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Discussion Starter · #42 ·
I have drilled virgin trunnions and it wasn't too bad, but he's using 4140 billet (probably the "pre hardened" type) instead of a forging. I don't use much 4140 in my shop, but I have found it pretty tough to drill and machine. You have to run at slow rpm and peck drill with good pressure to make sure you cut chips and not try to "rub your way through". If you fart around and dwell too long you'll work harden it, and that will make it even more difficult.

I havent found that machining 4140 isnt any harder then say 304 SS, all of my tools are carbide and most are coolant through. Say on like a drill (10mm) I am running 190sft and .003 per rev no pecking, breaking nice chips and cant hear the tool going in.

312285
 

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Helical lugs meaning that the lugs are more or less a section of a screw thread. 3mm pitch in this case.
312288


312289


The prints I posted earlier in the thread are the original 1968 Izzy prints, they're amazingly useful. Some of it is hard to read because of transcribing the Izzy factory dude's handwriting, figuring out which letters he meant, and then translating that to English, but I got it done and made a pretty model.

I've attached my model for anyone that wants to play with it. I must stress, verify everything. I'm pretty sure it's a good model, I've been doing this for a while, but we're talking about little pieces of metal that contain explosions next to people's faces. I'm probably missing a few small fillets and edge breaks here or there too, it's easy to get lost in the prints when looking for those.

Link here
 

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Discussion Starter · #44 ·
I cant access it without a password, I will go over, I didnt know there was a pitch on that I knew it was offset but I should be able to mill that in. Its hard to have everything modeled because when you cam it out at least for me in fusion I need chamfers to not be there in order to actually make my tooling cut it correctly.

Thanks for the help!!

Helical lugs meaning that the lugs are more or less a section of a screw thread. 3mm pitch in this case.
View attachment 312288

View attachment 312289

The prints I posted earlier in the thread are the original 1968 Izzy prints, they're amazingly useful. Some of it is hard to read because of transcribing the Izzy factory dude's handwriting, figuring out which letters he meant, and then translating that to English, but I got it done and made a pretty model.

I've attached my model for anyone that wants to play with it. I must stress, verify everything. I'm pretty sure it's a good model, I've been doing this for a while, but we're talking about little pieces of metal that contain explosions next to people's faces. I'm probably missing a few small fillets and edge breaks here or there too, it's easy to get lost in the prints when looking for those.

Link here
 

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Ah yeah looks like the link broke. I will have to fix it later when I get home, sorry about that. It's on my personal site and I'm still learning the ropes.

EDIT: Okay I think it's fixed.
 

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I havent found that machining 4140 isnt any harder then say 304 SS, all of my tools are carbide and most are coolant through. Say on like a drill (10mm) I am running 190sft and .003 per rev no pecking, breaking nice chips and cant hear the tool going in.
No, 4140 is not a problem in a machine shop, I was talking about the average builder with a drill press and drill bits from Lowe's. IMO, it's easy to get the holes aligned when you drill a receiver, so I would prefer one that's already drilled. Drilling the barrel pin hole accurately can be tough enough unless you have a sturdy drill press or a milling machine.
 

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Discussion Starter · #47 ·
I dont mind putting the holes in it, I just know AK purists wont want them in it although they wont want a billet trunnion either.

No, 4140 is not a problem in a machine shop, I was talking about the average builder with a drill press and drill bits from Lowe's. IMO, it's easy to get the holes aligned when you drill a receiver, so I would prefer one that's already drilled. Drilling the barrel pin hole accurately can be tough enough unless you have a sturdy drill press or a milling machine.
 
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