This jig is not a weld backing jig, it is more a truing mandrel. By that I mean the jig forces a true line thru the center of the receiver. You will still need to tweak, clamp, and massage the material into shape. It is sheet metal that has been torch cut and tossed in a bag with hundreds of other kits and banged around for who knows how long. The jig interfaces in several locations on the receiver to give you a consistent OAL(over all length) and a nice straight receiver. Starting from the rear there is a large disc that interfaces in the buffer recess, this helps with aligning the rear section as some are cut in not so nice ways and can be TRICKY. Just forward of the buffer alignment disc is your beam, this interfaces with your rails and carries the straight line from the buffer section forward to the shroud. In the shroud area there is another disc that interfaces with the barrel stop and the forward rod threads into the beam here. Finally we get to the nose section where there is a mandrel and 2 washers that sandwich the bushing and hold that assembly on the end of the forward rod. That makes 4 locations that are referenced every time you use the jig. Having built over 100 guns on a single jig and it still produces straight nice receivers like it did on the 1st weld. You have the best MG42 welding jig that has been produced to date, outside of a factory.
1.) Kit Prep- First and foremost clean the cosmo and slag off your parts. Next you want to remove your torched rails, I recommend getting a set(or 3) of take off rails that are already drilled. You can find a set that lines up with your holes or close enough for Gov. work. If you are replacing the bushing, now is the time to prep all this. If you want to blast your parts before welding, do it now. Also do your semi-auto mods now, keep it legal and all..
2.) Setup - All cuts are not created equal. Some guns are cut in just the right spots and they weld together in a few hours. Others can make you want to drive into the sunset and never return, but you will get it, eventually.. You want to take your shroud and set it aside for a little bit. Take the rear sections and your rails and get them bolted together(bolts sticking out not in). **There is a left and right rail.** You are making a mock-up of the rear receiver. Once you have that done, it can be fun with fat fingers, you are ready to start placing the rear receiver on the jig. You want to start with the jig disassembled, we will build the jig inside the receiver.
3.) Build the jig - Your jig is marked LEFT, this is the Upper Left facing side of the jig looking from the rear of the gun to the front. Take that and slide it into the rear of your mocked up receiver. The jig will interface in the rails as you slide it in. Now *here* is where you begin fitting your receiver and rails. You want the jig to slide in the receiver with some force but by no means do you want to beat it in there. Snug is what you want, the jigs are precision machined and hardened but you don't want to beat the jig out later and you will if you don't setup the job right. In other words take your time, test fit the pooh out of it, you only want to weld it once. Slide the jig all the way in about 1" past the rear of the receiver. You will have a LARGE alignment disc, a small spacer(about 1" round stock), and one of the bolts. Place the disc on the bolt first, then slide the spacer over the bolt, and thread the bolt into the rear of the beam. You want to get the rear buffer recess interfaced with the alignment disc and slide the receiver to the rear against the disc.
- Next we take the front mandrel and build the assembly on the nose of the shroud. If you don't do the nose section before the forward rod you wont be able to get the washer behind the bushing. Slide the washer with the flats over the threaded end of the nose mandrel. From inside the shroud slide the mandrel into the nose bushing. Now we can thread the forward rod into the rear beam with its washer in place. Slide your shroud over the forward rod, careful not to drop the washer off the back of the nose bushing. Using the provided tool, thread the nose mandrel into the forward rod. Finally install the nose washer and bolt. This isn't set in stone, as you use the mandrel you will figure out shortcuts. You can put the forward rod in before you do the nose here but I guarantee you slide the shroud on and forget the washer..
4.)Weld - You have your receiver on the jig, some pieces will need to be spaced and clamped, depends on your cuts. We typically use the cam, the grip, the top cover, and of course the rails to get stuff aligned. The jig forces a straight line thru the receiver shell and sets several distances for you, like the OAL and nose to barrel stop distance. If you weld the receiver sections crooked, you won't be getting the jig out without a fight. Take your time and get stuff aligned before you weld.
5.) Congratulations, you have successfully welded an expensive jig inside your expensive receiver. Now what... - Don't beat on it, I mean its your jig, but don't beat on it. Lets get this jig out so we can see how crooked your receiver is.. Start at the nose and remove the bolt. Next you will need the mandrel tool to remove the mandrel from your nose bushing. Now that we have done that we can slide the jig to the rear a little bit and the washer will come out from behind the bushing. Doing this allows us to remove the forward rod via the spiral holes and the round tool. Slowly unscrew the forward rod from the rear beam. It will slide out of the front of the receiver. Now we are left with the rear beam inside the receiver. If you did your job right, with a little persuasion, your beam should slide out of the rear of the receiver. Don't beat on it, get a redheaded step child for that...
Happy building..
