Hard Point design for the tub

Here’s the design for my hard-point for harness mounting bolts. It’s 3mm thick steel, and the channels are 2x1mm cuts. What you’re looking at is the underside. The channels and holes are to allow resin to flow through and past the hard-point. The big hole in the middle is where the 7/16 insert will go and get welded. Each channel has been tapered down at the entry point so the resin can easily flow into the part.

I’m hunting around now for prices to get them CNC’d. I need 6 per side (six point harnesses) and I’m getting a couple of spare for welding practice.

When they actually go into the part, they will need a layer of glass-cloth either side to insulate them from the carbon to avoid any galvanic issues.

Aramid floor tray is in

Here’s the floor tray, all nicely bonded in.

IMG_3334Here’s the floor-tray all nicely bonded in. You can see on the right of the picture how the floor-tray now replaces the cross-member I removed. I put several extra layers in there as well to pass even more force forward (than the 6 layers of 300gsm that’s already in there).

There’s also extra reinforcement, like a lardy-blokes truss, to take engine mounts if I decide to do that.

So Mark – tell us how you did it

IMG_3316 2


Here’s the part as it came out of the mould – all sharp edges and over-sized. Next job was to put it on the car – mark it up and trim it. That’s the boring bit and I don’t have any photos to document.



IMG_3324This is the chassis before the part is bonded to it. It had been blasted before powder coating, and I used the right high-temp non residue leaving breaker-tape to mask off the mating areas. The blasting heaves a fantastic key. I was worried originally that the tape wouldn’t make a brilliant barrier to rust after coating but it’s worked out fine. The reason being, the coating forms a seal against the tape so there’s nothing to get in – no air or moisture so no rust.

I marked the part up after clamping it down, and drilled for rivets. The rivets were just soft-ally headed ones to provide clamping force rather than to be anything structural.




Here I am as Clampy-McClamp-Face. I had every surface clamped before I drilled rivet-holes. If you drill-rivet as you go along the part, it starts to creep and your holes don’t line up. Clamping the entire thing before drilling keeps the accuracy.



IMG_3325Here’s a close-up of the rivet holes – I’m pretty pleased with how accurately the holes line up. Structurally it’s not really important, but attention to detail matters.








One post-trimming, bonded, riveted part in place. I used an epoxy two-part adhesive. It’s the slightly flexible stuff for parts under a lot of vibration.

Once the adhesive set (24 hours for full cure at 20C) it feels rock-solid.


First Pedal In

Jake the Peg

Here’s the first pedal in, with the box fully bolted down. This is the modified OBP pedal box I made a while ago. OBP were great about what I’d done, especially after I emailed them and jokingly asked if my warranty was still valid.

After I’d bolted everything down, it then dawned on me that I didn’t have clearance to get the clutch-pedal pivot bolt in, so it all had to come out.

I also greased the bolt shank as well (copper grease) just for good measure. The bolt half way up the pedal is for the clevis, so care needs to be taken not to over-tighten or else the pedal won’t move as smoothly as it should do. I’ll get the rest of the pedals in this weekend. Speaking of clevises, the clutch master cylinder is a 0.72 bore, which is

It’s a great feeling to take parts I modified a while ago, and be bolting them into the car for good. Having them fit is even better. The only mistake I made is not allowing for the extra 0.75mm either part has for powder-coating. However, whilst snug, it fits.

Height Adjustable Suspension – Part 1

In the spirit of “if you’re going to change anything, change EVERYTHING”, I have almost finished the brackets for the height-adjustable suspension. As well as making the suspension height-adjustable, I’m junking the old wishbones for the following reasons:

  • I’m going to t45 oval tubing for extra strength
  • I’m going to spherical bearings rather than bushes (ugh – bushes)
  • I want to make the suspension height adjustable so I can lower it when I need to


IMG_2956 IMG_2962 IMG_2964The welding rod here shows the line of force that actually happens, and the angles it has to go through. Firstly nearest you is the angle through the bottom ball-joint. That’s quite severe. the second is at the chassis bracket where it will have the bracket under torsional force.




In order to get the bracket just where I needed it, and at 90 degrees to the line of force I made a simple jig – one hole to locate against the ball joint, and one there the bracket bolt goes through. The jig was machined to be a tight 90 degree fit against the bracket so it would always be perpendicular to the line of force.


And here it is up close. The wishbone will have a 3/8ths spherical bearing that slots into the bracket there, and then the bracket can be height adjusted by moving it up the slots.

The bracket is then reinforced at the back and welded to the chassis.

Shocker bottom brackets are finished – part 1


here are the two brackets. Each is 6mm thick to give strong support to the bolt – it’s not rotating but being shoved backwards and forwards. If you don’t use a decent thickness of steel, the holes will oval in no time and the bracket will lose it’s precision and things will rattle about.

The shocker has a 1/2″ spherical bearing in there, and will be coming in at an angle of about 40 degrees from the vertical, hence providing some back gusseting support.




Also, the back plate was 2mm going onto 6mm steel, so needed a little careful welding. I made a mistake on the first one (which you can see above on the right – the fillet is too big). I was running 95A which is good for getting a good puddle up on 6mm steel with a 1.6mm rod. I forgot to take it down to 85A when putting the gusset in (2mm corner fillet). however, I spotted my mistake and this side here is the result.


Tomorrow, I pick up some more argon and then these will go on the car.


I have my new wishbone receiving brackets

Here they are. the gap between the bracket to receive the spherical bearing is 1/2″, and the width of the bolt is 7.9mm, and there’s a few spherical bearings that nicely fit in here. What bugs me isn’t the price of this (£56 per bracket) but the fact that they have been used. I wasn’t expecting to buy used when they’re advertised as new.

These brackets are a great option to receive the wishbones and of course can be height adjustable.


Resin to cloth ratio by weight

IMG_2088.JPGIMG_2087.JPGSo, here are the two sample pieces, as mentioned previously in this post. They’re rough and ready, and not pretty to look at. What’s more, I had an infusion issue so there’s more air in the part than I would want.

However, it’s worth looking at the following dry weight calculations:

Part Final Weight Dry Weight Diff % Resin
with Veil [1] 136 103 33 24.26%
No Veil 144 110 34 23.61%

So, the lesson is that the part absorbed about 24% resin, excluding that retained in the infusion mesh, pipework, etc. It is also very important to note that the 10mm core is cross-drilled every square inch with a 2mm hole and has resin channels scored in the underside to allow rising to flow over the other side of the core. this will have absorbed some resin as well, which won’t be there if a core isn’t used.

Next post, I’ll get these under the microscope and you can see what the bubbles look like. If I can find a text-book infusion part then I’ll compare against that to see what gets left behind when the job’s done properly.

[1]The veil part is an experiment I ran with a piece of polyester veil under the facing layer to see if it acted as an air-removal medium to make the facing layer more cosmetically pleasing. Due to me cocking up and getting air in the infusion, I have no idea if it would have worked. It certainly didn’t work for me as a backing layer (as advertised). it absorbed far too much resin, was a pig to wet out and didn’t easily go into corners, leaving bubbles behind the gel-coat which have to be repaired.

How much will my tub weigh?

So, based on the sketch I made on the white board (below), I need to calculate just how heavy the tub will be. The main reason I need to calculate this is to be sure the 19kg I’ve taken out by chopping out all that steel and removing the ally panels isn’t then replaced by even more carbon.












I made a trial part, consisting of:

  • 4 * 600gsm carbon (2 above the core, 2 below)
  • 2 * 200gsm e-glass (1 above the core, one below)
  • 1 * 300 gsm aramid (on the bottom, facing the tarmac)
  • 1 * 300 gsm carbon (on the top, to look pretty)
  • 1 * 10mm thick closed cell foam for the core (in the middle)

The layup is symmetrical around the core, apart from the aramid on the bottom and the facing carbon on the top. I have discounted the weight of clear gel-coat applied to the finished part (assume 1kg at the end).

The part measured approximately 103mm * 204mm, and weighed 130g. This meant a unit weight of 0.006 g/mm2.

From this, I fed the dimensions of the panels above into my CAD package. Given a surface extruded to 1mm depth, it will tell me the mass of the panel, to a bazillion decimal places.


Part count Unit Weight Total Weight Running Total
Tunnel Side 2 2.37 4.74 4.74
Tunnel Top 1 1.16 1.16 5.9
Back 2 1.0375 2.075 7.975
Base 2 2.7 5.4 13.375

So, if I go for this, the new tub will weigh 6 kg less than the original steel work.


  • 10mm closed cell foam is used uniformly. This won’t be the case – the sides do not need a 10m core – I will probably go for a 3mm core.
  • the base, back and top of the tunnel need to be strong in bending load, the sides need to be strong in lateral load. As such, I can use a thinner (or even no core) for the sides. I think I will save 1kg there.