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Posted: 4/29/2016 1:44:26 PM EDT
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I think it's time to get some numbered bits for sizing. I'll never use them as intended (drilling), is there an alternative? High quality gauges that can accurately measure small thicknesses? They have to be kinda long, so I don't know if feeler guages will be narrow enough and / or long enough.
Recommendations? If bits are the way to go, I'll do it. Lot of the cheaper sets are junk though. |
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Quoted:
I think it's time to get some numbered bits for sizing. I'll never use them as intended (drilling), is there an alternative? High quality gauges that can accurately measure small thicknesses? They have to be kinda long, so I don't know if feeler guages will be narrow enough and / or long enough. Recommendations? If bits are the way to go, I'll do it. Lot of the cheaper sets are junk though. What kind of accuracy are you aiming for, +/-.002" or +/-.0002"? Drills can be used as GO-NOGO gauges to a certain degree, for example in a #47 drill goes in, and a #46 drill does not, you know the hole is bigger than .0785" but smaller than .081", you have a range of .0025" |
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If you're trying to measure to accurately determine size, you'll need a very finely graduated set of precision pin gauges. That is not what you'll be doing when measuring the timing for your link.
If (as for your application) you're just trying to determine a fairly small range with reasonable accuracy, then drill bits will work fine - more than fine. Use calipers to determine actual shank size for each, as it can vary somewhat from the listed size depending on the quality of the drill bit set - that gets you an accurate range, regardless of the accuracy of the shank size. |
OP, Dano523 posted up a spec on hammer release a while back: #45 drill bit between bolt carrier and barrel extension - no hammer fall; #43 - hammer fall. You might want to confirm with him, but it sounded like an inexpensive numbered drill set would be good enough to get you running. 
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Quoted:
Can someone give me a "for dummies" rundown of what you are doing with drill bits in here? I have built 7 ARs and have never heard of this. I am not criticizing at all, just genuinely curious about what you guys are doing here. It's for full auto timing - semis need not apply. ETA specifically, measuring (so as to be able to shim or otherwise adjust) the bolt carrier gap at the point of sear release. |
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Quoted:
OP, Dano523 posted up a spec on hammer release a while back: #45 drill bit between bolt carrier and barrel extension - no hammer fall; #43 - hammer fall. You might want to confirm with him, but it sounded like an inexpensive numbered drill set would be good enough to get you running. Thanks. This is the only purpose I'll need it for. I'll look for a set that contains that range. |
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Quoted:
Can someone give me a "for dummies" rundown of what you are doing with drill bits in here? I have built 7 ARs and have never heard of this. I am not criticizing at all, just genuinely curious about what you guys are doing here. As stated, it for the release of the hammer off the auto sear in full auto rigs. Ideally, you looking for a gap of .084" from the face of the carrier, to the face of the barrel extension when the hammer is released. 
Hence as the carrier is just about to touch the face of the barrel extension, with the correct hammer release timing, the round is fired before the carrier has a chance to bounce back off the face of the carrier, and block the firing pin (in the case of the gap being too small and the buffer is not controlling bolt bounce instead). If the gap is larger, then it comes a point of which you are either going to speed up the cycle rate, or if the gap is way too large, then the hammer is going to strike the FP while the back of the carrier still has the FB blocked. As for gauges, standard drill bits work fine, since you are just checking to make sure that the timing is around the .084" range. So #44 (.086") works great as a no go gauge, and #45 (.082) work great as a go gauge. http://www.gearhob.com/eng/design/drill_eng.htm As for adjusting timing, that comes down to either mod'd the auto sear, or the catch shelf on the bottom of the carrier instead. Now this gets a little more complex when you have several uppers that you plan on pulling a single RR lower instead. |
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