Here is the spiral, with an extra layer of infusion mesh to carry it up on to the part. I’ve also ran my finger through the spiral to separate it a bit.

Spiral is down the middle, jointed by the t-pieces I printed.

Here you can see the spiral as it’s jointed and is taken around corners. It’s much easier to do it this way than bend the spiral through such tight radii.

Here’s the final part ready for the bag. I’m going to envelope bag it this time – I had a lot of struggles with a bag on the flange. I usually do better when I envelope bag it. The blue bits on the top are little cone-hats I made to give the bag some relief from the socket-headed cap screws. They’re in there against a modified t-nut so I can both use air to get the part out, and have a drain-hole afterwards. The red bit on top is one of the two vacuum exhausts. They’re positioned equidistant between the resin feeds. If I need to direct the flow of resin, I have four inputs, one at each corner.

So, here is the tub out of the mould. I had a lot of issues infusing this, and I’ve learned quite a lot whilst doing it. It’s gutting to scrap it, but it’s the right thing to do. Next time it’ll be right.
There are some high level mistakes that were mine, and they led to some lower level quality issues. It’s the first time I’ve done an infusion of this size and at the same time with a positive mould, rather than the usual negative mould. Doing it on a positive mould means I have to be very careful about the layer thickness otherwise I have a too large or too small gap between the part and the chassis rails I want to bond it to.

Some of the mistakes were down to layup technique, and some were down to getting the infusion wrong.
 I infused over a hexagonal core, and the hexagons were too large to not have a hole put through the middle.
Here’s another picture of the quality issues up close – now for the lessons learned:

Lessons Learned

• I over engineered the part – too much carbon meant it was too heavy. When I cut it open I had great consolidation – all the issues are cosmetic.
• In the spirit of making it ultra strong, I had core everywhere. Next time it’s going to be core in the floor, up the back and the top of the tunnel only. The core interfered with the close fit needed to bond it to the chassis. Again, this is due to a male mould. Normally I’d overlay layers in certain areas to achieve this. In this instance, I have to stick to the required layers to achieve a 2.5mm thickness up the sides and at the bonding areas.
• More holes in the core, and a thinner core
• The catch-pot imploded. I made one out of plastic. Air got in. A lot of air. I made one out of plastic and tested it for a week – it was strong. With the heat of the part (I had the tub heated to 35C) the pot weakened and imploded. Back to my all steel pot.
• The tubing sucks up a load of resin. I had 6kg mixed and it flew into the part. This caught me off guard and I didn’t have enough mixed. A small amount of air got in. If I’d had really strong vacuum (i.e. No pot death) I might have recovered.
• Have one KG of resin and hardener ready to mix. Even two.
• I took 4 attempts to get the bag on – next time I’m going to make a huge envelope bag instead – it should increase my chances of a perfect vacuum.
• No gel-coat. It’s a long layup and I was up against the clock. This drove some of the other mistakes. I’ll not be up against a schedule this time.

If I get another output that isn’t cosmetically great, I’ll spray it and be done. If it’s of a cosmetic quality, I’ll have it sprayed in two-part lacquer. This will give a great finish.

Problem

So, I need to decide which core to use in the sides of the tub, where I don’t really need huge stiffness like I do with the base, but I still need to do a trade-off between thickness, ease of working, stiffness and weight.

Weight wasn’t going to be my only trade-off here. I have some others to think about

• Ease of preparation started to become important when I started calculating the time required to prepare a standard foam such as the Airex. It needs to be scored every 20mm as a grid, and then at each intersection, needs to have a hole pit in (only 2mm or so) to allow the resin to flow through to the other side of the core. I did a square metre of it, and it took over two hours. Very tedious to do accurately.
• Ease of layup is also a significant factor. Some cores are very bendy, some are very rigid, and some will thermoform. I don’t want to choose a core of marginal better physical properties if it takes me days of frustration to get it into the stack. This isn’t just a simple flat sheet, but a large female mould with complex curves in multiple planes.
• Physical strength

Method

• Prepare three cores of the three materials I had readily to hand 3mm Soric (by Lantor), 5mm Airex T90 (from Trident Foams) and 3mm 3D Core (supplied by EC Fibreglass)
• Choose a very simple stack that demonstrates the properties of the core rather than the stack (so I chose 2 layers of 2o00gsm e-glass either side of the core)
• Infuse
• Trim all cores to the same size
• Weigh

• do a flex-test to see how rigid it is (clamp one end to a flat surface – hang a standard weight off the other end). You can see how the steel rule is horizontal, and the part has deflected.. 24g is the weight.

Results

• Weight – Soric (24g), 3D Core (23g), airex (29.5g). So, the airex is 2/5 thicker than the other two, and is 26% heavier.
• Deflection (therefore infer stiffness) – Soric 30.9mm, 3D Core 31.6mm and airex – 20.5mm

Ease of layup

1. Soric first – it’s more or less like a thick cloth, and will bend into most angles without being damaged
2. 3D Core second. It’s a bit like hexagons of foam which are stitched together. It will easily follow simple curves, and can be thermoformed into the tighter ones. It’s not great in tight curves and will separate at the meeting points between the hexagons
3. Airex last. It has some flex but does thermoform very well. However, getting the hot-air gun in there and pushing and shoving to thermoform it is going to be an arse.

Conclusions

• I was surprised a bit between the 3D Core and the Soric. Deflections were very similar for very similar weight, which is what one would hope to see. This means the cores were performing as a function of the distance they separate the cloth. I thought the Soric would hold a lot more resin than the 3D core mind, and the results were so close.
• The airex outperformed for stiffness, which is a symptom of the thickness it separated the cores. Interestingly, i could hear the fibers snap when i weighted this core, and it deformed at the end. Not sure why – further thought is needed.
• I will use Soric for the side pieces. The ease of putting it into the stack and having it follow tight curves makes it far better for me than the foam. The time and effort to score, hole, form and shape these pieces isn’t worth the extra 600g of weight the chassis will carry as a result.

This is for the side. It’s a complex shape so multiple pieces of card cut-and-shut. Once I’ve transferred this to a 5mm core I will cut the core and heat shape it to the side. 

I’m using solid core rather than flexible in pursuit of minimum weight.