Welding in new repair sections
As opposed to tacking on repair panels
cut out the rot to good metal and where possible to the original panel joins
offer up the panel for fit
repair panels are often just an approximation and need work themselves the bonnet hinge panel needed the radius ajusted as well as putting a curve at the end
trim the car back a little at a time and take great care to not remove too much metal
ready for welding
flange fitting and spot welding with a mig
6mm hole through the top panel and the bottom recieving panel cleaned to bright shiny metal
clamp it really tight and use a chill bar behind if there is any risk of burn though
mig set at 100-120A and wire speed right down low, this puts all the heat into fusing the flange and stops it building up fillerwire to a raised ugly blob
tack the joints going back and forth from one side to the other dont retack untill the panel is cold
once you are tacked every 10mm its time to grind back before starting to weld
keep the weld pool mostly on the thick panel and just catch the edge of the car
it will burn through somewhere
i use copper spoons to support the weld pool and help take some of the heat out of the metal just shape them to suit
always grind the weld back after each 10 mm section before going back and welding in the gaps
always wait till its cold before welding the next bit its unlikley that you can simply run a bead more a case of 1second tack move a couple of mm tack couple of mm tack you can sort of judge the heat of the workpiece by the colour through your mask as the glow dissapears
once its all done grind it all back using a flap wheel as its much less likley to gouge the work than a rigid disk
when its all done and any pin holes and melt back are filled its ready for priming and painting - no need for buckets of filler, a high build primer and a bit of hand sanding and it'll be ready
one i did earlier.....8 yrs ago!
more pictures at
http://www.flickr.com/photos/42745680@N02/?saved=1Sean
