Neck turning angles

[Hengehold]

I am turning the necks on a wildcat that is having the neck lengthened from the parent case (6.5 SLR). The wildcat will end up with a 30 degree shoulder. Should I be turning necks with a cutting bit with a 30 degree angle on it or do I need a 40 degree angle on the cutter so I won’t be making so much contact with the shoulder when I bump into it slightly and remove future doughnut material ?

-TH

 

[Toby Bradshaw]

Use a cutter angle that matches your case neck angle, so the cut looks like this:

 

[Brians356]

Use a cutter angle that matches your case neck angle, so the cut looks like this:

The cutter angle is apparently slightly greater than the shoulder, but that's the desired effect. If it truly matched the shoulder angle, wouldn't it have swiped the entire shoulder?
-

 

[Ledd Slinger]

Agreed. Use same angle cutter as is specifed in the case design. I have 30 degree and a 40 degree cutters for my 21st Century neck turner.

That reminds me...I need to get a 35 degree cutter too

 

[Ledd Slinger]

The cutter angle is apparently slightly greater than the shoulder, but that's the desired effect. If it truly matched the shoulder angle, wouldn't it have swiped the entire shoulder?
-

No. The shoulder angle face on the cutter blade is very short. The amount of shoulder you see turned on the case in the picture is the same length as the shoulder cutting face. It's machined to take off at a more radical angle after that so you don't hit the entire shoulder.

 

[LA50SHOOTER]

Gent’s
Not to be the source of controversy but I don’t agree with a couple of the post here-in. Unless one cuts just slightly past the neck / shoulder junction to eliminate or at least reduce the “growing” of the dreaded dough nut.
To do that on a 30 degree shoulder angle case one would need to use a 40 degree cutter. This was explained to me by the likes of Mr. Gordy Gritters back 10 years ago when I first started neck turning brass for tight neck chambers.

I’d like to hear what some of the short and long range bench rest and F class competitors have to say.

Before K&M developed the inside neck reaming mandrel for their neck turners the dreaded doughnut has been a controversial topic and how to deal with it.

I always just ever so slightly cut just a very minute amount into the shoulder right at the neck shoulder junction. I don’t have dreaded doughnut troubles. And case integrity is not sacrificed.

Regards

 

[Brians356]

No. The shoulder angle face on the cutter blade is very short. The amount of shoulder you see turned on the case in the picture is the same length as the shoulder cutting face. It's machined to take off at a more radical angle after that so you don't hit the entire shoulder.

Ah, a light dawns. Of course it can only swipe the width of the cutter edge. But which neck turner are you chaps using? I'm using the Hornady L&L lathe-style, and as I recall (not at home now) the cutter edge is longer than Boyd's, but I could well be wrong.

But, supposing that short cutter edge's angle perfectly matched the case shoulder angle, there's the danger you could cut a step 1/3 of the way up the shoulder if you advanced the cutter a few thou too far. If the cutter angle is slightly greater, you are more likely to just introduce a slight change of angle in transition from shoulder to neck junction. I.e. a slight angle mismatch is actually a plus, IMO. Does that makes sense? (I could draw a diagram, but I'm too lazy to break out the Visio.)
-

 

[Brians356]

Gent’s
Not to be the source of controversy but I don’t agree with a couple of the post here-in. Unless one cuts just slightly past the neck / shoulder junction to eliminate or at least reduce the “growing” of the dreaded dough nut.
To do that on a 30 degree shoulder angle case one would need to use a 40 degree cutter. This was explained to me by the likes of Mr. Gordy Gritters back 10 years ago when I first started neck turning brass for tight neck chambers.

We posted nearly concurrently. See my recent response. In essence I'm agreeing with you, but I don't think a 40-deg would be required for a 30-deg shoulder, something like 35-deg would suffice.
-

 

[gunsandgunsmithing]

I think that as long as you cut a few thou into the neck/shoulder junction, you should be fine regardless of cutter angle. I've turned a bunch of necks on a lathe and went far enough to remove a few thou from the juncture, with never an issue. I only set the cutter by eye to be close to the parent shoulder angle. Never an issue.Where that, or any neck turning that goes into the juncture can cause a problem is if you go too deep or if it's an Ackley, which headspaces on that juncture when fire forming from virgin cases. It rapidly affects the headspace. You just have to play with it but it can be a tedious operation, getting it just right for cases like the 6BRAI, for example and worse still on cases that headspace there and the case has been necked up. The brass in the shoulder area is thicker, so if you don't remove enough, you will have a doughnut. With it headspacing where it must be cut..it's tricky but doable.

Thankfully, most AI chamberings have available parent brass of the correct caliber but something like a 30x47AI, for example, would have two things going on at the same time that need to be properly cut for.

Throat and seat bullets accordingly, so that the heel or pressure ring are above the doughnut area and don't worry about any slight doughnut that may develop.

Another approach is to use a bushing die and enough neck clearance that any doughnut forms and stays on the outside of the case. It won't hurt anything there and will only help align the case in the chamber. The only down side is working the brass more due to the extra neck clearance.

 

[LA50SHOOTER]

We posted nearly concurrently. See my recent response. In essence I'm agreeing with you, but I don't think a 40-deg would be required for a 30-deg shoulder, something like 35-deg would suffice.
-

Agree, - More than the shoulder angle of the brass being neck-turned. - I pretty much use a 40 degree on everything because unless one is turning brass that already has a 40 degree shoulder (like 280 A.I.) then a 40 will do the job. - As it was explained to me 10 years ago, the idea is to just ever to gently go past the neck / shoulder junction. And I've noticed as well after fire-forming this ever-so-slight cut diminishes and continues to diminish as the brass is fired.

 

[Ledd Slinger]

Ah, a light dawns. Of course it can only swipe the width of the cutter edge. But which neck turner are you chaps using? I'm using the Hornady L&L lathe-style, and as I recall (not at home now) the cutter edge is longer than Boyd's, but I could well be wrong.

But, supposing that short cutter edge's angle perfectly matched the case shoulder angle, there's the danger you could cut a step 1/3 of the way up the shoulder if you advanced the cutter a few thou too far. If the cutter angle is slightly greater, you are more likely to just introduce a slight change of angle in transition from shoulder to neck junction. I.e. a slight angle mismatch is actually a plus, IMO. Does that makes sense? (I could draw a diagram, but I'm too lazy to break out the Visio.)
-

Your description of using a steeper angle to avoid creating a step makes perfect sense. I might have to test this on a couple trash cases. Over turn one case onto the shoulder with appropiate angle cutter to see if it makes a significant step. Then try the same with a steeper cutter angle to see if it creates a smooth transition of angles.

I use the 21st Century neck turner. Not sure if John actually makes the angles steeper and lists them for the appropriate case shoulder angle to avoid confusion... ie: 30 degrees is actually 33 or 35 degrees. I personally have no way to measure the true angle of such a small surface.

Anyhow, I've never had donut issues using the 21st Century so I'm not overly concerned with this. Very interesting comments tho.

 

[mikecr]

I am turning the necks on a wildcat that is having the neck lengthened from the parent case (6.5 SLR). The wildcat will end up with a 30 degree shoulder. Should I be turning necks with a cutting bit with a 30 degree angle on it or do I need a 40 degree angle on the cutter so I won’t be making so much contact with the shoulder when I bump into it slightly and remove future doughnut material ?-TH

Are you turning with the case at 260rem, or while fully formed at 6.5SLR?
In other words, what will the turn beginning shoulder angle actually be?

 

[Steffen Bunde]

Use a 30 degree cutter on a 30 degree shoulder.

 

[gunsandgunsmithing]

Use a 30 degree cutter on a 30 degree shoulder.

Not picking on you, but what happens if I use a 40° or a 90°.. or anything other than a 30°?

I just think we should understand why we do what we do rather than just accept any answer as matter of fact.

 

[Willie]

Forming brass for a 40* shouldered wildcat, I decided to try a 21st Century 40 * turner. Waited to turn until I had fireformed. Because the shoulder was not fully formed, results were poor. The 40* cutter was hit & miss at touching shoulder evenly.

I went back to my K&M tool and cut my normal amount into the shoulder. After 8 firings, no donuts, no problem. JMO, but I don't see the need for matching cutter angle to shoulder angle, to prevent donuts.

 

[Brians356]

Forming brass for a 40* shouldered wildcat, I decided to try a 21st Century 40 * turner. Waited to turn until I had fireformed. Because the shoulder was not fully formed, results were poor. The 40* cutter was hit & miss at touching shoulder evenly.

That makes sense to me. If you had purposely advanced even farther than just touching, it would probably cut a step up at the toe of the cutter, well up the neck. It's simple geometry.

But, the assumption is that both cutter and shoulder are both truly, say, 40 degrees. The cutter likely is very close. The case shoulder, I wonder, especially on an unfired case. For both fireformed and resized cases, we assume the chamber and die shoulders are precisely 40 degrees. All I'm saying is neck turning ain't precision machining, especially WRT cutting past the junction and matching up angles.
-

 

[mikecr]

It shouldn't matter that 30deg shoulders may rest a bit higher or lower, provided head spacing is correct.
Cutter angle should be greater than, or at worst, equal to local angle. If cutter angle was too low it would dig into shoulder separate from the neck turn.

I don't think it's common for cutters to exactly match local shoulder angles, as this would take some efforts to reach.
A die designed to produce an exact shoulder angle(for some reason), would not actually be at that exact angle, but at an angle accounting for spring back.

 

[gunsandgunsmithing]

It shouldn't matter that 30deg shoulders may rest a bit higher or lower, provided head spacing is correct.
Cutter angle should be greater than, or at worst, equal to local angle. If cutter angle was too low it would dig into shoulder separate from the neck turn.

I don't think it's common for cutters to exactly match local shoulder angles, as this would take some efforts to reach.
A die designed to produce an exact shoulder angle(for some reason), would not actually be at that exact angle, but at an angle accounting for spring back.

I agree Mike.
When I turn them in a lathe, I simply get the cutter "eyeball close" to the shoulder angle without much attention to being precise. Whatever you cut into the shoulder will be blown out in a firing or two, and be pretty much non existent from then on. Go too thin, and you can lose the neck. I've seen it several times but have never lost one myself, so what I'm doing must be working.

I think the single most important aspect of neck turning is consistency. I routinely have +/- .0001 without much effort. I see others brass run all over the place and can only assume something is wrong with their setup, too much heat or too heavy a cut. I don't know as I have no trouble keeping them very consistent.

 

[Hengehold]

Are you turning with the case at 260rem, or while fully formed at 6.5SLR?
In other words, what will the turn beginning shoulder angle actually be?

Good question. I haven’t really decided yet which would be the best approach but I think I would like to cut prior to fireforming.

At this point I am under the impression that if I turn necks before fireforming then I can cut into the shoulder a little and remove the thick shoulder material before it becomes a doughnut. This would be a pre-emptive approach to doughnut management. Cutting after fireform would guarantee the formation of a doughnut.

- Trevor

 

[Ledd Slinger]

Good question. I haven’t really decided yet which would be the best approach but I think I would like to cut prior to fireforming.

At this point I am under the impression that if I turn necks before fireforming then I can cut into the shoulder a little and remove the thick shoulder material before it becomes a doughnut. This would be a pre-emptive approach to doughnut management. Cutting after fireform would guarantee the formation of a doughnut.

- Trevor

On a different wildact that requires fireforming, I cut down onto the shoulder before fireforming, the again afterwards to hit the shoulder properly.