Making a Round Thing Square

Well, actually, making a round thing rectangular. I had an idea for a way to mount hood straps on the Beck TD, but after making the first piece I decided to go a different direction. But the process of making one was instructive, and I thought someone might stumble upon this post and learn from my fumbling around. Here's the final result:

It all started with a gift from my friend Phil - he gave me several slices of a cast iron rod to use in this project. 

I started by truing up the faces of a piece, and then while on the lathe, I drilled the center and tapped all the way through for a 1/4-20 bolt. Then I moved to the milling machine to make the rectangular projection, 1" x 3/4". The problem is that holding a round thing in the mill vise doesn't work well. I tried it, just for fun, and even a modest cut moved the workpiece and ruined the cut.

What I needed was a pair of "soft jaws" to hold the workpiece securely. The diameter of the rod was just under 1-5/8" inches, and to my great astonishment I found a 1-5/8" Forstner bit in my collection. I cut a likely piece of wood to use, and put it in the mill vise.

I then used a digital edge finder to find the center of the block. It's easy - touch the first side of the vise jaws, zero the Digital Read Out, and then move to the other side. Divide the number displayed by two, and then move back to that point, and you're at dead center. My indicator lights up when it touches, making it extra easy.

I used a small drill bit to mark spots near each edge, and then used them to mark the center line for later cutting on the miter saw. Then I was ready to drill a 1-5/8" recess near the middle:

I moved the piece to the miter saw and carefully cut it in two along the line. Result: a perfect set of soft jaws:

I used the jaws to securely hold the workpiece in the mill vise, and then it was just careful measuring to mill the rectangle. That, and plenty of time - with my lightweight equipment, I can only cut about 0.025" inch at a time, so each side took five slow passes. I spent nearly half an hour making that rectangular bump. You can tell this is low-tolerance work, because I'm using the end mill in the drill chuck instead of swapping out for a collet to hold it.

When done, it fit the intended hole perfectly. But as I said, I decided to do this a different way, so I have a nice little base for something with a 1/4-20 thread, and four more pieces of cast iron to chew up!