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

[Shrek]

reading the tool thread and having seen this video

I don’t see how it finds the center of the barrel to align the threads and shoulder with the bore. In the video the barrel is held in a collet and the lathe tool holder is fixed. In the “what tool to make” thread there’s a video of a CNC machine “truing” an action held in a fixed three jaw. In both of these videos I don’t see how it finds the existing center. Please educate me on this or is it not finding the existing center and just cutting a new axis and not aligned with the existing center axis ?

 

[carlsbad]

I think I know but lets see what those who actually have a CNC machine say.

 

[shortgrass]

After you would have the raceway straight up and down, I'd use a centering indicator (coaxial indicator)( in the quill) until I had center located and them push "X set zero" (set position), then "Y set zero" (set position) (you would have to choose a coordinate code [G54, G55 or whatever to enter these into] . There X an Y are zeroed. You'd easily get bored watching all the indicating, so it is not shown. Same way I'd set "zero" on a manual mill, except there'd be no computer to remember that for me! ;EOB In the video, he is not showing the centering process, just the cutting;EOB The cutting WOWS 'um, the entering tool height, max speed, cutting speed, feed rate and the endless lines of code that thread milling takes are quit mundane;EOB

 

[Tucker65]

On a lathe you still need to have you barrel or work dialed in and running true. The tools are touched off or measured with a tool eye or presetter. The machine then knows from that measurement where the tool is. You then make a few test cuts with the tools to verify they are cutting the correct diameter and if necessary tweak them in with tool offsets.

 

[Shrek]

Thanks ! I can see how that works now.

 

[carlsbad]

A CNC is only as good as it's setup.

 

[shortgrass]

A CNC is only as good as it's setup.

and programing ;

 

[Cloudrepair]

I use multiple methods when im dialing in parts on the cnc mill like probes,edge finders, coaxial indicators,coax to verify the probe and tenth indicators to verify the coax usualy gets me in a couple tenths. I havent done any recievers on a mill but i have done many bores very tight like that in size and location/true position.
If you want a couple thenths or closer, same tools just different methods of use and input

 

[Someoldguy]

So . . . .


Does the bolt body locate off the receiver bolt bore, or the bolt raceways?

Let me take a guess . . . yes.

I'm not trying to be a pain, but it seems to me there is no 'quick and hard answer' here.

If I'm wrong, PLEASE show me the error in my thinking.

And by and large, does it REALLY matter what the bolt body is doing in relation to the receiver body, until the time that the bolt is locked fully into the firing position within the receiver?

Sorry if this is old turf. But it seems relevant to the discussion.

 

[Will Henry]

The workpiece gets set up in a CNC machine the same as in a manual machine. It is only after the set-up is complete that the CNC can do it's stuff. For rapid repeatability, fixtures or parts holders are the thing. Still, if a part is to be accurately machined, the set-up has to be verified. When a part gets slapped into a jig with a chip under it and it is not checked, it will be crooked just as if it was improperly set up in a manual machine. For one-off jobs, the advantage to the cnc is the ability to optimise speeds and feeds and to perform a task while the machinist does something else. WH

 

[Cloudrepair]

So . . . .


Does the bolt body locate off the receiver bolt bore, or the bolt raceways?

Let me take a guess . . . yes.

I'm not trying to be a pain, but it seems to me there is no 'quick and hard answer' here.

If I'm wrong, PLEASE show me the error in my thinking.

And by and large, does it REALLY matter what the bolt body is doing in relation to the receiver body, until the time that the bolt is locked fully into the firing position within the receiver?

Sorry if this is old turf. But it seems relevant to the discussion.

If the bolt is going to do its job best it needs the body parallel to bore bolt face perpendicular to that bore and lugs and lug abutments perpendicular to the bore also and threads true and parallel to.
race ways will affect smooth running in and out of battery but not much else
This is just what I see

 

[Stan Taylor]

Carlsbad and Shortgrass hit right on the mark to get on here an explain in detail you really better have it together the turning center I have at work operates in code that Shortgrass said the G54 and G55 in our machine is the coordinates for length of materials I am working with so the machine knows where start once I pulled up the right program if I don't an hit start it is (OH shit)then if you don't hit the stop button before hand crash.

 

[MDSpencer]

Hold on! There is no “Y” on that style of cNc. Most all are “X” and “Z”. X is the diameter and Z is the length.

G54-G55 are just location offsets. He or she in the video is colleting and turning a thread no different than any of you would do on a manual.
That speed is needed for a decent looking thread. Too slow and the material will tare. I run a cnc latte every day. Including today.

 

[shortgrass]

Read the first post instead of watching the video. Tucker is action truing on a mill, not a lathe of turning center. He is thread milling the action threads. A mill has at minimum 3 axis, X and Y are table, Z is the quill up and down. G code is still used, just a little different than X and Z on a lathe. The video in the first post doesn't 'jive' with text that is written in that first post.

 

[jackson1]

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.

 

[shortgrass]

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.

As long as the tool holder doesn't move, just put another insert in and hit the start button. Single point threading makes pass after pass until the program goes to the next line of code. Just don't take the piece out of the chuck and try that without 'picking-up' the thread. The damn thing is smart! Threading single point is a "canned cycle". "Picking-up" the receiver thread, like Tucker65 does on the mill is a matter of adjusting "tool height".

 

[TRA]

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.

Most current controls have a thread repair function, if you know where to find it.

When a tool breaks all you have to do is replace the insert, and unless you are gutsy, back off the tool offset a little, as inserts are not perfect unless you have deep pockets.

 

[jackson1]

Good information shortgrass and TRA. In my experience, threading inserts don't like to work, if any of the original insert is remaining or an interrupted cut. I always liked to cut threads with high speed tools.

 

[DaveTooley]

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.

 

[shortgrass]

^^^^^^^ that's the deal! Don't break 'um, change 'um when they get dull! Problem solved!