chambering without reamer!
- Thread starter peterdobson
- Start date
It would be a great idea , for a one off ,of something close to a standard cartridge ...maybe a little over sized...more powder in just a little bigger package. Interesting. CNC probably not needed, but would be nice. If you could write the program for it ! Old man-u-well is still works well for me.
Cheers.
Brian
Cheers.
Brian
There is/was a company in New Hampshire using EDM (electro discharge machining) to chamber Thompson Contenders.
Blastattack
CGN Ultra frequent flyer
- Location
- Winnipeg MB
Why on earth would they do that? I can't think of a much more expensive way to make a chamber.
because they were producing very accurate barrels. If you find that interesting - check out the ‘cation’ process for rifling.
I believe a lot of barrels underperform because the chambering was botched while using a reamer. There is some good evidence that production barrels that are hammer forged with rifling, chamber and throat formed by a single mandrel (like Diemaco did/does) are more consistently accurate than hammer forged barrels that are separately chambered with standard reamers. It is interesting that Steyr’s new ‘Monoblock’ rifle has the barrel, chamber AND action (in one piece) all hammer forged on a single (?) mandrel which incorporates rifling, chamber and action .... they claim ‘sub’ minute of angle ‘out of the box’ with these firearms. I believe this may be due to the high level of concentricity they can achieve with this approach.
It may be that not every gunsmith takes the time or care to ensure they create a ‘good’ chamber.
Some of the best chambers I have seen were hammer forged along with the barrel but performance was no better nor worse than a reamed chamber. Consistency was very good but also not 100%. Minor dimensional variations in the throat seemed to be the most common flaw.
Probably is, due to the finite amount of control over the final product. Reamers are convenient.
I totally agree Bill... With a lathe and a reamer we can easily and cheaply chamber, making exact duplicates if needed. We both have under bored chambers before using the finish reamer and know of the difficulties when boring. CNC chamber boring is not really practical for a gunsmith.
Last edited:
Right! Quite practical! Gimme a break!
When many gunsmiths have to have another job to support their gunsmithing and their wife working as well... the CNC is a rich mans toy as far as gunsmithing is concerned.
Any idea on how much money has been earned by boring chambers rather than using a reamer? How many lifetimes to pay for a CNC lathe?
My customers usually pay for their machines in a year.
When it takes under two minutes of actual cutting, you've got lots of time to take on other work that actually pays your bills.
If you can just send me the design for the boring bar which is going to cut consistent chambers for me, without the use of a reamer, I'll be happy to give it a look. I spent enough time honing and lapping valve bodies which were bored that I have a little trouble visualising the process. The program produces a virtual product. I want to see the actual result when the chips are produced.
Seriously, if we are to produce a chamber with a body diameter of about .460", at the small end, like a 6BR, we can probably use a 3/8 diameter bar. We'll rough the body with a drill to about.406" then bore to the juncture of neck and shoulder. I think this could be done and be done pretty well. To produce the shoulder angle, the 3/8 bar won't work because it won't have the clearance so we'll have to go to a smaller diameter. No big deal although tool deflection is going to rear it's ugly head. To bore the neck, we can use a larger diameter bar with a small tip so deflection shouldn't be so much of an issue and we may be able to bore a pretty decent neck. Now for the throat. Reamers can cut a throat to within .0001" while producing a good finish and a transition angle which is precise. smooth and free of burrs. Maybe our special bar can do this as well but, given the interrupted cut and all, I kind of doubt it.
In addition, at some point, one or the other of the boring tools is going to dull or lose a tip. When this happens, the machine will go on, blithely, cutting away. The chamber will be ruined and this will be discovered after the barrel is removed from the machine. No big deal really. We can always fix it with a reamer.
Seriously, if we are to produce a chamber with a body diameter of about .460", at the small end, like a 6BR, we can probably use a 3/8 diameter bar. We'll rough the body with a drill to about.406" then bore to the juncture of neck and shoulder. I think this could be done and be done pretty well. To produce the shoulder angle, the 3/8 bar won't work because it won't have the clearance so we'll have to go to a smaller diameter. No big deal although tool deflection is going to rear it's ugly head. To bore the neck, we can use a larger diameter bar with a small tip so deflection shouldn't be so much of an issue and we may be able to bore a pretty decent neck. Now for the throat. Reamers can cut a throat to within .0001" while producing a good finish and a transition angle which is precise. smooth and free of burrs. Maybe our special bar can do this as well but, given the interrupted cut and all, I kind of doubt it.
In addition, at some point, one or the other of the boring tools is going to dull or lose a tip. When this happens, the machine will go on, blithely, cutting away. The chamber will be ruined and this will be discovered after the barrel is removed from the machine. No big deal really. We can always fix it with a reamer.
Are we talking gunsmiths or gun manufacturers? I've seen a lot of gunsmiths and have yet to see a CNC anything. I'm not against CNC either and I can see how it can cut a chamber with the right tooling, but the best I could afford in my life and pay for it was an old SB lathe and Bridgeport which I had to rebuild to bring back to spec. I'm just a hobby gunsmith too. I could never afford the insurance to run a gunsmith shop nor invest into a separate building. Who are these gunsmiths running CNC shops? Wow!
