Monthly Archives: October 2014

Transmission tunnel top, quantities used

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This is probably dull for any reader out there, but I just wanted to keep track of materials used for the tunnel top.

I mixed 300g of resin and 90g of catalyst at 40C (I put the mixing pot in a simple ban-marie), and then put it in the degassing chamber for 20 mins – it hadn’t finished but I was paying attention to the fact that I had the resin quite a bit hotter. It’s definitely like runny soup at this temp. Interestingly when you mix the resin at temperature, it degasses naturally much quicker, so there was a lot less foaming in the chamber – just some polite bubbling.

So, after the infusion, I had 45g of resin left. I’d also left the tap open for 30s after I’d closed the vacuum (a Warren tip) to make the part slightly resin rich to enable a better facing surface, and to have a slightly thicker layer in case I want to do a little polishing.

My rough calculations are that I’ve used are:

  • 300g of resin consumes a volume of 250ml
  • 0.3125 msq of 350g 2/2 twill carbon – weight 109g
  • 0.3125 msq of 200g 2/2/ twill carbon – weight 63g
  • 345g of resin comsumed – it’s not all in the part – the tube volume alone will account for 12g, and the peel-ply and flow-mesh absorb lots and lots of resin, as do the infusion spirals, etc.

    • So, crudely 550gsm (in two layers, which means more holes) consumes 1.06KG of resin, per msq. The actual weight of the remaining part will be a lot less than that. The larger the part, the smaller the ratio of resin wasted in consumables. Continue reading →

    An infusion went wrong

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    So, I was finally ready to infuse the transmission tunnel top, after deciding on a compromise. The compromise was to not spray the part with clear gel-coat first, even though I had some scratches in the mould. [1]. I reasoned that the scratches will leave a positive on the part, and that can be flatted off with some wet-and-dry and a little polishing.

    IMG_0137.JPGSo, I laid up the part (one layer of 350 facing cloth, and one layer of 200 backing), found to my surprise that I got the bag to seal first time, and set about infusing the part.

    DISASTER

    This is the first time I’ve had a stuck infusion, and as I think about it, it was a culmination of a bunch of factors all adding up together to cause issues. The factors were:

     

    • IMG_0138.JPGI decided to infuse along the short side and go up the full length of the part, rather than infuse across the shortest distance (I’m running low on infusion spiral)
    • it was 10C in the shed when I was mixing the resin, and I thought “It’ll be OK – it means I can use quick catalyst and it won’t go off all that fast”. I ignored the gloopy sensations.
    • I was feeling impatient, and thought I could get away with quick resin, allowing 10 mins for degassing because it was cold
    • my oven is out of action: it’s in pieces while I make it bigger for the transmission tunnel. I thought I had enough kingspan for the job, and I was short by one roof baton length. This is now bought and sitting in the boot of my car. This again was an incentive to go for the quick catalyst
    • when I was mixing it, it felt more viscous than normal, which should have been a warning that stuff was about to go wrong.
    • when I infused it, it got stuck half way along the part and the resin went off in the pot.

     

    So, I think the resin being too viscous meant it didn’t march along the part quick enough before it started to go off. If I’d used slow resin the infusion could have ran at the snails pace it was going at and it wouldn’t have been a problem. What’s more, I could have warmed the resin up (with the slow catalyst) and it still wouldn’t have been a problem. For the handbrake bracket, I actually had the resin at 40C to ensure it wetted the part out properly. So, this evening I will finish the oven, take the half-part out of the mould, salvage the cloth I can which I’ll keep for backing layers, and have another crack at it.

    [1] My compressor has died, and the replacement part (£160 if I can wait for a machine-mart VAT free weekend)

     

    it’s been quiet, but

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    The day job has been a little overwhelming, but I’m now feeling like there’s time for the car. This is a bit of a pity-me post, because there’s been a cavalcade of stuff go wrong on the car jobs. It’s been a cascade of things interrupting other things and generally getting in the way.

    Problem 1 – a mild amount of meh

     

    Do you feel intimidated?

    I have got myself a new sander to make the access hatches the right height as well as a host of other straight edge sanding jobs. It’s a great bit of gear, and the photo shows the gist of it. I have replaced my bench-grinder for it. First job is to secure it to the bench – best way for my bench is self tapping screws into the wood. Off I go, and find my screw-driver is running low. The power-tool superhero in my head says “No Problem! – we have AIR POWER”, so I put the screwdriver down and get my air-screwdriver. This leads me to problem #2:

    Problem 2 – My compressor carked it

    I asked the nice people on locost builders who think it’s probably a starter-cap. This is a £10 part, rather than the other issue, which is that I may have seized my all-in-one pump/compressor unit, which is a £150 part. Either way, until I find the time to get it out from its boxed-in sound reducing cabinet I built, I can’t attach the grinder (minor woe) but I also can’t spray the clear gel-coat on my transmission tunnel top, which is a larger pain in the arse. I’m 50/50 about spraying the gel-coat. It gives me two advantages: Firstly, I have some UV protection (minor) and secondly, I introduced some minor scratches in the mould, and having a gel-coat to polish reduces the risk of going through to the carbon if I want a super-excellent finish on the car. I can work around this a bit by making a the tunnel top a little resin rich. I’m only infusing the facing layer to start with.

    Problem 3 – my oven is too small

    I always knew this day would arrive. I knew my oven wasn’t big enough for the transmission tunnel, so I thought: “let’s make something of the day work out, and I’ll extend the oven”. It was at this point that I realised I miscalculated how much kingspan I had and couldn’t finish the oven.

    So, I have a broken compressor, an oven that needs work, and a part that I can’t spray.

    Solution: whiskey, and tomorrow I’ll lay the part without gel-coat and make it a little resin rich. I’m not looking forward to getting the compressor out and diagnosing it’s ills though.