Tub nearly finished

so, here is the tub, and here are some of the gaps. The gaps aren’t going to be a problem because all the in the corners need to have a radiused edge. I will be doing this with plasticine and the radius ball. At the end of this I should have really neat lined edges.

Then it’s ready for the mould making process. Actually it’s not, first I need to put all the flanges on in order to actually pu the mould  in this, but it’s nearly there.

I also have some of the polypropylene sheet in the tub which is still a little bit flexible. I’ll be getting in behind that with expanding foam to give it a backing layer to stop it flexing. I will need to cover some of the suspension with release sheet first otherwise the expanding form will stick to it and everything will be an unholy mess. I’m also going to have to take the engine and gearbox out now. I don’t want them to get covered in gelcoat when I start spraying.



Notes on applying Meguiar’s No 16 Wax

So, again, thanks to Vic, I’ve started applying wax to the transmission tunnel in order to both give it a decent shine and put a layer of release in there. The wax won’t be the only release agent I will use – i will also spray a healthy coat of PVA on there as well. When the whole thing is blue, it’s safe 🙂

The wax is Meguiar’s No16 paste wax, and is great stuff. It’s a lot thinner than the mould release wax I have used in the past, which took some polishing off with a micro-fibre cloth. This time, I have started using a red polishing head on my rotary polisher, and that’s making light work of buffing it. It should do considering it’s on a nice large flat surface.

Lessons Learned

  • Put it on thinly – if you clag it on you just spend more time polishing it off, wasting wax. A nice thin coat means the polisher can whiz over it and bring out the shine all the quicker
  • speed setting on the polisher is between 3 and 4
  • it takes a while to dry and glaze over – I left it overnight which isn’t the norm at all, and it was 5C in the garage. This, I think, is a reflection on my operating conditions rather than the wax

Testing Carbon Fibre before I commit – Part 2

So, here is the raw results file:

raw data

I’ve kept it there in the spirit of honesty, but the following distilled data into the graph is what really matters:

new graph


So the numbers that matter are those on top of the line – each of those is the number of KG force required to deflect the part by a given distance. You can correlate the colour to the number to the data in the top chart (click through for details)

Finally, there is the density/deflection ratio, which would show the ideal performing part if absolute strength wasn’t the most desired outcome.



There is a trade-off between core and layers, which is what would be expected. What actually surprised me the most was the difference a core makes.

The top line has two variables set – 4 layers of CF (rather than 2), and a 10mm core, rather than the yellow line, which is 4 layers and a 6mm core. The third highest line is the darker blue line, which is 2 layers and a 10mm core.

So, it’s layers over core but again, there’s a trade-off. The red line is 4 layers over a 3mm core, and you can see it yielded really quickly at 3mm with a very low amount of force (well, 98kg of force). Without doing any statistical analysis, I am observing that each 3mm of core seems to give me an extra 100kg of resistive force before yielding. However, I don’t know how far that scales.

Finally, you can see that there are a selection of flat lines near the bottom, and they are parts made without core. The seem to bend a lot and not yield. For my purposes though, they’re not suitable. Parts 6 and 7 (four and two layers), deflected up to 7mm without yielding, but weren’t much use to me.

As the thicker parts started to yield, we could actually hear them crack (quietly). I’m assuming that’s the fibres snapping. As such, the moment it starts to happen the part is compromised.

Testing Carbon fibre before I commit – Part 1


Some carbon fibre flat pieces were made and tested to see how far they bend for a given load. A load cell was used to measure the force.


So, before I go mad and put several hundred pounds of material into my CF tub, I thought it best that I do some clever investigation into just how does a composite structure bend, yield and break under various loads. So, I made the pieces, tested the pieces, and did some graphs, and came to some conclusions.


8 trial pieces were made of various thicknesses – different cores and layups. Each piece had a few things in common though:

samples 1

  • single layer of 300 gsm aramid for intrusion protection (if it were on the car)
  • this was balanced with a 300 gsm piece on carbon on the opposite layer to the core
  • one layer of 600 gsm either side of the core, and one layer of 200 gsm e-glass either side of the core for a little tolerance and flexibility.


samples 2I could then vary the thicknesses of the cores and extra layers of 600 gsm carbon I wanted to use. I opted for the following core thicknesses:

  • 10mm closed cell foam (CCF)
  • 3mm CCF
  • 6mm (2x 3 layers of 3mm CCF)
  • none


In order to test the bending load, I went to see my good friend Simon at Cornering Force. There are only so many people who like it when you call them at 8pm and say “Hey – do you want to stress test and break some carbon fibre?” After marking up each sample, we then put each on a support, resting on the bed of a mill, and pressed down on it with a load-cell. The load-cell had a 25x50mm contact face. The mill allows us to make vertical adjustments in 0.1mm increments easily, and the load-cell is accurate to the gramme.


The pieces were laid out on one sheet, and infused as one piece, and then cut to size afterwards. The vacuum feed was left on post infusion and for the curing cycle. The resin was degassed. This was to ensure the maximum amount of spare resin was removed until the gel stage. After gelling and the initial cure, they were post-cured at 60C for 12 hours, as per the manufactures instructions. This gave me the maximum strength possible for the sample for the least weight. I decided not to vary curing methods (e.g. length of cure) because a 12 hour, 60C cure is what I can achieve for a part as large as this.

The plan was to work out how much a piece would deflect, how it would yield and fail, and just what were the most significant factors in this – is it core thickness, is it amount of cloth? Did I turn around three times widdershins?

This was also a good opportunity to try a couple of techniques given to me by Vic at Scorpion CDL. I am always astounded at the wealth of technique he has and the quality of work done there.

Lessons Learned

I also had a slight infusion issue, which was the temperature of the resin I infused with. I had it at about 10C which was great for it not going off, but made it too viscous, and meant de-gassing it was a pain. It also meant the infusion was quite slow for such a small part. Further checking says 25C to 30C is a better temperature for this. I should have also wrapped more mesh around the input spiral which would have also alleviated this problem, but that was fixing the wrong problem – get the temperature right – let the resin flow.

Analysis and Conclusions

Coming in the next post.

Here’s the new transmission tunnel part – sides are mdc, and curved surfaces are body-filler. There’s an entire wooden frame in there keeping it all in shape.

I’m using some ultra sticky double sided tape to hold the side panels of the tub in place. You can see the stuff here. It’s incredible.

Here is the polypropylene plastic sheet forming the side of the tub mould. The tape gives me 0.7mm clearance between the sheet and the side, which is a good gap when I apply the epoxy adhesive to put the final tub in place. The adhesive has a maximum structural fill gap distance of 2mm so precision is called for.