I've gotten a few requests for information about building on a blank, so I decided to repeat here a post I put on another site which shall remain nameless. The job really isn't so hard. It's just really critical that the FCG holes and Saftey Selector holes end up in the right places. In this post, "Cold Steel Solutions" will be abbreviated, "CSS".


Building a Romanian RPK on a Cold Steel Solutions blank is very similar to building a Yugo on a Cold Steel blank. In fact the blanks are the same. Here's how I do mine:


  1. I start with an AKBuilder flat. I fold it using my flat-bending jig, then clamp the bent flat to the bottom of the CSS blank so the two are PERFECTLY centered. Do NOT use the template that came with your blank. It is wrong. Check and recheck this. Line up the fronts and the sides and disregard whether the backs line up. The flats and the CSS blanks are usually not the same length. I clamp them together with a pair of vise-grips at each end of the blank.

  2. Now I have a set of metal scribes I got from Harborfreight for $4 each. you can get a scribe inexpensively from Home Depot if you want. Use it like a pen to trace on the blank the outline of the magwell and the trigger hole on the flat. Remember that the outlines are backwards. This will not matter on the magwell, but the trigger-hole has a cut-out for the hook, and it will be on the wrong side of the blank. You can either draw it on the other side of the blank or do as I do, and cut two - one on each side. Do the same for the pistol-grip mounting block hole.

  3. Next take a $39 Harborfreight rotary tool (If you don't have one of these yet, get one - and spend the extra $10 for the 1-year warranty. The rotary tools wear out every five to seven AK's, and this way you get the replacement for $10 instead of $40.), and cut out the magwell. When you do this, do not cut close to the line. Leave the line and about 1mm of steel on the blank. This will give you something you can work with later to make sure your magwell is centered. As you cut, watch your cutting wheel, and don't wear them past about 3/4" diameter. You will need the small wheels when you cut out the trigger hole. This part takes about 30 minutes.

  4. At this point your blank is a receiver.

  5. Cut out the trigger guard using the same method. Use the small wheels you kept from the previous step, as the trigger guard hole is too small for a full-sized cutoff wheel. 15 minutes.

  6. For the pistol grip mount hole I drill a hole the same diameter as the narrowest part of the mounting thing hole, then I file it out to the right size. 15 minutes. You do NOT cut this one out when building a Yugo.

  7. Once you have these three holes cut the rest of your build is very similar to building from an AK-builder flat with one HUGE exception: You absolutely must, must, mustget your axis pin holes and safety holes perfectly round and perfectly aligned. To do this, here are some tips:
  8. If you don't already own them, get yourself a set of calipers. It's very difficult to get it right using a ruler, and the consequence of failure is a ruined receiver.

  9. Measure the axis hole from the bent flat receiver and transfer the measurements to the blank.

  10. Always measure from the front of the receiver - NEVER from the back.

  11. Always measure from the same point of reference - always the bottom of the receiver - or always the the top. Me, I use the bottom, because I want my trigger pin to lock up tightly with the shepherd's crook, but it's equally important for the bolt carrier to properly engage the hammer hump. When measuring from the bottom. get a small piece of 1/16" thick Home Depot steel, and hold it flat against the bottom of the receiver, and use your calipers to measure the distance from the bottom of the steel plate to the locations where you will drill your holes. Measure from the flat and transfer to the blank.

  12. When you drill ANY holes in your blank start a pilot hole with the smallest bit your drill will chuck - usually a 1/8" bit. Drill the pilot holes on both sides of the blank, then run a nail or drill bit through both sides. Look at the nail. Is it straight? If it's not you will immediately know.

  13. Remember - for the axis pins the 5mm holes go on the right, and the 7mm holes go on the left. I didn't think I'd have to tell you this, but I just discovered that I do. Ahem!

  14. When you see that you have drilled off-center holes that you will need to fix - and this will happen - don't panic. A simple rat-tail file will let you egg-out the pilot hole in the direction the hole needs to move. Do the same on the other side of the receiver. It's amazing how well you can fix off-center holes with this method. Do not egg either side more than the diameter of the axis pin that will pass through the hole. The axis pin holes have to be perfectly round. Don't use small reamers to file out the holes. They aren't made for this, and you will ruin them. Once the holes are egged-out so they line up, drill out the hole with a bit, then again with a reamer to get perfect axis-pin holes.

  15. The Center Support - When you drill this one do so with a 1/8" bit, and leave it that way. You're going to be welding rails in, and afterwards you're going to have to re-drill these holes to get them through the steel of the lower rails. At that point use the correct sized bit or reamer.
  Riveting on a blank is no different from riveting on a flat. You use the same techniques for lining up the holes. It's easy.
  That's it. The first time I buiilt on a blank it was a bitch, but I had no one to tell me these things. Yours will be considerably easier.


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Order Of Work
   
  Regardless of the build I'm doing - flat or blank - I always use the same order of work. The mistakes of many builds have taught me that this is the correct order, but your mileage may vary. My order of work is:
   
  1) Scribe and cut out magwell, trigger hole, and pistol-grip lug hole if needed.
   
  2) Drill and rivet in trigger guard and safety selector stop.
   
  3) Drill and rivet in front trunnion.
   
  4) Weld in lower rails.
   
  5) Drill and rivet center support.
   
  6) Press in barrel.
   
  7) Drill holes and rivet in rear trunnion.
   
  8) Drill FCG holes. This is really where the rubber meets the road. Do this wrong and everything before it is wasted. Do the hammer first, then the trigger.
   
  9) Drill and file the safety selector holes. This is going to sound dumb, but remember - the big hole goes on the right. I know, I know. It's obvious. Right. I got it wrong on my last build. The thing fit PERFECTLY - except the tongue stuck up instead of down. I had to weld in filler, file it down and smooth it, then re-drill through the hardened weld steel. Ouch!
   
  10) Heat treat the holes and ejector tip.
   
  11) Reassemble and test. A lot.
   
  12) Refinish the metal and wood.
   
Buying Rivets
   
  I've posted this before, but I'm going to do so here again, because it bears repeating.
   
  YOU DON'T HAVE TO BUY YOUR RIVETS AND CENTER SUPPORTS FOR $10 PER SET.
  I've found three sources where I can get all the riveting material I need. I can get about 100 sets of rivets and center support tubes for about $25. Beats the hell out of AK-Builder, and you'll never again get rivets too short. This list includes only one type of long rivet which fits the rear trunnion holes as well as the tubing I list from AircraftSpruce. It is 1.5" long, so you'll have to trim it, and it has a round head, so you'll have to hit it with a Dremel wheel to flatten it for the center support, but it works out to about $0.10 per rivet set which is somewhat cheaper than $9 per set, and you can afford to cut them out and throw them away if you mess up.
  McMaster-Carr
 
Part No Description
97300A100 Plain Steel Round Head Solid Rivet, 5/32" Diameter, 1/4" Length, Approx 250 Pcs/pk
97300A105 Plain Steel Round Head Solid Rivet, 5/32" Diameter, 3/8" Length, Approx 300 Pcs/pk
  Centaur Forge Sells the long rivets
 
Part No Description
532X1-34RI 5/32" x 1-3/4" Round-head Steel Rivets
  Aircraft Spruce sells the center support tubes1
 
Part No Description
03-00300 1/4" Outside diameter x 3/16" or 5/32" Inside Diameter 4130 tubes
  You buy the center support tubing in 1 foot lengths, so you'll have to cut it off using tubing cutters (15 seconds). To get the correct length of the center tube, use your calipers to
 
  1) Measure the width of the rear trunnion.
  2) Measure and sum the thicknesses of the lower rails.
  3) Subtract the summed thicknesses of the rails from the width of the rear trunnion.
  Mark your tube for that length and when you cut the tube, leave the mark. This method is more accurate than using AK-Builder's tubes, because not all trunnions and rails are the same size. Use tubing cutters on the tubes. If you use a saw or rotary tool/cutoff wheel your cuts would be straight, and when you press on the rivet the tube will want to bend.
  The short rivets are the same size as the "long short rivets" you get from AK-Builder. I trim them about 1/8" for the front trunnion using my dremel's cutoff wheel and a pair of pliers, and a hair more for the trigger guards. The long rivets (1-3/4") are too long for the rear trunnion rivets, so I trim them so about 7/32" protrudes. If I didn't egg out my rivet holes the that's just about perfect. On the center support rivet I do the same, make two dome heads, then use my dremel's cutoff wheel to polish down the heads on both sides, so they're just about 1/16" thick. the safety selector clears them perfectly, and they look gorgeous - about 7/32" diameter. Being able to control the length of my rivets has improved my build tremendously.
   
A Build Example
   
  Here's a receiver I'm doing for my M90A build. At the end of 2006 I bought one of the last M90A kits that Centerfire was selling at $200 (Why, oh why didn't I buy more???) I remember asking myself, "Why would anyone want an AK in .223? Oh hell I'll get one just on a lark." The hitch was that they came with only the front-end assembly. No FCG, safety selector, dust cover, trigger guard, stock tang, or stock. The good thing was they were brand new, as in still had the plastic stuck to the handguards. Although the M90A (I think) is designed to be an underfolder, I have plenty of Yugo underfolders, and if I'm going to have a rifle that uses the much-vaunted .223 round I'll be damned if I lose accuracy by building it as an underfolder. I took the stock tang off a Romanian RPK kit that has a shot-out barrel, and I'm going to build this one up as a fixed-stock M90A. I suspect it's going to be really nice when I finish it.
   
  I'm using a Cold Steel Solutions RPK blank with Cold Steel Solutions rails. I made the center support myself out of Aircraft Spruce tubing, and the rivets are all from McMaster-Carr and Centaur Forge. I'd like to point out the axis pins. Lots of guys, building on CSS blanks complain that their axis pins wind up being too short. I encountered the same issue on my first build on a blank. The problem I had was with the AK-Builder center supports I installed. They were made for thinner-walled receivers, so when I installed them in the thicker receiver they spread the walls further than they should have, and I wound up with pins too short. In subsequent builds I've done on blanks I've made my own center support tubes by buying the tubing from AircraftSpruce, then cutting them to length by subtracting the thickness of the lower rails from the width of the rear trunnion. This method has produced three perfect receivers and no need for longer pins. Notice the way the pins fit.
   
 
   
 
   
  The Cold Steel Solutions right-side lower rail extends all the way to the bottom of the receiver and goes for two inches along the right-hand receiver wall. When you put an extra spot weld at the bottom of the receiver you get a massively thick receiver wall almost 3mm thick, and it feels really good. Notice in the photo below how the right-hand lower rail supports both axis pins instead of just the hammer pin. On the other hand you have to mind the length of the center support rivet tube. The center rivet I made using a 1-3/4" long 5/32" domed rivet. I formed a domed head, then ground it flat with my dremel. Instead of the crappy tiny head you get from the AK Builder center support rivet, with a full-sized rivet you get a full-sized head.
   
 
   
  I'd like to point out here the importance of getting your axis pins straight. I've said it before, but in this picture I just finished them. Can you imagine getting to this point in a build, then having to throw away the receiver? Trust me you'll invent new words in your anger. When measuring start with the hammer pin. Put one end of the calipers on the leading edge of the receiver not the leading edge of the front trunnion. These are not always the same. Important point. In the case of the receiver above my initial holes were off by about 0.5mm, so I filed them out until they lined up, and proceeded with the drilling of consecutively larger holes, until my excellent AK-Builder reamers finished the job.
   
  Notice also the massive ejector that Cold Steel Solutions sells. It's longer and thicker which makes me feel better. You can see the tremendous size of the right-hand lower rail as well. Tomorrow I mount the stock tang and drill out the safety selector. After that I mount the barrel and assemble the rifle. Let's see if it works.