On 24/10/2020 14:37, Muddymike wrote:
On 21/10/2020 21:39, wrote:
One of my many projects is to restore the (large number of) 1930s
steel, Crittall, casements in my house, and the wooden frames they sit
in. The problems are that the windows have leaded lights and haven't
been maintained so many have been nibbled at the bottom by the rust
mouse, which lets-in the rot mouse. I've been getting the steel
sand-blasted to get the paint and rust off, cutting-out the rotten
bits (Rage2 chop saw - brilliant!) and welding-in new sections using a
couple of spare casements for sources of metal. The steel is a
modified H section and about 4mm thick so I'm bevelling the edges to
about 1/2 thickness and doing butt joints, either in-line or mitred at
45 degrees.
The problem is that the steel seems to slightly "run away" at the
edges of the weld, leaving a small pitt. When I look closely while
welding it seems to be generating small balls (not MIG spatter) but
I'm fairly certain it isn't galvanised. Any comments or advice from
experienced MIG welder wielders?
Without seeing an image its difficult to diagnose but it sounds like you
are either using too much heat or travelling in a straight line too
fast. If galvanise were still present you would get lots of white smoke.

Try using a weaving motion erring towards the thicker metal.

Mike
Yes, since Phil pointed me at the term "undercut" I've been educating
myself and the problem seems to be caused by travelling too fast on too
high a setting. When I tackle the next ones I'll slooow down and use a
lower setting.
I'm fairly sure it isn't galvanised because no popes have been appointed ;-)