MIMF

I am trying to make a small part that is 3/4" aluminum rod with a semi-circular notch with 1/8" radius cut perpendicular to the axis of the rod. So essentially a 1/4" hole off set so that the center is tangent to the circumference of the rod. Being a woodworker without access to a mill, I am thinking of ideas for how I could accomplish this with tools at hand but would like to see if someone out there has a better idea of how to do this.

How accurate do you need this to be? How many do you need to make?

Start by drilling a 1/4" hole across the grain of a piece of something hard, like maple, of an appropriate size. Then drill a 3/4" hole along the grain that intersects the 1/4" hole in the right place. Cut down to the top of the 1/4" hole, and then clean it out to make a 1/4" wide slot with a round bottom. Slide the 3/4" stock into it's hole, and file away at the side of it using a 1/4" chain saw file. Chalk the file first, so that it doesn't load up so fast with the aluminum, and have a file card handy. A better way to clean aluminum out of a file is to rub another piece of aluminum across the file teeth to dig it out. This usually works better than a file card.

Perpendicularity to the rod axis is pretty important, but exact with and depth of the slot is much less critical--it's basically going to function as a hook for something 3/16" thick. This is a one per instrument deal and my output is not likely to get over a few at a time. Your chainsaw file idea could work pretty well--I had not heard of those but it looks like the hardware store should carry them.

You could use a core box bit in a router table. Make a sled to ride a slot it the table and clamp the rod to the sled. A couple passes raising the bit till you reach the depth you need. Router bit will route the aluminum just fine.
Jim

Following up on the chainsaw file idea - check out chain saw files with “file guides”. Maybe make a wood sled to hold your workpiece, and a mating bottom plate with the file and guide secured in...along the lines of a tablesaw and a crosscut sled, but your file takes the place of the saw blade and you work the sled back and forth to notch the workpiece? Or maybe just clamp the workpiece in a vise and use the file guide riding against a perpendicular guide.

I would take another piece of rod of the same diameter--perhaps an off cut from the one you want to notch, if you had to cut it to length--clamp them in a drill press vice, or perhaps in a 1 1/2 inch slot it a piece of lumber and drill your hole dead center between them, et voila' a half hole notch in each piece.

No help on the tooling, but I’m curious what it’s for?

Thanks all for the tooling ideas. I have three feet of aluminum rod to get 4-5 ~2" pieces out of so I may try a couple options and see what works the best.

Karl, it's for a post that will go through the top into a relatively large end block to serve as the anchor or hook of sorts for the tailpiece on an archtop.

I did something like that on my 'Autumn' archtop. I used a 1/2" ebony post, with a piece of brass tube epoxied onto it, and that ran in a piece of stainless tube set into the tail block. The over sized top end of the ebony rod is shaped as a ball. It goes through a hole in the tailpiece which is formed as a cup around the bottom of the ball. The lower end of the post has a threaded rod set into it, and there's an insert in the bottom of the hole, allowing for easy continuous height adjustment. I was inspired by the way they do tailpieces on viols da gamba, with a notched post dovetailed into the end, and a square hole in the tailpiece, but I wanted to make the height adjustment continuous. You could do something similar by simply turning a groove all the way around the post and turning down it's end so you could thread it. It might be nice to have some way to stop the tailpiece from getting knocked off the top of the post; say a 'mushroom cap' screwed onto the top.

Alan, can you point me towards some pictures of that guitar? Apparently my searching skills are not up to snuff today.

I may have to take a couple of new ones: the old ones are buried deep.

Here's a shot of the tailpiece on the 'Winter' archtop. You can see the top of the ball on it's post, and catch a glimpse of the ebony inlay reinforcing the hole in the top. The tailpiece is Macassar ebony, as is all the dark wood on this one. The black outside of the pearl purfling on the tailpiece is actually a binding. The ball ends of the strings seat into back-angled holes in the top of the tailpiece, with short pins that are there to keep the ball ends from rotating and popping out. It's based on the Elliot pinless bridge design, but without the brass liners in the holes (which I didn't know about when I made it).

That's some finely crafted pieces of ebony there Alan.