Right Side Plate CNC build

[Karl_T]

I'm building a 1928 Colt Browning machine Gun (semi auto only) from a parts kit. Look on the lower right on this web page to see a finished item. http://browningmgs.com/Images_1919A4/Brownings.htm

This thread shows how to make the right side plate from scratch. FYI, this part is considered the receiver and is always destroyed when buying a parts kit.

The first job is getting a piece of stock ready. It has to be 14.47 long by 4.07 wide by .250 thick and FLAT. One side needs a mirror finish. The flat requirement has proven to be a real problem in the past, machine metal off and the part becomes a banana due to relieving stresses in the metal.

1) started with 3/8 HSLA plate stock and ruff sawed

2) Cut both edges parallel in the manual mill.

3) mount part in soft jaws and face 0.040" off both sides, gets rid of nearly all stress. Unclamp part and you have a banana. With this stock, bow was about 0.010"

4) remove 0.005" at a time with a fly cutter. Flip part and repeat until metal is flat and perfect on at least one side. Not shown, final cut uses the face mill again to get to 0.250 thickness.

 

[Karl_T]

OK, the real job is getting a correctly designed part. Can be a real challenge when there's no such thing as a print. In this case, I bought a partially completed RSP that had several minor problems. I measured the heck out of it and then resold it a couple days later. Couple years ago I did an FN30 and had to design from pics and estimating what it must be.

I use draftsight X64 to get as much detail as possible.

I hand Gcode but use draftsight for tool paths. this is done by creating a layer for each tool and drawing the exact path for it to run. Really quite easy once you're done this a few times. The layer is saved to a .dxf file and put into a .dxf to gcode converter. I use NCplot, purchased very cheaply years ago when the product was being developed and the author needed beta testers.

In a great many cases the same tool path is run several times at increasing depth each pass. This is hand gcoded using "parametric programming". Fancy word for just running the same code segment many times while increasing Z depth each pass.

Slots are a special case. experience has taught me to program a slot with a center line and offset amount, then loop the code several times to depth. This makes it extremely easy to make fine tuning adjustments right at the machine. Look in the slot program for how to use variables in gcode.

From this beginning gcode, "part 1" is made. It is for seed as many small errors are to be expected. With this gcode method an adjustment is made right at the control, no need to go back to design.

This job was done with nine tools. The face mill and fly cutter in the manual machine. Five drills and four endmills in the CNC. ThIs CNC is set up to adjust the table height for each tool change.

 

[Karl_T]

OK here's some CNC machine porn:

 

[Karl_T]

Here's the deburred part all fit together to double check its all in spec.

Still a bit more machine work to do before assembling the weapon but nothing major.

 

[sd624]

Nice work Karl. I need to get me a CNC setup. Either a new setup or convert one of my Bridgeport's over to it.

 

[barlow l]

What a gorgeous weapon. Going to turn heads at the range! Are you making the SA trigger and sear?

 

[MarkStephen]

Very nice. Not having a known good drawing and the lack of a proper sized mill has kept me from building one of these kits. I can remember when they were going for ~$200.00 a pop.

A bit more pricy than that today. anic:

Mark

 

[Karl_T]

Had a request for the drawings. here ya go