BOBW, have you looked at mounting your rotary table to an angle plate?

I finally got back to this today.  Found a nice 12 inch rotary table that goes both horizontal and vertical, picked it up this weekend.  Have a tool ordered the diameter (4 3/4 inch)  I needed to machine the back 2 radius's, but it has been lost in the mail for 10 days, as of today. 

So I decided to try machining the back 2 radius's with the rotary table and not be concerned about how flat they end up since these two surfaces appear to be just clearance and weight reducing cuts anyway.

Working through the process took some time today, so I only got the one done but it came out fairly nice.  I used a 1/2 inch carbide end mill that I ground .010 off the diameter, leaving just 3/16 at the cutting end at the full diameter.  This gave me side clearance so I didn't bump my finished surface at the frame bottom, where the trigger assembly slides into, but let me get up close to the side at the edge of the radius.

The original guns frame is setting beside the new frame in the pictures.
Bob

Well I think he has actually done it...




JMH

Today was the day to start get to the tough radius.  But, I thought I would start with how I did the setup for machining each of these radiuses.  It took quite a bit of time but it was necessary in order to get these done using the method I used.  Each one required starting from the beginning as explained next.

The first thing, in the setup, was to get the rotary table centered under the mill spindle, while the table was in the horizontal position on the mill.   I won't get into the details of how this is done because it's one of those tedious jobs that must be done.  Picture #1 shows the table centered up.

Then the mill table is offset on one axes to the desired radius.  In this case I wanted 1.125 inch.  Picture #2.

In order to clear the quill I had to raise the action frame 2 inches using blocks.  Once on the blocks, I aligned the layout, scribed line on the side of the frame, with the center of the mill spindle using a pointer locked into a collect in the spindle.  Picture 3 and 4 show the frame being lined up to the track the mill will take when actually cutting.  The red lines highlight the track but, the scribed line is the actual track that mimics the radius to be cut on the inside.

By doing the above, I have the frame setup so that the full length of the scribed line is on the rotary table precisely 1.125 inch from the center of the table.

This is tough to explain so I hope everyone understands this!
Bob

Now that's some creative set up work...



JMH

Outstanding work Bob! For us non-machinists it’s amazing, at least it is for me!

Holy Cow! I'm not even a beginner at machine operation and I was nervous just reading the description of how you did the job. But, then, I knew if anyone could do the job you could. 

Well, I got the radius scraped but it didn't work as well as I had hoped.  I believe the idea is sound, but I needed a more ridged setup.  First, the quill is extended out quite far, which I had no choice in order to get the table under the mill head, and then, the scraping tool is well below the quill. Second, in order for the quill to clear the face of the rotary table I had to raise the action frame 2 inches, with 123 blocks, off the table face…..I think this is the biggest issue.   Even though it is clamped tight I still don't believe it to be rigid enough.  The setup worked pretty well as long as I was taking very small bites, taking probably only tenths on each pass.  If I tried to take as much as a 1/2 thousands it would grab and dig in.  Might also be that I am off a little on the tool geometry and it was cause some of this digging in.

This first picture shows the tool.  It is .010 narrower than the 1.0 inch ID of the frame.  I silver soldered a piece of carbide on the shop made steel blank and then ground the carbide to what I wanted.  The round shank is 1 inch in diameter.  The actual scraping only used the sides of the cutter, each frame radius is .150 wide.

The second picture was taken during the setup and shows the leading edge of the scraper.

This third picture is the setup.

These last two pictures show the results.  As usual pictures make it look worse than it really is but, you can see the few place the scraper wanted to grab.  Since the design really only puts pressure from the breech block at the top of the radius, and only to seat a tough cartridge, I believe this will work fine.  I will polish it a little more with stones before the gun is finished and case hardened.
Bob