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Posted: 7/17/2011 4:28:46 PM EDT
| A friend asked me to post this. He did an 80% lower using the TM jig set. When he drilled the trigger or hammer pin, do not recall which, it was not perpendicular to the lower, he said one side was .07 " different from the other. Can he egg out the bad side and use KNS pins and maybe some alumaweld to fix this? He will also contact TM. And yes, it is a friend, not me. |
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70 thousanths is a ton.
a millimeter and a half. if it didn't function, or even if it does, i would consider tig welding the hole. after all you're right there machining the pocket anyway. and the out side would be a breeze. but then, how much can you pay a welder to fix a $69 lower? even using .170 Colt fcg parts wpould get expensive. finish it and try it. but try the crap out of it, i would be concerned with walking pins. it may work fine, then go ahead on. |
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Quoted:
I agree on the welding bit––would be the best route. Do you know how it got off that much using the jig??? Easy to do with an inexpensive drill press. If the drill bit isn't exactly square to the table, and you try to drill all the way through in one operation, you can get that much error. I ruined a Colfax lower on a Harbor Freight drill press that way. Strangely, my first 80% I did with no jig and no drill press That was one of the "old" style where the safety selector hole was already drilled. A dremel, some files, sandpaper, and a set of calipers was enough. I used a stripped S&W lower as a guide to mark the hammer and trigger pin holes, and drilled 'em by hand. Everything worked out just fine. Then I got the HF drill press, thinking I'd save a lot of time and effort. Bad move. |
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I wouldn't try to egg out the hole and fill it behind it, I'd make a small bushing, mill out a tight pocket for it and then epoxy the bushing in place. That will give a lot more surface area to bond and won't end up with the pin putting a lot of pressure on the back-filled epoxy. Think of it as kind of a non-threaded helicoil.
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This bushing and pin set might help. I have never used them. Just a thought.
TRIGGER BUSHING & HEX HEAD PIN ASSEMBLY |
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Quoted:
This bushing and pin set might help. I have never used them. Just a thought. TRIGGER BUSHING & HEX HEAD PIN ASSEMBLY Now that I know that kit exists, that moves to #1 on my ideal repair method list. With that kit you won't have to explain why there's a funny looking round birthmark on the lower; you can refer to your high-tech, low-friction, custom fire control group installation! ETA: I take back some of my initial enthusiasm because the bushing installation requires an odd-sized and difficult to find 1/4 x 40 tap, which they will also sell you for another $24.99, making the whole repair kit about $50 to your door. |
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I think I know which vendor I would buy that tap from! |
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I don't know why your friend is going to complain to the vendor, he simply had his setup out of square or not lined up.
Remember, if you go through a drill guide that's off center, it will force the drill to bend farther and farther the deeper you go. This isn't a jig issue, it's a poor workmanship issue. Precision machining usually involves thousands of dollars of milling machine, vises, blocks, digital readouts and indicators. How anyone truly expects to get perfection out of a jig and a clapped out drill press is beyond me. Hell, I HAVE all the aforementioned stuff and still have issues. |
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Whoops! That is not going to be a straightforward fix. There's no way to redrill it straight even going to oversized pins. 0.070 is far outside the boundary of an oversized pin anyway.
Let me point out also that 7075 cannot be successfully welded. Period. I just fixed a misdrilled hammer pin for a friend. It was perpendicular, but 0.034" displaced on the X axis. My solution was to overbore with a 1/4" center cutting end mill on the correct axis, then drill it out and tap it to 5/16 x 32 TPI (BIG hole). I made matching threaded plugs on the lathe using 7075 rod stock and ran them in with the threads coated with epoxy. I ran several experiments beforehand and tried red Loctite, but I think epoxy does a better job of filling and locking the threads in this case. After several days of curing, I machined the excess down, filed smooth, re-drilled, reamed, sandblasted and refinished. I'm confident that the repairs will last, but I wouldn't use the receiver for "life support" if you know what I mean. The repairs are undetectable to the touch, but the thread boundaries can be seen in the right light. The bushings above might be OK, but I think my method is better because it allows standard parts to be used and can only be detected on close inspection. Here is the patched lower under 3 coats of Molyresin with lighting to enhance its visibility: 
And this is the final test I did on a piece of scrap prior to cutting on the lower with normal lighting: 
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