Posted: 6/7/2025 6:11:09 PM EDT
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I'm working on an AK that I need to Redrill the trunion and barrel of. Currently the trunion is drilled to 8.6mm as far as I can tell. The barrel is drilled for 7mm. I'd like to Redrill the pair at the proper headspace for 11/32 ream the hole and then sink a 11/32 drill rod into the assembly. I can prepare the drill rod on my lathe, but I've never drilled a hole for a pin before. 1. What size drill bit do I start with in order to finish with an 11/32 drill rod pin. 2. Should my reamer be the true 11/32 or something undersized? Attached File |
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You need to decide what fit you'd like the hole to pin to be, first. Also, what's the exact dim of the pin? Is it .34375 exact, .3438, etc? You'll want to drill ~.020 under your final reamed sized. Which you'll choose based on the fit. If you want a press fit, I'd get a reamer ~.3415. |
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Originally Posted By User55645: You need to decide what fit you'd like the hole to pin to be, first. Also, what's the exact dim of the pin? Is it .34375 exact, .3438, etc? You'll want to drill ~.020 under your final reamed sized. Which you'll choose based on the fit. If you want a press fit, I'd get a reamer ~.3415. Ok got it. So if my fixed dimension is the size of the pin, then I work my way back from there. The rod I have selected is .3438 from mcmaster carr |
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Does this look correct? Attached File |
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Yes, those should be fine. A couple tips/tricks. Use lube/oil when drilling and reaming, obviously. Let the metal cool post-drill, before reaming. Clean the hole up and give it a slight chamfer, on the side you'll push the pin in on. Give the pin a slight chamfer. When cutting the pin (or anything hardened), I always use bare hands so I can feel how hot it's getting. Have a cup of water right there to dunk. You can certainly put the pin in the freezer to chill and contract a bit. I've even used pc duster and liquid propane (because they're cold and readily available) to chill parts more. A press (arbor, hydraulic, etc) is preferred, if needed. Get it set/straight, and go in a smooth and continual motion, not jerking. |
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I've only done press fits on pins a few times. I've never had any luck getting a .002"+ press fit to work well on a pin that small. AFAIK the barrel trunion pin on an AK only needs to be tight enough to prevent the pin walking. If I were doing it I'd take the pin down to .0005" over the actual hole dimension. But I also wouldn't assume necessarily that the reamer will cut exactly on size at the stated dimension simply because I use too many chicom reamers. At $32 that should be a quality reamer and maybe it will. But I'm certainly no expert either. |
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Thabk you for the help everyone, I got this done today and the results are perfect. Attached File |
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