Steel Copper Steel Sandwich???

[Smokehouse69]

I came across something interesting this afternoon, I am converting a G3 stock endcap into a endcap for an HK53 clone I am building. I was cleaning up some of my cuts with a dremel sanding wheel and while polishing up the back edge, I saw a thin band of copper between the steel on the edge.
Sorry about the crappy quality of the pic, it was done with my scanner, since I still haven't found my camera cable.
Anybody ever seen anything like this before?

[rpmfly2]

from an engineering stand point laminated materials are several times stronger than any solid!

[rustypirate]

I have seen some samples of the progressive stampings that form these pieces for HK rifles at the museum in Orbendorf, and I did not see any evidence of a layered material being used.

[Smokehouse69]

I know it's strange and hard to see in that scan, but I swear that there is a thin copper colored line between silver of the polished steel that runs completely around the endcap.

I blew up the original pic and cropped a section where it showed the best.

[cfish]

What was used to cut that piece. Any chance that it is rubbed off from the cutting tool??

[weasel_master]

Put it in amonia, if it's copper, it will turn the solution blue/green.

[Smokehouse69]

What was used to cut that piece. Any chance that it is rubbed off from the cutting tool??
It wasn't cut off anything, that is the end cap from one of the G3 stocks from CTD. I pulled the plastic stock off and removed the recoil rod and spring. The edge I'm showing is the edge where the stock is meets the metal.
After prying off the plastic stock I sanded the edge with a Dremel flapper sanding wheel prior to welding a metal plate across the back. I am making this an endcap for HK33 pistol build.

[bladeworks123]

I know from a friend who does progressive stamping of parts in the aerospace industry, that sometimes the pieces they use are two or three layers. This helps keep the stamped piece a consistant thickness instead of it getting thin where it is stretched tight into corners etc. It also keeps it from being stretched apart in the pressing process. They also sandwich thin plastics in between pieces sometimes to help deaden sound and insulate between the inside and outside of large panels. As sharp as some of the bends are on the reciever parts, this might make sense. I visited his shop in Wichita, where they have a huge press for forming fuselage panels and stamped engine parts. I don't remember how many hundreds of thousands of pounds the press exerts, but the ram as I recall was four feet in diameter. He put a copper penny in the press and it came out about the size of a coffee can lid and about the thickness of a piece of paper... and hot too. They also had a milling machine with a 24 foot diameter table for machining ring gaskets for rockets.

[bladeworks123]

It wasn't cut off anything, that is the end cap from one of the G3 stocks from CTD. I pulled the plastic stock off and removed the recoil rod and spring. The edge I'm showing is the edge where the stock is meets the metal.
After prying off the plastic stock I sanded the edge with a Dremel flapper sanding wheel prior to welding a metal plate across the back. I am making this an endcap for HK33 pistol build.

Did it give you any trouble when you welded it? I would think maybe if it was copper in there it might weld a little different.

[turbothis]

there is a guy in the valley here that has a press shop. he has several press's up to 500 ton. i stopped by there a while back to see what he could do and the machine just eats up the steel roll and pounds out shapes all day long. very kool!!!

[Smokehouse69]

Did it give you any trouble when you welded it? I would think maybe if it was copper in there it might weld a little different.
No, I cut out a piece of 16 gauge steel the shape of the inside of the open space. I used the portion on the plastic stock that fits into the socket as a template. Then I tacked it around the inside edge with my HF wire feed welder. Then just kept tacking alternating around and letting it cool in between the tack, stitching it together. A technique I learned welding sheet metal patches doing body work. I welded up a lot of rust holes in old cars.
Then I ground the welds down and filled in the pits, gaps an irregularities with JB Weld.
Here's a scan of it after welding and filling. I shot a coat of Krylon quick dry to find the high/low and imperfections. Black paint makes the flaws easy to find (another trick from working on old cars.) I'll sand it and fill it again until I get it as close to perfect as I can, then it'll be ready for Duracoating.

[bladeworks123]

I've got an Hk Stock mounting plate that got mangled a litttle and I don't want to use it. You have my curiousity up now, and when I have time I'm going to take a piece of it out and see if it is laminated, like yours appears to be.

[86thecat]

I'm going by memory here but isn't that piece assembled from an outer shell and an inner cup? IIRC it's normally welded in spots, but could be brazed together. Like I said, going from memory here so I might be mistaken.

[Smokehouse69]

Yes, you are correct it is apparently two pieces. The inner portion where the buffer mounts is pressed inside to the outer piece. They are apparently copper plated then pressed together and spot welded around the outside edge. The copper is apparently there as an aid to welding the two parts together into one piece.
I'm glad the mystery is solved.

[bladeworks123]

Hey guys!!! Guess what I just found out...:icon_biggrin: