Accurate neck turning: My experience thus far.

[Campbell]

Seasons Greetings and thank you all for your help to me this year.

I use the K&M kit and have found the following to give splendid consistency in neck wall thickness.

a) Do NOT use a power tool to drive the case on the first cut, do it by hand (if you will pardon the expression)

b) Anneal the case before lathing.

c) Ensure the case is a snug fit on the mandrel

d) Use a small amount of lube on the mandrel AND on the neck of the case.

Comments re the above: -

a) A power tool seems to be OK for fine finishing after the main cut has been made. I.e. where one is only removing the miniscule high spots.

d) I use a very high graphite content grease mixed with STP petrol additive.

I would welcome any advice to improve my understanding.

Cam

 

[Dusty Stevens]

Buy another neck turning tool for your first cut if your tool wont do it under power. Like a rougher and a finisher. I can cut from over .012 to .0085 to make a 262 nk ppc in one cut under power one pass with a k&m i havent adjusted in over 20yrs.

I use imperial on a qtip in the neck and put my turning tool in a bowl of ice water after every cut.

 

[DngBat7]

Buy another neck turning tool for your first cut if your tool wont do it under power. Like a rougher and a finisher. I can cut from over .012 to .0085 to make a 262 nk ppc in one cut under power one pass with a k&m i havent adjusted in over 20yrs.

I use imperial on a qtip in the neck and put my turning tool in a bowl of ice water after every cut.

Dusty, why not just put imperial on the mandrel, Is putting inside the neck better? Also, do you need any type of wax or cutting oil on the outside of neck when turning?

 

[nmkid]

I always use 2 passes no matter how little the cut. Used a power tool for years, no problems.

 

[rwj]

What wall thickness variation is reasonably achievable after turning?

 

[dcali]

I haven’t found the need for that much fuss. But I’m fine with plus or minus a tenth.

 

[dcali]

What wall thickness variation is reasonably achievable after turning?

If you’re really anal about it and are willing to scrap a few cases, you can get it all plus or minus half a tenth. But plus or minus a tenth and a half is easy.

 

[Dusty Stevens]

Dusty, why not just put imperial on the mandrel, Is putting inside the neck better? Also, do you need any type of wax or cutting oil on the outside of neck when turning?

Its hard to put it on the mandrel and if its warm it just melts off. I lube the inside and whatever scrapes off on the case mouth lubes the outside. I do this while my cutter is in its ice bath cooling back off. You could put it on the mandrel just fine- i just use the cooling time to put it there instead of doing nothing while the cutter cools then taking another step lubing the mandrel

 

[michaeljp65]

What wall thickness variation is reasonably achievable after turning?

When i first started neck turning i was reading of people saying .0001" was an acceptable variation, on reading this i just laughed because when i was turning for my .262 chamber the best i was getting was anywhere between .0082- .0087" target was .0085". But just recently i changed from a .262 chamber to a .265" turning to a target of .0094" im now getting .0093-.0095" with PMA tool and keeping the turner on an ice pack after each case.

 

[memilanuk]

Keeping the mandrel lubed - I use Sinclair neck turning lube applied to the mandrel with a chip brush - and the turner cool and temperature stable - I use a zip-loc baggie filled with ice in a bowl, and set the turner in/on it between cases - helps immensely as far as getting consistent results without having to go super slow and making an already tedious task even more miserable.

 

[fatelvis]

Out of curiosity, what happens if you don’t cool the cutting assembly between cuts? Does the mandrel swell and become to tight to spin the case on it? Thanks

 

[memilanuk]

Other's experience may vary... but what I saw was that as the heat migrated from the mandrel to the body of the turner (K&M, in my case) which holds the cutter in relation to the mandrel... the +/- tolerance of the cut would change - usually '+'.

I have a large round/knurled body that someone made a long while back that goes over the original body, making it much easier to hang onto when you're doing larger batches - and it also acts a little bit as a heat sink for the original body. Set it on top of the ice baggie between cases, while removing the turned case and inserting the new, taking a moment to swipe the chip brush across the mandrel to replenish the lube... seems to work pretty well.

 

[LA50SHOOTER]

Out of curiosity, what happens if you don’t cool the cutting assembly between cuts? Does the mandrel swell and become to tight to spin the case on it? Thanks

In my experience it leads to neck thickness variations.
When starting off with everything cool the thickness will be a certain (target value) thickness. If the mandrel and cutter are warmed up then the thickness of the necks become slightly thicker when measured with a precision ball micrometer.
Using a larger tool that helps dissipate the heat helps some and using an ice pack when the tool isn’t in actual use. I can normally hold 0.0001 tolerance if I don’t rush the process. - when doing larger batches of brass, I try to break it up in to secession where I turn 50 pieces and then take a break and do something else. Using 2 tools I’ve found also helps some when removing material that is thicker, and you can rotate back and forth between tools. Use one tool to remove part of the thickness and the other tool for the final pass cut.

 

[dcali]

I use a Sinclair NT 4000 (great tool, by the way), which is a large aluminum tool that absorbs heat quickly and evenly. With carbide mandrels, I haven’t found the need to worry excessively about heat or resort to ice baths to hit a reasonable tolerance (+/- .00015). I simply take break when the tool gets warm. It cools fairly quickly on its own. I use a bosch power screwdriver that is easy to turn slowly, not a drill, which I find cumbersome, hard to control and prone to overheating.

Like many things in shooting, I think we sometimes make things as good as we can instead of as good as is needed. If you really want to nail the thickness as close as is humanly possible, you’ve got to go slow and you may have to take two passses. And you’ve got to watch the heat.

 

[rwj]

For those owning air compressors, have you tried venturi tubes for cooling?

 

[Phil]

Are you guy`s using carbide mandrels???

Do these get the "Cooling Treatment" too??????

 

[rwj]

Are you guy`s using carbide mandrels???

Do these get the "Cooling Treatment" too??????

I’m starting with ones that are nitride coated...

 

[michaeljp65]

I use PMA carbide turning mandrels. I do 10 at a time slowly, lots of measuring between each turn. Thats to allow things to cool a bit. I also put the turner on a ice pack when i put it down between turns. I do about 10 then go off and watch tv or do something else for an hour or 2 then get into it again.

 

[dcali]

Are you guy`s using carbide mandrels???

Do these get the "Cooling Treatment" too??????

Carbide is worth the money. Every penny. They do not get the tool anywhere near as hot and brass doesn’t stick to them. They are much better than steel. You still “need” an ice bath to keep it at room temp (if you needed it in the first place. I don’t bother- the tool gets warm but can still hold the tolerances I want. )

 

[rogn]

I use a carbide mandrel and I use RCBS case lube on both the case neck and the mandrel. Seems when I only lube the mandrel the tightly fitted neck just wipes the lube off. Plain oldfashioned STP seems the best lube for this but cleanup is a nightmare.