Another Day In The Life Of A Gunsmith.

Wednesday, March 03, 2010 Filed in: Gunsmithing, My Life

Many people tell me that they'd love to have my job: "it must be fun to play with all those cool guns and get paid for it!"

Lest others be deluded into thinking that this business is all fun and games, allow me to supply a dose of reality: somedays it literally doesn't pay to get out of bed.

Last Thursday was just such a day. It started with the need to make a 'spud'. No, not a potato - a 'spud' is a metal pilot that aligns a cutter with a bore. They're used as guides for such things as chamfering chambers and crowning barrels.

You can buy them ready made, but they come in one size per caliber-specific application. The problem is that if the spud is even .001" off, the quality of the cut will be destroyed. They need to be fitted precisely to the hole in which they will be inserted, and the ready made variety never are. If good work is to be done, they have to be custom made to fit the work.

Over the years I've made a wide range of spuds in various sizes, and because of that selection I usually have one that will fit properly. Occasionally, though, I run into a situation where I need to make yet another one, which is what happened on Thursday. I needed a .216" spud, and the closest I had was .214" - not nearly good enough to properly crown the .22LR barrel on which I was working.

Not a problem! I picked out some appropriate metal and chucked it in the lathe. I made a couple of cuts to get close to finished size, but when I measured the diameter I found that it tapered by roughly .002" throughout the length of the piece! The spud is only a couple of inches long, so a .002" variance in that length is huge. It renders the part unusable.

It's also not supposed to happen.

Annoying, but not insurmountable. I thought that the lathe probably just needed to be re-leveled, which hadn’t been done for a couple of years. I leveled the lathe (which takes a couple of hours if done very carefully), made a test cut, and....it was still off!

Grrrrrr.

The next step was to check the lathe’s tailstock for alignment. The tailstock, which supports the end of work in a lathe, has to be precisely aligned along the lathe's longitudinal axis. Otherwise, it pulls the end of the piece left or right, which leads to a taper such as I was finding. I spent the time aligning the tailstock, and a quote from the movie "Ruthless People" poured from my mouth: "Now THAT oughtta do it!"

It didn't.

I went back, tweaked the lathe level, and aligned the tailstock again. The problem persisted.

Put yourself in my place: I've got a top-notch Austrian lathe, the best Swiss measuring instruments, and I'm making parts displaying precision more appropriate to a Kalashnikov clone produced in an unlit cave factory outside of Jalalabad. Something was wrong, and I had to find it. The only hitch was that it was now dinnertime, and due to skipping lunch I was as hungry as could be. The problem would have to wait until the next day.

Friday morning I came into work determined to find the cause. Double checking everything revealed no clues. I replayed the issues in my head, while at the same time resting my hand on the tailstock. I looked down, and it came to me: the live center in the tailstock must be the source of the problem. It was the only thing I'd not checked.

A live center looks like this:

0009911-11

The cone-shaped bit is inserted into a hole in the piece being machined, and the other end goes into the tailstock. The cone revolves on precision ball bearings, keeping the piece aligned as it's rotated by the lathe. Any rotational error will result in inconsistencies in the finished part.

A quick check with a quality (Swiss) test indicator confirmed my fears: .0025" wobble. I checked the piece I'd machined, in several orientations, and sure enough - not only was it tapered, it was also slightly oval, which is exactly the error a worn live center would produce. Bingo!

I ordered up a new live center from my favorite online tool supplier (www.mscdirect.com), and on Monday the smiling UPS man delivered it to my door. The center quickly proved to be the answer; the rotational error was less than .0001", compared to the .0025" wobble of the old one.

With the new center a perfect spud was easily produced, the barrel was beautifully crowned, and the gun will soon be on its way back to a happy shooter.

It only took me a day and a half, plus a not insignificant amount of cash to find and fix the problem. So, want to tell me again how you wish you had my job?

-=[ Grant ]=-

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