Fabricating the Differential Mounts

Finished Diff

Finished differential, differential mounts, and rear sprocket

Thirty-four years ago I designed a car for the SAE collegiate Mini-Baja competition. The differential was inadequately supported in the middle, and although it didn’t break on us, it broke the next year and sidelined the car. I’ve felt guilty ever since, so that’s one mistake I’m determined not to repeat. This one should be adequate…

Later I plan on fabricating some sort of container or plugs to keep the oil in the diff.


Building a Workshop Gantry Crane

I need to be able to lift the engine into the chassis, but due to the lowered floor of the work area a standard engine lift won’t work. While I’m at it, it would be nice to be able to lift the entire assembled car off the build table, turn it ninety degrees, move it to the door, and roll it out of the shop. Below is the solution. Sorry there aren’t any plans. The build process was “go to your local metal recycling center, buy some scrap beams, clean them up, cut them as necessary, and weld them together”. I’m getting more comfortable with winging it in the machine shop.

Also shown below is a mount I built to mount an angle grinder on the lathe. Parting-off has always been a problem. I’m just about to make the engine mounts, requiring at least 36 cutoff operations, and I figured I’d better solve the problem. I have a cutoff tool but only purchased a small number of carbide inserts; the inserts wear out really fast and I either have to order more from the US or drive at least an hour to a store that MIGHT have them. This baby works great, giving a clean straight cut. Just have to be careful not to let the abrasive get into the lathe.

Designing and Fabricating the Steering Rack Mount

Rack Mount

Steering rack mount, ready to weld gussets.

Next step in getting the car rolling is to mount the steering rack. These parts were not laser cut but were cut with angle grinders and my bandsaw, because they’re, um, a design improvement. Yeah, a design improvement, that’ll work. It took me months to find a blade for my bandsaw, because Thailand. Anyway, now it’s useful for these kinds of tasks.

Once again we have something that looks simple, but took a great deal of thinking to arrive at. As Steve Jobs said, “Simple can be harder than complex: You have to work hard to get your thinking clean to make it simple.” I used to do almost exactly what Steve Jobs did; in fact, he once called my boss to persuade him to cancel the design we were working on, because Jobs was going to do it better (he didn’t). So I understand precisely what Jobs meant about simplicity. That might help explain why this was my fifth complete design for this subassembly. One downside of mechanical design: when you’ve sweated out an elegant design, anybody can take a casual glance at it and say “OBviously”. To which I reply, “OK, there’s probably an even better design out there somewhere. Let’s see you find it.”

Also attached are a few of the finite element analysis (FEA) tests that I performed to verify and improve this design.

Rear Suspension Rocker Arm Mounts & Nose Mounts

Rocker Bushing

Rear suspension rocker arm mount shaft bushing

Above you’ll see that my welding continues to improve, although slowly. In response to the deleted commenter of the day, yes, we do use dyslexic dwarfs to do our welding, but we get ours from Lithuania. Good guess, though!

Next we have photos of the rear suspension rocker arm mounts. As these have to be positioned correctly in three dimensions and three axes, and none of those are X, Y, or Z, it took about a week to get these fabricated and fitted. Starting with laser-cut pieces proved useful as that gave me a known-good shape to start from, but some of the frame rails could be a few millimeters off. Also, every time I weld on something it distorts. Both halves of the rocker arm mounts must be precisely concentric and exactly the correct distance apart. Unfortunately they are not connected directly to each other in order to allow for rocker arm movement between them so there’s plenty of opportunity for them to move, even though I did the welding with the rocker arm shafts in place. In the photo with the control arms installed, you’ll see one answer to that: a long piece of steel rebar turned to fit inside the rocker arm shaft bores. Pounding on that with a rubber mallet would move the bores back into alignment a bit at a time.

Also, nose mounts. In the end these look terribly simple, but it took me a lot of thinking about how to do this. They have to be strong enough in one direction to lift the nose of the car with a pivoting jack, and in the other direction they have to support the downforce of the front wing. Also, they can’t protrude or be sharp so as not to injure another driver in a crash while taking the tremendous force of a forward impact, and have to allow the nose to be adjusted in three dimensions and two axes for proper body fit. Body installation begins here; the rest of the body will be keyed off the nose.

Nose Mounts

Nose attachment points laser cut and welded in place.