Re: Building a Yugo M72

29
lurker wrote: Sun Aug 18, 2019 2:46 pm i don't care about AKs
Wow. Never imagined I would hear that from someone. :lol:

People usually have opinions about AKs.

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It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.

- Franklin D. Roosevelt

Re: Building a Yugo M72

31
With the barrel stubs all depopulated it's time to move back to the receiver and it's dreaded rivets. I did a bit of cleanup on the front trunnion, mainly grinding off some of the leftover spot welds and the outside bits of the long rivet that goes in the bottom front of the trunnion. It still has work and I'm trying to be careful there so no real progress.

Where I haven't worked yet though is the rear section of the receiver. This has the stock, rear trunnion, sling mount and the bits that surround the trigger riveted on, with a really inconvenient chunk taken out where the fire control holes were drilled (I believe this is because those holes were drilled for full auto). The rear trunnion is attached to the remains of the receiver with more of those annoying long rivets on the sides, as well as a short rivet on the bottom (I think this might be unique to RPKs or maybe just to yugo AK pattern rifles). The trigger guard and mag release is held on with 4 short rivets on the front and the rear has two more short rivets. The sling mount is just held on with a piece of sheet metal that is folded through a slot.
right side.jpg
left side.jpg
inside.jpg

Re: Building a Yugo M72

32
Someday I will have a 6 ton press and all the fixtures to make AK's.

I would love to build an M77 .308. Zastava SWEARS they are going to import those again. Someday. Getting a parts kit may be easier.
In a bacon, egg and cheese sandwich the chicken and cow are involved while the pig is committed.

Re: Building a Yugo M72

33
ErikO wrote: Wed Aug 21, 2019 10:48 pm Someday I will have a 6 ton press and all the fixtures to make AK's.

I would love to build an M77 .308. Zastava SWEARS they are going to import those again. Someday. Getting a parts kit may be easier.
If we knew then what we know now.... I would have bought one. I assumed they would be around forever.
It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.

- Franklin D. Roosevelt

Re: Building a Yugo M72

34
Removing the sling mount was easy, just take some small pliers and straighten out the tabs that hold it in then slide it out through the slot. I wish everything about demilling this was this simple.
sling mount.jpg
Getting the rear trunnion out from the receiver is the same as it is for the front trunnion. Flatten the rivets, center punch them (hopefully in the center), drill deeper than the face of the receiver then grind the rivet flat. Then stick the receiver in a vice and pull it off. The same extra spot welds that were on the front trunnion were also present here which makes pulling this thing apart that much harder. But it got done.
rear trunnion.jpg

Re: Building a Yugo M72

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I've been away from this project for a bit due to vacation, and also some frustration with some demilling.

A few weeks ago I was trying to get the rivets out of the rear trunnion, and I failed miserably. One of the issues with eyeballing the center of a rivet is if you try and drill the rivet from both sides you run the risk of missaligning the drill holes, then you end up with a fun disaster like I had where I broke a cobalt drill bit off inside of my rear trunnion. Not even broke off like "Oh just grab it with a pair of pliers and twist it out" either, full on broken off with nothing exposed. I tried some different ideals on how to get it out, including pounding with a hammer, drilling it with a better drill bit (end result, another broken drill bit). In the end I just gave up and bid on a new rear trunnion from gunbroker. I also invested in this tool from ak-builder to help you drill in the center of the rivet: https://ak-builder.com/index.php?dispat ... t_id=30649

Took the new tool, drilled through one side of the new rear trunnion's rivet heads, ground them off and then tried a different technique of pounding the partially drilled rivet out with a punch. This technique worked much better than my old one.
rear rivets.jpg
Once I did the bottom rivets the rear trunnion came out nice and easy (this trunnion wasn't spot welded anywhere near as solid as the old one).
rear trunnion.jpg

Re: Building a Yugo M72

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The last major bit of demilling was taking off the buttstock. This was simple enough, just take off the recoil pad and loosen the bolt that held the stock to the old trunnion.
stock bolt.jpg
Once I undid that a couple good smacks with a hammer and some levering with a screwdriver and the old trunnion popped off.
stock and trunnion.jpg
That basically concludes the demilling process! The only thing left is to drill out the remains of a long rivet in the front trunnion that refused to budge.

Lessons learned so far:
  • If you're demilling a receiver buy the damn AK-Builder rivet tool, it makes everything super simple.
  • Have extra drill bits.
  • Get a 1/2" Brass Punch and a 3# hammer for depopulating the barrel

Re: Building a Yugo M72

39
It's been a bit and there hasn't been much progress on the M72 project. The next big stage is completing the receiver.

A lot of people seem to go with the cheap route for the 80% receiver and buy a flat blank thats been pre-drilled. This requires you to press it into shape, weld on the rails and center support and heat treat it. Thats a lot of work and requires tools I don't have space for. Childer's Guns sells pre-bent, welded and heat treated receiver blanks. These are more like AR-15 80% blanks that need drilling. In this case the holes for the fire control group and selector lever. These are heat treated so drilling the holes should be a great time.

I had this engraved with the yugo lettering for safe, semi and auto, and took it to my local engraver to put the serial from the torched receiver on the new one.

Right Side
IMG_20191009_194657.jpg
On the left side I had childer's engrave the Zastava logo, which it turns out isn't right for this year of M72 but whatever.

Left Side
IMG_20191009_194705.jpg
You can see the insides here. The rails and center support are all preinstalled and welded in. Less work for me.
inside.jpg

Re: Building a Yugo M72

40
At first when I got the receiver blank I thought those nice dimples were where you were going to have to drill the holes. But the location didn't really make sense. It didn't take long to realize that those were the dimples from welding the rails onto the inside of the receiver. Childers to the rescue with a convenient plastic layout guide:
layout guide.jpg
This also comes with holes for the front and rear trunnions but i had those pre-drilled (it actually lacks the M72 front trunnion holes that are on the bulge of the receiver, but those were pre-drilled as well).

The idea here is you line up the guide with the front and top of the receiver, clamp it down, then use a 1/4" transfer punch to mark the center of the hole you need to drill.
clamped on.jpg
I did the center marking (and took pictures) but then I managed to screw up the end cap on my form 1 suppressor by not getting a hole perfectly aligned, which quickly made a fancy titanium cap into a fancy piece of trash. The plastic layout guide isn't meant to be used to guide a drill, but the Form1 forum I frequent gave me an idea and I ordered a set of 1/4" drill bushings. These press nicely into the guide holes and should do a much better job of keeping my drill centered where its supposed to be.

Re: Building a Yugo M72

42
K9s wrote: Wed Oct 23, 2019 11:32 pm With all that work, is it fun? Worth it?
I enjoy having projects to do, even if they end up costing more than I thought they would like this one. I do wonder if I would do this again, probably not for another RPK, but given what I've learned I might do another 80% yugo AK depending on how difficult populating the barrel turns out.

Re: Building a Yugo M72

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Well now its officially a gun I guess!

Drilled the 1/8" pilot holes for the FCG, hammer and selector. The idea of using the drill bushings worked great and all the holes feel lined up when I put a 3/32" bit through them.

Still need to open up the holes to their final sizes, which depends based what the hole is for. Still researching exactly what sizes things should be.
IMG_20191023_221900.jpg
IMG_20191023_221907.jpg

Edit:
Some quick digging found the hole sizes needed:
Ejector Side Drill Sizes
Selector - 5mm (Pre-Drill with 4mm)
Trigger - 7mm (Pre-Drill with 4mm)
Hammer – 7mm (Pre-Drill with 4mm)
Center Support – 4mm

Operator Side Drill Sizes
Selector – 10mm (Pre-Drill with 4mm)
Selector Slot – 7/32” (Pre-Drill with 4mm)
Trigger - 5mm (Pre-Drill with 4mm)
Hammer - 5mm (Pre-Drill with 4mm)
Center Support – 4mm
On the Operator side, the selector slot is finished by removing material between the 10mm Selector hole, and the 7/32” selector slot hole for a final "keyhole" shape.

Re: Building a Yugo M72

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offensivename wrote:
K9s wrote: Wed Oct 23, 2019 11:32 pm With all that work, is it fun? Worth it?
I enjoy having projects to do, even if they end up costing more than I thought they would like this one. I do wonder if I would do this again, probably not for another RPK, but given what I've learned I might do another 80% yugo AK depending on how difficult populating the barrel turns out.
I’m really enjoying watching this. Thank you for the detail and the pictures. Also appreciate your attitude about enjoying projects. I started to go down the road of an 80% lower but I’ve never finalize that decision. One of the reasons is because I recall that I struggled to add a simple dust cover scope rail on a Yugo M92. I haven’t had a problem drilling rear trunnions to add folding stock adapters for example. But when I went to drill that dust cover I managed to put one of the holes where a weld was (That was some hard steel), and then ended up breaking a tap off in the hole that I drilled. I just ground it flat on the inside and left it as the rail covers it from the outside but it drives me crazy knowing it’s there. Between that and a similarly stupid Mosin T53 sight mod project that I attempted, the wind has been taken out of my DIY sails...

I’m vicariously enjoying yours though.

Re: Building a Yugo M72

49
I finished up my form 1 suppressor last week so this is back to being my only project. I went ahead and drilled out the operator side of the receiver to get the holes to their proper size. I still need to cut the metal between the selector hole and the other part of the selector (the big hole to the smaller hole directly forward of it). This is where the selector lever slides in.
IMG_20191112_195629.jpg

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