Wednesday, September 16, 2009

I can smell the metal shavings and hear the cussing...

Will's learning to cut & thread barrel shanks. Next he'll be cutting chambers.

Watching that stuff get done really gives one an appreciation for good gunsmiths.


HTRN said...

The funny thing is, everybody thinks that the cutting is the hard part.. It's the dialing in of the barrel to make sure it's running tru with the lathe spindle that can drive you bonkers.

What I am surprised at is the fact that his instructors didn't show him the upsidedown toolholder trick, where you thread away from the shoulder, instead of towards it. Makes it alot easier - just set a stop as a starting point.

And oh, Tam, if you want to see a real good video on threading and chambering a barrel, Richard Franklin has one that's pretty good.

Tam said...

"And oh, Tam, if you want to see a real good video on threading and chambering a barrel..."

Me + Machine Tools = Bad Idea.

Fortunately, I know people who are the bomb-diggety-shizznit with them. :)

og said...

"Me + Machine Tools = Bad Idea."

Really? I had you lamped for a shop geek from the first time I met you. You certainly have the right attitude.

Ed Foster said...

Gotta remember, Mauser barrels don't set up against the front of the reciever like other bang-bangs, they torque up against that internal ring the Extractor cut is in.

Always a good idea to skim the front of the reciever ring nice and square, then get a good measurement of the drop from the internal ring to forward edge of of the reciever. That, plus .002 for torque loss, is the distance you'll want between the back of the barrel and the shoulder.

Or, just face the reciever ring and the forward face of the internal ring at the same time, but I think that's going a bit overboard. The little sucker is dead square with the threads, and I don't usually mess with it.

HTRN said...

Ed, remember, no matter what, you're still cutting a thread on the barrel to a shoulder, regardless of where the barrel actually contacts, so cutting threads with the cutter mounted upside down, and the spindle running in reverse means that possiblity of crashes goes from "very easy" to "highly unlikely". Of course, you have to have a really rigid toolpost that can take upward forces - it can't really be pulled off in a rocker post, but in an Aloris? No sweat.

Tam, I wasn't suggesting you go out and give 4 grand to Grizzly for a G4003G(a "Gunsmiths lathe",snort), but rather to see what is actually involved and have it explained if you are interested. He's also got a really good bedding video.

libertyman said...

Just in the interest of accuracy, wood workers make shavings, and machinists make chips. Good post.

Ed Foster said...

HTRN, I turn the major O.D., square off the back face, and qualify the shoulder, then undercut the junction betweem the shoulder and thread .050 wide and deep, just like on the original Mauser. That way the shoulder never gets touched again, and stays undinged.

I cut the thread slowly (in back gears) and stop the spindle by reversing the motor when I get to the undercut. That way I can keep picking up the thread exactly at the same place on the lead screw each time.

I polish the thread each pass with some fine wet-or-dry paper wrapped around a three sided file (same 60 degree included angle as the thread), and fit the action exactly, with just a bit of drag between barrel shank and reciever thread.

The upside down thing leaves me confused. How do you tweak the tool holder around to make certain you're actually at a true 60 degrees? I put on a 6x loupe and set the tool against a finished piece of threaded stock.

My biggest moan about rebarrel jobs on Mausers is when somebody leaves a gap between the barrel shoulder and the reciever ring. Yes, I know the back face is what locks up in compression against the interior ring, but it looks like suck.

It's still better than locking up the shoulder against the front of the reciever without solid contact on the inside ring, and they always shoot erratically when you do, but it's not all that hard to bed solidly inside and still get a nice professional looking no gap closure between barrel shoulder and reciever ring.

I mean Jeez, the Europeans did tens of millions of the things during one war or another.

Also, isn't it odd that the Mauser has an inch thread instead of a metric thread? 1.050 by 14 t.p.i. doesn't equate to anything metric.

I figure ol' man Mauser stole the stacked column magazine from James Paris Lee when they were both working at Remington after the Civil War, and I guess his toolroom mockups were cut on an American/British lathe.

HTRN said...

There's a coupla ways of squaring up the toolpost - I personally use the "put a block on the front of the Aloris, with a 6 inch rule on it" close the toolholder, and then loosen the nut holding the toolholder to the compound. Position said toolpost infront of the side of the chuck. crank the crossslide in till the rule almost touches the side of the chuck. push it square, and tighten down. This all done assuming that the compound is already set to 29D. It's actually harder to explain than to do. Toolpost is now square to the lathe. You just gotta make sure that the lathe bits are square in the holders, and the side of the chuck is square. Another way to do it is to use a ground test bar, indicated true, and then use the same clamped rule method. Other than that, setting up to cut the shank length is the same. The advantage is, I can cut a thread with a undercut relief that's close to half a thread width(in the case of 16 threads, that would be .032), because you're starting at the shoulder, and then moving away from it - remember, you're starting point is up against a carriage stop. This technique of running upside down and reverse is especially good for cutting internal threads in blind holes - no chance of bottoming out where you can't see to keep from bottoming out.