Gunsmithing Chambering on a 5-axis VMC

[derek1ee]

Is there anyone out there doing barrel chambering on a 5-axis VMC?

With the B axis turned 90 degree, and barrel mounted vertically, and the bore roughly colinear to the spindle, a touch probe should be able to go down the bore, probe multiple point to calculate how much B/C axis need to turn for perfect alignment, then rough out the chamber with drill or end mill, chamber with reamer, and thread mill the external thread.

With CNC lathe, all the cutting is automated but there's still a significant amount of human labor to dial in the bore. This sounds like one way to fully automate the process.

So curious if is this approach is used? And if not, why (accuracy of the 5-axis trunnion)?

The only reference I can find is @LRI using a similar approach for muzzle thread and receiver blueprint, but I think their chamber work is still done on a lathe?

 

[Bugholes]

You might have trouble differentiating between the lands and grooves
smaller bore barrels are gonna be tough to reach inside
barrel curvaturwill be n additional challenge

 

[TheBigCountry]

I heard deathbydiscount is the king of chambering barrels.

 

[derek1ee]

You might have trouble differentiating between the lands and grooves
smaller bore barrels are gonna be tough to reach inside
barrel curvaturwill be n additional challenge

Thank you for your insights, a few follow ups if you don't mind -

I think being able to differentiate land/groove will largely comes down to programming the macro. Obviously moving the spindle to probe the bore different is different than spinning the barrel in a chuck with a fixed dial indicator, or do you think lathe have a nature kinematic advantage here?

e.g., Renishaw OMP400 has a sub-micron repeatability and can be outfitted with an extra-long, small ball end stylus. The difference between land/groove is ~0.004" which is huge compare to the accuracy of the probe + good machine combo. So a simple approach may be to have one macro per twist rate, and per # of land/groove, and then clock the barrel so that one of the land is positioned at 12 o'clock when the barrel is installed in the fixture. This way, the macro can just go down any distance and know based on the twist rate and number of land/groove, where the lands are to approach/probe. More advanced programming may use spindle orientation, it can probe the bore at a fixed height every some degree to figure out where the lands are.

But on barrel curvature, I'd think this is actually what makes this approach interesting. On the lathe, the barrel is clamped in chuck, a true bore system for example that fully constrain it in all degree of freedom. And set screws are used to dial the true bore system colinear to the spindle bore. Which, is obviously a manual process. With a long barrel, spider is used to support the muzzle end, which if not careful, may over-constrain the barrel.

On a 5-axis trunnion however, B/C axis is the "true bore system". And because the barrel is stationary, it just needs to be securely fixtured into the machine table, like how @LRI does in this photo I found on their website.

Obviously this is all theoretical, more of a thought exercise and maybe at some point become my excuse to buy a 5-axis machine, but now I'm just a hobby/self-taught machinist with a 4-axis mill and I've never done a few chamber work for myself on my manual lathe. So my apology if this sounds stupid, and I very much appreciate the insights from experts like you.

 

[derek1ee]

I heard deathbydiscount is the king of chambering barrels.

While removing the human element can speed up manufacturing and lower cost, automation, CNC tools, probing, in process inspection, tool setting and auto compensation is also what gave us the ability to buy prefits for modern actions. If you have more helpful insights on why this may be a good or dumb idea, I'd love to hear them, but if not, you now where the bear pit is.

 

[iceng]

Not worth it, with consumer production equipment.

Its why we have specialist rifling machines, and no one uses "production" machines.
Can a 4 mill rifle a barrel ? Probably yes. Is it sensible ? No way.

Can a chamber be cut with a single point boring bar ? Corse it can, however we get specialist chamber reamers to do it "properly".

Same with anything you want bulk production on.. you buy specialist equipment. Look up the tesla giga-press. Yes they can make tesla car chassis / frames with existing tools and machines, however specialst custom one off machines do it better.

 

[TheBigCountry]

While removing the human element can speed up manufacturing and lower cost, automation, CNC tools, probing, in process inspection, tool setting and auto compensation is also what gave us the ability to buy prefits for modern actions. If you have more helpful insights on why this may be a good or dumb idea, I'd love to hear them, but if not, you now where the bear pit is.

 

[Terry Cross]

e.g., Renishaw OMP400 has a sub-micron repeatability and can be outfitted with an extra-long, small ball end stylus. The difference between land/groove is ~0.004" which is huge compare to the accuracy of the probe + good machine combo. So a simple approach may be to have one macro per twist rate, and per # of land/groove, and then clock the barrel so that one of the land is positioned at 12 o'clock when the barrel is installed in the fixture. This way, the macro can just go down any distance and know based on the twist rate and number of land/groove, where the lands are to approach/probe. More advanced programming may use spindle orientation, it can probe the bore at a fixed height every some degree to figure out where the lands are.

You are going to have a lot of things to account for and filter out by probing the bore.
Your probe is going to have to sort out whether it is touching a land or groove of an already off axis bore during the first part of the process to plot enough known points to program the correction, then repeat at another location to account for bore curvature taking into account the twist rate.

What if you instead dropped a custom made indicator rod into the bore and then probed the OD of the rod close to the blank and another OD about 3 to 4" above that. Bringing both diameters on axis would account for everything including bore curvature.

Could using this approach save enough time in simplicity of the probe routine to make it worth while manually inserting and removing the indicator rod during setup?

Me and Preston had JGS make us up some long indicator rods years ago and I actually went back to this way after using long stem direct readings from the bore for a while. It is consistently repeatable and is relatively fast. I have checked the dialed in barrels a few times with the long stem direct method and everything confirms. It is now my preference and I feel that I am not giving up any accuracy in the setup.


.

 

[derek1ee]

You are going to have a lot of things to account for and filter out by probing the bore.
Your probe is going to have to sort out whether it is touching a land or groove of an already off axis bore during the first part of the process to plot enough known points to program the correction, then repeat at another location to account for bore curvature taking into account the twist rate.

What if you instead dropped a custom made indicator rod into the bore and then probed the OD of the rod close to the blank and another OD about 3 to 4" above that. Bringing both diameters on axis would account for everything including bore curvature.

Could using this approach save enough time in simplicity of the probe routine to make it worth while manually inserting and removing the indicator rod during setup?

Me and Preston had JGS make us up some long indicator rods years ago and I actually went back to this way after using long stem direct readings from the bore for a while. It is consistently repeatable and is relatively fast. I have checked the dialed in barrels a few times with the long stem direct method and everything confirms. It is now my preference and I feel that I am not giving up any accuracy in the setup.


.

Thanks Terry for your insights! With so many people going with long tip indicators to directly dialing in the bore, it's great to hear what real experts do. And yes, I think an indicator rod would indeed make probing a lot simpler. Curious to hear your thoughts on the actual machining part between 5-axis mill vs lathe, and why not more people (or yourself) isn't doing it this way.

 

[derek1ee]

Not worth it, with consumer production equipment.

Its why we have specialist rifling machines, and no one uses "production" machines.
Can a 4 mill rifle a barrel ? Probably yes. Is it sensible ? No way.

Can a chamber be cut with a single point boring bar ? Corse it can, however we get specialist chamber reamers to do it "properly".

Same with anything you want bulk production on.. you buy specialist equipment. Look up the tesla giga-press. Yes they can make tesla car chassis / frames with existing tools and machines, however specialst custom one off machines do it better.

I think there are different "levels" of production. Making batches of hammer forged barrel blanks are quite different than a small shop chambering 10 precision rifle barrels a day, though they are both "production". But I am curious as to what you mean by "worth it" specifically, the time saving/reduction in human error vs. the cost of a 5-axis machine? A Haas TL-1 widely used by many is certainly also a consumer production equipment and not something specifically designed to chamber barrels.

Off topic, but you actually touched on something else I've been meaning to ask - what makes reamer "more proper" than single point cutting the chamber?

 

[Terry Cross]

Curious to hear your thoughts on the actual machining part between 5-axis mill vs lathe, and why not more people (or yourself) isn't doing it this way.

I cannot speak for others. My reasons are solid and I do not feel limited at all in my business growth by not going that route.


1: KMW is not a "production" shop and it never will be. Even if I won the lottery, I would not be re-working the shop to turn out a bunch of barrels per day or week. A bunch of shops have already dropped TL-1s and TL-2s on their floor to start kicking out "pre-fits" and Remage style DIY installable barrels.

To me, (and I am likely wrong) trying to compete in that market is 100% about who can offer a pre-fit barrel at the lowest cost compared to other shops using the same or similar quality blanks as a starting point.

In terms of margin, it becomes a race to the bottom against other shops hungry for the same market. Everybody is pretty much offering the same chamber spec choices and muzzle prep work. At that point there is no value added feature you can offer that others aren't already doing.

That is not my lane and I have more than enough new projects developed that need to be executed on.
These projects are unique to the market and originated here (which brings me satisfaction and motivation). The potential for margin is 10 to 100X what any improved barrel output could ever bring to the table.

It takes me about 50 to 55 minutes from the time I walk up to my manual with a barrel blank in hand until I am pulling it out of the chuck with all breech work and inspection done. So for my particular shop, barrel chambering is not where my bottleneck is. Finishing and detailing is where I struggle with scheduling and time.

2: For me to justify a 5X mill, I would absolutely have to have it running all the time. Whether it be barrel blanks or aluminum billet, something would have to be turned into chips all day, every day. If I were to walk past it and not hear a spindle or tool changer being busy, I would stress the hell out. That is too much capital to sit there part time and I do not think the ROI calcs would be in my favor.

3: While certain intuitive programing inputs are available, I would still be starting at kindergarten level with programing tool paths and just as importantly learning all the weasel craft that comes only from experience. Bottom line, I would not have the expertise to extract efficiencies from a 5X mill.

So I am 100% making it clear in this post that I am not an authority on CNC production machining.
I can run the shit out of SolidWorks and I am decent with basic machine setup and geometry. I will try to do what I do better than anybody else and let other shops make my parts that are needed in quantities of 100s, 1000s or 10, 000s. Whether it is a custom wound spring, an injection molded part, a turned part or a complex milled part, I will find the best shop inside the U.S. to run them and then trust them to do what they are very good at.

.

 

[derek1ee]

I cannot speak for others. My reasons are solid and I do not feel limited at all in my business growth by not going that route.


1: KMW is not a "production" shop and it never will be. Even if I won the lottery, I would not be re-working the shop to turn out a bunch of barrels per day or week. A bunch of shops have already dropped TL-1s and TL-2s on their floor to start kicking out "pre-fits" and Remage style DIY installable barrels.

To me, (and I am likely wrong) trying to compete in that market is 100% about who can offer a pre-fit barrel at the lowest cost compared to other shops using the same or similar quality blanks as a starting point.

In terms of margin, it becomes a race to the bottom against other shops hungry for the same market. Everybody is pretty much offering the same chamber spec choices and muzzle prep work. At that point there is no value added feature you can offer that others aren't already doing.

That is not my lane and I have more than enough new projects developed that need to be executed on.
These projects are unique to the market and originated here (which brings me satisfaction and motivation). The potential for margin is 10 to 100X what any improved barrel output could ever bring to the table.

It takes me about 50 to 55 minutes from the time I walk up to my manual with a barrel blank in hand until I am pulling it out of the chuck with all breech work and inspection done. So for my particular shop, barrel chambering is not where my bottleneck is. Finishing and detailing is where I struggle with scheduling and time.

2: For me to justify a 5X mill, I would absolutely have to have it running all the time. Whether it be barrel blanks or aluminum billet, something would have to be turned into chips all day, every day. If I were to walk past it and not hear a spindle or tool changer being busy, I would stress the hell out. That is too much capital to sit there part time and I do not think the ROI calcs would be in my favor.

3: While certain intuitive programing inputs are available, I would still be starting at kindergarten level with programing tool paths and just as importantly learning all the weasel craft that comes only from experience. Bottom line, I would not have the expertise to extract efficiencies from a 5X mill.

So I am 100% making it clear in this post that I am not an authority on CNC production machining.
I can run the shit out of SolidWorks and I am decent with basic machine setup and geometry. I will try to do what I do better than anybody else and let other shops make my parts that are needed in quantities of 100s, 1000s or 10, 000s. Whether it is a custom wound spring, an injection molded part, a turned part or a complex milled part, I will find the best shop inside the U.S. to run them and then trust them to do what they are very good at.

.

Again Terry thank you for your detailed reply, lots of food for thought and I really appreciate it!

 

[hero's machine]

A benefit of Terry's setup in a VMC is that there's simply no sag to worry about.

Great thing about machine tools is that we can build whatever our imagination and wallet allows.

 

[lariat]

I have 5axis machines for production parts. That kind of setup for a barrel would be nightmarish unless the machine and fixtures were dedicated to the effort, at least for my shop.

Regarding the trunnion: if you are flipping B vertical that thing has to be tight and dialed in. And totally repeatable. I use mine almost daily and also verify my zeros and ensure everything stops a the degree intended.

Terry can correct me but thread milling the barrel is one thing, but the chamber is a whole nuther matter. Depending on how the barrel is held there are chatter concerns, etc. have I used boring bars and other lathe tools in mills? You bet your ass I have but those that can do this I will sit at their feet and listen.

 

[Terry Cross]

Terry can correct me but .......

It doesn't matter what words you type after that sentence, Terry IS NOT qualified to open his pie hole in that realm of tech conversation.

For real.

I couldn't even power up your machine without electrocuting myself.
I would probably piss myself and that's a bad thing.

I do think attempting to singlepoint a chamber could be a Mongolian clusterfuck.