# Resin to cloth ratio by weight

So, 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.

# Method

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.

# Conclusion

 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.

# Assumptions

• 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.

# Lotus fully adjustable hubs – prototype for mine?

So, a while ago, ceebmoj from the project cyan blog asked me about some fully adjustable hubs my friend Simon (from Cornering Force – chassis dynamists) made some fully adjustable hubs for his Lotus Esprit race car, and I said I’d get some photos. It’s total car pron.

This is what the blank looks like – made from a piece of billet aluminium about 50mm thick. You can’t laser cut this that thick, so it is water-cut under-size by about 5mm all the way around. This is because the jet is less accurate on the far side of the cut. However, the facing side of the cut is accurate. So, you then start on the facing side and machine it all the way through accurately. Then you have both sides accurate.

This is the hub with the bearing bolted on. Simon found a bolt-on bearing that was the right size for the Lotus. Then, of course, the hub was designed to take the bolt pattern.

Now we have it from the other side with the caliper and disk attached so you get an idea of just how it is fully mounted. The piece at the bottom allows fully adjustable bottom wishbone height by varying the shims.

Here is the shiny lovliness going up the back.

I hope you pleasured yourself over this, and normal service will result soon.