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9/22/2017 12:11:25 AM
Posted: 10/3/2005 6:04:09 PM EDT
My $2.00 question for the day is, When building from flats(tapco), how do you determine how high, or low in the reciver to mount the front trunnion, and once it is there, how do you bend the top of the reciver to fit in the grooves in the trunnion? Just so noone says "the trunnion holes are already there" They offer flats without trunnion holes, and I think that is a better Idea, just so you can make sure all of the parts from the kit fit in the reciver properly.

I have already screw-built two ak's and I ordered one more kit, and I recently purchaced a shop press so I can remove the barrels, so I am going to take apart the screw builds and rivit them togeather. The last builds were with 100% recivers(ohio ord.) and with those, all I had to do was locate and drill trunnion holes, everything was already lined up(lower rails, upper rails, and the part of the reciver that bends into the trunnions). The more I read, the more I get afraid of this project, but I am willing to risk a couple of $13.00 flats to try and "roll my own".

Any help is appreciated.
Thanks in advance.
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Link Posted: 10/3/2005 6:33:34 PM EDT
I know its not done but if you look at the pics on these pages I think you will get the idea...

ar15.com/forums/topic.html?b=4&f=51&t=76448
Link Posted: 10/3/2005 10:59:55 PM EDT
[Last Edit: 10/3/2005 11:02:14 PM EDT by MochaJava]
When you build from a flat I assume you are using a jig. On the jig I used there was a provision for bending over the top rails at the correct height for the trunions. The rails will eventually have to be trimmed for the bolt carrier, trunions and magazine. We used a letter "I" (I think) drill bit laid on its side to correctly space the lower rails from the top rail in preperation for welding and to keep them parrallel to the top rails. The rails were then clamped in place and welded.
Link Posted: 10/3/2005 11:14:46 PM EDT

Originally Posted By MochaJava:
When you build from a flat I assume you are using a jig. On the jig I used there was a provision for bending over the top rails at the correct height for the trunions. The rails will eventually have to be trimmed for the bolt carrier, trunions and magazine. We used a letter "I" (I think) drill bit laid on its side to correctly space the lower rails from the top rail in preperation for welding and to keep them parrallel to the top rails. The rails were then clamped in place and welded.



I'm pretty sure it's a letter "C" drill for spacing the rails...
Link Posted: 10/4/2005 1:40:27 AM EDT
The spacing of the rails varies... some have reported using using drill bit ranging from "C" to "I". The imnportant thing to remember, is that you need to line the rails up with the front trunnion. Once the rails are lined up, then afix it to the sides of the receiver.

Link Posted: 10/4/2005 4:12:50 AM EDT

Originally Posted By Mack_Bolan:
The spacing of the rails varies... some have reported using using drill bit ranging from "C" to "I". The imnportant thing to remember, is that you need to line the rails up with the front trunnion. Once the rails are lined up, then afix it to the sides of the receiver.




Correct... In my last build I used a "G" bit....

When building AKs itr is a good idea to have a BIG set of drill bits that you keep nice and NEW to use for spacing... This is a set I got at HArbor Freight....

quarterbore.com/images/amdbuild5/amdbuild-5-spot-welding-rails-09.html
Link Posted: 10/4/2005 6:15:13 PM EDT
Thanks for the info guys. So the upper rails will already be the correct hight for mounting the trunnion, but I will have to trim them to the proper width?
Link Posted: 10/4/2005 6:40:26 PM EDT

Originally Posted By DFARM:
Thanks for the info guys. So the upper rails will already be the correct hight for mounting the trunnion, but I will have to trim them to the proper width?



Correct. You will have to trim a little to install the trunnion. The trunnion will slide in on the upper rails of the receiver. After that, you then trim the upper rails so the bolt carrier will slide freely. After making sure the BC fits, you need to cut reliefs so the carrier can be removed after the rear tang/block/trunnion has been installed.

After the trunnion is riveted into place, you can install the lower rails so the tops are even with the trunnion. Make sure that the upper and lower rails are parallel to each other. This might be confusing, but if you do a search there are a couple of pictorials that illustrate this very well.

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