Making a "saddle bushing" for a large diameter curver surface

[jmarkwolf]

I want to fabricate what I think is called a "saddle bushing". It provides a flat mounting surface on a curved surface.

The application is for mounting the DRO arm to the top of the Bridgeport Vram, where the hoist ring goes.

It's fast and easy to fabricate such bushings from aluminum round stock using hole saws with relatively small diameter curved surfaces (see attached).

But the top surface of the Vram is pretty large, something in excess of 6" I suspect. I have a contour guage and will determine this later.

I have never attempted cutting such a large concave radius before.

I have a new-to-me Bridgeport, and an RF-31 clone mill/drill and an 11" by 26" lathe in my shop. I suspect a boring head might be tool of choice here, but I don't have one.

Any clever ideas for accomplishing this task?

 

[Tom Griffin]

Sounds like a band saw and belt sander job to me. You could do it on your lathe, but why waste time making a complex machining set-up when it's not required?

Tom

 

[TDHofstetter]

Make a V-block? That'll do the same job.

Or... if you want it more "perfect", do ya have a rotary table for the mill? Or would you be unhappy mounting that piece near the rim of your lathe's faceplate with a counterweight on the opposite side?

 

[wolframore]

If it is 6" then what if you ground it on the face of a 6" grinding wheel. I suspect it's the same radius as the bar it's attached to. Looks like couple inches at most. - oh just re-read the obkect in the picture is not what you're building...

Also what about mounting it side ways on a vise and using a flycutter for that radius? - wouldn't work for the larger stuff...

What if you made a pivoting mount for a vise for the mill. something that big would need a long cutter. - could you post a picture of the actual part? Is it round?

Not sure if any of the ideas would work... just suggestions.