Neck turning adj idea needed.

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Blue68f100

Blue68f100

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I was in my shop and was going to turn some necks on my 224V brass and decided I did not want to change the settings on my K&M trimmer. So I decided to make me one. That was the easy part, the hard part is coming up with a way to precisely control the cutting tool. The cutting tool is made from 3/16" dia solid carbide rod I had laying around. Using my tool grinder with a diamond wheel I was able to contour the bit to match up to the 30 deg shoulder angle for most calibers. Locked in place with 2 set screws. Neck trimmer.jpg
The only way I've come up with is to use apposing threads, RH and LH. I need to be able to buy the screw and tap in left hand. It's a PITA to cut metric threads on my lathe. And I do not like threading blind holes with no run out, my lathe does not have a brake. This limits my selection since most of what I'm finding is mainly 6-32, 8-32, 10-24, 10-32, 1/4-20,28,40, 5/16-18,24 and a few Metric M4-0.7mm, M5-0.8, M6, M7, M8-1.0mm. A LH 1/4"-40tpi (0.0025") and RH M4-0.7 (0.02756") which yields 0.0025", but runs backwards. There are quite a few combos that give me ~0.004"/turn. It would be nice to have 1 turn = 0.001" But it looks like that is not really practical with whats commercially available.

I will probably solder or epoxy the thread to the cutter. Being carbide, threading/drilling it is not an option for me. I don't have a EDM machine.

Lets see what the engineers in this nice group can come up with. I know there is something I'm missing.

Calling our resident Master Builder JMorris....
 
Walkalong said:
Which is why some people just buy another one, or two.

Nicely made neck turner there. Just play with until you get it right and then snug up the set screws leave it?
Click to expand...

That is what I did with the one I built .... used feeler gauge to set locked it down .... worked fine....

I didn't bother with carbide ....I just used high speed steel( broken drill bit)..
 
Blue68f100,
Your on the right track with the RH/RH when the tool bit is fix. That will slow down the advancement. May I ask why you want 1 turn = .001" Are you still planning on putting index marks every 22.5 degrees or something like that for even finer settings? Or is there a reason you are happy with .001" increments?

I wish I had a machine shop to play with. My brother use to have one in his garage and I use to have access after business hours and use the scrap bin for materials. I was a draftsman at the time so drew up all sorts of stuff and made it with his assistance. Don't have that luxury anymore.

Me personally... knowing Ken Markle makes great stuff and his cutting bits always cut like butter.... I relegated all of my older neck turners to course cutting and always bought Ken's for the final cut and never changed them after that. I was heavily into BR at the time and it was the price of doing business sort of speaking.

Keep us updated on your project though. I'll see if I can't come up with a combination that meets your criteria. hint: spreadsheets are your friend for this type of work! ;)

Steve
 
The direction of movement is depending on where the courser thread is. If the courser thread is the adj knob and the inner is the cutting bit it will move the cutter inward. So there is really unlimited combos just degrees of movement. Finer the threads finer the adj can be.

As far as adjustment range of 0.001", it's just a wish, which is not going to happen. I want the fine control for doing the initial adj/setting, so I do cut too much when I'm reducing the necks. Once set I will probably never change the adjustment as long as I have that caliber.
 
Update,

After scrounging through my recycled screw stash and taps I came up with 2 adj combos that work well. One is 36 tpi outer, and a M4-0.7mm pitch which yielded 0.00022"/turn. Since you normally only need a 0.003" max range this works The other is a 38 tpi with a 40 tpi inner yielding 0.0014" / turn. I cut the outer threads on my lathe. The 38 tpi is not a tap that's listed, lathe only. Then the 0.7 pitch seams to only be used in the 4 mm screw, course thread.
Neck trimmer w-adjuster.jpg

I still need to secure the carbide cutter to the inner adjusting screw. Currently I slotted the screw head and cut a blade on the carbide. This works for going in but does not pull the cutter back. The adjuster is currently a press fit. Will probably change it to a locking screw to make assembly easier.
 
What if the cutter was at a set point and you moved the dowel towards and away from it with opposing screws, not unlike how you use opposing jaws of a 4 jaw chuck to precisely locate an object.

Thread pitch doesn’t really matter as long as you can come up with a method to make precise adjustments even if it’s a small fractional a turn.

Like this wheel affixed to the Allen wrench.

42E95C8F-612B-4E1B-B004-3968EFB3392F.jpeg

Or you could use a method that requires less figuring. And just insert a micrometer in one end and machine the face of a bolt square to back it up. Only thing after that is a precision slot for the dowel to ride back and forth in. Then you just lock the cutter in one place.

899CB4B7-0050-4C8C-AB8E-2190346B477E.jpeg
 
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Got a chance to run these on my 224V brass. I was very surprised that taking the wall thickness all the way to just below 0.0128" did not clean up all of the necks. I have bunch that have a small ring a the mouth ~1/16" back. Decided to leave that, determined it would require the brass necks to be turned below 0.0125" to clean up. Since I'm shooting these out of an AR, don't want them too thin. Which brings up a question for those of you turning necks.

On a standard minimum spec chamber (not a custom that requires a specific wall thickness) how thin do you cut the necks? Stay within SAAMI specs?
 

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