A lot of thinking went in to designing and building this chassis jig. There are so many different design angles and material you can use. I’ve seen versions made out of channel, I-Beam, rectangular, square. There are open designs, full table designs, or combinations of both.
When you boil it all down there are a few basic requirements: square, flat, true, and parallel. My home shop is relatively small. It’s a 40 x 25 concrete/wood structure. It houses a twin post lift, a 9′ x 3′ bench, my main tool box, a 4′ x 4′ plasma table, a wood heater, and several other benches and shop equipment. My daily drivers and my race car all now call it home as well.
My basic design called for a 12′ x 5′ structure and it had to be mobile. This is far from ideal, but I knew if I could build a truly square and flat piece I’d be fine. I also decided on a fairly open design with three cross beams and no solid top. This would give me full access to the underneath of the chassis.
A little bit of research found me what a standard perfection spec on a chassis jig is. I’d been told that being square and true within 1/8″ would not give me any trouble down the road when setting up my car.
1/8″ is a little wide for my taste.
Anyway, I settled on using 3″ x 3″ x 3/16″ (.1875″) square structural steel tubing. I can already hear the hymning and hawing of the I-Beam religious out there, but I-beam is not flat. And right now a trip to the machine shop with two 12′ I-beams is not my idea of a swell time.
A call to my local steel yard netted me all the steel I needed, pre-cut to my specs for a great price.
First thing I needed was a very level and large surface to build on. The garage floor area between my lift posts was perfect for this. I had purposely requested the masons put no pitch towards a drain in the area and to make it as level as possible so I wouldn’t have a bank roll of shims stacked under the lift posts. So my large level area was acquired.
I laid out the outside rails and outer cross members and proceeded to tweak and probe them for the better part of a week before I was satisfied enough to tack weld them together.
All the while we (me and myself) listen strictly to every Ramones album on random, primarily because they are awesome. And most everything else sucks.
You really can’t use just a square to make sure that each corner joint is true. Not unless you have a very, very, large and perfect square. This is where that 1/8″ spec comes in. Basically measure corner to corner and corner to corner and bump the assembly until everything is in spec. An 1/8″ in spec. Wrong! A little patience and you can do better. Perfect or 1/32″ was good enough for me and that what I settled with.
The main beams are parallel.
The cross beams are evenly spaced.
The casters are good for 1000 lbs. a piece.
And she sits 29 1/2″ high so my average size human body can crawl around underneath it.
Now, it’s not finished yet. The adjuster feet are in the mail and the UniStrut and coupler nuts are on the floor next to the car. I have to cut up some round tubing to brace the legs and add the mounts for the adjuster/leveling feet. Finished product next time and 240sx disassembly with some criticism on what I originally did wrong when I succumbed to peer pressure and rushed things to get on the track the first time around.
Chassis builder, engine builder, cynic