Expanding & turning arbors w/ 0.001" diff?

[mikecr]

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?

Perfect is Sinclair's at 1thou diff, and this is contingent on NEW brass (not fired).
Someone said the expander mandrel should be .0005 less than the turning mandrel. That's dead wrong, probably misspoken..
Are you measuring the mandrels themselves?

 

[Mooster1223]

Yes, I'm measuring the mandrels. In fact I measured them with a mic today and still have a 0.002" difference.

 

[rardoin]

Perfect is Sinclair's at 1thou diff, and this is contingent on NEW brass (not fired).
Someone said the expander mandrel should be .0005 less than the turning mandrel. That's dead wrong, probably misspoken..

That would be me....yes...meant to imply 'greater' than the turning mandrel. I want a near interference fit when running the case mouth over the turning mandrel. Thanks for catching that Mike.

 

[230grRN]

Just throwing this out there for anyone that may have interest. I have a local shop that will grind up mandrels in carbide in any diameter you want up to .375" for $40 ea. to fit the sinclair turning tools.

 

[avidflyer]

Pro tip - if you don't need to neck up/down, just skip the expander and turn straight out of the box.

I can't fit new 6br brass over a NT mandrel how do you turn with out?

 

[dkhunt14]

I can't fit new 6br brass over a NT mandrel how do you turn with out?

I just did a 100 and the fit was that tight it stopped my gear motor. I had to expand them. Matt

 

[dcali]

Huh. I've never had a problem. Just use some oil and they fit. Tightly, but they fit.

 

[jlow]

Huh. I've never had a problem. Just use some oil and they fit. Tightly, but they fit.

Having the brass fit tight over your turning mandrel is not as good idea as it seems. Yes, the tighter the fit, they are then not slopping and the cut seems like they would be more precise. The bad thing though is too tight a fit means they will generate more heat when you spin the brass, and warm brass expands and that in turn means you will have an inaccurate deeper cut than cooler brass.

 

[savagedasher]

Doesn't the distances between the cutting blade and the mandral determine the thickness . Larry

 

[dkhunt14]

Doesn't the distances between the cutting blade and the mandral determine the thickness . Larry

Larry when the turner and brass heats up the dimensions change. Also a good way to Gaul or score the inside. Matt

 

[savagedasher]

Larry when the turner and brass heats up the dimensions change. Also a good way to Gaul or score the inside. Matt

Lube seems to still work . Mobile 1 . Larry

 

[dcali]

It does heat up a little more, but you have to take the difference between the tool expansion and the brass expansion, and given the smallish increase in temperature, in practice I've not found the heat to be an issue. They all come out the same. Maybe I'm just lucky, but with a little lanolin and some care and they come out just fine without expanding. I probably wouldn't do it that way for large volume turning, but I've gotten good results doing a box at a time.

 

[savagedasher]

It does heat up a little more, but you have to take the difference between the tool expansion and the brass expansion, and given the smallish increase in temperature, in practice I've not found the heat to be an issue. They all come out the same. Maybe I'm just lucky, but with a little lanolin and some care and they come out just fine without expanding. I probably wouldn't do it that way for large volume turning, but I've gotten good results doing a box at a time.

I went so far as to use a lathe . Put and dialed in a pilot Used the tail stock to hold the case . They came out as good as I can meisure . The other I cut with a neck tuner . The Es were the same and no difference in groups. I think necks that are 0.001 is great .. Larry

 

[boltfluter]

I went so far as to use a lathe . Put and dialed in a pilot Used the tail stock to hold the case . They came out as good as I can meisure . The other I cut with a neck tuner . The Es were the same and no difference in groups. I think necks that are 0.001 is great .. Larry

My method is to turn a mandrel with my lathe and not remove it until done with cases. Mandrel has zero runout. Make mandrel for a light press fit for brass. Friction drives the case. I move cutter by hand to neck shoulder junction and then power feed/cut towards chuck. Never move the cross feed during the entire process. Makes neck turning fun. Well almost fun. Lol.

Paul

www.boltfluting.com

 

[savagedasher]

My method is to turn a mandrel with my lathe and not remove it until done with cases. Mandrel has zero runout. Make mandrel for a light press fit for brass. Friction drives the case. I move cutter by hand to neck shoulder junction and then power feed/cut towards chuck. Never move the cross feed during the entire process. Makes neck turning fun. Well almost fun. Lol.

Paul

www.boltfluting.com

Never is fun but sure makes the neck the same . Larry

 

[Arkrunner]

Dura lube from Walmart works as well or better than Mobil 1. Really slick an no heat build up

 

[Joe R]

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?

Mooster1223,
Your problem is exactly what many of us have gone through. Many guys promise solutions but the reality is that most of the stuff they sell to us doesn't really do the job they claim to do. The tool you mentioned like many others. Just this week I had to pay my gunsmith to shave .040 off the bottom of two Redding dies that couldn't push back the shoulder of the brass because they bottomed out in both of my presses. Sorry, I digress.

The solution to your problem is a mandrel that will expand the necks to the exact amount to complement the mandrel of your turning tool. Here's where you can find the solution to your problem and more http://forum.accurateshooter.com/threads/the-ultimate-solution-to-neck-tension.3909740/

Regards,

Joe