[How-To] Bore and Turn in a single operation, possible?

[strantor]

There may be a better way to size necks?

Yeah, with a press and die. Not sure why you would want to remove brass in a lathe. A press and die shoves the metal back to where it's supposed to be rather than cutting it off, which would result in a weaker case.

Maybe he's changing the caliber of the brass (ex: turning 9mm cases into 380)? That's the only reason I can see for removing metal, but wouldn't explain the setup being discussed.

 

[dml66]

Regarding machining the cartridge brass, a normally the neck is swaged for an interference fit for the bullet. It would seem that a practical approach would be to swage the o.d. followed by reaming the i.d to size . Is there a concern with concentricity?

I'll confess to never reaming a hole for precision. I have used reamers to fashion brass holders for various purposes. My understanding is reamers will "follow the hole" which, if I didn't bore the hole to begin with, may not be the best approach. What did get me interested in reamers is the potential for very good to excellent surface finish which is important me; I chickened out .

 

[dml66]

Yeah, with a press and die. Not sure why you would want to remove brass in a lathe. A press and die shoves the metal back to where it's supposed to be rather than cutting it off, which would result in a weaker case.

Maybe he's changing the caliber of the brass (ex: turning 9mm cases into 380)? That's the only reason I can see for removing metal, but wouldn't explain the setup being discussed.

I don't want to turn this into a ammunition thing since this isn't a gun forum but, since you mentioned it, there are other reasons for altering the neck wall thickness of rifle brass than conversion from a parent cartridge.

 

[RJSakowski]

As I think about it, when resizing brass, the resizing die swages the o.d. of the form fired brass to a smaller diameter and the expander opens the i.d. to the proper size. If the neck is too thick, then it would be the o.d. that needed to be turned down. This would be a simple operation requiring only a single tool. To ensure uniform neck thickness, I think it would be useful to make a custom live center to keep the i.d. of the neck running true while turning the o.d.

In the distant past, I had resized .30-06 cases to .308 Win and had to turn the necks down as well as trim to proper length. I don't recall having any issues.

 

[jwmay]

This isn’t a gun forum, but we do have one here.

GUNSMITHING & FIREARMS

Show us your gunsmithing & firearm projects and accessories here. Discuss any topics regarding gunsmithing here.

www.hobby-machinist.com

I’m not the guy with advice on the topic, but you may find something in there.

 

[dml66]

I think it would be useful to make a custom live center to keep the i.d. of the neck running true while turning the o.d.

That's the trick. It's easiest to do, I think, if the brass is pressed onto a turned (or trued) mandrel, then turned. This done using the tailstock to guide onto, and remove the piece from the mandrel. The direction of the carriage is left-to-right in this case. It doesn't need to be a fit which may distort the brass by being pressed, or removed removed from the mandrel, at least not when the axial turning force is decided by a very small depth of cut.

 

[strantor]

I don't want to turn this into a ammunition thing since this isn't a gun forum but, since you mentioned it, there are other reasons for altering the neck wall thickness of rifle brass than conversion from a parent cartridge.

This is a machining forum, true, but many people here are into machining as it pertains to guns and many threads here are gunsmithing threads. It's a pretty gun-friendly place and I've never seen anyone taken to task over discussing guns.

I'm personally curious about what you're doing, and the unspoken reasons. I have done some reloading but am by no means an expert. I am aware of the case trimming die but haven't heard of any other tools or processes that remove metal, especially thinning it like it seems you're doing. That doesn't mean it's wrong, just means I haven't heard of it. If you're not comfortable discussing it I respect that, but if you could at least drop a couple of buzzwords for me to Google I would like to learn.

Edit:
I found the right words to Google. Case neck turning.

 

[RJSakowski]

I would use a live center with replaceable tip. Make a custom tip with a cylindrical geometry and a light press fit. Finger pressure type. I have a case trimmer chuck that I mounted in my three jaw chuck for trimming or polishing cases. It is a half turn release so it is quick to insert and remove cases. I would insert the case in the case trimmer chuck and then insert the live center into the neck followed by tightening the chuck. This should keep the case concentric with the lathe spindle. Then proceed with turning the neck o.d. and back the live center out.

If your lathe will accommodate one, there are also collets to hold the case which would probably have better concentricity. You would have to make the mating socket and possibly use a drawbar to close.

 

[dml66]

This is a machining forum, true, but many people here are into machining as it pertains to guns and many threads here are gunsmithing threads. It's a pretty gun-friendly place and I've never seen anyone taken to task over discussing guns.

I'm personally curious about what you're doing, and the unspoken reasons. I have done some reloading but am by no means an expert. I am aware of the case trimming die but haven't heard of any other tools or processes that remove metal, especially thinning it like it seems you're doing. That doesn't mean it's wrong, just means I haven't heard of it. If you're not comfortable discussing it I respect that, but if you could at least drop a couple of buzzwords for me to Google I would like to learn.

Edit:
I found the right words to Google. Case neck turning.

When I landed on this site as a hobby machinist, I felt very welcomed, and still do. That guns aren't off-limits is music to my ears as I enjoy the shooting sports immensely, also as a hobby.

Turning the outside of rifle brass necks is well-known, there are many affordable, and easy ways to accomplish the task; PMA, 21st Century and many others, I own most of their products . Turning the inside of necks is more tricky, I think. I've turned both the outside and inside of necks on my lathe; whereas concentricity along with cylindricity was measurably improved, surface finish on the inside turn gave me pause. Further bullet seating and target results, measured, convinced me to abandon inside turning. Not because it can't be done, it's a matter of I could not do it. Exchanging axial imperfections, the result of extrusion, for radial imperfections, the result of single-point turning, is anyone's guess as to which is better, or worse, or if it even matters.

Then I wondered why, if conventional outside cutters could do such a great job with respect to finish, why couldn't that same approach be used for inside turning? So, being a gluten for punishment, I decided to give it another try with a new family of boring bars.

 

[dml66]

I would use a live center with replaceable tip. Make a custom tip with a cylindrical geometry and a light press fit. Finger pressure type. I have a case trimmer chuck that I mounted in my three jaw chuck for trimming or polishing cases. It is a half turn release so it is quick to insert and remove cases. I would insert the case in the case trimmer chuck and then insert the live center into the neck followed by tightening the chuck. This should keep the case concentric with the lathe spindle. Then proceed with turning the neck o.d. and back the live center out.

If your lathe will accommodate one, there are also collets to hold the case which would probably have better concentricity. You would have to make the mating socket and possibly use a drawbar to close.

Work holding cartridge brass in a lathe chuck has been a challenge for me. The only approach I've found that will spin a neck with close to zero runout is chucking a straight-shank collet chuck in a 4-jaw. I use a straight-shank ER20, or ER25 collet chuck, itself chucked in a 4-jaw. The trick is mastering the 4-jaw; with practice it becomes 2nd nature. Having said that, some brass hops in the ER collet ready to rock, most of them don't. For the most part, it's time-consuming overall.

This is why once I have a piece trued-up, getting it turned; inside, outside or both, is desirable.

Maybe there are better, faster ways to guide eccentric work into concentricity, I'm just using what works for me.