Fred in NC
Member
Although I can drill and sand the end of the barrels fairly square, I always need a little adjustment so the end of the barrel is square with the tube. Pen mills can do the job, the problem is that they don't stay sharp for long.
The jig pictured below allows me to sand the end of the barrel square with the tube. I use the disc sander until I see the brass, and then use this jig to true up the barrel. It fits 7mm barrels only.
I used my mini metal lathe to build it. It is made from 2 bolts: One 5/8" x 4" and one 1/4" -20, 4".
The end of the 5/8" bolt was trued up, to make the face flat, and the sides rounded. Then a hole 1-1/2" deep was drilled in the middle of the face with a 7/32" drill. This was done right in the late. The hole was then tapped with a 1/4" - 20 tap, so that the bolt could go in about 1/2".
I cut the 1/4" bolt leaving about 1-1/2" of the unthreaded part. I chucked the threaded part in the lathe, and rounded the unthreaded end a bit. Then I sanded smooth until it was a nice fit inside a 7 mm tube.
The 1/4" piece bolt was then reversed in the lathe so the threads would be exposed. The threaded part was turned down to get rid of about 1/2" of the end threads. At the point where the threads meet the solid part of the bolt, a shoulder was cut about 1/32" deep, to get rid of the threads.
I used a piece of PVC for a handle. The bolt is then mounted on the shaft.
I use sandpaper with a heavy cloth backing, cut about 1" square. I use an old 7mm tube, with the edges sharpened, as a punch. The resulting hole is just a bit smaller than the bolt. I just loosen the bolt a bit, and push the sandpaper all the way back, and hand tighten the bolt. This holds the sandpaper securely. I have been using 80 grit.
To sharpen this mill, just replace the sandpaper.
The jig pictured below allows me to sand the end of the barrel square with the tube. I use the disc sander until I see the brass, and then use this jig to true up the barrel. It fits 7mm barrels only.
I used my mini metal lathe to build it. It is made from 2 bolts: One 5/8" x 4" and one 1/4" -20, 4".
The end of the 5/8" bolt was trued up, to make the face flat, and the sides rounded. Then a hole 1-1/2" deep was drilled in the middle of the face with a 7/32" drill. This was done right in the late. The hole was then tapped with a 1/4" - 20 tap, so that the bolt could go in about 1/2".
I cut the 1/4" bolt leaving about 1-1/2" of the unthreaded part. I chucked the threaded part in the lathe, and rounded the unthreaded end a bit. Then I sanded smooth until it was a nice fit inside a 7 mm tube.
The 1/4" piece bolt was then reversed in the lathe so the threads would be exposed. The threaded part was turned down to get rid of about 1/2" of the end threads. At the point where the threads meet the solid part of the bolt, a shoulder was cut about 1/32" deep, to get rid of the threads.
I used a piece of PVC for a handle. The bolt is then mounted on the shaft.
I use sandpaper with a heavy cloth backing, cut about 1" square. I use an old 7mm tube, with the edges sharpened, as a punch. The resulting hole is just a bit smaller than the bolt. I just loosen the bolt a bit, and push the sandpaper all the way back, and hand tighten the bolt. This holds the sandpaper securely. I have been using 80 grit.
To sharpen this mill, just replace the sandpaper.