Monthly Archives: January 2014

Designing and Fabricating the Steering Rack Mount

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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

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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.

More Laser-Cut Parts and Panels

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Laser Cut

Second batch of laser-cut parts.

I received my second batch of laser-cut parts, this time from a new supplier that has some more reasonable aluminum. They did a reasonable job, but man were they slow. It took three visits and more than two weeks to get a quotation, then I forget how long to do the work. Then when they were finished, I had to call them to find out. This is Thailand.

The parts are cut from both steel and aluminum of several different thicknesses, and include the radiator and oil cooler mounts, differential mounts, some engine mounts, the entire pedal cluster, parts of the steering column, chain tensioner, nose mounts, steering rack mounts, steering column mounts, lap belt mounts, chassis side panels, seat panels, the firewall, fuel tank, and even an idler sprocket.

Laser Cut Panels

Laser-cut panels including sides, seat and fuel tank

Fabricating the Pushrods & Upper A-Arms / Wishbones / Control Arms

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Finished

Finished set of control arms, tierods & pushrods

The upper control arms are all identical except that the bearing cups are mirrored from the left to the right so that the snap rings are on the bottom. If I can find a way to stake the spherical bearings then all four could be identical. Staking is a process that uses a hydraulic press to deform the bearing cup into a chamfer around the circumference of the spherical bearing, holding it permanently in place.

I printed out the layout of both control arms onto size A0 paper, glued the paper to a sheet of plywood, and drilled holes for the centerlines of each rod end and spherical bearing. This gives me a jig I can use for tack welding the parts in place. Washers under the bearing cups locate them vertically for tacking. The bearing cups proved a little too thin to weld without distortion, so I had to re-cut the spherical bearing bores after welding. Luckily I have an indexable end mill of just the right diameter, and running my mill at high speed with a lot of coolant gave a good finish on the bores. I then pressed the spherical bearings into place before painting as I wanted to make sure there were no glitches that would require messing up the paint to fix.

I sprayed Jotun Penguard 2-part epoxy paint directly onto the steel after first making sure the steel was scrupulously clean with a Scotchbrite pad on an angle grinder, followed by a cleaning with acetone and paper towels. The finish came out beautifully.

Custom Radiator, Lathe Cooling, Suspension Progress

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Time for a few miscellaneous updates.

Lathe Coolant

Homemade lathe liquid coolant system

I was always dreading having to machine steel. I had to do it  slowly to keep the temperature down and avoid chatter, even though I use carbide cutter inserts. Then I read somewhere that home hobbyists tend to be afraid to run the lathe & milling machine at high enough RPM to keep the cutting inserts happy, but  if they do it will cause the insert to overheat and be cooked in two seconds. I figured I can find the cojones to run my equipment at maximum speed as well as the next guy…

So one day I was browsing at my new favorite store, Hardware House in Rayong, and I saw a gallon container of cutting coolant fluid for sale. I’d had no idea of how to find this stuff in Thailand, or even how to ask for it, so it was pure luck to stumble over it. Or you could call it diligence in going up and down every aisle in Hardware House looking for things I might need. They also had flexible fluid squirters and 12-volt water pumps, so I put together my own fluid cooling system, pictured above. I drive the pump with an automotive battery charger which allows me to reduce the voltage and amperage to get the correct flow, and it works like a charm! Now I can cut steel like I used to cut aluminum.

Front Shocks

Front shocks, shock mount, and rocker arms test fitted

Anodizing and Plating Success

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Found a supplier of anodizing and plating services up in Chonburi called Thai Silvec. I kind of got the impression they’d never had someone just walk in the front door with parts that needed plating and anodizing, but they accommodated me just fine. Very serious Japanese management, everything organized and clean, and reasonable prices. They gave me a detailed quality report when they delivered the parts, so now I know just how much allowance to leave for plating a mating parts. For next time, that is. This time around, I’ve had to do a lot of hand work to get everything to fit due to the stack-up of plating and anodizing thicknesses. At least I had them mask the wheel bearing bores, so the bearings later pressed in smoothly.

First Laser-Cut Parts

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Below is our proof-of-concept for laser cutting parts in Thailand. Choices of material are extremely limited– ya got yer steel, see, and ya got yer aluminum. Unfortunately the aluminum is 1100, which has the structural strength of mozzarella, so I had to provide my own 6061-T6 to be cut. That didn’t reduce the price much, though. Redesigned some parts to match the available steel, which luckily is considerably stronger than cheese. I don’t yet have a sheet metal bender or supplier, so some parts have a slot cut where they are bent by hand and welded to shape as seen in the last photographs.

Part Eleventy-seven, In Which We Finally Lay Up a Body

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Finished Body

Another view of finished main body.

Time to lay up the first set of body panels. In some photos you can see the joggles laid into the molds with duct tape so the panels will overlap smoothly. Nine coats of mold release wax and there were no problems releasing parts from the molds, although at times I did have to work a bit. Each mold required about a day of finishing work to remove ripples due to waviness in the body buck. As I’ve said before, don’t build a body buck the way I did it. Instead, immediately after completing the X-Y grid of cross sections, lay about 3mm of fiberglass on top to give a good solid surface, then use body putty on top of that. You’ll be finished in half the time it took me. The only place you should use foam is where actual carving is required due to the complexity of the shape, like the sidepod air inlets. Yes, I know the main roll hoop forward braces are still not there. Patience…

One problem I found out the hard way is that a chemical in some brands of duct tape inhibits gelcoat curing. In the end, gelcoat that had been in contact with some kinds of duct tape never fully cured and had to be cleaned out with acetone. Also, the joggles formed with duct tape were too sharp for the fiberglass mat to conform to, resulting in bubbles under the gelcoat that have to be scraped out and reworked. Gelcoat is probably more trouble than it’s worth given its weight, so next time I’ll just prime and paint the body panels to finish them. The sharp joggle corners need to be filled in with fiberglass roving before laying mat on top.