Neck turning mandrel to neck fit

[Keith Glasscock]

I'm looking for the experience of the guys that do a lot of precision neck turning.

How tightly do you like to have your mandrel to neck fit and why?

I'm expanding cases for my 284, and, not counting the donut, the mandrel fit seems a touch loose to me. I've had to return all of my cases after fireforming and sizing, so the last bunch I did was a tight fit - tight enough I could get it on and off without excessive force, but it was touching the mandrel all the way around. From what I can measure with a tubing micrometer, I held .0003 on all of them. Most of that was from not maintaining consistent tool temperature.

I'm planning on annealing (expanding force was all over the place) and then sizing them to get the fit I want. Does this seem like a good plan?

Thanks,
Keith

 

['Freak]

With Sinclair’s you first run it over their expander mandrel first which is .001” less than bullet diameter and then turn on their turning mandrel which is .002” less than bullet diameter.

 

[asauer]

If you have donuts, that will limit you in how tight you can get, in my opinion. Don't want the fit so tight you have to force the brass onto the mandrel at that point- I've been there before...
The thing to keep in mind with annealing is you're removing the work hardening, so you will lose some springback in the necks. I'm no expert though. I'd say mine hover right around .001" over size (21st century mandrel and turner).

 

[artbosco]

I'm looking for the experience of the guys that do a lot of precision neck turning.

How tightly do you like to have your mandrel to neck fit and why?

I'm expanding cases for my 284, and, not counting the donut, the mandrel fit seems a touch loose to me. I've had to return all of my cases after fireforming and sizing, so the last bunch I did was a tight fit - tight enough I could get it on and off without excessive force, but it was touching the mandrel all the way around. From what I can measure with a tubing micrometer, I held .0003 on all of them. Most of that was from not maintaining consistent tool temperature.

I'm planning on annealing (expanding force was all over the place) and then sizing them to get the fit I want. Does this seem like a good plan?

Thanks,
Keith

Keith,

Purchase your Expander Mandrel and Neck Turning Pilot from the SAME Manufacturer and problems should be minimized.

The Manufacturers have the gap or lack thereof [Roger Miller at K&M just told me he believes there should be no gap, that the neck brass should ride the pilot with ease. Not loose, but not tight] all worked out for you and their complimentary tools.

Mix the two items from Different manufactures and quality/the end result starts to fall apart quickly.

 

[/VH]

Busdriver,

I haven't done a lot of neck turning but I have turned a few for 6ppc and 6.5x47L. With the ppc, I turn fire formed, from Lapua .220 R brass. With the 6.5, I turn new Lapua brass. I use pumkin expanders and turners for each. I can tell you that with either cartridge; if I expand a single piece and immediately turn it, it will fit the turning mandrel looser than when I expand a 'batch' and then turn necks. I believe this is due to spring back of the brass over time. So, I am thinking you might be able to play with time between expanding and turning to get the fit you are looking for.

In my case, I prefer to expand one and turn one. Doing it this way, I think, is easier for me to control tool temperature (everything pretty much stays cool and tension, though looser, seems more consistent). I also feel that with my setup, if I don't turn a piece within just a few minutes of expanding, that I have more tension than I think I want (which will also cause the turner to heat faster).

Hope this helps.

 

[Keith Glasscock]

Thanks to all who have replied.

I am using a Sinclair expander and turning tool with Sinclair mandrels. I'll remeasure the brass I expanded yesterday and see how the fit is today.

In my mind, there is precision within the limits of the process (i.e. using mandrels that are designed to be used together), then there is precision to the maximum potential (i.e. optimizing mandrel fit, dealing with the donut, etc.).

Given that, does anyone think that there is more precision available if I optimize the mandrel fit?

 

[bigedp51]

Neck thickness varies between lots and manufactures and on top of this you have the brass spring back rates so there is no "perfect" mandrel fit. What you can control is the thickness of the lube you place on the mandrel and how far off the neck floats from the mandrel. Meaning Imperial Case Sizing Wax or Hornady Unique would give you a tighter fit on the mandrel than light weight oil.

 

[artbosco]

Thanks to all who have replied.

I am using a Sinclair expander and turning tool with Sinclair mandrels. I'll remeasure the brass I expanded yesterday and see how the fit is today.

In my mind, there is precision within the limits of the process (i.e. using mandrels that are designed to be used together), then there is precision to the maximum potential (i.e. optimizing mandrel fit, dealing with the donut, etc.).

Given that, does anyone think that there is more precision available if I optimize the mandrel fit?

More precision available?

At the cost of sanity ... no.

Do you know how small 3/10,000 ths [.0003"] of an inch is? ???

 

[Joe R]

I don't use a hand held neck turner, I use a Gracey neck shaver and the cutter spins at 1,480 rpm while I slide the case in the case holder. That is way faster than the hand held turners, so you can disregard the following:

Imperial Sizing Wax (ISW) did not provide enough lubrication and caused heat problems, motor oil made a mess. The best stuff I've found to put inside the necks for turning and for sizing cases is good old Petroleum Jelly. It's almost too good. You have to use even less than ISW. $2 will get you a 13 oz jar at Walmart.

 

[Patch700]

Imperial Sizing Wax (ISW) did not provide enough lubrication and caused heat problems, motor oil made a mess. The best stuff I've found to put inside the necks for turning and for sizing cases is good old Petroleum Jelly. It's almost too good. You have to use even less than ISW. $2 will get you a 13 oz jar at Walmart.

For those that are "Purists" you can simply put this into your empty redding tins...lol

 

[Keith Glasscock]

Thanks to all who have replied.

I am using a Sinclair expander and turning tool with Sinclair mandrels. I'll remeasure the brass I expanded yesterday and see how the fit is today.

In my mind, there is precision within the limits of the process (i.e. using mandrels that are designed to be used together), then there is precision to the maximum potential (i.e. optimizing mandrel fit, dealing with the donut, etc.).

Given that, does anyone think that there is more precision available if I optimize the mandrel fit?

More precision available?

At the cost of sanity ... no.

Do you know how small 3/10,000 ths [.0003"] of an inch is? ???

Nope, not a clue except for the fact that I know how to use a vernier micrometer and I'm expected to be able to measure my own work.

Let me try again - when I last turned necks by expanding then turning , I was only able to hold .0006 and the difference between the thick side and thin was ~.0003. When I turned with a tighter fit on the returning, I got better results. I was wondering if anyone else had seen similar outcomes or if I had another variable I didn't account for.

 

[M99]

I don't use a hand held neck turner, I use a Gracey neck shaver and the cutter spins at 1,480 rpm while I slide the case in the case holder. That is way faster than the hand held turners, so you can disregard the following:

Imperial Sizing Wax (ISW) did not provide enough lubrication and caused heat problems, motor oil made a mess. The best stuff I've found to put inside the necks for turning and for sizing cases is good old Petroleum Jelly. It's almost too good. You have to use even less than ISW. $2 will get you a 13 oz jar at Walmart.

Have you tried using Thread Cutting oil that is spec's for Brass? That's what I've been using, although I don't spin the brass at the speeds you do. It works in machine shops that use automated threading machines at high speed.

 

[47WillysGuy]

FWIW: I ground my neck turn pilot .00075 of an inch less than the neck expander and use a Makita driver to turn the case and the pilot still gets warm. I cut 5 cases then, stop and cool the pilot. I guess more clearance would prevent the pilot from heating so quickly, but I like my end results. I use lots of lube.

 

[Joe R]

M99 said:
Have you tried using Thread Cutting oil that is spec's for Brass? That's what I've been using, although I don't spin the brass at the speeds you do. It works in machine shops that use automated threading machines at high speed.

I don't know what cutting oil is and I don't know how I would use it. I'm not machinist, I'm just a guy that turns necks. The shaver does have a small oil cup to cool the shaft. See the drawing below.

 

['Freak]

Their carbide turn mandrels are supposed to tighten the results a bit, for another $50.