M*CARBO Brotherhood

Router or drill press?

Elgin . you only have to have one ruined by a apprentice to make it worthwhile to remove box and lockup when you dont need it . sames as my 12"X12" marble lapping block…

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Router for cutting and drill press for safety and trigger pins. If I built any I’d use a 5d tactical pro jig :wink:. If I built one I might have messed up one set of trigger pin holes. All ifs and asking for a friend.

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Another difference I noticed is the drawing you posted uses a 3/8" end mill whereas the one I used shows a 7/16 end mill for the FCP. Once again leaving slightly more material. The difference in corner radius would be 0.1875 and 0.2188. Theoretically the larger end mill and corner radiuses will concentrate stress less in the corners making it stronger and less likely to crack.

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OK, true in theory, however cracks will likely happen where the material is at it’s “Least” so doubtful it would ever crack in the radius. Never actually had a frame crack so just speculating. Maybe I’ll look around and find out what is actually “Mil-spec” as far as radius and the material between the takedown pocket and the safety lever.

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Stress concentrates in corners, the sharper the corner, the greater it concentrates. I’m no mechanical engineer, just going by experience in a retaining ring/bearing I manufactured for a company years ago. The part was originally designed with a 1/64 (.0156R)inside corner radius and was having failures in the field. Engineers changed that radius to 1/32 (.0312R) and there was never another failure. I would have never believed such a minor change would have solved the problem. In the case of the lower, I really don’t think it will make a difference. Just past experience tells me to take away the least amount of material as possible.

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You know, that’s something I’m going to check on the 5D next time I have it out, the bit diameter does not really set the radius, the jig does. Curious what it’s giving me, since the subject came up.

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on the 80% jig the collar on the guideplate on the router and the top plate on the jig set the radius.

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Yes, just wondered what that radius was.
It can’t be less then the collar or guide but it could be more.
Here is a great guide 0% forging and a mini mill, and yes, 7/16 diameter at the corners of the fcg pocket

www.arlower.ray-vin.com

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I use a small cnc mill for this stuff so the program generates the radii. I have the original prints in pdf form and it shows the fcg corner radii as .4375" and the filet radii as .015". It is better to sink the selector holes before maching the pocket. Keeps the drill from walking.

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Yes, if using a jig and a router or a cnc mill you can generate a radius larger than the cutting tool used. On a manual mill it is pretty damn tough to generate a perfect radius as your X and y axis moves would have to be perfectly in sync to generate a perfect radius.

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manual mills are the reason i still believe that some of us as a species should have been born with three hands. :+1: :+1: :+1: :+1: :crazy_face: :smiling_imp:

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Yup, but I enjoy running a manual mill more than any of my CNC equipment. That sense of accomplishment when that perfect part comes off the machine is hard to beat.

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like the first time you cut a perfect circle without a rotary tables…within .0005 of course…

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I had a brain fart when I said the fcg had .437 radius. It is actually half of that which is .218". To form the radius would require a 7/16" endmill.(within a few thousandths of an inch). Sorry about the screw up.

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@GinNC, I understood what you meant.

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