gunplumber
May 09, 2009, 13:50
Just for the heck of it, I did some inch lightening cuts on my L1A1s with CAI import IMBEL Type III receivers. I do not (yet) offer this service. I consider this "practice" and a way to determine where the issues with cutter types and fixturing will be.
http://www.arizonaresponsesystems.com/wp/falinchcuts-01.jpg
http://www.arizonaresponsesystems.com/wp/falinchcuts-02.jpg
http://www.arizonaresponsesystems.com/wp/falinchcuts-03.jpg
http://www.arizonaresponsesystems.com/wp/falinchcuts-04.jpg
A The upper part of the original cut A is done with a keyway cutter and extends underneath the dust cover rail. I used a 3/8" end mill and didn't go as deep - it ends at the same point as the dustcover rail
B The clearance for the dustcover tabs is done either with the receiver vertical or with a 90 degree milling head, so as to make the bottom part of it a radius. I didn't have the time or interest to fixture it this way. I made the rough cut with a 1/4" ball end mill vertical, followed by a 3/32" end mill to get the front part close to square, then by hand with a 3/32" cutter on a Dremel to blend the two.
C Here the sand cuts are similar but the radii are slightly different. Also note (not labeled) that the long horizontal cut is relatively easy and just reduces the rail in height by 50%
D I left out Cut D because I forgot until I'd already refinished and then figured it wasn't important enough to me to redo.
E E show where my 1" dia x 1/4" keyway cutter differs slightly in contour to the original cutter.
F F is a difference in the metric from the inch where the inch has more material, so no amount of fancy cutting will exactly match. Best I could do was keep the same style.
G On the metric III, G is an angled cut, which I just made square. The cutter used on the original has rounded edges. Mine is square. The closest I could get was to go back over it with a 1/2" ball end mill to at least chamfer the edge. Also notice where it "pulls away" at the end of the cut, the radius is more shallow, indicating a larger diameter cutter on the original
H Inch UK cocking handle grooves are ended with a stress-relieving circle, I left it out (ok, I forgot to do it). Also, the inch cocking handle is slightly thicker - that is, a metric handle will fit on an inch receive with a slight looseness. To put an inch handle on one cut for metric, one mus sand the back of the cocking handle by a few thousandths of an inch - takes me about 4 minutes on the belt sander (careful, it gets hot!). I also welded in the scallop and detent at the end of the rail for the metric cocking handle plunger.
I I shows the limitations of my buddy's engraver. A nice unit, computer controlled, but old and runs off DOS. It does not have anything but one font. I could not do the M/M, or the decimal point centered in 7.62, so I stamped that by hand afterwords. Also, I had some trouble with font height. The program has me determine the length of the characters, and it defaults for height. Since the spaces between characters is wider than the original, they are also shorter.
J This was my first experiment receiver and I'm somewhat proud of it, because it was cut in half (long story) and this entire rear section is made from scratch. Note the weld line. This was a Springfield Armory SAR 48 in .223, so I also welded up the small corner of the SA Logo and the ". . . .oa, IL"that was visible after the mag well outside cut, and the linear cut for the .223 mag catch.
K K shows the rounded receiver ring. I roughed it out with a ball end mill and finished with a 1/2" sanding drum on a Dremel
L The front of the inch pattern mag well has a scallop cut - I did not have the resources (or the machining brilliance) to fixture for this cut, so I approximated it with a 1/2" sanding drum on a Dremel.
M This is the original serial number from the NGL IMBEL, and to avoid altering it, I had to move the lightening cut up a hair and reduce its width. I used to have someone with an uberninja CNC engraver who could deepen the engraving by a few thousandths more than the depth of the cut, so it would still be clear after the fact, but I no longer have that available. This is the primary reason why these cuts are not for every receiver. Location of serial number and other engraving (such as a gear logo) complicate it. ATF used to allow for moving serial numbers (such as to checker a handgun with # on front strap), but recently have gotten really nasty about even mentioning the idea.
http://www.arizonaresponsesystems.com/wp/falinchcuts-01.jpg
http://www.arizonaresponsesystems.com/wp/falinchcuts-02.jpg
http://www.arizonaresponsesystems.com/wp/falinchcuts-03.jpg
http://www.arizonaresponsesystems.com/wp/falinchcuts-04.jpg
A The upper part of the original cut A is done with a keyway cutter and extends underneath the dust cover rail. I used a 3/8" end mill and didn't go as deep - it ends at the same point as the dustcover rail
B The clearance for the dustcover tabs is done either with the receiver vertical or with a 90 degree milling head, so as to make the bottom part of it a radius. I didn't have the time or interest to fixture it this way. I made the rough cut with a 1/4" ball end mill vertical, followed by a 3/32" end mill to get the front part close to square, then by hand with a 3/32" cutter on a Dremel to blend the two.
C Here the sand cuts are similar but the radii are slightly different. Also note (not labeled) that the long horizontal cut is relatively easy and just reduces the rail in height by 50%
D I left out Cut D because I forgot until I'd already refinished and then figured it wasn't important enough to me to redo.
E E show where my 1" dia x 1/4" keyway cutter differs slightly in contour to the original cutter.
F F is a difference in the metric from the inch where the inch has more material, so no amount of fancy cutting will exactly match. Best I could do was keep the same style.
G On the metric III, G is an angled cut, which I just made square. The cutter used on the original has rounded edges. Mine is square. The closest I could get was to go back over it with a 1/2" ball end mill to at least chamfer the edge. Also notice where it "pulls away" at the end of the cut, the radius is more shallow, indicating a larger diameter cutter on the original
H Inch UK cocking handle grooves are ended with a stress-relieving circle, I left it out (ok, I forgot to do it). Also, the inch cocking handle is slightly thicker - that is, a metric handle will fit on an inch receive with a slight looseness. To put an inch handle on one cut for metric, one mus sand the back of the cocking handle by a few thousandths of an inch - takes me about 4 minutes on the belt sander (careful, it gets hot!). I also welded in the scallop and detent at the end of the rail for the metric cocking handle plunger.
I I shows the limitations of my buddy's engraver. A nice unit, computer controlled, but old and runs off DOS. It does not have anything but one font. I could not do the M/M, or the decimal point centered in 7.62, so I stamped that by hand afterwords. Also, I had some trouble with font height. The program has me determine the length of the characters, and it defaults for height. Since the spaces between characters is wider than the original, they are also shorter.
J This was my first experiment receiver and I'm somewhat proud of it, because it was cut in half (long story) and this entire rear section is made from scratch. Note the weld line. This was a Springfield Armory SAR 48 in .223, so I also welded up the small corner of the SA Logo and the ". . . .oa, IL"that was visible after the mag well outside cut, and the linear cut for the .223 mag catch.
K K shows the rounded receiver ring. I roughed it out with a ball end mill and finished with a 1/2" sanding drum on a Dremel
L The front of the inch pattern mag well has a scallop cut - I did not have the resources (or the machining brilliance) to fixture for this cut, so I approximated it with a 1/2" sanding drum on a Dremel.
M This is the original serial number from the NGL IMBEL, and to avoid altering it, I had to move the lightening cut up a hair and reduce its width. I used to have someone with an uberninja CNC engraver who could deepen the engraving by a few thousandths more than the depth of the cut, so it would still be clear after the fact, but I no longer have that available. This is the primary reason why these cuts are not for every receiver. Location of serial number and other engraving (such as a gear logo) complicate it. ATF used to allow for moving serial numbers (such as to checker a handgun with # on front strap), but recently have gotten really nasty about even mentioning the idea.