In some of the build pics the steel tubing is all shiny and clean while in others it is a bit greyish. Now the tubing that I bought in the past for other projects were also greyish coloured.

Is this something to be concerned about?

I usually do'nt sand the joint I'm about to weld to shiny metal although I know the cleaner the joint the better the weld, but I've read somewhere that the greyish part also serve as a kind of rust inhibitor. What do you suggest.

Also, I've read somewhere that if there is a gap of more than 1.5 mm between 2 tubes making up a joint, it is safer to cut a new to piece to get a better fit.

The grey coating is a rust inhibitor, depending on the supplier, some of it is weld thru. I always wire brush the joint to be welded, no matter what it is coated with, you can never have it to clean....

David

cassidy, if you take the time to file the tubes carefully to get a perfect tight fit, you will have less of a problem with distortion.

I think the ideal is a tight fit with a bevel to help ensure good penetration.