Turning case necks?

[ntsqd]

A couple comments in the mandrel thread got me pondering this question. I'll preface it with saying that turning necks is not yet something that I have done.

So, the hypothetical situation is a SAMMI spec chamber with COTS brass of whatever mfg might be preferred by the user, and because it's more likely than not, let's say that we don't know what the neck ID dimension in the chamber actually is - only what it should be. Lets go with setting the neck ID with a mandrel was the last step in brass prep. In theory that should push any variation in neck thickness to the OD of the neck.

The case neck turning options that I can see are:
Turn to specific clearance in the chamber (using the chamber reamer drawing for the chamber's neck ID, I realize this far less than ideal)
Turn to a specific case neck OD
Turn to a specific case neck thickness

What would you do if whichever you chose resulted in not all of the case neck being cut by the cutter?

 

[ShtrRdy]

I would buy good brass and not bother with turning necks.

 

[ntsqd]

OK, but let's say that turning of the necks is indicated or desired for whatever reason that is beyond the scope of my question. What would you do if your choice resulted in necks that are not fully machined?

 

[Bitteroot]

I would buy good brass and not bother with turning necks.

Ditto

 

[Bitteroot]

OK, but let's say that turning of the necks is indicated or desired for whatever reason that is beyond the scope of my question. What would you do if your choice resulted in necks that are not fully machined?

Can you clarify what you mean by not fully machined ?

 

[Turpentine21]

OK, but let's say that turning of the necks is indicated or desired for whatever reason that is beyond the scope of my question. What would you do if your choice resulted in necks that are not fully machined?

I've not had a problem with not being able to turn from case mouth to shoulder or even beyond..

For chamber dimension I will measure the outside neck diameter of my fired cases. Particularly the hotter loads. That gets me close enough for what I'm doing. You may choose .003 for neck expansion when using this method to account for some spring back. Or over anneal a few cases and fire them. You will get very little spring back. Just my redneck method but it works for me.

When sizing Lapua 30/06 brass down to 6.5 you're going to get neck thickening and work hardening. I'll anneal, size, mandrel and then turn to my desired thickness. Target neck expansion is .004.

 

[Varmint Hunter]

OK, but let's say that turning of the necks is indicated or desired for whatever reason that is beyond the scope of my question. What would you do if your choice resulted in necks that are not fully machined?

That is fairly common, if not actually desirable, for a SAMMI chamber. The goal isn't to thin the necks, it's just to get a uniform neck thickness. When I was turning necks, I only cut deep enough to take off the high spots. That usually resulted in about 50-60% of the neck getting turned.

Now that high-quality brass is readily available for most cartridges, I just buy good brass and leave it at that.

 

[ntsqd]

Can you clarify what you mean by not fully machined ?

Say that you determine that the case necks should be .015" thick and then when you turn them you find that some areas of the necks are thinner than that, so those areas do not get machined.
Or you use Turpine's "redneck method" of determining that the case necks should be some specific OD, but when you turn them to that OD you have areas on the necks that didn't get cut at all.

Maybe going with high end brass removes this situation from consideration, but for the sake of discussion lets assume that such brass is either not available or not in the budget and Frontier or Winchester or Remington or whatever brass is what we have to work with.

Getting uniform neck thicknesses and then thinking about what happens when your goal isn't fully supported by the brass that you have to work with is what lead me to start this thread. Where do you compromise and why?

 

[Turpentine21]

Say that you determine that the case necks should be .015" thick and then when you turn them you find that some areas of the necks are thinner than that, so those areas do not get machined.
Or you use Turpine's "redneck method" of determining that the case necks should be some specific OD, but when you turn them to that OD you have areas on the necks that didn't get cut at all.

Maybe going with high end brass removes this situation from consideration, but for the sake of discussion lets assume that such brass is either not available or not in the budget and Frontier or Winchester or Remington or whatever brass is what we have to work with.

Getting uniform neck thicknesses and then thinking about what happens when your goal isn't fully supported by the brass that you have to work with is what lead me to start this thread. Where do you compromise and why?

There are going to be some imperfections on the inside and the outside. Turning deeper, say .013 instead of .014 will make the outside more uniform. Even after a case is fired, there will still be small undulations regarding wall thickness. Perhaps not much but they will be there. Especially when measuring to the .0001. My goal isn't to get them absolutely perfect. If that even exists. It's just to get them to my number and closer to perfect than they were. It can be a rabbit hole if you let it. But I'm comfortable in the fact that I can't shoot the difference.

 

[ntsqd]

I wouldn't expect .0001 capability from a neck turning tool. They should be capable of .001, but not .0001 Even with @bamban's method and tooling it is going to heavily rely on his skill to hold .0001" To hold that kind of tolerance I'd set up some way to hold the cases in a Spindex on a surface grinder. I wouldn't go there, either. That's orders of magnitude too far down the rabbit hole......

Small divots in the case neck kinds of imperfections would have me debating whether to scrap that case or not. Assuming an abundance of cases I would scrap it. Inconsistency in the turned surface would have me looking at why the tool isn't cutting correctly. Parallel high and low concentric rings in the neck would have me looking at my turning technique and adjusting it to get rid of those.

But areas on the neck that don't get cut at all, leaving a case neck looking something like the bore of a not 100% lapped set of scope rings where the turning tool made contact and cut some of the surface, but not all of the surface, would leave me in the quandary that I'm attempting to discuss with this thread. Do you go another .001 deeper and hope it cleans up (& knowing that you'll have to cut all of them that way)? What if it doesn't? Scrap that case? Or does this just not happen even with lower cost brass?

 

[Mikecr]

Say that you determine that the case necks should be .015" thick and then when you turn them you find that some areas of the necks are thinner than that, so those areas do not get machined.

That's not a problem.
Why do you think it would be (maybe I'm misunderstanding)?

 

[bamban]

I wouldn't expect .0001 capability from a neck turning tool. They should be capable of .001, but not .0001 Even with @bamban's method and tooling it is going to heavily rely on his skill to hold .0001" To hold that kind of tolerance I'd set up some way to hold the cases in a Spindex on a surface grinder. I wouldn't go there, either. That's orders of magnitude too far down the rabbit hole......

Small divots in the case neck kinds of imperfections would have me debating whether to scrap that case or not. Assuming an abundance of cases I would scrap it. Inconsistency in the turned surface would have me looking at why the tool isn't cutting correctly. Parallel high and low concentric rings in the neck would have me looking at my turning technique and adjusting it to get rid of those.

But areas on the neck that don't get cut at all, leaving a case neck looking something like the bore of a not 100% lapped set of scope rings where the turning tool made contact and cut some of the surface, but not all of the surface, would leave me in the quandary that I'm attempting to discuss with this thread. Do you go another .001 deeper and hope it cleans up (& knowing that you'll have to cut all of them that way)? What if it doesn't? Scrap that case? Or does this just not happen even with lower cost brass?

0.0001 tolerance does NOT happen as matter of standard in any DIY environment. Not to mention being useless in our application.

My take.

 

[ntsqd]

That's not a problem.
Why do you think it would be (maybe I'm misunderstanding)?

Where it cut will be .015" thick, where it did not cut will be something less than that thick. If you're going to accept that why bother turning to get a uniform neck thickness in the first place?

0.0001 tolerance does NOT happen as matter of standard in any DIY environment. Not to mention being useless in our application.

My take.

Exactly what I was thinking. While I might have the means to get there I see no reason to try. I suspect that the ".0001" was a typo.

 

[Turpentine21]

I wouldn't expect .0001 capability from a neck turning tool. They should be capable of .001, but not .0001 Even with @bamban's method and tooling it is going to heavily rely on his skill to hold .0001" To hold that kind of tolerance I'd set up some way to hold the cases in a Spindex on a surface grinder. I wouldn't go there, either. That's orders of magnitude too far down the rabbit hole......

Small divots in the case neck kinds of imperfections would have me debating whether to scrap that case or not. Assuming an abundance of cases I would scrap it. Inconsistency in the turned surface would have me looking at why the tool isn't cutting correctly. Parallel high and low concentric rings in the neck would have me looking at my turning technique and adjusting it to get rid of those.

But areas on the neck that don't get cut at all, leaving a case neck looking something like the bore of a not 100% lapped set of scope rings where the turning tool made contact and cut some of the surface, but not all of the surface, would leave me in the quandary that I'm attempting to discuss with this thread. Do you go another .001 deeper and hope it cleans up (& knowing that you'll have to cut all of them that way)? What if it doesn't? Scrap that case? Or does this just not happen even with lower cost brass?

Sorry. I just meant 10000ths. Range. You can get to say if I'm shooting for .014. I'll expect .0135 - .0145 or so spread. But .0001. No. Ain't happening
Sorry for the mixup