank to the diameter you wanted. Then, turned it around and turned the part on the muzzle end that you were gonna' cut off. The "bushing" fit snug on the diameter that was turned, or the bushing could be centered by the use of the 4 set screws that were 90* apart, and was then inserted into the spindle bore. Kind crude, but it worked. There is about always some sort of 'work around' if ya' just look for it.

I chamber on a 16” Southbend. I just extend the barrel.

 

[Roeder]

NO one uses collets that chambers using a CNC! They have a chuck mounted on the spindle!

I think these folks are looking at U-tube videos. Not necessarily the same as the real world!
The OP links to a video that shows a barrel chucked in a collet and a high speed threading operation. Kind of a "Gee Whiz" demo. I have known of guys that put fresh centers in a barrel blank and turned the tenon end to an exact size and then chucked in the CNC with soft jaws that were bored to the same size. It would still be necessary to indicate to check. This was many years before the current "Gordy Gritters" method became popular. Just take the video for what it is: a demo.

 

[MDSpencer]

I you bore the jaws correctly. They can easily be as accurate as a collet. But why true a Remington on a CNC. It’s not gonna be anymore accurate. An it will be done by some who have little tooling experance. So buy a Stiller or Bordon or Pierce. Quit wasting

 

[shortgrass]

I chamber on a 16” Southbend. I just extend the barrel.

There's another 'work-around'....

 

[butchlambert]

Chad Dixon, the owner of Long Rifles Inc. has explained in depth about how he sets up Remington actions in a stationary chuck mounted on the mill table and then as you say "double indicates" a mandrel in the action to achieve e centerline set up. He also explained how he picked up the existing thread for a thread milling operation. Using CNC, he re-cuts the face and lug abutments and thread mills the threads to the centerline of the action with one set up.
To answer your question: Of course anyone "double indicates" a mandrel or in the case of a barrel, 2 points within the bore to set up for CNC machining.

I perused Chad doing a receiver in his mill. He indicated a mandrel and I asked him how he shimmed his chuck to dial in the other axis. He didn't answer that question. Maybe he has learned how to take 2 different measurements to properly set up the receiver before machining.

 

[Dusty Stevens]

I perused Chad doing a receiver in his mill. He indicated a mandrel and I asked him how he shimmed his chuck to dial in the other axis. He didn't answer that question. Maybe he has learned how to take 2 different measurements to properly set up the receiver before machining.

But the threads will look “trued”

 

[shortgrass]

I you bore the jaws correctly. They can easily be as accurate as a collet. But why true a Remington on a CNC. It’s not gonna be anymore accurate. An it will be done by some who have little tooling experance. So buy a Stiller or Bordon or Pierce. Quit wasting

For a skilled,'slick' programmer/operator, and the machine properly fixture and doing the work repetitively, several, one after the other, I can see it on a CNC mill. I think Longrifles Inc. does most all of their work on computerized equipment. There are bound to be others that go that way too. Those who use CNC for their gunsmith machining are not doing 'one at a time'. Fast and repeatable, that's what CNC is all about. And I do know this, stand a 'kid' or a dumb a$$ that know nothing about tooling in front of a CNC and you're asking for trouble!

 

[Dusty Stevens]

For a skilled,'slick' programmer/operator, and the machine properly fixture and doing the work repetitively, several, one after the other, I can see it on a CNC mill. I think Longrifles Inc. does most all of their work on computerized equipment. There are bound to be others that go that way too. Those who use CNC for their gunsmith machining are not doing 'one at a time'. Fast and repeatable, that's what CNC is all about. And I do know this, stand a 'kid' or a dumb a$$ that know nothing about tooling in front of a CNC and you're asking for trouble!

It took me a very long time just to learn how to deal with chips with fixtures