Using copper pipe as a backing for butt welding....

[1320King]

Hey I have a really stupid question. I am butt welding some floor pans on my 69 camaro and I am burning through the sheetmetal.

Can I use a copper pipe as backing so I can fill in the holes. Will I get shocked or injured if I hold the end of the long copper pipe with my hand in order to keep it pressed against the metal I am trying to weld???

Will the copper pipe stick to the back of my welding material

[Hotfoot]

I use a large copper pipe coupling (unthreaded, was made for solder) flattened out in my big vise, with a hooked end welding rod inside, then a "L" bend about a foot out the handle. I smear mine with splatter free, and it works fine. I actually prefer putting some backer sheet metal back there and just welding it in place...gives much nicer welds with twice the thickness to take the heat.

[brianpgriset]

Will I get shocked or injured if I hold the end of the long copper pipe with my hand in order to keep it pressed against the metal I am trying to weld???

You shouldn't, so long as you have a good ground on the cars' sheetmetal body. Remember, the electrons flowing for a weld ONLY want to find ground along the easist possible (ie least resistance) path. Why would the electrons want to go through your body which has a resistance around 10,000 ohms (depends on alot of factors) when it can go through the sheetmetal car body to the clamp, which is virtualy a closed circuit? Now you can see the importance of a good ground. Now, say you accidentally set the ground clamp in your lap, them hold this copper tube and then try to weld, the ONLY way electrons can flow is through your body, and, if enough potential (voltage) is present, it'll do just that. Ask me how I know this.

[LNGXDRM]

Experience is always the best teacher. Sounds like that might have hurt a bit!

[1320King]

You shouldn't, so long as you have a good ground on the cars' sheetmetal body. Remember, the electrons flowing for a weld ONLY want to find ground along the easist possible (ie least resistance) path. Why would the electrons want to go through your body which has a resistance around 10,000 ohms (depends on alot of factors) when it can go through the sheetmetal car body to the clamp, which is virtualy a closed circuit? Now you can see the importance of a good ground. Now, say you accidentally set the ground clamp in your lap, them hold this copper tube and then try to weld, the ONLY way electrons can flow is through your body, and, if enough potential (voltage) is present, it'll do just that. Ask me how I know this.

I figured it would be better to ask and be safe than get shocked and then learn my lesson!

Thanks for posting this and it does inform me of why the ground is so important!

[1320King]

I use a large copper pipe coupling (unthreaded, was made for solder) flattened out in my big vise, with a hooked end welding rod inside, then a "L" bend about a foot out the handle. I smear mine with splatter free, and it works fine. I actually prefer putting some backer sheet metal back there and just welding it in place...gives much nicer welds with twice the thickness to take the heat.

Yep I thought about using a backer...but I didnt want to see that backer welded to the bottom of my floor pan....or to the back of my quarter panels when I do them. Thanks for the reply Hotfoot! I will get some of that splatter free!

[MAC702]

Using a copper backing piece is a very good way to do the job in question. I have several pieces of copper (some of them long and hand-held) that spend their lives doing jobs just like it. Next week, I myself will be welding floor pans on my new-to-me 61 Ranchero. That's pretty much how I'll do it, with .023" solid wire and argon/CO2 shielding gas.

[TX-WJ]

..............the ONLY way electrons can flow is through your body, and, if enough potential (voltage) is present, it'll do just that. Ask me how I know this.

How do you know?