Turning problem

Dave Short said:
Al, I guess I see what you mean...............I have to lay the tool on the block, make sure I take it off before I answer the phone or go take a whiz, and remember to pick it back up before I make another cut...WOW.........................and then theres that 5 minutes to take the mandrel out after only 200 cuts, spin it against a patch coated with Flitz, and put the mandrel back in..................Man, I'm going to have to re-think this whole thing................................Pure TORTURE! UGH!

What I'm trying to say, Al, is it's a breeze.
-Dave-:)
Click to expand...


LOL

al
 
Free for the asking ...

I have a "Lee Zip Trim Case Trimmer Universal 3 Jaw Chuck Case Holder and Stud" that I'll give someone for the asking.

It's has been sleeping in a drawer waiting for the end of the world.

If someone can use it, it's yours, free gratis. I'll even pick up the postage. My way of giving back. The first name and "domestic" address in my private message box is the winner.

I've gone to the K&M tools and couldn't be more pleased. Art
 
Drilling two holes in the tool and mounting it to a hunk of aluminum will make a nice heatsink. It also makes the tool easier to hold, just as was said above. I did this for both reasons when I did mine. Use some CPU thermal heatsink compound between the parts. It really helps. Also, lube the necks inside and out, or lube both the mandrel every case and the outside of the cases. I use imperial wax both inside and outside the necks to reduce the amount of heat generated. I perfer keeping the horse in the barn, rather than closing the door after it left.

I also reground the cutters on all my K&M tools and put on a more proper tool angle for cutting the brass. At the same time, I changed the shape of the cutter to fit my shoulders better.

I use a 540 rpm HD drill that's probably never run past 100 rpms. Speed is a big part of how hot the parts get. Of course if the parts get hot, so does the tool.

I can't speak for the steel mandrels as I only own carbide versions on all my tools. I like the interior finish when using carbide too much to ever change. With a proper tool angle, it's a nice burnished interior that's just beautiful.

Lastly, if you're really really serious about getting every neck exactly the same, the best setup in my opinion is to use two tools, and make only a finish cut with the second one. I have done this but don't generally bother anymore.
 
K&M Tool Holder

Here's the holder I make. I originally made it primarily so the tool would be easier to hold but it turns out the heat sink feature may be the best feature of all. I use carbide mandrels with a little Flitz for lubrication. With the carbide mandrel the Flitz makes for a super finish on the inside of the necks.
 

Attachments

  • K&M Tool Holder.jpg
    K&M Tool Holder.jpg
    13.7 KB · Views: 218
I really don't want to knock a tool like the K&M, but really Alluminum is
not an ideal material as the coefficient of expansion is very high.
I do use one, because it sets quickly, but only for a first cut.
Have made my own neck turning tools for yrs, and they are all
heavy and steel. My second cut is with a tool that weighs
a bit over a pound. I place it in a vice and can hold .0001
maybe less in 50 cases. That this shows on the target is
doubtfull to me.
 
It's a dicey deal - -

I have 3 different case neck turners, a Pumpkin, a Stiller and a Marquart. I have two expanders, a Sinclair and a Jones. The Sinclair is bigger then the Jones.

I have several devices to turn the cases, an 18 V hand drill, a Fixed turing device with it's own motor and a 1/2" Craftsman drill motor with a trigger that has a screw in it to limit speed.

With the cases I make, all of the turners will heat up. I have them set to take some off with the Pumpkin being the last turner I use. The Sinclair expander is on the small side to be able to use the Pumpkin.

The Craftsman Drill Moror will turn whatever one chucks up in it. The other two won't.

I am taking a lot of stock off cases that most of you will never make so no big deal BUT, where does one find a selection of different sized expanders?
 
Bob Kingsbury said:
I really don't want to knock a tool like the K&M, but really Alluminum is
not an ideal material as the coefficient of expansion is very high.
I do use one, because it sets quickly, but only for a first cut.
Have made my own neck turning tools for yrs, and they are all
heavy and steel. My second cut is with a tool that weighs
a bit over a pound. I place it in a vice and can hold .0001
maybe less in 50 cases. That this shows on the target is
doubtfull to me.
Click to expand...

Bob,
I'd like to see a picture of the tools you made if you have one.
 
Getting a picture on here might be a problem, my new Sony
camera is still in the box.
A really good ( zero clearance ) fit is neccessary to hold
tight tollerances . I am actually expanding up a tenth in my final
turn.
I want to point out that no matter how the expand up is accomplished, the shoulder junction yields less and springs back
after expanding. The pilot then rides on that junction as a narrow band
and part of the neck at the mouth. This causes a thinner area about
2/3 of the way down the neck. Very difficult to measure.
The old original RCBS case lube is one of the best
 
It is a common misconception that a tight case neck to turning mandrel fit is needed to hold tight tolerances on neck thickness. If you let the case and the tool alignment be determined by the cutter's pressure on the mandrel, the neck thickness will be the result of the distance between them. Many turning setups do not allow this, and for these it is true that the fit has to be tight, but along with that tight fit come the problems of friction and heat. At the root of all of this is the common misconseption that a a tight fit is required. This has driven manufacturers to furnish expanders that give this fit lest their products be viewed as inferior, and not sell well.

Early on, I used a simple Sinclair turner with a steel turning mandrel. After tiring of brassing and heating problems, I chucked the turning mandrel in my 3/8" drill, wrapped some 320 grit wet and dry around it and gave it a short spin. I was able to relieve the fit of the expanded case necks just enough that the heat and brassing problems were eliminated, as long as I kept the RPMs low. The necks seemed to be of uniform thickness. At this point I only had a 1" micrometer with which I would measure my loaded round's necks.

Some time after that I was using an expander that was sized for my K&M turner that I use for my finish cut (.262 neck 6PPC) and making the rough cut with one of my old steel mandrel Sinclairs, that was set up for a smaller expander. The fit was too loose for precise results if you held the driver and tool tight, but I found that by just keeping the turner from rotating in my hand and keeping a loose grip on the cordless drill, I could get accurate cuts, and not have brassing or heat problems. The other part of the method, which I have mentioned before, is cutting to the shoulder rapidly (making an ugly cut) and then coming back to the case mouth very slowly. That way, the cutter is cutting in both directions, and keeping the neck pinned to the mandrel. (Yes I have a neck mic. that reads in tenths.)

The K&M has a carbide mandrel and removing most of the brass on the rough cut slightly loosens the neck's fit on it, but if I wanted to only make one cut, and I thought that the fit was too tight, since I wouldn't risk reducing the diameter of my carbide mandrel, I would figure out the size differential that was needed based on my earlier experience, and order a custom expander from K&M.
 
A thermal expansion calculation is in order

Original post snipped down:

"I will start with a .0120 neck and by the time I have cut 20 necks I will be cutting .0123 or 4. "

I don't think this change in neck thickness is caused by thermal expansion of the aluminum case turner body. Going from 70 degrees to 120 degrees doesn't move the material that much. And there is not much material between the mandrel and cutter to move anyway. I might be mistaken but some engineer type might calculate this and settle the question.

Anyway, after you get the tool up to temperature, thermal expansion won't have any effect that you can measure because the temperature won't be changing very much if at all.

Turning in two steps with good fit between case neck and mandrel will give perfect results. Maybe only one step if you're not turning much meat off the case. Use a good lube. I use PG2000 but others work well too.
 
My first turning tools were all aluminum body, and changed dimension
with temp fast. From 68-70 deg to 98.6 as held in my hot little hand
gave me lots of cases for checking jam and the scrap barrel.
There are few if any case holders that have zero runout, so a case
presented to the cutter is wobbling all the time. If volume is your
goal, its the way to go. Take a field trip to a plumbing shop and
watch how pipe is threaded. Everything is floating and nothing comes
out straight. That Speedy and Jackie turn necks on a lathe and
tight mandrill is a big departure from your handy dandy cordless.
I have just checked the thickness of an aluminum neck turner
in an area about 1/2 " thick. At 68deg and then after placing
it in my pocket for 10 mins. It was .00024 thicker. That the
cutter is clamped down almost that distance from the mandrill
would allow similiar changes in wall thickness. Loaded round
dia. at that rate could approach a half thous in variation
 
Good morning Bob,
Pipe threaders don't use an internal mandrel, and so they are not similar enough to use for a valid comparison. Many of the common lathe turning setups have the case turning with the mandrel, so they are not comparable to a hand held tool.

I am not saying that heat is not a factor if the fit is tight. I AM saying that with a tailored fit less heat is produced without the sacrifice of precision, and that having less heat is a good thing because you don't have to go through so much monkey motion to deal with it. If one is using one cut with available pairings of expander and turning mandrels, then steps need to be taken to deal with the results of the heating that will invariably take place, but with a slightly altered fit, there is much less heat, and good necks can still be produced. If you get good results, and are satisfied with the method that you use, then nothing further is required. All I am saying is that I do something different, and also get good results.

Boyd
 
Henrya,
We could look up the coefficient of expansion of aluminum and figure it out, but I think anyone who has cut a case with a room temperature K&M tool and continued on to cut just a half-dozen cases non-stop will tell you the wall thickness increases by 2 or 3 tenths. All it takes to prevent this is to simply make sure the tool body is about the same temperature when each case is turned.....choose a method and have at it.

-Dave-:)
 
Pete...

Pete Wass said:
I have 3 different case neck turners, a Pumpkin, a Stiller and a Marquart. I have two expanders, a Sinclair and a Jones. The Sinclair is bigger then the Jones.

I have several devices to turn the cases, an 18 V hand drill, a Fixed turing device with it's own motor and a 1/2" Craftsman drill motor with a trigger that has a screw in it to limit speed.

With the cases I make, all of the turners will heat up. I have them set to take some off with the Pumpkin being the last turner I use. The Sinclair expander is on the small side to be able to use the Pumpkin.

The Craftsman Drill Moror will turn whatever one chucks up in it. The other two won't.

I am taking a lot of stock off cases that most of you will never make so no big deal BUT, where does one find a selection of different sized expanders?
Click to expand...

if you are using the pumpkin you should be using his expander. you should have no problem taking all the metal off the neck in one turn of a .330 necked BR with one pass, well lubed and not too fast a turn. The Nielson expander and turning mandrel are perfect fits.
 
Looking at the numbers.

Looking at the numbers.

The coefficient of thermal expansion is:

Aluminum 1.37e-5 in/(in * deg F)
Tungsten Carbide 3.90e-6 in/(in * deg F)

On my Marquart tool, the distance from the center of the mandrel to where the 1/8" cutting tool bit is mounted is 0.5 inches.

To calculate the amount of expansion, the equation is:

dL = L0 * dT * alpha

dL is the change in length
L0 is the original length
alpha is the coefficient of thermal expansion

Assuming an initial temperature of 60 deg F and a final temperature of 120 deg F which is warm to the touch, then the expansion is:

dL = 0.5 * (120-60) * 1.37e-5

dL = 0.000411

The carbide mandrel's radial expansion is:

dL = 0.1215 * (120-60) * 3.90e-6

dL = 0.0000284

Since the mandrel moves the brass closer to the cutting tool and the aluminum moves the cutting tool away from the brass the actual change in distance is the aluminum expansion minus the carbide expansion.

The change if cutting depth for a 60 degree F change in temperature is 0.000383 inches.

I warm my Marquart in my pocket before I start neck turning and turn at a slow rate and the Marquart stays at about the same 90 deg F temperature as I neck turn. The distances are probably different on other neck turning tools but the procedure is the same.

Good Hunting... from Varmint Al
coyotel.gif
 
Varmint Al wrote:

"The change if cutting depth for a 60 degree F change in temperature is 0.000383 inches."

Excellent!.
Thank you, Al!

This is definitely telling us something about the process of turning. Good fit, good lube and a tool warm up seem the order of the day.

I turn in a drill press with an old style Sinclair aluminum body turner and plenty of lube. I set-up the cases to a gentle wring-on fit. I can barely feel the case going on and off through the drill press handle. Hard to put on by hands though. I also turn several dummy cases during set up which I guess is warming it up to "operating temperature". The turner body never gets more than warm to the touch. Next time I turn a batch of cases I'll check the temps with my little non contact thermometer to monitor the temperature rise.
 
Bob Kingsbury said:
Varmint Al,
You are of course speaking of wall thickness. Therefore
loaded round dimension could be twice that amount.
Click to expand...

marquart.jpg

Correct on wall thickness. The calculations are linear and would only be half as much with half the temperature change. Also, on my Marquart tool, there is a washer that clamps the 1/8" tool bit to the aluminum body. I took the measurement from the center of the screw to the center of the mandrel. That might not be the "effective" length. It could be closer to the edge of the washer.
I wrote about the temperature effects a long time ago on my Reloading Page: http://www.varmintal.com/arelo.htm#Neck_Turning

Good Hunting... from Varmint Al
coyotel.gif
 
Do yourself a favor

Back off the cutter so it is not hitting the case,lube the inside of the case.Push the pilot into the case,if it does not slide in and you have to push it in you do not have enough clearance between the pilot and the case,that is you problem,that is where the heat is coming from.I have both factory steel and carbide pilots also some home made drill rod pilots and never had that problem.
 
You must log in or register to reply here.
Back
Top