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Machining an AR lower from a forging

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  • #16
    vince, did youget pink marpat for log book covers yet?

    I like the pink furnature...the g/f was just oogling a pink framed tupperware pistol th other day at the store...yay!

    Toph
    -- An AR-15, a good, loyal guard dog, and a nymphomaniac that runs a liquor store. The simple life.

    -- All great things are simple, and many can be expressed in single words: freedom, justice, honor, duty, mercy, hope.

    An appeaser is one who feeds a crocodile, hoping it will eat him last.

    --Sir Winston Churchill

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    • #17
      I'm a machinist and I won't put the time into finishing 0% lower. KUDOS!!!! it looks GREAT!!!!!!

      I've spent a lot of years machining aluminum here's a couple of unsolicited suggestions:

      it looks like you machined mostly dry. next time try a light squirt of WD-40. aluminum can be a bear when you're hogging on it and try to stick to your cutters. 7075 isn't as bad as 6061 though. a light coat of WD-40 will do wonders. a lot of machinists swear by a mixture of mineral spirits and kerosene as a lubricant for machining aluminum, but WD-40 does better.

      and 2 flute endmills work a lot better than 4 flute in aluminum. 2 flute endmills have more room for the chip to evacuate thus you can push them harder before you get any galling on the cutter. OSG makes 3 flute aluminum cutting endmills that work even better than 2 flute. the best aluminum endmills are 3 flute solid carbide with geometry designed for aluminum.

      HTH,
      Luv

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      • #18
        [quote]
        I'm a machinist and I won't put the time into finishing 0% lower. KUDOS!!!! it looks GREAT!!!!!!

        I've spent a lot of years machining aluminum here's a couple of unsolicited suggestions:

        it looks like you machined mostly dry. next time try a light squirt of WD-40. aluminum can be a bear when you're hogging on it and try to stick to your cutters. 7075 isn't as bad as 6061 though. a light coat of WD-40 will do wonders. a lot of machinists swear by a mixture of mineral spirits and kerosene as a lubricant for machining aluminum, but WD-40 does better.

        and 2 flute endmills work a lot better than 4 flute in aluminum. 2 flute endmills have more room for the chip to evacuate thus you can push them harder before you get any galling on the cutter. OSG makes 3 flute aluminum cutting endmills that work even better than 2 flute. the best aluminum endmills are 3 flute solid carbide with geometry designed for aluminum.

        HTH,
        Luv[/b]
        Thank you, and yes, it IS pretty time consuming.

        Thanks for your suggestions Luvman, I definitely appreciate it.

        I'll try some WD-40, I've got a 1 gallon can around here someplace. I had considered using lube of some of the ops, but my feeds and speeds are so low, in deference to the lightweight machine, it didn't seem worth the mess. I've seen the mineral oil/kero thing before, but heated with kerosene exclusively for a few years and developed a strong dislike for it's "aroma". I was also having some difficulty with parts moving under pressure, as below, and adding lube seemed like it would take me the wrong way.

        I do have some two flute cutters, and due to the points you raise, did try them at first for many of the cuts. They seemed to hammer at the work excessively (something I'm doing?), and I was/am worried about my work shifting under the clamps.

        The part shifting under pressure has been a bit of a problem, and a friend with quite a bot of experience suggested my parts may be too smooth, so I may try to alter the texture in the future. It occurs mainly when the side of the forging is against the fixture plate, against the angle block. I tried degreasing the parts and clamping pads, which helped a little. The biggest problem is cutting the magwell, and then fire control pocket after doing the mag well, which limits my ability to put extra clamping pressure in that (hollow) area. Might be time to make a press-fit block for the magwell, to keep from clamping partly over the void.

        Except for the (blind) fire control pocket, chip accumulation and recutting the chips hasn't been too bad, but that fire control pocket is a bugger, and unless I pull out and blow it clear each pass, I end up with a LOT of dust EVERYWHERE. I'll try to figure out a way to get a two flute cuter to run more smoothly, maybe I should up the RPMs I using at that point.

        I do have a short three flute cutter for aluminum, and am using that for shallow finish cuts like the pistol grip pocket, which has a corner radius of .250" and the cutter does a great job.

        Thanks for your assistance!
        Ed

        The beatings will continue until morale improves.

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        • #19
          you can only get as rigid as the machine. if your 2 flute cutters seemed to be hammering you might not have been turning them fast enough.

          for example when machining aluminum in a CNC with a rigid setup and a 1/2" endmill my rpm will be somewhere between 7000 and 10,000 RPM with a feed rate between 42 and 100 ipm (inches per minute). averaged out that's about 1 inch of travel per second +/-. when machining aluminum like this you can expect a mirror like finish as long as you can keep the chips away from the tool and the tool well lubricated.

          we both know you can't go that fast with manual machines. seeing your setup what I'd do would be to use a 1/2" cutter and max out the rpm (I'm assuming your mill will do about 2K - 4K RPM). also I'd start my pockets with standard length endmills. due to lack of rigidity I'd only try to go about .050" to .150" depth of cut (as deep as the setup will allow without moving). feed as fast as you're comfortable with. your chips shouldn't be dust but more like little flakes and should want to fly away from the cutter (this won't happen as your pocket depth increases). when you get as deep as you can with a standard length EM then switch to a long flute EM. and of course back off your speed (long flute cutters love to chatter). if....well when the long EM chatters try feeding a little harder. putting more load on the cutter will generally reduce chatter (vibrations).

          one other point: ENDMILLS HATE TO BE PLUNGED STRAIGHT DOWN. PERIOD. to get around this in blind pockets what you can do is start at one end of the pocket and barely touch the cutter to your work. them feed across and at the same time feed down. this should create a 2-5 degree ramp. this is best accomplished with a powerfeed. but can be done just feeding both axis by hand. when you reach your desired depth, feed back to your starting point without changing depth. then rough pocket to the desired size and start another ramp.

          large depths of cut challenge the rigidity of your setup. when dealing with less rigid setups it's normal to want back off speed and feed. metal cutting tools are designed to be run at certain speed and feed ranges which varies with cutter type and material. when cutting above or BELOW these ranges cutter life and surface finish suffer. try backing off your depth of cut first.

          and as you're already learning manual machining is more of an art than a science.

          I hope I've explained this well and that I don't sound critical.

          you've got an excellent looking lower there. you should be proud!!!.....hell I would be if I'd gotten motivated and actually did it. and I'd probably scrap a lower or 2 trying to machine like a CNC

          Luv

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          • #20
            Hey Guys,
            There is a lot of great information in this thread, that I wouldn't want to get lost, so it's been pinned.
            Respectfully,
            Harry
            "It's better to live one day as a lion, than one hundred years as a sheep", Old Roman Proverb.
            "For those who have fought for it, freedom has a flavor the protected will never know", Author Unknown.
            "Cry havoc and let slip the dogs of war!", Shakespeare, Julius Ceaser, Act III, Scene I.

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            • #21
              Hey Ed,

              Brother this is some very nice work. Good to see folks still building projects from scratch.


              Take care, Vern
              "with the patience of an oyster....I watch and wait"

              Training the US, one shooter at a time.






              http://www.centralvirginiatactical.com

              Comment


              • #22
                Harry & Vern, thank you!

                Luvman, I don't take your assistance as being critical. Quite the contrary, I am not very far up the learning curve on this stuff, and your comments are appreciated and make a lot of sense. Thank you.

                The two-flute cutter . . . yes, judging from your comments, I have been turning too slow, WAY too slow. I've sorta been "erring on the side of caution", and using the "high speeds + stupidity = greater damage" theory, so I've been running my regular cutters at less than 1,000 RPM, and my boring head ops have been down around 200. . .

                Funny you should mention bringing down my quill as I advance across the work . . . I have done this a little, especially on the lower I've done for a single shot .50BMG upper (pictured below) where I removed a lot of material on an open cut to remove the unnecessary mag well bulk. Since I hadn't seen it mentioned in the TONS of stuff I've read, I felt like a hack and kept it to myself, LOL.

                Speaking of CNC and AR lowers, there is online program info if you want to make one from billet. The pics there look VERY cool, and one of the partially contoured lower looks as though it's "melting" up out of the bar stock. Those pics are over at CNC Gunsmithing, but I just went over there and the site is down/suspended for some reason. This has happened before, and I suspect there is some lag/inattention to their accounts payable issues. Hopefully, they'll be back up soon. http://www.cncgunsmithing.com/
                There is also CAD/CAM stuff over at the other "HomeGunsmithing" site I linked, but I think you have to be a contributing member to access the best stuff.








                I SERIOUSLY need to figure out this anodizing thing next . . . might have to wait for warmer weather, due to required temps.
                Ed

                The beatings will continue until morale improves.

                Comment


                • #23
                  Well Ed,

                  I can't help with the anodizing part.

                  maybe one day I'll get around to making myself a lower. I doubt it'll be anytime soon. I don't have after hours access to a shop I like I used to. I work as a lead in a production lean environment so I can't just set a machine up for toys unfortunately. maybe one day I'll run across a mill and lathe for the garage.

                  there's nothing wrong with cautious. it shows you're sane. now if you ever find yourself playing with a surface grinder stay cautious. I've always been one to run balls to the wall when I feel it's safe, but surface grinders still make me nervous. I guess all the grinder horror stories my high school shop class teacher told us actually sunk in.

                  if you ever find yourself in KY look me up.

                  I'm Luvman on all the popular gun boards.

                  Comment


                  • #24
                    [quote]
                    Well Ed,

                    I can't help with the anodizing part.[/b]
                    I've researched it pretty deeply, and am getting to the redundant stage. I have suitable power supply, and now need to buy some supplies, containers and tank heaters. Once I'm fully equipped, I'll have to find a way to get my ambient temps up some, and jump into it with some test pieces.

                    maybe one day I'll get around to making myself a lower. I doubt it'll be anytime soon. I don't have after hours access to a shop I like I used to. I work as a lead in a production lean environment so I can't just set a machine up for toys unfortunately. maybe one day I'll run across a mill and lathe for the garage.[/b]
                    I've always wanted a few machine tools too, and ran across a great package deal last winter. I actually sold some scopes to make it work. . . I got the mill, complete with stand, DRO and a slew of attachments & tools, and also bought a small Austrian Emco 8x18 lathe, also heavily accessorized . . . I've been running the mill a lot, but have done nothing with the lathe yet. It's sorta small to do much, and so my "urgency level" is much less. If you sign up and watch that HomeGunsmithing board, there are very often great deals, and the guys there talk about all the cool stuff for sale on EBay too.

                    there's nothing wrong with cautious. it shows you're sane.[/b]
                    We *could* debate that, LOL.

                    now if you ever find yourself playing with a surface grinder stay cautious. I've always been one to run balls to the wall when I feel it's safe, but surface grinders still make me nervous. I guess all the grinder horror stories my high school shop class teacher told us actually sunk in.[/b]
                    Agreed, more like a launcher in many cases, and it there's anything that will suck your hand in any faster than a (wood) molding machine, I reckon it'd be that dang surface grinder. I really haven't had application for one, thankfully.

                    if you ever find yourself in KY look me up.[/b]
                    Thank you, will do. I am actually looking to retire down toward eastern KY, and was down there late Nov looking at property east and south of Lexington. Beautiful area, need to find work though.
                    Ed

                    The beatings will continue until morale improves.

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