Practical MIG welding - Jigs
Jigs come in all shapes and sizes. Generally you'll need them when bits of metal need to be precisely aligned - anything from suspension mountings to a couple of bits of bar than need to be straight.
I thought I'd make a page with some pictures of jigs i've used in the past, hopefully they'll give you some ideas for your own jig.
Rear Suspension Jig
I made this jig to line up some new suspension mountings on my Renault 4. It's constructed from 4 steel plates welded to a scaffolding pole. The dimensions were calculated from hole co-ordinates in the factory workshop manual.
The rear suspension was bolted to each chassis member using 3 bolts. Problem with the Renault 4 is if one of the holes is out by more than 1mm the car will sit to one side.
I had to weld in some completely new suspension mountings (the old ones had fallen off) so the only way to get things close was to use a jig.
Simple Rear Suspension Jig
This jig is much more simple. It's job was to set the height of the lower suspension mounting on an Aston Martin and is constructed from a couple of bits of tube and a bit of square bar.
It's a 4 link suspension. There's redundancy in there as you only need 3 links to hold everything in the right place. Therefore the fore-aft position is controlled by the suspension on the other side of the car and I only need to take care of the vertical positioning.
The work was completed with the suspension still attached to the car so I could check wheel alignment before welding.
Body Jig (for Sill Welding)
Staying with the Aston here's a body jig. The intention was to hold the gap between the A pillar and B pillar while the sills were removed.
Normally a simple steel bar welded between the pillars would be enough, but in this case the gap started off too wide. I made the jig adjustable and made the jig in two pieces with bolt between them which I could tighten to reduce the gap. Once the gap was correct I welded the two parts of the jig together.