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It’s a dream that so many of us have: building our own chassis from scratch. Then reality kicks in. Where does such an endeavor start?
Last time we showed you the starting point for such a project, covering the layout and fabrication of the flat upper and lower sections of our Lotus Seven clone. With these sections done, the time came to put in the uprights and turn our two-dimensional sections into a full three-dimension chassis.
While many chassis are built in jigs, this chassis is a one-off for us, so we didn’t go through that extra effort. Instead, we used the flat, level surface of our table and lots of measurement to make sure our chassis dimensions stayed correct. We probably spent more time measuring than fabricating, but the result is very square and true.
Whether you’re building a chassis, a set of sawhorses, or anything in between, follow along to learn our methods for a precise build.
1. In our first installment, we built the upper and lower front sections of this chassis on our 5×7-foot fabrication table.
2. We started the next level of the project by lining up the lower section’s centerlines with the centerlines established on our table.
3. Our upper section needed to be at a height of 13.25 inches. To establish our height, we clamped some 1/8 x 2-inch steel scrap left over from another project to our upper section.
4. We precisely set the 2-inch steel to the back end of the lower section. We then ensured it was square to both the table and the bottom section. That way, any measurement at any height to the 2-inch steel could be used as an accurate reference. Next, we attached the upper section using clamps and, of course, squared it off.
5. At the front of the chassis, where the upper and lower sections are a different width, we used a larger square to make sure the upper section was precisely centered. Touching the edge of the upper section with one leg of the square and measuring with other leg, we checked each side for an identical measurement to our centerline.
6. We used a couple of levels to double-check our measurements. Since we had leveled our table, the chassis would be level as well. Some levels, like the torpedo level in the foreground, have a groove in the bottom so that accurate checks can be made even on round tubing.
7. We cut our uprights and fit them to the chassis using the methods described in our previous story. The four uprights in the front leaned in two directions, so we spent quite a bit of time sanding and filing to get the angles and lengths perfect. If an angle or length is slightly off, it’s likely that the dimensions of the chassis will shift during welding. We spent about 2 hours making these uprights and scrapped three attempts that didn’t fit well enough. It’s better to scrap a piece and start over than try to weld in a poorly fitting part.
8. Due to the angles of the uprights, clamping them in position wasn’t very practical. We used small magnets to hold them prior to welding.
9. We started tacking the uprights in position. We put a tack in the corner of one upright, then its diagonal. We did this because there is a bit of shrinkage as the weld cools, which can move the piece. Welding on the opposite diagonal tends to equalize the movement and keep the piece in place.
10. After every weld, we re-checked every measurement. The most important dimensions to us are the diagonals. We like to keep them within 1/32 of an inch–about 0.031 inch–of each other. We check them in several areas as we weld. If any measurement is off, we stop welding and correct the problem.
11. While this picture looks just like the previous one, there is one big difference. With our tack welding done, we removed the clamps holding the chassis to the table. If we’d done a good job of fitting and welding, the chassis would hold its dimensions without the clamps. In this case, it did. Taking our time, measuring often, and correcting problems right away added up to success.
