ARS NOTES.
BUILDING AN AK-74
(updated 10-06-2009)
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Introduction | |
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This tutorial is for building an AK-74 from a Bulgarian parts kit and a NoDak Spud NDS-2 or NDS-2SF receiver. I recommend you also read my AK-47 (AKM) tutorial as this one builds on the other. The principles are the same, but I made some improvements to my tools and techniques in this one.
While there are many principles that are applicable to other receivers and parts kits, some of the specifics of this tutorial are unique to the NDS-2 and NDS-2SF receivers. This is not the only way to build an AK, but it is the way I have found to be most time and cost effective. I developed these instructions through my experience with over 500 AK builds. My goal was to arrive at the most time and cost effective procedure that would maintain the superb quality standards for which Arizona Response Systems is famous. Many of the tools you will see are not cost-effective for building just one or two rifles. This is the greatest stumbling block for the home hobby builder. The tools necessary to do an excellent job are expensive to purchase and require complete machining capability to fabricate. One would need to build at least 5 high quality AKs to break even on the tooling cost compared to purchasing complete rifles from a reputable manufacturer. For this reason, I do not recommend building an AK yourself if your sole purpose is to "save money". You won't. If on the other hand, you enjoy this kind of work and the satisfaction of doing it yourself is worth the higher cost, you will find building an AK to be a fun and challenging experience. This tutorial is protected under Federal Copyright Laws. You may provide a link to it, but you may not publish it elsewhere. If you have suggestions for improving this tutorial, or something is unclear, please e-mail me and I will see about editing it. Do not call or e-mail me for help with your build. This tutorial does not cover folding an AK flat. With the exception of those folding flats purely for the challenge, I consider folding your own flat to be a gross waste of time and money. When an Economy NDS-3 receiver can be purchased for $50, and a Premium NDS-1 or NDS-2 for $85, it makes no sense to me to buy a bunch of additional equipment and then struggle through the most difficult and critical part of the build, and then have to pay to have it properly heat treated. For best results, I recommend you follow the sequence in this tutorial - while some steps can be done in a different order, others cannot. Make sure that the finished rifle will comply with all federal, state and local laws. Use appropriate safety equipment, particularly eye protection.
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"Alternative" Build Methods | |
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You may have come across some people claiming to have an easier "alternative" to correctly riveting an AK. One such notion is the "Screw Build". This is not an equally valid alternative but a fundamentally unsafe method used by ignorant fools who cannot grasp the differences in application for different types of fasteners. That a particular grade of button-head cap screw may be "harder" or "stronger" than a comparable rivet misses the point of application. During firing an AK will flex across all thee planes, yaws and is subjected to significant rotational forces and harmonics. Screws are a completely inappropriate fastener for this type of strain. Rivets, in contrast, are ideally suited.
Another method advanced by some unwilling to build an AK correctly is welding. There are guns that are welded, such as the HK, Uzi, and AR-70. Welding in and of itself is not an inappropriate method for attaching a sheet metal receiver to a machined trunion, but doing it safely with the proper depth of penetration, requires a high level of skill and equipment. It cannot be done safely with a Stick or MIG welder. An experienced TIG welder with appropriate heat treating and normalizing ovens can possibly obtain satisfactory results. I emphatically recommend against it.
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Demilling Parts Kit | |
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The term "Demiling" comes from "DeMilitarizing" or turning a military (restricted) part into something that can be sold on the open market. The Romanian AKM-47 rifle, as a machinegun, may not be imported into the US for commercial sales. An importer can "demilitarize" the rifle in a customs warehouse by torch-cutting the receiver into at least 3 pieces. The result is not a classified as a firearm under US law and can be sold with no restrictions. We must continue the demiling process to reduce the cut rifle to usable components. Demiling correctly is an important part of a successful build and likely the most time-consuming task. Improper demiling can create greater difficulties later.
Since the demiling process is essentially the same for all AK types, I have moved it to its own page.
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Riveting Front Trunion | |
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Unlike the AK-47/AKM and the Romanian AK-74, The Bulgarian AK-74 has a 8-1/2 degree angle to the left side of the front trunion. |
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I began holding it with 9 degrees of angle blocks, but this wasn't quite right and it was time consuming. |
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I ended up making a small fixture that matched the 8-1/2 degree angle so I could clamp the trunion for drilling the right side holes. |
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There are three critical dimensions on this fixture. It must not interfere with sliding the receiver on. The 8-1/2 degree angle must match, and it must not protrude past the front of the trunion. |
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Trunion with fixture mounted in mill vise, and showing the necessary gap. This is only necessary for the right side holes. |
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Align with hole. |
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Slide receiver on and drill |
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The holes for the left side do not require a fixture as there is plenty of clamping area. Align with hole and drill |
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Align with hole and drill |
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Align the bottom rear hole, slide receiver on and drill. |
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Due to subtle variations in the location of the holes from one trunion to another, it is important when doing multiple receivers to keep the trunions matched with their receivers. |
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Using a rotary tool, deburr the inside of the holes. Using your squeeze, install the rivets as shown in the AK-47 (AKM) Build Tutorial. Front one side, then front other side. Then middle, then rear. Alternating sides reduces receiver twist. |
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It is imperative the rivet sit flush before compression. Any cant of the first rivet will cause the trunion to move inside the receiver, and on a subsequent rivet, to result in a canted rivet head. |
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I did a poor job in seating this rivet, and part of the shaft expanded on the outside of the receiver. The only fix is to remove it and try again. When we did the original kit remill, there was no concern for marring the cut receiver sections, but now there is. That is why any time spent getting the rivets right the first time is much better than removing and redoing - there is significant opportunity to mar the receiver in removing a rivet. |
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I fixture the receiver in the endmill and cut the rivet head off. This also helps identify the exact center of the rivet for the next step. |
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align on the center of the rivet and drill through. If you have any doubt that you have found the exact center, use an undersize drill. You do not want to enlarge the hole in the trunion or the receiver. |
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new rivet seated correctly
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Riveting Rear Trunion | |
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This is my "old" method. Index mill or drill press to hole location, slide receiver on, mark hole location, remove from trunion and clamp receiver with support block and drill. The problem is with marking the hole location with a drill,the tip (even a split-point) wants to wander when it touches the hardened receiver. Even using a carbide endmill for marking and clamping the receiver to the trunion allowed for some wandering. Since hole location is critical, I'd drill undersize to give me a little wiggle room later. |
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Secure the rear trunion in mill vise or drill press by inserting a scrap piece of 3/8" square bar stock inside the tang. Align the end mill or drill with the back rear trunion hole. |
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Slide the receiver on and clamp. Mark the location of the hole. Do not drill through yet. |
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slide receiver off, and align on front rear trunion hole, slide receiver back on, clamp and mark hole location |
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clamp receiver in vise with a 5 degree angle block, being careful not to crush the swell on one side of the trigger opening. Insert a piece of wood or metal to support the receiver. |
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drill holes through with a cobalt or harder bit. On a Bulgarian, the front trunion hole is 4mm, slightly smaller than the 4.2mm rear hole. |
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The above method gave me a few problems. The rear trunion would cant downward under the pressure of the bit - I just couldn't clamp it tight enough not to move and even a slight movement will interfere with the exact fit of the rivets. My solution was to make my 3/8" scrap metal holder a little more intricate. |
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After rounding the front on a belt sander and cutting a relief hole for the raised mold mark, I welded two more pieces of 3/8" square bar stock to the sides, with a clearance for the 12 degree angle of the tang. I drilled some holes in a piece of flat stock and milled it to be just a few thousandths lower than the tang. Now when I clamp it, there is greater surface area for friction and the parallel sides allow me align it off the bottom of the vise. |
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Fixture with trunion in vise.This method worked so well I could drill while fixtured, instead of marking and drilling as two separate operations. A new cobalt drill bit cost $4 and was good for about 10 holes. I bought some carbide 2-flute chisel point bits at $14 each. They were good for 50 holes at 600 rpms (less at higher speeds) and once I fought my way through 80 holes on one bit, although the cost versus time ratio rapidly diminished as the bit dulled after 50 holes. Remember the front hole is smaller, so stop once you're through the receiver - don't enlarge the rivet hole in the trunion. |
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I did need to support the rest of the receiver during drilling with this screw jack, but it was firm enough to eliminate the clamp and just hold with my fingers. A big time saver in production work. |
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deburr the holes from the inside. The duller the bit, the more flaring you will have around the inside of the hole that will need to be removed. |
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clamp the receiver to the trunion. A C clamp will work, but parallel clamps work better. Make sure the upper rolled edges of the receiver fit into the grooves of the trunion. If not, chase the trunion grooves with a small cut-off wheel on a rotary tool. |
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Even with great care in the previous steps, there is an occasional hole that is misaligned. As long as the hole will be covered by the rivet head, it is okay to slightly oval the hole in the receiver (not the trunion) to obtain proper alignment. |
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Chase the hole with a 4mm or 5/32" drill. It is important that the rivet sit flat. The slightest angle will cause the receiver to shift when the rivet is compressed. |
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The Bulgarian trunion is countersunk and rivets with a "v" neck are superior to those with a flat neck because they draw the receiver into the trunion and transfer the shear force from the rivet shank to the trunion. On some of the receivers on the market that are not heat treated, the metal will draw nicely into the countersink. On NDS receivers, which are slightly harder than some of the original receivers I've tested, a small chamfer around the hole will help pull the receiver in. |
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ready for rivet |
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insert rivet |
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I am using a pneumatic squeeze. There are directions on the internet for modifying bolt-cutters to obtain a similar squeezing action. |
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perfect rivet |
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once the front rivets are in, remove the clamp, and chase and chamfer the rear hole as needed. I found my 11/64" drill bit to be a tight fit (which is good) on my AKbuilder.com rivets, so I clamp the receiver in a vise and tap the rivet in with a small hammer. It is important to get a full seat of the rivet before moving to the press. |
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I made several adjustments to my tooling from when I did the AK-47 (AKM) build tutorial. One thing I did was to make a holder for the components. This is more than a "gee that's nice" because I have difficulty maintaining concentration in tedious, repetition (Classic ADD/ADHD). This way I have less chance of accidently drawing the wrong ram. I also put a high polish on my top receiver support, which eliminated the need for using a non-marring washer. Finally, I re-did the bottom receiver support to precisely match the rivet location and depth. This eliminated the need for a starter block and a finish block. |
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set up with press |
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close-up of improved top and bottom support plates. A parallel support plate reduced my "bent" rivets (previously 1 in 10) by half. |
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improving my top and bottom plate kept the receiver in perfect perpendicularity with the ram and eliminated the need for forming the third (partial form) ram |
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I had to chamfer the end of the clamping bolt to clear the hinge on a triangle side-folding stock. I found that this made it wedge into the top receiver support plate and made withdrawing the centering ram difficult. It also started to gouge my top reiver support plate. So I made a second one without the chamfer. The more material bearing on the plate, the better. |
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This is a minor time saver for production work. By marking the side of my press with a line, I avoided raising the press more than was necessary to fit the next ram in. |
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Use the alignment ram to center on the rivet. Slide on the top support plate around the alignment ram. Tighten down the clamping nut with a wrench to snug. Withdraw the ram. This became another unexpected time saver. With the top and bottom plate polished and in exact perpendicularity to the ram, I could leave the clamp in place for the whole operation. Insert the flat ram and compress the rivet half way. On my unit, that was 3-1/3 pumps on the jack. This is an important step, and instituting this intermediate step greatly reduces the chance of a rivet bending sideways as it compresses. By expanding the rivet shaft before forming the rivet head, the now-larger shank doesn't have the same tendency to bend when you use the head-forming ram. The clamping bolt will often need retightening at this point, as the other side of the rivet has also drawn into the receiver slightly. Tighten before removing tension from the press. Insert the head-forming ram and compress. On my unit, this is an additional 3-1/2 to 4 pumps. Remove parts and inspect. |
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Occasionally there will still be a slight lip on the receiver or trunion. This is a good time to remove it, as it may prevent the stock from fitting properly. |
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I have found a series of Bulgarian rear trunions marked #1-#5. I am unable to determine a pattern to the slight dimensional differences - that is, #3 may have a dimension larger than #1, but #5 has this dimension the same as #1. I suspect these are to identify the mold that made them, and not related to size.
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Additional Receiver Prep | |
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Installing US Gas Piston | |
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Riveting Trigger Guard and Adjusting Magazine Fit | |
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Installing Barrel and Checking Headspace | |
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Metal Finishing | |
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Since the metal refinishing process is essentially the same for all rifles, I have moved the metal refinishing section to
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Since the wood refinishing is essentially the same for all rifle, I have moved the wood refinishing section to Refinishing AK-74 (AKM) Furniture
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Finished Rifle Images | |
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Black furniture |
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Bulgarian blond furniture |
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Plum furniture |
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East German furniture with folding stock |
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Romanian Red furniture (from the AKM build tutorial) |
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black furniture with Ultimak rail and Konus red-dot sight.
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