cutting a partial r into a long bar of material

[pgump]

I'll try to make this as clear as possible.
I'm trying to cut a 1 3/4" r, .150 deep along the length of a bar of plastic. The bar is 7" long (the axis of the cut) and is 1 1/2" wide, 1/2" thick. I'm using a 2" dia endmill cutter with the Bridgeport head tipped at approx 31° from vertical. This should create the 1 3/4" radius cut. I realize the cut will be slightly eliptical but should be close enough for what I want.
The long bar will sit on top of a 3" pipe (3 1/2" od).

Is there a better way to do this or optimize the cutter and angle for a given radius? I didn't find any formulas in the Machinist handbook.
Thanks in advance
Pete

 

[griffengm]

Pgump,
Please clarify: is the resultant radius concave (into the bar) or convex (out from the centerline)? In other words, are you using a ball endmill or a corner rounding mill?

Griffy

 

[pgump]

Sorry,
It's concave (into the bar) so that the bar has the same dia as the pipe it sits on. standard endmill not a ball

 

[MikeHalloran]

A small flycutter and a bit with a modest nose radius would allow a better finish for the same feed, or a faster feed for the same finish.



Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

You have found the easiest way to produce large concave radii without special tooling.