21st Century Neck Turning Tool
- Thread starter SGK
- Start date
Running the necks over the expander mandrel doesn't move the interior thick parts to the outside. Before turning, once fired brass moves has all the high spots moved to the inside. So, one needs to find a way to move everything to the outside surface before using the expander mandrel and turning that the neck's interior doesn't have much variation. I find that a Lee collet die does a pretty good job of doing that.
Dusty Stevens
Shiner
does your measurement repeat at the same spots around the neck? it sounds to me like measurement error of some type
mikeeg02
Michael Glantz
How many did you do at a time? Are you using lube? How much are you taking off in a pass ?
If you're taking in excess of .001" I've found it's best to actually run the trimmer up and down the neck twice at the same setting. Makes for a more consistent finish. Also, it seems like the more you take off, the more likely it is to "gouge" and actually make low spots. If you're taking more then a skim coat off, it almost seems (for me anyways) to make a single pass a maybe two tenths short and then a final skim coat to get you where you want to be.
Also, if you go too fast or do too many at a time, heat will change your depth of the cutter. Patience is key.
If you're taking in excess of .001" I've found it's best to actually run the trimmer up and down the neck twice at the same setting. Makes for a more consistent finish. Also, it seems like the more you take off, the more likely it is to "gouge" and actually make low spots. If you're taking more then a skim coat off, it almost seems (for me anyways) to make a single pass a maybe two tenths short and then a final skim coat to get you where you want to be.
Also, if you go too fast or do too many at a time, heat will change your depth of the cutter. Patience is key.
I get much better results using a power screw driver than turning by hand. Feeding to the shoulder and then feeding back off of the case. I am using a K&M neck turning tool. Just a thought.
Paul
Paul
Thanks for the comments. The mic has a ball anvil. I'm using the lathe version with an electric drill. I try to do very slow passes and second passes. I'm not doing large volumes. I will look again at my measurement techniques - will try to spend some more time with it this afternoon. I do wonder about Straightshooter's point. I also wonder if I am getting a close enough fit on the turning mandrel.
With the 6mm Creedmoor cases I am doing at the moment I originally turned the necks to a target of 13.5 thou but now, based on the advice of my gunsmith, I think I need to turn them to 13 thou. I did make a mistake the first time I turned the necks - I put them through a sizing die (ahead of the expander mandrel) with a bushing size designed for the turned neck not the unturned thickness. This has knocked some of the necks slightly out of kilter with the shoulder but I understand the neck turning lathe should key off the neck in any case and the cost of this error is merely a slightly uneven scuff of the shoulder by the cutter. The necks should still turn evenly - and, when there are no uncut areas, the thickness should be constant no matter where measured on the cut surface. This of course assumes all irregularities were transferred to the exterior face ahead of turning; to Straightshooter's point this may be a poor assumption.
With the 6mm Creedmoor cases I am doing at the moment I originally turned the necks to a target of 13.5 thou but now, based on the advice of my gunsmith, I think I need to turn them to 13 thou. I did make a mistake the first time I turned the necks - I put them through a sizing die (ahead of the expander mandrel) with a bushing size designed for the turned neck not the unturned thickness. This has knocked some of the necks slightly out of kilter with the shoulder but I understand the neck turning lathe should key off the neck in any case and the cost of this error is merely a slightly uneven scuff of the shoulder by the cutter. The necks should still turn evenly - and, when there are no uncut areas, the thickness should be constant no matter where measured on the cut surface. This of course assumes all irregularities were transferred to the exterior face ahead of turning; to Straightshooter's point this may be a poor assumption.
Straightshooter1 is wrong in every regard..
I don't know what you have going on, but you should not size new cases to be turned with any die.
Just hit em with the expander mandrel & turn. The xpander mandrel does push thickness variances outward where they can be turned away.
One potential issue with the 21st lathe design is that it does not provide for full floating of one side. Yes it wiggles, but about a centerline, and that is not floating. The shellholder is not floated either.
So any axis misalignment will lead to angular misalignment, and the cutter/neck relationship is no longer parallel.
If you have a wiggle due to your mis-sized necks, that you described as resulting in an axis shifting at necks, then you could have the cutter digging in with the wiggles, causing thickness variances.
I don't know what you have going on, but you should not size new cases to be turned with any die.
Just hit em with the expander mandrel & turn. The xpander mandrel does push thickness variances outward where they can be turned away.
One potential issue with the 21st lathe design is that it does not provide for full floating of one side. Yes it wiggles, but about a centerline, and that is not floating. The shellholder is not floated either.
So any axis misalignment will lead to angular misalignment, and the cutter/neck relationship is no longer parallel.
If you have a wiggle due to your mis-sized necks, that you described as resulting in an axis shifting at necks, then you could have the cutter digging in with the wiggles, causing thickness variances.
Are we talking about the same thing when referring to the "expander mandrel"?
In my case, I'm thinking of a mandrel as depicted in this pic:
Attachments
Dusty Stevens
Shiner
If it isnt very hard to run your case onto the turning mandrel its not going to work well. I mean it has to have lube and be spinning to even go on there with quite a bit of force. Lots of heat buildup
Straightshooter, stop firing necks, and down sizing necks(especially with a collet), before neck turning.
Take NEW brass, run that Sinclair expander mandrel through it, and neck turn.
Best results with a motor driven case holder and handheld turning body. Given this, new cases can wiggle (they will) all over, and you don't need a tight mandrel fit, the turning will be fine.
It really takes extra efforts to screw it up.
Take NEW brass, run that Sinclair expander mandrel through it, and neck turn.
Best results with a motor driven case holder and handheld turning body. Given this, new cases can wiggle (they will) all over, and you don't need a tight mandrel fit, the turning will be fine.
It really takes extra efforts to screw it up.
Bumping for reference and questions...
@mikecr you said stop firing necks.
What would be the process for brass I have with 3 firings on it?
40 pieces total 3x fired
60 pieces new
Brass is lapua
Inside neck measurement .3085 on fired brass.
Neck wall thickness. 0165
Should I turn to .0145 or .015?
@mikecr you said stop firing necks.
What would be the process for brass I have with 3 firings on it?
40 pieces total 3x fired
60 pieces new
Brass is lapua
Inside neck measurement .3085 on fired brass.
Neck wall thickness. 0165
Should I turn to .0145 or .015?
For fired brass I would....
Clean brass
Anneal
Full length resize (no bushing)
Trim
Lube inside of neck
Run expander mandrel in
Turn neck to desired thickness
With new brass, I just lube the necks/expand/turn.
How much neck clearance do you want/need?
"Ditto"
More than I have. Lol
I'm thinking about triming .0015, with the minimal clearance I have this should get me out of the preasure zone, and make for minimal sizing of the neck.
I'd rather take a little off at a time and test than to remove to much.
Here's a shot of the gear I'm picking up.
I believe I need a cutter head with proper cutting tool, expander mandrel, turning mandrel?
A couple of things to look for. First the expanded case neck should be a snug fit on the mandrel. Lightly lube the inside of the neck. You should be able to turn it with your fingers but feel some resistance. The second, wobble on the rear of the case in the chuck. Any wobble will show up in the neck. (picture is exaggerated). The case head may not be 100% centered in the chuck. There are slight variations in case head diameters.
Regarding #2: This picture depicts that cutting unit as being fixed (without wobble of it's own). If it's hand held and the chuck is also hand held where the fit of the neck to the mandrel governs it to where the neck axis is in line with the mandrel axis. When either the cutting unit is fixed or the chuck, the axis alignment can be a problem with getting the alignment right and with any wobble you get the issue as illustrated.
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Ccrider
Gold $$ Contributor
This is key to getting consistency. If your mandrel is not opening the brass, it is not large enough. If you can slide the mandrel in and out with your hand, the neck needs to be sized down to properly use that mandrel.
Also, I have had good results retrimming after firing a time or two. Just do the exact same thing to each piece of brass and you should get consistent thickness.
Petros284
Site $$ Sponsor
Just some food for thought. We (21st Century) have some lathe upgrades that are coming out to minimize any potential binding from excessive wobble. In testing these have shown great results! We have recently been adding these to the power lathe and soon the standard lathe. We also will be offering these upgrades as a kit for those who already have lathes. These upgrades are going to be added to the driver assembly and the Neck Turning tool.
The number one issue that can happen with the lathe is set-up is having the Neck Turning took too tight on the L-Bracket.
One thing that NEEDS to be done with the lathe when you are using it is to be sure the Neck Turning tool is loose enough on the L-Bracket not to bind up. Not loose enough to rotate when turning brass though. If the tool wants to rotate, a little pressure from the left hand on the tool will help. There is a “feel” to the setup of the tool and if it binds you will feel it. Loosen the Neck Tool on the bracket until it doesn’t feel like it binds.
Feel free to email me with any concerns or questions. Pete@21stcenturyshooting.com
The number one issue that can happen with the lathe is set-up is having the Neck Turning took too tight on the L-Bracket.
One thing that NEEDS to be done with the lathe when you are using it is to be sure the Neck Turning tool is loose enough on the L-Bracket not to bind up. Not loose enough to rotate when turning brass though. If the tool wants to rotate, a little pressure from the left hand on the tool will help. There is a “feel” to the setup of the tool and if it binds you will feel it. Loosen the Neck Tool on the bracket until it doesn’t feel like it binds.
Feel free to email me with any concerns or questions. Pete@21stcenturyshooting.com
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