MG34 semi auto Q & A

Post by **Pirate** » Thu Apr 20, 2006 6:13 pm

This will be the thread to ask questions or post coments on the semi auto MG34 build

Gunmetal · Post by **Gunmetal** » Thu Apr 20, 2006 7:09 pm

I don't have a question but a suggestion. I was planning on setting up to brass bars like the steel ones you have there or milling one large piece of brass flat bar stock slightly wider then the bolt. This way you could use a larger filler rod and fil the large gaps, layering it as you go until you have replaced the lost section on the side. Once I was done with that then I plan on using some brass round stock and fitting it in where I can. I have used large brass blocks to fill large gaps like that in the past and they are still in good shape. If you access to a lathe you could make a 2 piece brass jig to go in each end and weld it up.

I just picked up a few kits and a cut reciever so I've just started put brain power to it, If I come up with something I will post some pics. I'm in the process of getting power to my shop, so my welders and machines are out of comission right now.

Post by **Pirate** » Thu Apr 20, 2006 7:23 pm

due to the fact that this is a heavy machined receiver filling in large gaps is not the best approach. I had considered this but after looking at the receiver I decided it would be better to fill the gaps with receiver sections.

Gunmetal · Post by **Gunmetal** » Thu Apr 20, 2006 7:27 pm

What is your concern with that? My concern would be the brittleness of the weld to reciever transition, is this what you have in mind?

Gunmetal · Post by **Gunmetal** » Thu Apr 20, 2006 7:33 pm

I don't have my reciever sections here yet but have you concidered using thick walled square stock for the middle section and welding the front and rear piece to it? I know this wouldn't look authentic but you could install rails like on the MG42 on the inside? Weld in a piece of tubing for the recouporator, etc...

Post by **Pirate** » Thu Apr 20, 2006 8:50 pm

Gunmetal wrote:I don't have my reciever sections here yet but have you concidered using thick walled square stock for the middle section and welding the front and rear piece to it? I know this wouldn't look authentic but you could install rails like on the MG42 on the inside? Weld in a piece of tubing for the recouporator, etc...

Why do that? I have overlapping sections. I plan on cutting and mating the sections to get the proper length, then weld them together. Filling a 3/8" gap with weld is not the best aproach for this type of receiver when filler sections are available.

Gunmetal · Post by **Gunmetal** » Thu Apr 20, 2006 10:58 pm

I guess I was thinking for those that weren't lucky enough to score overlap pieces like myself. Yes, you can face all those and make life easier for yourself. I wish I would have been looking while I was at KCR, but that is the way it goes.

Gunmetal · Post by **Gunmetal** » Sun Apr 23, 2006 7:24 pm

Does anyone have a formula or way to determine shrinkage on a reweld of this kind? Pirate is this something that you think will be a considerable concern? Have you any ideas on how to weld up the inside portions of the recouperator tube or can this be left open on the inside?

Post by **Pirate** » Mon Apr 24, 2006 6:47 pm

Gunmetal wrote:Does anyone have a formula or way to determine shrinkage on a reweld of this kind? Pirate is this something that you think will be a considerable concern? Have you any ideas on how to weld up the inside portions of the recouperator tube or can this be left open on the inside?

I was planning on doing some tests to determine shrinkage, however since I was able to get another set of cut parts I plan on filling up the gaps to minimize having to fill big gaps and all
the problems associated with that.
the recuperator tube will have to be drilled out after welding to clear it. long drills are readily available.
I am finializing the design for the weld jig and will be getting a price to have some made. basically the jig will hold the parts in proper alignment and keep them from shifting during the welding process.. it will also set the length of the receiver. anyone interested in a jig pm me and I will start a list to get an idea of how many to get made.

Post by **garyd** » Tue May 09, 2006 7:09 pm

is the sear the only thing you weld to use a old reciever and make it semi auto

Post by **Reichpapers** » Tue May 09, 2006 11:30 pm

Might want to get AK47Dennis (father of the first BRP copy build) to talk...he did his 34 receiver a year or two ago.

Post by **panaceabeachbum** » Thu May 25, 2006 9:56 am

here is a link to the thread ezfeed did on the mg34 semi build last year with some comments and advice from ak47 dennis on his build http://www.weaponeer.net/forum/forum_po ... PN=2&TPN=1

here is another link to some pics of another fellows welding jig he is using for his reweld http://www.weaponeer.net/forum/forum_po ... N=1&TPN=19

Pirate if your interested I would be happy to give you a qoute on the welding jig hat might help get the cost down, based on the pics of yours and the jigs in the other threads, and the one I have built its not a real complicate jig. Just a friendly offer , nothing more

Post by **Blanksguy** » Thu May 25, 2006 12:59 pm

Questions:

1: If costs were not a "factor"....is it better to use "Copper" or "Brass" as a backing prior to welding an SA34 DEMILed-receiver ?
.....and what is the minimum thickness that would be required ? (...if you were using say copper-sheet over a steel-bar.).

2: If your SA34 welding-jig would fit into the kitchen oven.......Would "pre-heating" the DEMILed receiver to about 400 degrees (once it is set up in a jig) help in keeping the warpage and growing under control if you kept the temp. of the parts between 300-400 degrees?

Regards, RichardS.
Blanksguy2001@chartermi.net

Post by **Sevo** » Thu May 25, 2006 1:25 pm

Blanksguy wrote:Questions:
2: If your SA34 welding-jig would fit into the kitchen oven.......Would "pre-heating" the DEMILed receiver to about 400 degrees (once it is set up in a jig) help in keeping the warpage and growing under control if you kept the temp. of the parts between 300-400 degrees?

Regards, RichardS.
Blanksguy2001@chartermi.net

How would you get close enoug to it to tig it.. i wear thin gloves when i tig for better control.. I dont think i coudl handle all that heat

Sevo

Post by **Blanksguy** » Thu May 25, 2006 1:32 pm

SEVO,
When I am rebuild Haley-Davison motorcycle engines....we heat up the cases and/or heads to do some of the work.......

....you are right though.....I should have said: "..and then take the pre-heated SA34 jig with the pre-heated DEMILed receiver for welding....out of the oven and over to your welding area for welding....but leave the oven in the kitchen. Note....depending on how fast or slow you weld....the question may require you to walk back and do the "pre-heating" of the jig and parts back up to 300-400 degrees."

Also note......wear heavy-gloves when moving these "pre-heated" parts and jig.

Justs questions at this point for those that have tried welding with different "backings"...and minimum thickness for sheet-material.

Regards, RichardS.
Blanksguy2001@chartermi.net

Post by **panaceabeachbum** » Thu May 25, 2006 1:51 pm

Blanksguy wrote:Questions:

1: If costs were not a "factor"....is it better to use "Copper" or "Brass" as a backing prior to welding an SA34 DEMILed-receiver ?
.....and what is the minimum thickness that would be required ? (...if you were using say copper-sheet over a steel-bar.).

Regards, RichardS.
Blanksguy2001@chartermi.net

Copper in any welding aplication , besides the higher heat resistance of the copper, the brass releases poisinous gasses when at or near welding temp

none123 · Post by **none123** » Thu May 25, 2006 1:59 pm

Sevo wrote:
Blanksguy wrote:Questions:
2: If your SA34 welding-jig would fit into the kitchen oven.......Would "pre-heating" the DEMILed receiver to about 400 degrees (once it is set up in a jig) help in keeping the warpage and growing under control if you kept the temp. of the parts between 300-400 degrees?

Regards, RichardS.
Blanksguy2001@chartermi.net
How would you get close enoug to it to tig it.. i wear thin gloves when i tig for better control.. I dont think i coudl handle all that heat

Sevo

Thick gloves and long sleeves. You quickly learn not to rest your hand on the part. It's common to pre-heat certain metals like Al, and when welding heat treatable steels, cast iron...ect..

Post by **Pirate** » Thu May 25, 2006 7:33 pm

Blanksguy wrote:Questions:

1: If costs were not a "factor"....is it better to use "Copper" or "Brass" as a backing prior to welding an SA34 DEMILed-receiver ?
.....and what is the minimum thickness that would be required ? (...if you were using say copper-sheet over a steel-bar.).

2: If your SA34 welding-jig would fit into the kitchen oven.......Would "pre-heating" the DEMILed receiver to about 400 degrees (once it is set up in a jig) help in keeping the warpage and growing under control if you kept the temp. of the parts between 300-400 degrees?

Regards, RichardS.
Blanksguy2001@chartermi.net

The jig I have designed holds the parts in alignment firmly. it is steel and should expand and contract the same amount as the receiver., unlike an aluminum bar. I am also using filler sections so there will be no large gaps to fill and will minimize warping and shrinkage. trying to fill very large gaps with weld will cause problems and it is best not to do it that way.

Post by **panaceabeachbum** » Thu May 25, 2006 11:13 pm

panaceabeachbum wrote: Pirate if your interested I would be happy to give you a qoute on the welding jig hat might help get the cost down, based on the pics of yours and the jigs in the other threads, and the one I have built its not a real complicate jig. Just a friendly offer , nothing more

Post by **panaceabeachbum** » Thu May 25, 2006 11:18 pm

filling the large gaps with weld may cause problems with warpage but structuraly it will be sound, the bolt and bbl lock together during high pressure event and the rec does nothing more than align all the various parts. The most stress its under is stopping the rearward travel of the bolt during the recoil cycle. Having a donor for filler pieces would be nice but this rec isnt highly stressed like a bren or other type that rely on the rec for lock up