Vertical Head Drive Plate - What material should i make it out of?

I'm just getting around to getting the high speed universal vertical head cleaned up and fitted to the kempsmith universal horizontal mill and i need to make an adapter plate to drive the thing. The design couldn't be simpler. A 5 inch OD, 1 1/8 inch ID x approx 1 1/12 inch thick donut with a slot milled across the diameter to accept the drive dogs, four counter-bored bolt holes to mate up with the NMTB 50 taper spindle face and two 1/4 inch keyways broached into the ID to drive the shaft.

I have an old rusted disc of mystery metal (wheel weights from my Dad's garden tractor) that i could make this out of but it's very soft. Although the design is simple, there's a couple hours of work involved (i work at a glacial pace) and I learned from woodworking a long time ago, unless practicing, make stuff out of the best material you can afford. So, what's the right material to make this part from? I was thinking of just getting a slug of Durabar and going from there.

What say the cognescenti?

I would use 8620, machines good, not hard like 4140, cheap and most alloy shaft suppliers should have it. If you can not find some 1045 or stressproof would work but 8620 is my pick....Phil

If a 50 NMTB spindle nose, make that part fit OVER the 5.0625" O.D. of that spindle nose - even if just a short "snap" fit

Then every time you put it on it will run true

Agree with Phil. I work at a company that makes high-end rotary tables, and we use the hell out of 8620. Stuff cuts great, flame hardens good, and is durable. 1045 also works well, but doesn't machine as good.

I know this is a bit late in replying, but have been indisposed for an extended period. Got a chance to sit down and see if there were many posts on Kempsmith mills.

jdleach said:

Agree with Phil. I work at a company that makes high-end rotary tables, and we use the hell out of 8620. Stuff cuts great, flame hardens good, and is durable. 1045 also works well, but doesn't machine as good.

I know this is a bit late in replying, but have been indisposed for an extended period. Got a chance to sit down and see if there were many posts on Kempsmith mills.

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Thanks Jim, I already took a swing at this pitch and hit a foul ball. That is, i bought a chunk of 8620 and machined the drive plate. I attempted to register it using the taper but failed. Next attempt i will take John's advice and register it on the OD of the spindle. The 8620 material did machine nicely. Although it was a fail, i learned a lot. By the way, i love that kempsmith.