It’s been a busy summer/fall/early winter, but I’ve managed to make a few chips in the shop over the past few months. First up, dad had a front tractor axle that needed a little work. The hole drilled through it wasn’t quite at the needed 5 degree angle to allow for proper assembly, so he ground out the sleeve that had been welded in and I gave the boring operation a try.
Clamping the part was a little easier than I thought it would be. It’s a heavy beast, and is as long as the entire mill table. There’s a pair of blocks near either end that worked great for aligning it on a a horizontal plane, then I just had to clamp the center section in the vise. I tipped the head forward by 5 degrees to complete the setup.
I seem to have lost the feeler clamp screw for my trusty Blake Co-Ax indicator, so I used an edge finder to pick up the hole center instead.
I didn’t have a boring bar long enough to plunge all the way through, so I bought one just for this project. I selected a bar tipped with C2 carbide since the cut would be interrupted due to being a slightly different angle than the original hole. I started by setting the boring head to a small enough diameter that it would just start cutting at the bottom of the hole (where the offset between the existing hole and my new cutting axis is greatest). I then adjusted the boring head to make the hole a little larger, set the powerfeed, and bored again. It was long, slow work, but I finally got to the point where I had better than 50% circumference all the way through. Finally, I turned a matching sleeve on the lathe that dad could weld into the axle hole for the whole assembly to ride on an axis pin.
A friend is assembling a new upper for his AR, and one of the components is a Sentry 7 adjustable gas block. Unfortunately, the freefloat handguard he’s using makes adjustment of the metering setscrew almost impossible. Dremeling out a simple slot would fix things just fine, but would look pretty ugly – milling the slot would look much cleaner.
The problem is, how do you clamp a round object while also properly indicating it so the cut is right over the central axis? After a bit of pondering, I came up with the above solution. I first drilled and tapped holes in a 1″ square aluminum bar and clamped that into the mill vise. I used strips of tape on the vise jaws to protect the anodizing on the handguard, and then used a pair of 1/2″ bolts to secure the handguard – tightening the bolts works to wedge the handguard against the top edges of the jaw faces, perfectly centering and aligning the handguard.
At that point, milling the slot (really just removing the web from between two holes) was a piece of cake.