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Expanding & turning arbors w/ 0.001" diff?

Mooster1223

I have a 21st Century lathe. I'm getting inconsistent results. I though the issue was my stainless expander / turning arbor so I purchased his Titanium nitrite set hoping for tighter tolerances. There is 0.002" diff between the expander and the turning arbor. I can easily put the case on the cutter. To me, it seems like there is too much play which does not lead to consistency. Are there any sets with 0.001" difference? Am I barking up the wrong tree?
 
I use a 21st Century lathe in .223 caliber. I have trouble measuring accurately below .001" with the equipment I have, but I'd say my expanding and turning mandrels differ by about .0006" or .0007" more or less; certainly not .002".
 
Mooster1223 said:
I have a 21st Century lathe. I'm getting inconsistent results. I though the issue was my stainless expander / turning arbor so I purchased his Titanium nitrite set hoping for tighter tolerances. There is 0.002" diff between the expander and the turning arbor. I can easily put the case on the cutter. To me, it seems like there is too much play which does not lead to consistency. Are there any sets with 0.001" difference? Am I barking up the wrong tree?
Click to expand...
Put a drop of oil on it . Or try some o or oo grease in it . Larry
 
The expanding mandrel should be about 0.0005" greater in diameter than the turning mandrel; there should be no slop when the case is slipped over the turning mandrel. You should be able to hold tolerances at 0.0005" or less, typically less.
 
Last edited:
rardoin said:
The expanding mandrel should be about 0.0005" smaller in diameter than the turning mandrel; there should be no slop when the case is slipped over the turning mandrel. You should be able to hold tolerances at 0.0005" or less, typically less.
Click to expand...
I have no idea why anyone would worry about
Haveing necks turned to 0.0005 to start with.
Not many people can even meisure that close.
Larry
 
savagedasher said:
I have no idea why anyone would worry about
Haveing necks turned to 0.0005 to start with.
Not many people can even meisure that close.
Larry
Click to expand...
I turn necks to get consistency in 'neck tension'. The more consistent the neck wall thickness within an individual case and between cases, the more likely my loaded rounds will be consistent with each other. I strive for the best tolerances, within reason, on everything I do (shooting related or not). My tooling/techniques gives me tolerances well under 0.0005" when turning necks without doing any unusual steps or taking more of my time than anyone else does; just the proper tools and application of such. I posted this to let the OP know what he should be able to expect from proper technique and tooling. I will not debate the level of precision needed to get an improvement on target or whether or not neck turning needs to be done at all with a normal chamber neck. IMO, if I am to turn necks, I should have a ball mic that can measure to the ten thousandth to check uniformity, not necessarily shoot for tolerances that small.
 
Sinclair says their expander mandrel is supposed to be .001” fatter than the turning mandrel. The expander mandrel is supposed to be ~ .001” less than a bullet’s diameter while their turning mandrel is supposed to be ~ .002” less than the bullet’s diameter.
 
Pro tip - if you don't need to neck up/down, just skip the expander and turn straight out of the box.
 
rardoin said:
I turn necks to get consistency in 'neck tension'. The more consistent the neck wall thickness within an individual case and between cases, the more likely my loaded rounds will be consistent with each other. I strive for the best tolerances, within reason, on everything I do (shooting related or not). My tooling/techniques gives me tolerances well under 0.0005" when turning necks without doing any unusual steps or taking more of my time than anyone else does; just the proper tools and application of such. I posted this to let the OP know what he should be able to expect from proper technique and tooling. I will not debate the level of precision needed to get an improvement on target or whether or not neck turning needs to be done at all with a normal chamber neck. IMO, if I am to turn necks, I should have a ball mic that can measure to the ten thousandth to check uniformity, not necessarily shoot for tolerances that small.
Click to expand...
dkhunt14 said:
Boy I must be fussy then because I turn to .0001 to .0002. When you start turning the first will get tighter. It takes more then one pass to get them close. Matt
Click to expand...
Matt that is closer then tolerance then used on wrist pins in a race motor . Larry
 
No one has mentioned this... but its a fact because i talked to john and did it myself...

You have to buy johns/21st century expander die and his mandrels for it too... his expander die and mandrels match up to the manderals on the 21st century lathe...


If you using a sinclair expander or such, the manderals wont match up for use with the lathe..
 
I wish that there were 1/2 thou size mandrels available (.0005") and that actual measured mandrel diameter - was advertised on the C21 web site.

I have resorted to making my own custom expanding and turning mandrel sizes, to fit my C21 tooling and brass needs - which is a pain. I love all the C21 tooling, just not a great selection on mandrel sizes available.

I also have mandrels that are ID stamped with the same number, but the diameters measure differently...?

Frustrating, because i want my mandrels to fit my desired brass dimensions, not being forced to make my brass fit the available mandrel dimensions.
 
SG,
My understanding is outfits such as Pacific Tool&Gauge (and others) will make mandrels to any size you request.

Alex
 
I found with my 21st century turner you have to match the expander and mandrel ...you can not use one stainless steel and one titanium nitrite. they both have to be the same..at least with mine I tried a titanium nitrite expander and a stainless turner to save a buck and they do not fit well...you have to use both the same..
can anyone confirm this?
 
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