Need guidance...case neck thickness

[L.Sherm]

His rurnout could very well be from the 3 jaw. Did you run a tenth indicator on your mandrel in your 3 jaw. If you have a 4 jaw could probably get it indicated in alot closer

 

[Edd]

.. If he's happy with his results why crap on them?

Because he is wanting to learn how to do something new. He deserves to be told how to do it the correct way. Then if he decides to do it a different way that's fine.

 

[redleg1013]

Run out is a deviance of concentricity, in this case to the mandrel upon which the neck was turned, which is what we're addressing. So yes, you're talking about two different things.

 

[redleg1013]

I have thoroughly read and re read the information in this entire thread. I also received some PM coaching from Dusty which was very helpful. I opted to try things out on my lathe, instead of purchasing expensive dedicated equipment. I followed Dusty's advice and took the expander out of my sizing die and measured how much my neck was being worked, surprisingly it was not that much. I then turned down a mandrel the exact size of my expander, which took a couple of tries. I ground a tool with the proper angle to allow me to just kiss the shoulder and I set my depth of cut to try and leave about 20% untouched. I still have not purchased a tubing micrometer to be able to measure neck thickness and concentricity, but by taking such a light cut and leaving a portion of the neck untouched I am comfortable with the process. Measuring with a .001 dial indicator I have less that .001 run out on my necks after turning indicating less than .001 variance in thickness. It has been fun, and I'm able to crank them out surprisingly quickly. Still havent had an opportunity to shoot and see what difference it all makes, but hopefully this week work and weather will cooperate. Been waiting on a new beam scale to arrive too. But just wanted to thank everybody who offered up so much useful advice.View attachment 126210

You may have thought of this and if so please forgive my presumption.

Since you know the size of the mandrel (hopefully you used a micrometer and not a dial caliper) you can touch the tool off of a feeler gage of whatever thickness you want to turn your necks to, if you want absolutely uniform, no deviance results.
As long as you do not remove your mandrel from the three jaw, it will be true to the jaw. If you take it out then you'll need a four jaw to indicate the mandrel back in.

I applaud your desire and willingness working out a solution instead of just buying something online.

If you are happy with getting less than a thou of deviance after a skim cut, good on ya.

 

[birdiemc]

That's a problem turning them on a lathe. I don't consider .001" thickness variation, after turning, acceptable. I rarely see more variation than that before turning.

If I turned the necks on my brass and ended up with .001" variation, I would consider it wasted time and effort.

I said I have less than .001 run out because there would be somebody to chime in and say how do you know how much run out you have unless you are using .0000000000000001 dial indicator. The needle is not moving, which would seem to me about .0001- .0002 at most. but I seem to remember something about significant digits or figures or something like that from science class, basically if I have a .001 precision instrument I can only report a measurement in .001 of an inch reliably. Right?

 

[birdiemc]

His rurnout could very well be from the 3 jaw. Did you run a tenth indicator on your mandrel in your 3 jaw. If you have a 4 jaw could probably get it indicated in alot closer

The mandrel was turned in the 3jaw and left in it. I broke the mount for my tenth indicator so just checked it with the .001, no movement at all, which is the case when turning and not removing from the chuck. Once I remove it from the chuck I will have to switch to my 4jaw then indicate with my tenth indicator.

 

[Edd]

I said I have less than .001 run out because there would be somebody to chime in and say how do you know how much run out you have unless you are using .0000000000000001 dial indicator. The needle is not moving, which would seem to me about .0001- .0002 at most. but I seem to remember something about significant digits or figures or something like that from science class, basically if I have a .001 precision instrument I can only report a measurement in .001 of an inch reliably. Right?

Depends on your instrument and your method. Most of my measuring tools read in .001" increments but the distance between the marks is wide enough I can report reliable measurements to within .0005". I would expect yours to be the same. If you set your indicator on the case neck, leave the lathe off, and spin the case on the mandrel by hand, I would expect you can make a guess to within .00025".

 

[birdiemc]

You may have thought of this and if so please forgive my presumption.

Since you know the size of the mandrel (hopefully you used a micrometer and not a dial caliper) you can touch the tool off of a feeler gage of whatever thickness you want to turn your necks to, if you want absolutely uniform, no deviance results.
As long as you do not remove your mandrel from the three jaw, it will be true to the jaw. If you take it out then you'll need a four jaw to indicate the mandrel back in.

I applaud your desire and willingness working out a solution instead of just buying something online.

If you are happy with getting less than a thou of deviance after a skim cut, good on ya.

I didnt think of that. Good idea.
I just set my cross slide and left it alone so they were all the same. I have a slight step down at the shoulder the case mouth contacts so the cutting tool doesn't make contact. But that's a great idea for setting up for next time.
And shamefully no I didnt use a micrometer. I didnt even use a caliper, I just set my depth of cut then checked with case neck fit after I was done.

 

[birdiemc]

Depends on your instrument and your method. Most of my measuring tools read in .001" increments but the distance between the marks is wide enough I can report reliable measurements to within .0005". I would expect yours to be the same. If you set your indicator on the case neck, leave the lathe off, and spin the case on the mandrel by hand, I would expect you can make a guess to within .00025".

Yes I agree completely but like I said, I figured somebody would come along and say you cant possibly without a .0001 indicator.

 

[redleg1013]

I didnt think of that. Good idea.
I just set my cross slide and left it alone so they were all the same. I have a slight step down at the shoulder the case mouth contacts so the cutting tool doesn't make contact. But that's a great idea for setting up for next time.
And shamefully no I didnt use a micrometer. I didnt even use a caliper, I just set my depth of cut then checked with case neck fit after I was done.

All part of being a machinist. Enjoy your setup.

 

[Edd]

Yes I agree completely but like I said, I figured somebody would come along and say you cant possibly without a .0001 indicator.

Somebody might, but so what, you know better.

 

[dok7mm]

This thread has been well covered, with a lot of good info and little bits not so good, so I'll chime in.
First of all, BR shooters are not the only ones, who can benefit from neck turning ( trimming is an OAL thing). With so many reloaders going to bushing dies, we find that consistent neck thickness = consistent tension, when using type S dies. More and more LRH are learning to pick their brass first, measure the turn that brass needs for 100% cleanup, then fit it to their reamer neck dimensions. They then order FL dies that do not oversize their brass. Neck clearance can be .002 - .004, or more, as they wish or whichever their rifle shoots the best. I like to start at 3 thou, then try .004.
It's advantageous to monitor neck thickness as they get fired, because if you have dies and a chamber that don't match up, you may find that shoulder creeping into the neck. Many, new to turning, are afraid to turn into the shoulder enough to prevent, or delay, donuts. Not a problem, unless you're putting bearing surface past neck/shoulder junction. "Knock on wood", I've turned 4,000 + cases, cut well into shoulder, and never left a neck in the chamber. I can't tell anyone how much to cut into shoulder,as there is no good way to measure it.
I do not chamfer or debur prior to turning, unless it's done at the factory.
I feel a chamfer thins the neck slightly, causing a slight bell, on case mouth edge, and catches on leading front of cutter, causing a jerky action that can deform the neck edge. As for debur of factory trim, the cutter takes it off. I just expand, lube and turn, then chamfer and debur.
As for turning brass for factory rifles, that already have 6-8 thousands of clearance, DON'T. It's far better to size neck down and then expand with a mandrel die to 2-4 thou under bullet diameter, for your desired tension. And, remember tension is more about how much of the neck is sized, than what size bushing or mandrel is used.
Last thought......wide cutters do not make for a smoother cut, proper feed rate makes a smooth cut. Wider cutters actually increase friction somewhat and therefore, the temperature of the case neck and pilot. Also, rig up a spacer for your ball micrometer, so that you are always measuring at same point, from case to case.