Right, so, you’ve seen the video about laying up, and here is the final layup ready for the vacuum bagging stack. It also shows extra corner bracing and there are similar reinforced corners underneath in aramid.
The stack I have gone for is as follows:
- 6 layers of mould release wax to ensure a good barrier and a shiny finish
- one layer of GC50 clear gel-coat to give it a good shiny finish and UV protection (which it won’t need under the bonnet)
- three layers of chemical release agent
- 2x 350gsm CF, for the initial outer facing layers
- 1x 250gsm Aramid for intrusion protection
- 1x 200gsm e-glass for a little bit of flexibility in the part
- 1x 3mm soric for the core
- 400g of infusion epoxy mixed with 120g of catalyst (slow)
Rather than go for a standard side-to-side infusion I went for a circular infusion down to the centre. This stuck me as better because going edge to edge would require the resin to also climb back up the vertical slope and could spend time infusing into the corners. The vacuum will drag it up eventually, but it could be a pain. Furthermore, if there is a long wait as it gets into the final corner, you end up with the situation where resin is going into the catch-pot and the part isn’t yet fully infused (which is money down the drain). At least this way the infusion is relatively uniform, and gravity is acting on my side.
Once infused, I baked it at 50C for 12 hours in the oven, and then pulled the infusion stack off. Following is the video of me using the air-line lazy method for getting the first part of the stack off (the vacuum bag). I also used a new kind of peel-ply (knitted rather than the standard spikey flat stuff). It’s great for this kind of infusion because it will pull under vacuum into all the difficult corners. However, it remains a little stretchy after infusion, so it requires more effort to tug/haul/swear out.
Once the entire infusion consumable stack is removed, the part is left in the mould and the second stack is laid upon it in reverse order (without the GC50). The mould performed well and managed to split without too much trouble and about 50-75g wasted resin. I know Warren (who manufactures parts at volume) has a much more refined process for managing resin amounts – he writes the amount a part needs on the back of the mould. My parts are one-offs, so there’s no need to stress about that.
Once I had split the mould, and got the first half off, the second gave up the ghost really easily and I had a part! This was a hell of a moment because it’s the first time I’ve gone from idea to composite part in 3 dimensions. On the part you can see the extra shiny side, which was incredibly easy to get to. I washed the chemical release agent off with warm soapy water (didn’t seem to make much of a difference, to be honest) and then I put a little Farcela 300 Polishing compound on to a cloth and gave it a bit of a rub – no real application of elbow grease required and this is the result.
The part has been partially trimmed (dremmel with a steel slitting disk, P3 safety mask) and offered up and it’s a great fit. You can just see the deliberate fitting gap between part and chassis, which should be between 1 and 2mm for the adhesive to work well.
This time the view is slightly different in order to show the clearance a little more between the part and the chassis. I had deliberately left a min of 5mm to allow for some absorption in a side-ways impact. I could have taken the footwell deeper if I hadn’t welded in the extra strengthing bar you see there to complete the cradle around the engine.
Sorry about the crap qualitty of the photo, but this is where you shove your feet. It has been sized to take size 11 trainers so most normal feet will fit fine. For final fitting, I’ll trim that remaining lip off, and bond the part of the contacting edges only. If I decide to go belt-and-braces, I will make some 90 degree angle and bond that onto the chassis and wrap it around on to the part.
Stronger than steel, far better shape, and I’ve not yet made a weight for weight comparison with the steel I cut out. I’m proper thrilled.