reweld, how safe is it?

mwc · Post by **mwc** » Thu Apr 14, 2005 12:02 pm

hi all,
im new to the site, and ive been reading up on the DIY semi 42s. theres a lotta info ive found here, but im curious about how safe a reweld of a mg42 receiver is?

ive been trained to fear rewelds based upon the sometimes shoddy m1 garand receiver reworking in the 50s and 60s....and then i read some of the posts on 1919a4.com about brp mg42 rewelds that showed weld cracking in relatively little no. of rounds (and thats in SA fire too) from receiver torque/twist on firing.

given this, so how safe is a reweld? i know rewelded sheet metal (mg42) and rewelded intricately machined chunk of and heat treated steel (m1) is like apples and oranges. certainly the m1 garand receiver actually absorbs firing energy directly because the bolt locks directly into the receiver and welding will affect such important receiver characteristics as heat treat and receiver dimensions.....so good welding and jigging is critical. but does the sheet metal and design of the mg42 require such critical work/prep? the firing stress is in the barrel ext/ and bolt and trunion, and the rest of the receiver is there to hold the gun together.....yet the lesser level of firing stress still can lead to weld cracks on the brp semi 42? anyone have any insights on the durability and safety of this type of rewelding? tia
mc

Post by **TOM R** » Thu Apr 14, 2005 12:32 pm

If you properly clean the cuts and tig with the proper heat it should work fine remember this was welded sheet metal from the original factory, and unlike a 1919 the reciever dosen't take the brunt of the recoil, all mg 42 are welded; new, old, fa, sa, c&r, hope this helps

Otis Cambell · Post by **Otis Cambell** » Thu Apr 14, 2005 12:50 pm

What type welding process was originally used on the receivers? As I recall TIG has created after WWII.

Post by **TOM R** » Thu Apr 14, 2005 1:01 pm

I think they used spot welds for some of it

Otis Cambell · Post by **Otis Cambell** » Thu Apr 14, 2005 1:47 pm

Any idea on what they used to weld long welded areas on left side of receiver fwd of the trunnion ?

Karbinator · Post by **Karbinator** » Thu Apr 14, 2005 2:36 pm

MWC--Welcome !!

Good rational question. I seen that thread yesterday as well.
Akdennis has lots to say on the subject.
:P

Jason · Post by **Jason** » Thu Apr 14, 2005 3:07 pm

I am very close to having mine in working order. I'll be keeping a very close eye on the welds and will report on any problems, that is if it dosent blow and I loose the two fingers that I type with

Post by **TOM R** » Thu Apr 14, 2005 3:57 pm

just mount it on a tripod and rig a string to the trigger and stand back

mwc · Post by **mwc** » Thu Apr 14, 2005 4:50 pm

thanks karbinator,
well my take is that a weld failure on a mg42 isnt neccessarily a out of battery kaboom, but rather the gun will fall apart.

i dont have any practical experience and am only thinking out loud on a mg42 reweld. seems to me that a contiguous sheet metal receiver can absorb the torque and twist of firing b/c the sheetmetal naturally flexes and is meant to do so......but if you cut it and reweld it, esp a poor weld with voids/contaminations and/or heat induced brittleness of the metal, then that is the weak point in which the stress of firing will manifest itself.....in cracking.
the mg42 locks in the barl ext/trunion/bolt and so the receiver takes less brunt than the m1 garand...but there is still the impact of the bolt to the buffer in the mg42 which puts stress esp on the rear portion of the receiver, as well as the natural twist of the receiver when the bolt is recoiling......
so jason, i dont think itll blow up so much as maybe the stock/rear portion of the receiver will come off in a catastrophic failure of the welds...
but do keep everyone posted!

minimizing weld weakness seems very important like tomr said: no contamination, proper heat, and correct filler.....i think the orginal factories used flux coated stick/arc welding...so flux core mig seems ok to use since its similar to the welding originally used. what would the proper wire be? is assume a low nickel wire since the receiver is prolly 1018 or similar steel? getting good penetration with proper heat (cherry red b/w the joint?) and filler, and should be ok right?

Post by **TOM R** » Thu Apr 14, 2005 5:14 pm

my prob with the stick welder or flux core wire is being able to go slooow, my feed only goes so slow

Karbinator · Post by **Karbinator** » Thu Apr 14, 2005 5:55 pm

MWC,
You know, I've been thinking about this for sometime, and am glad it's come up again about welds.
Seems like everyone doing these rewelds are filling in the cut area, Then grinding out the outer/inner buildup to get that original "non welded reciever" look(and so the bolt will move

). I bet that's where the fatigue takes place--where the weld was ground down, and the welders original thick connection once was.
There needs to be some overlay, so as to grab/penetrate more reciever metal. A good sloping taper where the two cuts join would be Very impotant. This way your fill would penetrate more reciever by width profile. Nor after grinding level would you lose the width penetration.

Ok. But still--- will that hold it?
Well, there's only one way to find out !!
I've been thinking about having some fancy metal overlay the outer areas of the welds--and then tap welds. Or, a long thin flat bar running the length of the reciever just under the Top cover from trunnion area back.These could go as far down as the rail rivets (even be predrilled, and take on the rivets) These are only thoughts out loud as well. I do want to rapid fire it without EVER wondering what/if "that noise" was something coming from the welds.

Post by **drooling idiot** » Thu Apr 14, 2005 5:59 pm

your much much much better off with a TIG weld, there is so much more control over the heat and addition of filler metal.
as for the weld cracking under the buffer pounding I'd guess the metals about 10GA in that area if the weld better than decent it should hold a small truck in the air on static shear load. granted not the same as dynamic impact but even BPR's SA42 doesn't have a reputation or history with problems on the rear cut. anything between there and the trunnion is reinforced by the rails.
my .02

M/W · Post by **M/W** » Thu Apr 14, 2005 6:01 pm

I wouldn't be surprised if they didn't use a resistance weld much like a piece of pipe is formed.

Jason · Post by **Jason** » Thu Apr 14, 2005 8:14 pm

karbinator, when I welded I gound down the outside but left as much as possible on the inside for the same reason you are talking about. the only weld build-up that was taken off the inside was the areas were I needed to for the function of the internals.

M/W · Post by **M/W** » Thu Apr 14, 2005 8:48 pm

Many times when a weld fails, it's not the weld itself that fails. It's the parent material adjacent to the weld. I had a materials class many years ago that compared weld failures and what caused them. I wish I could remember that far back. I'm happy now when I can remember what happened yesterday.

Post by **salt6** » Thu Apr 14, 2005 8:55 pm

Why not weld a reenforcement plate on the inside to back up the welds?

Steve

Karbinator · Post by **Karbinator** » Thu Apr 14, 2005 9:16 pm

Steve...YES !!..inside/outside....somewhere to double up, and widen up the "bite" . Where on the inside could it be done?> Somewhere Under the rails maybe? It would be easier on the eye if possible on the inside.

skip

mwc · Post by **mwc** » Thu Apr 14, 2005 11:06 pm

karbinator,
gussets are a good idea, better even if hidden :P
also, m/w brings up a good point: the area around the weld.....the slag area of the torch cuts: are they weakened by contamination when slag formed?

Karbinator · Post by **Karbinator** » Sat Apr 16, 2005 7:18 pm

slag.... remove it with a wire wheel, or grinder (don't hit the important corners but so much) until slag dissapears. Degrease your kit after assuring all parts have arrived(then grind). This way you're not imbedding any oils underneath your beveled grinds..

skip