thud
02-10-2004, 09:28 PM
Well, I finally got it done.
http://home.earthlink.net/~kono3082/images/TAPCO flat AK build 01.JPG
The receiver is a TAPCO flat that I folded. The stock is a Galil that I got from FAC; it's welded open, so it's legal. I have dubbed it "the kit from hell", not because of the TAPCO flat (that was easy), but because of everything else that went wrong with the build.
Folding the flat was the easy part. I'll post something about the folding jigs when I get a couple of bugs worked out. The initial fold (the bottom fold) was easy. The top rail folds were more difficult and caused the jig to deform (hence, the bugs to be worked out). I heat treated the entire receiver, which indirectly caused many problems (see below). I plug welded the two lower rails and filled and redrilled the hole for the hammer pivot pin on the lower rail. A lot of adjusting was needed to get the bolt to slide properly.
After consulting with a few un-named experts (who really are experts), I decided that I needed to heat treat the entire receiver. Actually, I don't think that full heat treating is necessary for the average person; we just don't put that much stress on the rifle. To reduce the amount of scaling, I decided to coat the receiver with a mixture of borax, boric acid, and iron oxide (its a flux used in brazing). I brought the receiver up to 1600 deg F and quenched it in water; I then immediately tempered the receiver at 900 deg F and air cooled. I should have removed the flux before I tempered; the flux mixed with the quench water, formed an acid, and etched the steel, and I got shallow pitting ALL over the receiver (less than 0.001 inch deep but it looked like shit). Testing later showed that all I needed to do was preheat the furnace to 1600 deg F, place the receiver inside for about 5 minutes and quench. The amount of scale formed is minimal, and I didn't need the flux (anti-scaling). I ended up spraying the receiver with an automotive filling primer to fill the etching.
Heat treating the holes (trigger and hammer) is easy, if you have a MAPP torch. Heat the hole to a bright straw or yellow color and immediately quench in water. Do that to each hole. Next, brighten up each hole with 400 grit sandpaper; with the metal around the hole "shiny" you can easily see the color change when tempering. Again, with the MAPP torch reheat the whole side of the receiver slowly (keep the torch 6 inches or so away and play the flame back and forth across a wide area) until the bright metal turns dull dark grey; let cool at room temperature. You are done.
I made a set of go/no-go gauges from cherry picked, long Wolf brand cartridges. I epoxied a 0.005 inch shim to the longest one and used the next longest one to set the headspacing.
I pressed the barrel to the slot originally set in the trunnion; this turned out to be 0.20 too big, so out came the barrel again. I welded over the slot and ground down the weld, then polished the barrel where it fit the trunnion. I repressed the barrel and set the headspace. I then redrilled the barrel through the trunnion and used the original pin to pin the barrel. My un-named experts (see above) warned me that I needed a sharp drill to redrill the barrel. My Drill Doctor kept the bit sharp; I had to sharpen it twice. After all this I found a small crack in the trunnion radiating up through the guide ears for the rear sight (just where the pin comes out of the trunnion). This area is not subjected to major stress during firing, but it is a concern. I did a complete penetration
weld over the crack and will watch this area very carefully for the first 1000 rounds.
I built the adaptor for the Galil stock, but that is a whole different story.
I also built a jig to stamp out a serial number on the receiver along with the caliber. That was partially successful and cost way too much in time and effort.
I finished the rifle by parkerizing it and GunKoting it. I used the satin black GunKote.
I am going to go back and add three 12 oz tinners rivets to each side rail. I just don't trust the plug welds. The rivets will just add additional strength to the alignment of the rails.
http://home.earthlink.net/~kono3082/images/TAPCO flat AK build 01.JPG
The receiver is a TAPCO flat that I folded. The stock is a Galil that I got from FAC; it's welded open, so it's legal. I have dubbed it "the kit from hell", not because of the TAPCO flat (that was easy), but because of everything else that went wrong with the build.
Folding the flat was the easy part. I'll post something about the folding jigs when I get a couple of bugs worked out. The initial fold (the bottom fold) was easy. The top rail folds were more difficult and caused the jig to deform (hence, the bugs to be worked out). I heat treated the entire receiver, which indirectly caused many problems (see below). I plug welded the two lower rails and filled and redrilled the hole for the hammer pivot pin on the lower rail. A lot of adjusting was needed to get the bolt to slide properly.
After consulting with a few un-named experts (who really are experts), I decided that I needed to heat treat the entire receiver. Actually, I don't think that full heat treating is necessary for the average person; we just don't put that much stress on the rifle. To reduce the amount of scaling, I decided to coat the receiver with a mixture of borax, boric acid, and iron oxide (its a flux used in brazing). I brought the receiver up to 1600 deg F and quenched it in water; I then immediately tempered the receiver at 900 deg F and air cooled. I should have removed the flux before I tempered; the flux mixed with the quench water, formed an acid, and etched the steel, and I got shallow pitting ALL over the receiver (less than 0.001 inch deep but it looked like shit). Testing later showed that all I needed to do was preheat the furnace to 1600 deg F, place the receiver inside for about 5 minutes and quench. The amount of scale formed is minimal, and I didn't need the flux (anti-scaling). I ended up spraying the receiver with an automotive filling primer to fill the etching.
Heat treating the holes (trigger and hammer) is easy, if you have a MAPP torch. Heat the hole to a bright straw or yellow color and immediately quench in water. Do that to each hole. Next, brighten up each hole with 400 grit sandpaper; with the metal around the hole "shiny" you can easily see the color change when tempering. Again, with the MAPP torch reheat the whole side of the receiver slowly (keep the torch 6 inches or so away and play the flame back and forth across a wide area) until the bright metal turns dull dark grey; let cool at room temperature. You are done.
I made a set of go/no-go gauges from cherry picked, long Wolf brand cartridges. I epoxied a 0.005 inch shim to the longest one and used the next longest one to set the headspacing.
I pressed the barrel to the slot originally set in the trunnion; this turned out to be 0.20 too big, so out came the barrel again. I welded over the slot and ground down the weld, then polished the barrel where it fit the trunnion. I repressed the barrel and set the headspace. I then redrilled the barrel through the trunnion and used the original pin to pin the barrel. My un-named experts (see above) warned me that I needed a sharp drill to redrill the barrel. My Drill Doctor kept the bit sharp; I had to sharpen it twice. After all this I found a small crack in the trunnion radiating up through the guide ears for the rear sight (just where the pin comes out of the trunnion). This area is not subjected to major stress during firing, but it is a concern. I did a complete penetration
weld over the crack and will watch this area very carefully for the first 1000 rounds.
I built the adaptor for the Galil stock, but that is a whole different story.
I also built a jig to stamp out a serial number on the receiver along with the caliber. That was partially successful and cost way too much in time and effort.
I finished the rifle by parkerizing it and GunKoting it. I used the satin black GunKote.
I am going to go back and add three 12 oz tinners rivets to each side rail. I just don't trust the plug welds. The rivets will just add additional strength to the alignment of the rails.