[GRM+ members read this article first. Subscribe and gain access to more exclusive content for only $3/month.]
Sooner or later, the time will come for you to scratch-build something with steel. It may be as trick as a chassis or an A-arm, or something as pedestrian as a sawhorse. No matter what you build, the quality of your layout and the fit of your parts will directly affect your outcome. Follow along to make the cut.
1. First, you’ll need a surface to build on. Begin by cleaning a table and establishing a centerline. We were lucky enough to find some nice steel tables at our scrapyard for about $200 each–we did some cleanup and added wheels to make them what they are today. Previously, we did just fine with a set of good sawhorses and some medium-density fiberboard (MDF) mounted on steel tubing to keep it straight.
2. With a centerline established, draw out the dimensions on the table. Several sizes of squares, several rules, a tape measure and some protractors will help you stay accurate. A trip to a big-box store with about $100 will cover a nice set of measuring devices like these.
3. Next, rough-cut all of your material. Our favorite tool for this is a horizontal bandsaw, but other cutting tools work just fine. Try to rough-cut your material so it’s oversized by 1/32 to 1/16 inch, then trim it to fit.
4. Rough out a few pieces, then move on.
5. Move on to finishing and fitting them, that is. We like to use a bench-mounted disc sander, like this $169 unit from Grizzly. There are less expensive tools you could use, including handheld grinders and even files, but we find this kind of sander and its miter guide help us work quickly and accurately. Don’t completely trust the miter, but instead rely on a protractor and test-fitting to get the angles just right.
6. With our parts cut, start to clamp them to the table using your pre-drawn lines as guides. If you’re using a wooden table, you can screw scraps of wood in place as guides. With steel tables, you can use magnets, or even tack-weld parts to the surface. Clamps are also an option, but do require some investment. Just like rough-cutting, you must also rough clamp. Measure, tap the pieces into place with a small hammer, re-measure, and repeat until every part is in the perfect position.
7. Perfectly fitting the parts is the key to easy welding. Our parts fit right on our lines, and we triple-check the dimensions. If you use clamps, place them close enough to the joint to keep it accurate, but not so close that they foul your welding position. Also, note the cleanliness: Wire-brush the steel and clean it with prep solvent.
8. Two tack welds will hold the joint. Don’t finish-weld until the whole piece is tacked together. That way, you can make corrections if the welding warp starts to affect your dimensions.
9 & 10. Don’t measure twice and cut or weld once. Measure scores of times, and remember, the most important measurements are the diagonals. After welding each joint, check all the measurements to make sure nothing has moved. If it has, fix it before welding any more.
11. We build up several of our project’s flat parts this way. The next step is to turn them into a three-dimensional piece–in this case, a Lotus 7 chassis, which we’ll finish in the next installment.
It may seem pedantic, but when measuring diagonals, you get more precision from measuring from or to points rather than flats.
In pictures 9 & 10 above, the tape measure is hooked on the flat, on the angle cut of the rear cross piece. If the angled pieces that go towards the front are a little bit short or long, and that would be missed by the measurement. If, instead, the tape measure were hooked on the point of the rear cross piece, it could still miss if the angled pieces were a bit short, but would catch if they were a bit long.
The same way at the front, although from the pictures he might already be doing this. Pick a specific point of the joint, then use that same point when measuring the opposite diagonal. This gets a bit more challenging when the welding filet is in the picture.
A dream of mine. But I don’t trust my welding ability. It’s fine for gates and fences and misc projects that I’ve built but not a chassis or suspension parts.
Lotus 7. I wasn’t far off, I thought he was building a go-kart chassis…
Another good article, looking forward to the next one!
My first time building “a frame” was to make a cart/stand for a Snap-On (actually, a Lenco Spot MkII) spot-welder. With sitting at its original elevation (on the floor), the cables couldn’t reach to the insides of the trunks I was reinforcing, so I had to get it up in the air to be useful.
The machine itself was found on ebay for about 1/4th its original cost, and it works perfect!
I took the finished project (and the machine’s glaring RED cover panel) to a local powder-coating shop and had them match it the rest of the welders.
More pictures here: ebay-find SnapOn-Lencospot-II | spcarsplus.com photo gallery
You’ll need to log in to post.