Bob,

My bet is that it is going to do just fine.  I see you used a positive rake angle.  I wonder  a how neutral negative rake would have performed?  I have to tell you that I check a couple times a day for updates on the project, and I looking forward to each new post.  No pressure though…

AJ

Lynn and AJ,  the rake on the tool was a big “I don’t know” for me.  A real machinist would probably have a better idea what it needed to be.  I put an 8 degree rake on it thinking I would still have material to regrind it, if needed.  The tool started out doing a very nice job at taking the outside edge of the radius that the end-mill left, but got to grabbing as the tool worked down into the flat area on each side.  

That being said, I decided last night, while reading AJ’s reply, to regrind the toot to zero rake, re-setup, trying it again and see what happens.  It’s not going to hurt anything to take 2-3 thousands out of it.  I have a small gun show I’m showing at here in town this weekend, so it will be next week before I can get to it but will let you know how it goes.

Lynn, I did consider lifting the tool and tried it, but a bridgeport, at least mine, does not return precisely to the same point.  Like I mentioned the depth of cut was fussy, so with any little change it didn’t cut…or, dug in, depending on how the mill returned to the stop. So, no, I did not lift it, but when I was done the carbide was not chipped and was still very sharp. 
I chose to use the rotary table because the cutting tool was much simpler to make, but using your manual hand operated tool, I could have setup a much more robust/rigid setup using a heavy angle plate.  
Bob

Bob,

Something else that you might want to give consideration to trying, would be to remove the rotary table handle and turn it with an electric drill. A little bit more speed may help avoid chatter.

LRF,   

Another thing that might cause the tool to dig in is the location of the cutting edge on the front of the scrapper.  Since the cutting edge is forwarded of the center line of the tool, any rear flex would cause the tool to nose dive into the cut.  If the cutting edge was on, or behind, the center line, flex would cause the tool to move away from the surface.  However, the tight working space would make it difficult to move the cutting edge closer to the scrapper center line.  This is just another challenge to this difficult project that Bob is doing such a great job on!

AJ

LRF,

Not sure I explained my thoughts well regarding the center line.  I hope this rough sketch explains what I was trying to convey.  Basically, the tool flexes in an arc.  If the cutting edge is forward of the center line of the tool, the flex causes it to dig in.  If the cutting edge of the tool is on the center line, or behind it, the flex causes the edge to move away from the work.

Bob,

You are doing an amazing job on a very complex task, and any thoughts I have in your execution are purely 20/20 hindsight brainstorming.  The tight window you have to work in really dictates how tasks can be accomplished, making some ideas impossible to incorporate.  Keep up the great machining!

AJ

That's some fine work...



JMH

A month ago, we were all contemplating how that concave cut would be accomplished, and today you got it done.  Great work Bob!