Front Keel Jig Finished

Front Keel
Front keel jig holds a mockup of the front keel, precisely
positioned in three dimensions and three axes front and rear
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Building the Roll Hoop

Roll Hoop on Drawing

Roll Hoop on Drawing

I’d been poking around local tool stores for a while, looking for tubing benders. I’d found and purchased a 3-wheel tubing bender, but so far no mandrel-type benders. I need both types. Finally, someone suggested I try a shop that builds headers and exhaust systems, and bingo, success, not 100 meters from my daughter’s school. They have a huge floor-mounted motorized unit with all the necessary mandrels. Of course, on the same day, I found a shop selling mandrel-type benders but it appears I don’t need one now. So the header shop says, sure, they can build the rollover hoop, although I’d have to wait about 10 days as they’re booked solid until then. The price was right, however. Really right.

Rollover hoop in place

Rollover hoop in place on chassis jig table

They don’t have much (any?) experience working from drawings, unfortunately. When I went to pick up the two samples, the boss mentioned they’d bent the top section 15 degrees forward. I pointed out on the drawing, “You mean like here, where it says 10 degrees?” Oops. “We’ll fix that for you by tomorrow afternoon.” So I go back the next day and everything looks fine. I take them back to the shop and lay them out on the full-size drawing I’d given to the shop so they couldn’t possibly get it wrong, and, well, they’re not even the same as each other. One is about 15 mm too narrow. The other needed a half hour of work on my tubing bender to make it match the drawing, but we’re on our way!

I’d like to meet all the SCCA rules for Formula 1000, but sourcing the required tubing in Thailand is difficult. The prototype will have to be an adaptation of the US rules to fit tubing sizes and types available locally. Where SCCA rules require seamless or drawn-over-mandrel tubing for the roll cage, I’ll be using ERW (electrical resistance welded) tubes. I’ll also be modifying the required diameters and thicknesses a bit. That means this first prototype won’t be able to be homologated under SCCA rules for racing in the US, but realistically that wasn’t going to happen anyway. I visited a shop called “Boon Racing Pattaya” and talked to the owner about tubing. He said everyone in Thailand uses ERW for roll cages and recommended I visit Chinatown in Bangkok to buy any unusual sizes or types.

Lower Front A-arm Front Attachment Point

Front Suspension Jig Point

Lower Front A-arm Front Attachment Point

The first jig hard point will be the lower front A-arm front attachment point. This may look a little odd if you’re only acquainted with street-car derived race cars, as the lower front A-arms almost meet in a point under the car, much like a Formula 1 flexure. This gives the suspension the optimum geometry for minimal camber change under body roll, and is part of the reason street-car based race cars can’t come close to the performance of a purpose-designed formula race car. The jig attachment point is fabricated from 3″ x 1/4″ steel C-channel, cut to the basic shape with the plasma cutter, ground with an angle grinder closer to its final shape, then the reference faces were milled on the milling machine to an accurate final shape. Then I turned up a small cylinder like the one that will be welded into the chassis, to serve as a spacer to locate the braces when they are welded to the chassis table. In the photo, the braces have not yet been welded to the jig crossmember.

Table Damage

Plasma cutter erodes concrete tabletop

In the process, I learned something not to do with the plasma cutter. I laid the C-channel on a concrete table for cutting, and the plasma stream went straight through a quarter inch of steel and seriously eroded the concrete. Hard to believe this took only seconds to happen!

The plasma cutter is an amazing tool. Cutting through this much steel with a 14″ portable cutoff saw, well, after 15 minutes I gave up. Once you know what you’re doing with the plasma cutter, a cut like this takes only 10-20 seconds.

Plasma Cut Edge

Raw edge cut by plasma cutter

 

Here’s what the raw cut edge looks like. Those ripples are from the shaking of my hands as I move the cutter. When cutting, you feel no resistance at all, but if you go too fast the cut won’t go all the way through the metal. When first using the plasma cutter, it took me a while before I figured out what I was looking at. The welding helmet has to darken so much, and the plasma is so bright, that you can only see a tiny area around the beam. Eventually I figured out that, if you view from the right angle, you can see the actual beam which is as narrow as a needle. Once you can see it you can control it better.

Quick Tour of the Machine Shop

I’ve been gathering the tools to build race cars since before I realized that was what I wanted to do. Before I finished building the house, I bought the really big machines at an open-air market in Bangkok and had them delivered through an opening in the machine shop wall that was later sealed up. Back then the truck could drive through the front fence and back right up to the front of the house, making delivery much easier. I’ve since lost track of the Bangkok open-air machine tool market, and would appreciate any info on how to find it again. Bangkok is a big place.

Milling Machine

Milling Machine

Lathe

Lathe

Bandsaw

Bandsaw

Drill Press

Drill Press

Tubing Bender

Tubing Bender

Tubing Bender Mandrels

Tubing Bender Mandrels

TIG Welder

200-Amp TIG Welder

Plasma Cutter

40-Amp Plasma Cutter

Building the Chassis Jig Table

Chassis Jig Table

Chassis Jig Table

As I plan on building many of these cars, and they must all be exactly identical, I have to start with an absolutely flat, true, square, level, solid and repeatable surface. To that end I designed this chassis jig table out of 3″ and 4″ x 1/4″ steel C-channel. Over 500 pounds of it. I initially started the gardener off cutting steel, and although I told him it had to be perfect, 45 degrees seems to mean anywhere between 43 and 47 degrees to him so that didn’t work.

Next I hired my long-time Honda repair & upgrade mechanic to work for me full time, but he mysteriously stopped showing up for work and his phone stopped working after a week or two so I ended up building the table myself.

Anyway, now I know the table is as perfect as hand tools and my milling machine can make it. I figure it’s plus or minus less than half a millimeter over its length of 3.3 meters. The table sits on eight 5/8″ bolts that serve as adjustable feet, and in adjusting the table I found out just how out of level the concrete floor of the operating room is. I figure if I really want to make it perfect, I can flood the pit you see in the photos so the surface of the water is exactly level with the surface of the table, but that might be excessive.

Painting

Painting the chassis jig table

This was also a good chance to practice my welding. The Thais think TIG welding is exclusively for stainless steel so I didn’t even bring up the idea of TIG welding 1/4″ steel channels, for which they would use plain old arc welding. I bought a fancy 200-amp all-adjustable TIG welder, the most high-end one I could find locally, but the sales staff said Thai people don’t use the pedal controls and so they are unavailable in Thailand, even though the plug for the pedal is clearly visible on the front of the unit. Unfortunately all the TIG welding videos and tutorials I can find on the web pretty much assume you have a pedal control. After I got chased out of another welding store for riffling through their plasma cutter tips, looking for one that fit my machine, I decided it might be easier to just look on Ebay US. What do you know, I found everything I need from a supplier in China. So I ordered from my computer in Thailand, on the US Ebay site, from a vendor in China, and paid with PayPal, and the supplies arrived before I expected them.There was a bit of a problem clearing customs as they didn’t believe the invoiced value on the box ($13, heh, heh), but DHL took care of everything and found my house without me giving them any directions. That’s a first.

TIG welder foot pedal

TIG Welder Foot Control

And what a difference the pedal control makes! What was previously almost impossible becomes fairly easy. Now I think I’ll get some more practice by welding up some playground equipment for my daughters.

In case anybody needs it, here’s a free copy of the chassis jig drawings, four sheets of size A0 in PDF form. I just uploaded this file again as there was an error on the first page of the previously uploaded file, so anybody who downloaded the file before September 11, 2011 might want to get the latest version where you can see the top-level isometric view on the first page.

Also, note that there have been a couple of changes since this drawing was made. The holes for the feet are spec’d for 3/8″ bolts, but I upgraded them to 5/8″ (15.88mm).

Drawing Thumbnail

Download Free! Chassis Jig Drawings

Then, while building the table, I found it was a little hard to adjust without some diagonal bracing to hold it in place while attaching the top crossmembers. I added the diagonal braces you can see in the photo, made of 1/2″ x 1/2″ x 0.062″ square tubing, pounded flat at the ends, drilled, and bolted to the tops of the leg assemblies with 1/4-20 bolts. This way I could adjust the table for squareness and it wouldn’t change when I tightened the top crossmember attachment bolts.