The turnbuckle link is shown for demo purposes only and is not the real item.
I’ve finally started the rear A Arms.
I spent hours checking out tons of options but went with my first attempt.
I wanted a design where I could loosen a lock nut, twist a turn-buckle link and lengthen one of the arms. However, with each design I knock out, I kept looking at everything thinking, ‘Blimey! That looks complex’, or ‘What happens if just one nut comes loose’. Some designs just looked weak and flimsy and were thrown straight out.
I sat in-front of the laptop flapping my forearm up and down, pretending it was an A Arm, twisting my wrist like some escaped lunatic. It was whilst I was performing these contortions, I looked at my first attempt and thought ‘Why -redesign the wheel?’
I wanted a set-up that would enable me to adjust the toe in/out, along with the camber and caster practically at the side of the road.
The reason I haven’t gone with the standard Haynes Roadster geometry, is because this vehicle is actually 4 inches wider than stock. The reason why I haven’t used polyurethane joints on all the joints is because this vehicle has been design with Anti-Squat. The outer joints would need a small degree of rotational capability as the wheel rises and falls.
Anti-Squat geometry stops the rear from ducking down under acceleration. Drag racers often employ 4 bar linkages with high anti squat angles, for traction of the line, however as anyone who remembers the old Rover SD1, it’s not necessarily good for cornering whilst breaking. I’ve only used a very small amount of anti-squat, as it’s never really been a huge problem in the Sevenesque type vehicles.
This is my final (or first) CAD design. Note the geometry and length of arms was already fixed by my Kangaloosh and Suspedit Calcs, it was a case of which arms I could put turn-buckles into, which joints would need to be rose joints etc.
Getting the threaded inserts into the ends of the tubes was a complete pain in the butt. The internal dimension of the tube was 29mm. The threaded inserts I’d bought, were advertised with an external dimension of 32mm. I had bought a 32mm drill especially for the purpose. The first problem was because of the large drill size and the 3mm size difference. As soon as I started to drill out the tube, it gripped and jammed the drill. If I was quick I’d release the trigger, but if I wasn’t, it tried to rip my arms off. It didn’t matter how gentle and slow I went, the result was always the same. I finally got the hole deep enough, only to find out the inserts I’d bought were in fact 33mm. Knowing what a major headache doing this was, I will make the next ones on the brother in-laws lathe.
Have you ever had one of those moments where you make one component at one end of the workshop and you’re really surprised that it is a perfect fit for something you made months ago at the other end of the workshop?
This was one of those Smug moments. Sure, I’d measured everything 30 times in all dimensions, but it’s still good when things just slide into place. As a quick check, I even checked my diagonals from a dot on my front cross-member and I was just double smug to find that the outer rose joint was virtually perfect. When I say virtually, I had to hold the arm at roughly the right inclination (normal ride height) whilst holding a measure in the other. The result was less than 1mm out.
Given that I didn’t make a gig for the arms and simply used micrometres and inclinometers – thats’ not a bad result…. Smug Smug Smug…..:)
Well, not so Smug really. 🙁
All the welds are tacked with the MIG. I want them TIG welded by a professional. This is when the distortion is liable to happen. Sure, I can’t flex them by hand, or even with a hammer, but never under-estimate a bit of heat!
I might just make a simple jig after all.
One of my fears has been put to rest. I was worried that the clevis joint on the turn-buckle would flex. As a quick test, I clamped the clevis on with a pair of mole grips and placed a long tube over the thread. Not a millimetre of flex. In fact it made a tune-full tuning fork type noise. Once the car is finished no doubt I’ll keep an eye on these joints, but for now I’m happy. If they are good enough for the Le-mans boys, they are good enough for me.