6 Feb 2009

Picked up some 1/8″ plate for fabricating brackets (for just about everywhere.) The OEM drivetrain-side mounts are bolted on and will guide how the chassis-side mounts fasten to them. The mounts need to be fairly strong since they have to handle vertical loads of maybe 5x for hitting worst-case potholes (about 2000lbs total.) Then there’s engine torque which can be 600 lb-ft or so, depending upon traction and gearing. In fact, the worst combination is to be at full throttle – at the edge of adhesion – and hitting a bad pothole; the shock loads through the engine mounts are quite large. And, if builders bolt on a supercharger and wide racing slicks and go drag-racing there’ll be even more force. That’s why they’ll all be triangulated; though it adds tubing, it’s better to be a few pounds heavy instead of having the drivetrain drop out half way down the track…

Speaking of brackets, someone asked how complete the chassis is. I asked if I should include the time to make brackets in my answer. That is, the chassis is probably 70% done if brackets aren’t included, but probably 30% if they are. Brackets take a ton of time, probably as much as doing the tubing; it’s just how it goes. Oh, and once again the rule-of-thumb is proving correct, that each end of a tube takes about 30 minutes to fully fabricate. Have six tubes to make and weld? Figure six hours to do it. Hmmm, doing some quick math, there’s roughly 100 tubes in the car so that means roughly 100 hours to build the chassis, then probably that much time again for all the brackets. Actually, these numbers are high because that’s how long it’s taking <em>me</em> – and the first car always takes the longest. Once it’s documented, future car’s should go much faster, especially when it comes to the brackets.

Along with the correct fuel filler from Aircraft Spruce came their latest catalog – great bathroom reading! Go to their site and order one; it has a lot more stuff in it than the website.

And finally, several people asked how I like using the┬áMakita LC1230 saw – it’s a beast. The blade turns a lot faster than expected and I learned a lesson early on. In hindsight it’s perfectly clear what happened and why, but it was pretty exciting. I wanted to cut a round tube at an angle, so set the vice and tightened it down. The blade just barely touched the tube – and it shot out of the saw at about Mach 7 across the garage. (The wife coming out and asking what the noise was, “uh,… nothing.”) The problem was two-fold, clamping round tubing in a vice with flat sides, and cutting it at an angle. The projectile tube had an impressive spiral pattern of teeth marks all down its side. Lesson learned, I now only cut round tubing at 90 degrees since I haven’t made an adaptor to properly hold it. For square tubing it’s fine, with the cut end is absolutely clean, with not even a tiny burr on it.