iron contamination from painted mild steel?

[Corgan]

Hi guys,

I plan on building an open jig to make table frames on. Basically the plan is for a close to perfectly flat table frame with no top, about 1200x1200 or so, allowing me to assemble and clamp square tubing frames of various dimensions for tacking up at a more comfortable working height than concrete slab level :roll:

I wasn't sure if using painted mild steel SHS would be alright for this purpose, or will i get surface contamination from clamping stainless to it? i.e does the paint on stock painted shs act as a protective barrier or not?

Thanks in advance
corgan

[Kody]

If you make a table frame using any form of mild steel to use for assembling and welding stainless steel you will severely damage the stainless steel. Any tiny amounts of mild steel grit or rust or whatever, will, when it comes into contact with stainless steel, will form awful rust spots. If the stainless steel is left to sit on the frame and both metals touch, rust will also form just from the damp/humidity or from any source of moisture. You will need to fully isolate the two metals so they never come in contact with each other. If you paint the mild steel with a high quality paint this can help a huge amount to isolate the two metals. You may find that spatter from the welding will bounce onto the mild steel and stick there. This can really damage the surface of the stainless as it is moved around. You might be better off if you covered the surface of the bench/frame with a sheet of stainless steel to begin with. You will obviously (I guess) be welding the stainless steel using a TIG welder. TIG welding usually doesn't produce any splatter and is the best way to weld stainless steel. Most important of all, keep the welding area isolated from any grinding zone that is nearby. The metal particles from the grinding wheels will totally destroy your stainless steel. These particles spread a long way from the grinders. :)

[Corgan]

thanks for the reply Kody,

I am actually doing things the hard way and stick welding currently. I will probably bite the bullet, rent some gas bottles and start tigging instead though, i do have experience with tig welding.

It's a little tough to be too careful as I have limited space which unfortunately means i use both mild and stainless steel in the same grinding areas etc. I sweep up as thoroughly as I can and change all abrasive wheels when working on some stainless, and I try not to rest it on bare mild steel either. afterwards I go over the whole thing meticulously with a scotch brite, so hopefully i'm not doing too much damage. I have a few pieces that were made months ago and have not noticed any rust spots yet, even ones that I was not so careful with.

it's good to hear the paint can effectively minimise the problem too, i'd hate to have to build this jig out of stainless for cost reasons, lots of square tubing lol.

thanks
Corgan

[Stustoys]

Corgan,
Wouldn't only the surfaces you were going to clamp to need to be S/S? You could build most of the jig from MS and cover the used parts in S/S. Assuming I am understanding what you are trying to do.

Stuart

[Corgan]

that's a very good point stu, i could cover the clamping points with some ss sheet metal. not sure why i didnt think of that :doh: thanks!

[Jekyll and Hyde]

that's a very good point stu, i could cover the clamping points with some ss sheet metal. not sure why i didnt think of that :doh: thanks!

Because, as I keep realising when on this site, the best ideas are so damn simple you don't even think of them :doh:. Usually, in my case, caused by a preconception of how I SHOULD approach whatever it is.

[Stustoys]

No problems corgan, glad I could help, hope it works for you. I've had many many :doh:moments here myself :D
Stuart