An old dog learns a new trick

[Will Henry]

So, you know those precision ground pin sets that some guys use to indicate barrels? I'm too cheap to pony up for a box of those, so I just turn out my own little buttons for barrel set-up. I mean, a machinist should be able to turn out a round button of a given size, right? Indeed, he can. Now, there are some guys who would then laser etch the button and 3D print a little box to put them in. I don't do things that way. I use the button, then set it down on the toolpost, from whence it falls into the chip tray and gets tossed out. Alternatively, I put it in the drawer with others and go through them with a mike when I need one to fit a barrel. I got to thinking, "What I need is a little expandable arbor I can use for set-ups." I was sitting in my recliner (a favorite pass time) planning out how I would make these when I happened to think of an old Bushnell bore sighter I had in a box somewhere. I remembered, it had expandable arbors! I figured, nothing ventured, nothing gained, so I dug out the old kit. I think Dad had bought it sometime in the mid-sixties. I set up a barrel in the lathe, using the usual plug at the muzzle and reaching into the bore at the breech. It was running close to zero. I stuck the appropriate arbor into the muzzle end and put the dial on it. It showed about .0002" TIR. I removed the arbor and put it back in. Same thing. I adjusted to get the TIR closer to zero then tried it again. It was repeatable. I moved the dial out an inch and checked again. No change. I removed and replaced the arbor a half dozen times, and it was consistent. This is my kind of tool! Cheap, requiring no effort on my part, and if not foolproof, at least easy to use.
This was the 30 caliber arbor. I'll try the smaller one on the next 6mm I do and I have a 9.3 in the line up I can try the big one on. I may still try and make some which are a little more caliber specific, but if these all work, the motivation isn't really there. WH

 

[LVLAaron]

there are some guys who would then laser etch the button and 3D print a little box to put them in

HEY!

 

[Will Henry]

HEY!

I named no names. WH

 

[DShortt]

I'm often surprised when I realize the newest thing is little more than a reinvention of the wheel.
Good on you!

 

[RCE1]

My vintage collimators use arbors for different bore diameters. They have a spring on the side which would cause the arbor to be off center? I'm thinking of a Sweany SiteAlign.

I'd love to see what yours look like.

 

[Will Henry]

These are an expanding arbor. There are three of them in the kit. I always thought they were kind of a Mickey Mouse system. I may have been wrong. The arbor is hollow and has four slits which allow the mandrel to expand when the coned inner rod is drawn inward. The other end is tapered and sits against the inside of the crown. A crooked crown would defeat the intent. I'll show it in my next video. WH