Method to "Counterbore" flats on cast iron

[Reddinr]

Hello again. I am mounting a stepper motor onto a thickness sander and removing the crank. I don't want to take it apart but want to do the machining more or less by hand. I'll have a simple control panel of some sort.

I plan on a bolt-circle template for the four small screws for the stepper and that mounts to the 1/2" center shaft, but I want to counterbore ~1/2" diameter shallow, coplanar flats for standoffs to sit flat at each mounting hole. The material is cast iron and there isn't that much thickness to play with. Ideas for doing this by hand? The counter-bore bits I have are not large enough diameter for the flats.

I was thinking about another (thick) template with 1/2"+ holes and a stubby end-mill and a hand-drill. I wonder if that will work? I've got one chance.

 

[whitmore]

Instead of trying to machine the cast material, could you use spherical washers? It might take some
extra washers as shims, but that wouldn't weaken the metal as much.
McMaster has 'em, kinda pricey, but a lathe and ball turning attachment can be a fun DIY .

If I understand the situation, the fastening mainly just has to have enough shear strength for the torque
of the motor, but motor position and orientation is critical.

Four posts, ball-ended, four ball-dished washers, and you can face off the posts for the motor
alignment...

 

[Reddinr]

Never heard of spherical washers... looking up...

OK. Looked. Those are pretty cool! The torque will be pretty low so those might just work.

 

[ChazzC]

Never heard of spherical washers... looking up...

OK. Looked. Those are pretty cool! The torque will be pretty low so those might just work.

They make using mill table clamps a lot easier.

 

[Firstram]

You could also tape off a dam in the area you need flat and pour a JB Weld pad.

 

[tq60]

If there is room, make. A cross plate that goes across the open area, if this is for the top of item in photo.

This allows attachment from sides, then smaller screws with standard flathead taper can be used.

Creates a mounting plate away from the thin stuff.

Sent from my SM-G781V using Tapatalk

 

[Reddinr]

...A cross plate that goes across the open area...

So, that's interesting and gives me a thought. Maybe vertical plates that extend the sides of the cast iron structure and a top plate that the motor mounts directly on would work. The cast has angles and curves everywhere so I will need to see if that works. I already bought the washers but now I'm looking at this option too. Might still need the washers regardless.