Gun Barrel Chambering CNC Style

[Cheenist]

I’ve got to run a boatload of gun barrels and the job is going to repeat. Now I’m not a gun manufacture and don’t know much about them. My customer likes my work and I have made a fair amount of barrels for him on my Haas SL-20 so I’m not a complete newbe. My customer does the chambering in house but now wants me to. The customers in house process is; first, the barrel is turned complete, second, he adds the barrel extension and torques it to 150foot pounds, third, he rough reams followed by the finish reamer…all on a manual lathe. At the rate I’m going to be making these barrels his process isn’t going to cut it. Are any of you guys making barrels? The “head space” is plus/minus .003. I would like to rough/finish ream the chamber in my CNC lathe THEN add/torque the barrel extension. Can I maintain the headspace with this process? I just can’t see a real barrel maker “finish reaming” chambers by hand!! His other barrel supplier makes and ships as many as 800 barrels a day. I’ll be doing around 300 every month. I was going to post this on the gunsmithing forum but most of those guys seem to be doing custom work.
Thanks,
Carl

 

[Alum chips]

Ok, I ASSume the barrel extension is because the barrel is to short to get all the way though the headstock?? If so then the extension has nothing to do with the head space.
On a side note I ASSume you are using a receiver to ck head space...If you are or have anything with a serial # on it shoot me a PM and I will walk you thought the legalities. I have been licensed manufacture since the '80s.
Gary

 

[wesg]

AR-15, judging by the drawing. The extension contains the locking lugs. Holding +-.003 on headspace shouldn't be an issue with machining to dim' before installing the extension.

Other thought is concentricity of the chamber, but I suppose if they're allowing .003 on headspace than they're also not too concerned about runout. You'll probably want to use a floating holder to deal with this.

 

[Cheenist]

wesg,
Yep, some type of AR-15. The barrels are 4140 hammer forged, delivered with the bore/rifling complete...consentricty is around .004 TIR and better. I am holding the reamer in an ER collet and the holder is dialed in, but not floating. I chamfer first, drill, then rough and finish ream. Next using a boring bar I add a .062 radius to blend the chamfer to the chamber. The chuck jaws have been bored true. The reamers as shown in the photos have a pilot..so adding a floating holder is probably a good idea. I had a problem a while back with the barrels pushing back in the chuck during the rough turning passes, but solved it with a spindle stop and increasing the chuck pressure to 400psi.
Any advice is welcome.
Thanks,
Carl

 

[Seekins]

I highly doubt the bore and the outside of the barrel are concentric enough that you can assume the bore is running true. I do quite a bit of gun smithing and have seem some with as much as .020 runout on the outside of a barrel that was turned between centers. Most of them are about .005-.008. The rifled bore is deep hole drilled then rifled and its not strait thru the barrel either, so you have compound problems when trying to cut a strait chamber in a hole that is crooked and most likely not spinning concentric.

I know these are probably production barrels, but never less a crooked chamber will give your customer more problems than you could imagine. Not only can it be crooked, but it will be oversize as well. IF it is cutting over sized which is easy to do when the bore has run out and the reamer is held hard (not floating to allow for miss alignment) the casing will expand more than its supposed to and can cause problems.

The barrel nut can be put on before or after. They are held to a fairly tight tolerance. You just have to decide what process you want to do it in. I would....thread and do whatever you need to the outside of the barre, Rough ream and then finish ream. Both reamers would be carbide and both in floating holders. If you get your process down there is no reason why the barrel nut could be the last thing you do. You just need to figure out how much head space you will loose when you tighten down the nut.

The gun industry is very small and a few barrels that don't shoot will give you a bad reputation fast. Then your customer wont have any orders to send your way...If you can do a very good job both you and your customer will do very well.

I would highly suggest getting a floating reamer holder and also some carbide reamers. Contact Dave at Pacific tool and gage and he can set you up with everything you need to do a very good job. 1-541-826-5805 They are in Oregon

 

[Cheenist]

Seekins,
Thanks for the info. Floating reamer holders are $325.00ea. sheeesh!..and I’m going to need two. The customer is providing the reamers and one of the finishing reamers is carbide. I have been inspecting the blanks by placing a pin in the bore and rolling the blank in vee blocks. I record the runout on the barrel and check it again after turning. I can improve the runout slightly as the tailstock center attempts to pull the barrel on center.(that was an awkward sentence). The customer also provided Go and No-Go gages to check the head space. The way the hammer forged blanks are made is a hole is drilled thru the blank then the blank is slid over a carbide mandrel that has the rifling grooves. Then carbide hammers come in from four directions and hammer the blank around the mandrel. The process takes a couple of minutes then the barrel is slid off the mandrel complete with rifling grooves and incredible finish in the ID. A very cool process.
Thanks for the help.
Carl

 

[SwissPro]

I've been peripherally involved with several barrel turning projects involving us providing turnkey machines and automation.

For hammer forged barrels we used 4-axis Okuma lathes. Usually with a programmable follow rest in the lower turret, the barrel on centers with the chamber end being driven by a face drive center. But we've also pinch turned eliminating the follow rest, which is faster but a whole lot more difficult to get running right.

After turning on centers the ID and OD are concentric enough to machine the chamber by swallowing the barrel in the spindle which was bushed. Then the chamber was machined by single point boring and roller burnishing in 2-axis Okuma.

In another projct we used a cheapo HMC to machine the chambers. We probed the machined the chamber and thread milled the threads. The big problem was the low cost HMC. We had to laser calibrate it, adjust the servos, and do a bunch of other stuff to make it accurate enough.

 

[Cheenist]

Haas SL-20 with live tooling here. I had planned to do the barrels in two operations but I just could not get rid of chatter from the threading tool. The first operation would be turning, threading and chambering while only two inches of the barrel sticking out from the chuck. This operation went as planned. The second operation I hoped to hold the barrel on the now finished chambered end and turn, thread and crown. I just could not get rid of the chatter when threading. The barrel was sticking out 13 inches supported by the center. I also tried several different centers, a Royal super precision CNC center, a brand new Skoda heavy duty center….nothing! The turning went fine but the Kennametal Top Notch 28tpi cresting threading insert was making me pound my head against the lathe. I started with 750 rpm and went as high 1250rpm and as little as 250rpm…. didn’t work. I started with a DOC of .010 and went as deep as.025…nothing. Checked tool height, change to a new insert…I got nothing! Someone here recommended a laydown style insert so I checked the catalog and other than orientation I can’t see any reason this style insert would make any difference. So now I’m up to three op’s…First, turn, thread and chamber, second, turn, thread and crown the end you not supposed to look into and third….holding on the chambered end, rough and finish turn the barrel. By the way I’m rough turning .075 DOC at 600 rpm with a trigon insert and finish turning with a DNMG431 insert at 800 rpm and .010 feed in non critcal areas and .005 on the precision diameters. Inserts were provide by Curtis from exkenna. Suggestions, ideas anyone??
Thanks,
Carl

 

[wesg]

Coolant through the bore for chambering, or just backing out to clear chips? Get one caught in there and the barrel is scrap.

One thing I forgot, torquing the breech extension on, and 150 lbs-ft seems absurd to me, may shrink the chamber a bit. May not be an issue if these are Nato spec to begin with, but worth looking at.

As for threading, never done any but on a manual lathe so I'm running quite a bit slower than you are and taking much lighter passes. Looking at 'the books' for CNC threading, with the cutting depths they recommend, looks to be impossible to me. Maybe you'd get away with doing it in 2 op's if you cut the depth per pass from .005 on the first to .001 or so on the last few.

 

[HuFlungDung]

My observation with regard to laydown thread inserts, is that some of them are available with a raised edge for a chipformer, and they will curl a beautifully smooth chip off both sides of the thread.

Top notch is kind of a get 'er done workhorse, but not a real high performance threading system. For one thing, there is way excessive clearance ground on the trailing edge of the insert, demonstrated by the fact that you can thread right hand or left hand with the same insert. In a troublesome situation, that excess clearance is going to work against you.

Also, some laydown threading systems use angle shims to tilt the insert to create the extra clearance required on high leads.

 

[Stuart Caruk]

I used to use single point top notch style threading tools in my Haas HL1 lathe until I too came up with a job that no matter how hard I tried, I couldn't keep the tool from chattering. I too used Kenametal tooling. In frustration I tried a laydown style insert and the problems just dissapeared. Now about all I ever use unless I simply don't have the proper insert is lay down threading tools. Don't ask me to explain why, they just seem to cut way better threads.

Our Integrex does it one better becasue we can alternate one side of the thread, then the other as we whittle in to the minor dia. the thread quality is superb.

I'd try the lay down threading tools before getting too frustrated.

 

[Joe788]

In another projct we used a cheapo HMC to machine the chambers. We probed the machined the chamber and thread milled the threads. The big problem was the low cost HMC. We had to laser calibrate it, adjust the servos, and do a bunch of other stuff to make it accurate enough.

Dan, this was how I was going to mention doing it. I'd put 80 barrels on each 500mm tombstone, hit em with the MP700, then plow through the reaming with 1000psi coolant thru.

What kind of HMC were you guys doing it on? Please don't tell me it was an
HS1!

 

[WILLEO6709]

the problem with chambering reamers is that most are straight flute....the dam things will load up. Peck reaming to clear can allow chips to get under the cutting edge, which can cause rings in the chamber. I can't see where thru coolant can be useful...the reamers unless custom made are not ported for it. The pilot on the reamers makes flushing the chips out the front impossible, so chips must come out the back. Pratt and whitney manufactured chambering machines in WW1 era, they backflushed from the muzzle.

 

[Joe788]

the problem with chambering reamers is that most are straight flute....the dam things will load up. Peck reaming to clear can allow chips to get under the cutting edge, which can cause rings in the chamber. I can't see where thru coolant can be useful...the reamers unless custom made are not ported for it. The pilot on the reamers makes flushing the chips out the front impossible, so chips must come out the back. Pratt and whitney manufactured chambering machines in WW1 era, they backflushed from the muzzle.

Yeah, coolant thru wouldn't be terribly useful for those specific tools posted. You'd need to get a hole edm'd through the center, with an intersecting hole just above the pilot. You can blast chips out of just about anywhere using 1000psi coolant!

 

[Perry Harrington]

Fixture the muzzle with a coolant port through the draw tube. If you put coolant in the muzzle, it'll blow past the rifling into the chamber, evacuating the chips.

 

[Cheenist]

Perry,
Thanks, but if you check the reamers in the picture you would see that the pilot would block/restrict any coolant coming in from the muzzle end, not to mention the impractically of getting coolant to enter the barrel from that end which would be about in the middle of a 50 inch long moving and rotating drawtube. Coolant flows out the slots in ER style collets flushing/blasting chips but I will have to come up with somthing different If I get floating holders as these will deflect the flow. Maybe there's a reason these aren't being done by job shops...hmmmm.
Thanks for the suggestions.
Carl

 

[Seekins]

I use a muzzle flush system from Pacific tool. The cutting oil in the POS lathe i use flows thru the barrel and past the live pilot ok, but i dont have hardly any pump pressure either. They also make pilots just for this if it is a issue.

The unit i have mounts onto the end of the barrel as it sticks thru my headstock.

The biggest thing is you dont want to be re-cutting chips and chamber reamers load up very fast. It will probably load up on you every .08-.1" DOC and need to be cleaned. A .223 isnt as bad as some others.

 

[CBlair]

You can use a dremel tool with a grinding wheel to modify the pilots with longitutinal grooves to allow coolant to flow from pilot to clear chips. If the barrels are shorter than your draw tube then this would be a bit of a problem. Most people that I know of who do this are using manual lathes so this is not an issue.

Charles

 

[Alum chips]

First off you need to give Dave a call at pacific too. He has seen and over come all of the problems you have now and will have....1000's of times.
As far as the muzzle flush goes its the only way to go on these reamers. Here is a shot of one of the first Ultra reamers released. So it must be 8-10 years old...notice the slots/groves cut under the pilot. Those are for a muzzle flush. I don't think you can get one of his without these now.
Gary

 

[Perry Harrington]

Perry,
Thanks, but if you check the reamers in the picture you would see that the pilot would block/restrict any coolant coming in from the muzzle end, not to mention the impractically of getting coolant to enter the barrel from that end which would be about in the middle of a 50 inch long moving and rotating drawtube. Coolant flows out the slots in ER style collets flushing/blasting chips but I will have to come up with somthing different If I get floating holders as these will deflect the flow. Maybe there's a reason these aren't being done by job shops...hmmmm.
Thanks for the suggestions.
Carl

I was pointing out that the *rifling* already present would allow the coolant to pass. The combined area of all the rifling should be similar to just 1 little hole down the center of a tool.

For getting coolant to the other side, affix a rotary union to a coupling that you attach to the muzzle. The hose comes out the off side and to a pump. You could get more elaborate, like spindle liners and a hard line to the barrel, rotary union and hose at the end of the spindle.

For grabbing onto the barrel, ever seen one of those push-to-release tap collets that Kennametal has? The collar works just like a quick disconnect, except the balls have no where to go when a tap is in there and grabs the shank. When you push the release collar the tap comes right out. Same design, just add a face engagement seal for the muzzle.