Machining an cotter for the armor milling machine averarm support

When I bought this mill it came with an overarm support but no means of holding it to the overarm proper. There was a hole through the support casting at a right angle to the overarm hole, and it was clear from looking at pictures of other peoples mills that there was supposed to be a cotter there to hold it in place. I decided to try and make a cotter to fit, and looked online for information on how to do it. Not much showed up, although I got enough detail to think I could figure it out.

boring out the hole to fit a "cotter"

First I felt I had to bore out the hole to fit a bit better since it looked "as cast" and was very rough inside. It might not have mattered, but I thought it was a good idea. I think I should have come up with a better way to hold the piece then just clamping it in the vise, but there are not many flat surfaces to work from, and I did not have many hold-down clamps at that point.

turned cotter blank from 12L14 steel and threaded for bolt.

Then I turned a piece of 12L14 to fit, and drilled a though hole for a grade 8 bolt most of the way in. I drilled and tapped the last bit of the cotter to fit the bolt (I can't remember the thread size off-hand).

boring out the recess to hold the overarm

Then came the scary bit which involved using the boring head on the horizontal spindle to make a cut to pass the overarm. I look at this and cringe, but it held so...


When that was done I split it with a hacksaw, faced then ends and deburred everything. I also parted off a little slab as a washer.

It works!

And waddaya know, it works! Now I just have to figure out how to rebush the hole for the arbor and I will be ready to use it.

And, just because it is such a nice piece of work, here is a shot of the shop made boring head that fits on the threaded portion of the Armor Milling machine spindle.

Shop made boring head