Nick Müller wrote:
Andrew VK3BFA wrote:

I tack welded each corner, that went ok, but when I finished the seams,it
was twisted.

The first step was OK, the second wrong. :-)

After tack welding one side, flip it over and tack the other side.
Without experience, let it cool down (If you know what you do, you don't
have to let cool down). Check flatness. Now start welding where you
would like to shorten (or where the angle is below 90 deg.). Always
check angles and flatness and correct with the next weld.

A bit confusing, but there is only one thing to remember:
If you weld a seam the point where you started to weld will shink less
then the point where you end welding. Say you have a 90° joint and start
at the inner point, the 90° will come out more. If you start from the
outward, it will be less than 90°. If you start at the middle and weld
inwards/outwards you will have very little shinkage.
If you got the feeling, you can put the parts together _out_ of angle
and when you have finished it will be dead 90°.
It is more complicated if you butt weld two flats:
If you lay the flats down and weld, you will end with: both ends
pointing upwards and slight V lengthwise.

Only practice will get good results. It also helps to clamp (but it
won't stop distortion). Don't think that MIG/MAG will solve the problem.

But with a OA-torch you can pull everything straight. :-)


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

Thank you to all who replied - some of it I have to think about - BUT
- will make up a jig I can clamp the work to to keep it rigid while I
weld it. Alas, at this stage my welds look like they were put on with a
butter knife - I count it a GOOD day when I dont blow holes and have to
fill. But it will get better, - practice, practice, practice... this
metal work business keeps on generating the need for more
tools/accessories as I go along.....

BTW - a few people I have spoken to over the years report this
phenomena - some days, you just start welding and it goes like a dream
- other days, its so awfully bad and horrible you have to walk away in
disgust!. Is this some arcane knowledge, a spell I need to recite, or
just the way it is?
Andrew VK3BFA.

"if a machine breaks down, its no good going and using another one.
They all belong to the same union..."
Anon.