How stable is a steel frame?

The welded steel frame with epoxy leveling is a well established design but the comment has been made more than once that welded steel contains stresses that will distort the frame over time unless the whole thing is heat treated. My two questions are:

1) Has anyone got some real life experience of a frame that has changed shape over time and how badly has it affected your machine?

2) If I eventually get round to welding up a new base frame for my machine will throwing it on a bonfire of old palettes etc. count as adequate heat treatment?

I'm not a good welder. I'm better at grinding than welding - but most hobbyists will admit to that. I *thought* the main concern was deformation whilst welding, and that's mitigated with taking time, alternate side stitch welding, clamping etc.

There may be truth in your points, but I don't recall these figuring heavily in these forums.

Well, let us put it this way I've built several dozen steel-framed routers from small to 10 x 5, and no one as yet phoned me up to complain and trust me they would.!!

Well that's good news! I'm aware of the immediate danger of heating during the welding itself but had got it into my head that there was a potential long term problem as well. I'll go away and worry about something else instead.