Cutting a chamber neck with a boring bar?

[Shawnba67]

I noticed most of my reamers have a slight bevel at the end of the neck.
Is this there because the chamber needs it?
Or to aid the reamer in cutting the chamber?
It wouldnt be hard to do with the bar but if it doesnt need it it doesnt need it.
Thanks much

 

[swd]

I think it keeps the chamber from shaving the bullet when you chamber a round.

 

[hoz53]

I noticed most of my reamers have a slight bevel at the end of the neck.
Is this there because the chamber needs it?
Or to aid the reamer in cutting the chamber?
It wouldnt be hard to do with the bar but if it doesnt need it it doesnt need it.
Thanks much

They have CNCs now that cut the whole chamber with a boring bar

 

[shortgrass]

They have CNCs now that cut the whole chamber with a boring bar

Hoz, there have been CNC lathes in existence for 30+ yrs. that could cut a chamber. It's the programing. If you can cut a contour on the outside of a 'part', you can cut a contour on the inside of a 'part'. The limitations being in the tooling and the programing. That said, I want to stand by and watch a .224 Texas Trophy Hunter chamber being cut and then examine that chamber myself. A boring bar small enough in diameter to cut the neck and then cut the freebore and throat would have to be tiny. I especially want to see how that bar/tool would react to the interrupted cut of the rifling while it cut the throat. And, I don't care if the bar, itself, is made of carbide. That's sticking it out of the tool holder a very long distance.

 

[243winxb]

reamers have a slight bevel at the end of the neck. Is this there because the chamber needs it?

SAAMI chamber drawings seem to all have it. Some are shorter then others.

So my guess is , yes, its needed.

 

[hoz53]

Hoz, there have been CNC lathes in existence for 30+ yrs. that could cut a chamber. It's the programing. If you can cut a contour on the outside of a 'part', you can cut a contour on the inside of a 'part'. The limitations being in the tooling and the programing. That said, I want to stand by and watch a .224 Texas Trophy Hunter chamber being cut and then examine that chamber myself. A boring bar small enough in diameter to cut the neck and then cut the freebore and throat would have to be tiny. I especially want to see how that bar/tool would react to the interrupted cut of the rifling while it cut the throat. And, I don't care if the bar, itself, is made of carbide. That's sticking it out of the tool holder a very long distance.

Thanks for the Weekend Update Shortgrass. I knew CNC lathes have been around that long. They are being used to cut chambers now on some production lines correct? You do make a good point about the small boring bar. You have the experience- How would you do it?

 

[TRA]

The programing is the easy part. The program can be written in a matter of minutes. There are boring bars available that can do some amazing things. All it takes is money. Obviously a long small caliber wildcat would be difficult, 6ppc on up would not be overly difficult. Forging will probably be the method for production rifles.

 

[hoz53]

The programing is the easy part. The program can be written in a matter of minutes. There boring bars available that can do some amazing things. All it takes is money. Obviously a long small caliber wildcat would be difficult, 6ppc on up would not be overly difficult. Forging will probably be the method for production rifles.

Thanks-

 

[carlsbad]

If I were going to do this I'd want a custom boring bar that was as large as I could get it to the shoulder with a 1/4" diameter extension with the cutting edge. Still it isn't going to be easy.

I use a small boring bar to cut perfectly coaxial muzzle brakes and they go quite deep but are challenged by chatter.

I'd screw a cap onto the front of the chamber and bore it to the diameter you are trying to achieve to ensure my DRO was set up perfectly. Then take it off and do the neck. I would have my compound set up to do the bevel you describe AFTER the boring was done.

I assume you are trying to make a neck that required turned brass into a no-turn neck or something similar.
This is whey neck and throat reamers are popular.

--Jerry

 

[shortgrass]

Cutting the body of the chamber and the shoulder would be the easy part. TRA is correct , a guy could spend a pile of cash on boring tools for small dia. holes with deep applications before he was satisfied. Some of the tool techs , employed by the tooling makers, can be of help while others are nothing more than salesmen. So there's always some trial and error and R&D. Shorter cartridges, like TRA mentioned, would definitely be easier to 'deal with', but there's more to life than short cartridges. Take the 7mm STW, just for instance. You'd be hanging a boring bar out past 2.8"+ and the bar would have to be small enough to enter a smaller than 5/16" 'hole", as SAAMI says the neck is .320" tapering to .319" and I wouldn't trust a 5/16" twist drill bit to cut a true 5/16". So, I'd still attack the neck, freebore and throat with round tools. Chucking reamers can be bought in .001" increments so the neck could be any 'custom' diameter you could buy a reamer for, and the throat reamer incorporates the freebore so it can be set to cut to any depth you might want. But what do I know, the vast majority of bars I deal with in the job shop are 4" to 14" in diameter and I haven't had to bore a hole with a bar smaller than 1 1/2". I left the 'small' stuff behind when I left the Acme-Gridley multiple spindle automatics, and the chambering I have done has all been with finish chambering reamers on manual lathes. I don't remember who it is, but there is someone out there doing custom chambers with CNC and boring bars, not just 'production' chambering. There are several doing CNC chambering with finish reamers.

 

[hogpatrol]

If I were going to do this I'd want a custom boring bar that was as large as I could get it to the shoulder with a 1/4" diameter extension with the cutting edge. Still it isn't going to be easy.

I use a small boring bar to cut perfectly coaxial muzzle brakes and they go quite deep but are challenged by chatter.

I'd screw a cap onto the front of the chamber and bore it to the diameter you are trying to achieve to ensure my DRO was set up perfectly. Then take it off and do the neck. I would have my compound set up to do the bevel you describe AFTER the boring was done.

I assume you are trying to make a neck that required turned brass into a no-turn neck or something similar.
This is whey neck and throat reamers are popular.

--Jerry

Jerry, Are you using an insert tool for the brakes? I bought a few 3/16" that a fellow member was selling on here awhile back, run at a high rpm, light cut, no chatter and nice smooth finish. I set them just a skosh above center. Have used them on the Harrel's ported and radial brakes, 6.5 rifles and larger.

 

[carlsbad]

Yes, I'm using a widia. I have 2 of them. I think the one that was sold here on the forum has a Dmin of .280. It uses a tDHH-07 insert. I have a smaller one that cuts a Dmin of .250 and uses the trigon shaped (W) insert. Both cut very well but are challenged when I hang them out enough to cut a 4 or 5 baffle muzzle brake--which is about how far you would have to hang them out to cut a chamber neck.

--Jerry