Well it works, but not easily. I had to re-sharpen four times. Chipped the corner a couple of times getting too ambitious on the cut. Will relieve it a bit more to make the end of the radius smoother. Maybe a bit more foot on the bottom. Anyway, I’ll practice some more before I tackle my receiver.

Rodney, thanks for taking the time and trying this.  It looks like the chiseling went well until you started into the bottom side of the cut.  Having the clearance to move the tool will be important.  I can’t see the heel in the pictures, but think it should be very short, not long like one might think, giving the tool more leverage to help maintaining the correct depth.  This may also help with not chipping the tool.  Also short, lighter strikes with the hammer so the tool moves very small amounts.

This radius is right at .150 wide and while I have not measured the length I think its about 1.250 long with the additional bottom section being straight at .250 more.

I’m still in the drawing stage of this project so I’m not thinking real hard about machining other than have the proper measurement when I do start moving metal.

That being said, and thinking about this problem radius, I have been thinking about a hardened insert set into the frame, held in place with the hammer screw and one other.  Using it as my guide in roughing out this radius, and then fine tuning it with light chisel cuts and a riffler type files that will follow the curve of the insert.  This would also help maintain consistency between the two sides.
Bob

I've cut similar arc cuts with the mill; I simply freehand in the cut as close as I can with an end mill, and then finalize by mounting a grinding stone, carefully dressing it square and true, and grind to the line.  I think I can freehand mill more precisely than I could chisel.

I see the difficulty, Bob.  I had looked at Rodney's pictures, not your drawing.  No easy way to get at that.  

Only production method I could think of would be a small radius tip on a 1/2" belt sander held in a vertical mill, and cnc control to swing the arc, after it had been roughed in with an end mill.  The cnc equivalent of your riffler filing after the rough in.  

Might be possible to hold a scraping tool in a mill collet with locked quill/shaft, and swing the receiver with a rotary table to take a thin scraping cut.  then advance the cut using the table feed.  Essentially automate Rodneys chisel cuts.  A boring bar might work for the tool.

Video is to big sorry. Bob if you want I can email it to you

Lynn,
One thought I have had on this, from the beginning, is how can one get a rotary cutter down inside the frame, so this can be cut consistently from side to side.  While I have questions, that I’m sure you will answer, this looks to be the answer.  Great idea!  Yes, please send me the video, I think you have my email.  If not, it’s in my profile. While I’m not ready to start machining, we will be talking in order for me to totally understand your thoughts.
Bob

bobw wrote on Nov 6^th, 2024 at 12:06pm:

I emailed it tell me if you got it.

steel-pounder wrote on Nov 6^th, 2024 at 12:56pm:


From the beginning I figured EDM would be an option.  But I do like to see if I can do all the work in my shop.  So I will probably give Lynn’s idea a shot before going that route.  Thanks.
Bob