flat panels out of 3 layers of 450g CSM.
The plan is to try and get four panels made, ready for the next stage of the tub, which is the sitting in squab part either side of the transmission tunnel. It’s also a chance to practice my wet-lay technique.
I also think that if I am skinning both sides of a steel space-frame section with a diagonal in, then I don’t need the diagonal at all. Come to think of it, how brave should I go – make a full panel and dump the steel altogether? I could make a full panel and use a CF tube as a cross-brace if I wanted. If I made a panel it could be made from front-to-back uni-directional so I will be able to do it in two skins and a good core layer
Repeat to self –
I will not replace all the steel for a composite tub.
I will not replace all the steel for a composite tub
Now that I’m off to make the panels out of poly-resin I’m doing it outside, so hopefully I won’t poison the household.
I’ve been asked multiple times why I invest so much time and money, thought and energy into this build.
You need to listen to the “Space Tourism” episode of Infinite Monkey Cage (with Brian Blessed). There’s a bit where Martin Ince says that we need to drive around with Brian Blessed on a flat-bed truck … and then Brian comes out with
and I need to say: “You there! Get off your sofa, stop watching homes under the hammer, AND GO OUT AND MAKE SOMETHING”
Brian managed to put it very well.
So, I managed to get the wet-lay done last night. It took a couple of hours and about 4 litres of resin. The stuff I was using was simple non Lloyds approved resin from Leeds Fibreglass Supplies which worked well. I mixed it at 2% catalyst and in 2L batches. It only started to gel-off right at the end of the tub, which was a success. Also, the resin was pink not blue, and turned gray as the catalyst started to activate.
The part came out of the mould in about 90 minutes which was a fair fight. I’m really glad I used PVA again because it’s water soluble. You just get a thin wedge in (I used a plastic bog-spreader) and spray some water down. It slowly starts the separation and all is well. Keeping forth the birth metaphor, you can see the birthing remains stuck to the part. PVA is like a skin (rather than EasyLease which is a chemical barrier).
Here’s a nice shot down the top of the tunnel, or chute, or birth canal, if it were. What you can’t see is the quality of the surface finish. It’s actually quite shiny but there’s little sunlight to reflect off it (cloudy overcast day).
It’s not all perfect though – no matter how much resin I poured on and how manic I got with the bubble-buster (i.e. special wet-lay roller) I just couldn’t sort some of the white patches and it’s come through the mould. There’s the odd bubble between the layers (which I will live with – this is the master buck, not the part) but there’s also some dry patches of glass on the face.
Next steps are to dress the surface issues and then seal for a part … can’t wait.
- Making a master part from the failed mould was the right thing to do. Not only am I confident I have a good part but it was a step forward after the frustrations of the mould not working due to bad mould material choices.
- Thoroughly wet through the first layer. Don’t get resin on most of it and then try and catch up later. If I’d done this, even though I may still have had bubbles, I wouldn’t have had dry spots.
- Filleting wax is great.
- I rushed this a bit because I was concerned resin would be gelling off. Not so.
- 2% catalyst was right for this part in these temparatures. I was working with “winter catalyst” which is more aggressive.
- Laying large (300mm) strips down the side into the middle with lots of overhang into space means the glass is balanced on top of the part and doesn’t fall down into the mould. Once set, the overhang can be cut off and reused in smaller bits.
- Having lots of supplies (i.e. spare glass and resin) means you’re not fretting about running out (which I did last time) which meant rushing.
- Styrene stinks, and gets through the brick-work from the garage into the house. I need to think about what to do here.
This post is basically a lessons learned post. Thankfully the first thing I did meant all the other lessons learned have ultimately only caused harm to my wallet and my schedule.
After failing to get a seal on my mould, and in discussions with Warren, the best way forward with this tunnel is to take a fibre-glass part from it which won’t need a vacuum. It can just be laid in. This means I can crack out a quick part, ensure excellent surface finish, and then make a mould from that using a full mould making system.
The first thing to do is apply release agent to the mould, and I went for spraying in PVA (to make it all blue).
PVA Spraying Lessons Learned
- advice – not a lesson because i didn’t make this mistake – use a clean airline, not one that goes through an inline oiler.
- make sure you attach your airline fully to your spray gun, else it may fire free, hit the deck and spray dust and crap onto your mould
- you want a light mist each pass – anything heavier and you may get runs
- when you’re spraying near the bottom, you may blow crap from the floor onto the part
- because the mould is very smooth and well finished, you don’t need to spray loads of PVA in to go blue, you can do it with a wipe of the cloth. meh – that was plenty of time wasted, but at least I now know how to put it down in such a way that i can take a part off concrete.
- Spraying a mould this size to get that much blue meant I used nearly a litre of PVA.
Laying in fibreglass lessons learned
- for three layers of 450gsm chopped strand mat, your remaining last litre of resin isn’t enough. Not nearly, nearly enough.
- trying to put the glass in in 6 big pieces just means it all falls down
- don’t try to fit the glass to the mould and flange – let it hang way down each side – that way the weight of the glass stops it falling into the mould.
- OR, cut yourself lots and lots of 6″ strips of glass and lay them in – it’s not a competition to get the smoothest inside of a part – that comes later with the proper infusion part.
- it’s handy having a skip outside to throw away the glass that has only some resin on.
- it was sensible to cut my losses when I did
- I’m really relieved that I used PVA release agent – it’s water soluable
- I will pull what I can out of the mould, wash the release agent out (from where I manked it up with grit from the garage floor)
- Blast it with the power hose and start again
- I’ll wipe in the PVA this time
- I now have a 25 litre drum of resin and the right amount of catalyst – no chance this will happen to me again.
So, after discussing my mould-making woes with Warren last night, I got this message:
Composites can be a cruel mistress – that’s why there’s only a few of us bonkers enough to do it for a living.
That’s the truth.
I’m kind of in a James May place here, which there’s pleasure in learning the skills and looking at what you’ve done, thinking … I did that, and I did it well.
Wow – this mould is becoming a saga but it’s worth it to get it right.So, as you can see from the two pictures, the mould is finished and ready to pull a part.
So, the plan to get a part out of this mould was as follows:
- do a trial bagging session to understand how the bag falls in under vacuum and get a good handle on the pleats. write off the bag afterwards.
- lay in the first two layers and set them – this gives me a chance to examine the the quality of the finish and lets me decide if I like it before continuing. If I like it, I can put the part back into the mould and infuse the further layers into it.
But … DISASTER.
The mould isn’t remotely air-tight. I think it boils down to a fundamentally bad assumption on my behalf, namely that the wood I ordered would be vac-tight. It’s not. I did a test on a patch of it and couldn’t get it to hold vac at all. And that’s before I go investigating the other bits of it where it mates and the flanges for the three-piece aspect of it.
So, rather than faff about for a week and get nowhere and waste a load of bagging material, I called Warren for suggestions.
His idea was a step beyond my initial one (throw it into the skip) which was to lay a chopped strand mat part in there (no need for a vacuum seal with simple wet lay) and then take a mould from that.
This has many advantages:
- 3 layers of 450g CSM is cheap
- I can trial fit the part to the car. It’s not going to be anything like the final part (13mm thick) but will give me ideas
- it’s a one-off, so best bet is get the part finish as good as possible and then I can use a standard moulding kit to make the final, vac tight mould.
- I tried a hybrid technique of using part making material for mould making, which didn’t work
- you can use any old cheap bits for pattern making but moulds require precise application of the right materials and chemistry for resin infusion
- I have a good mould but nothing like strong enough or sealed enough for epoxy resin infusion
- cut your losses
- growth through pain. 80% of learning is experiential – I have learned so much getting hands-on like this.
So, I can now see a positive from this, which is I will have a part that can be wrangled into the shape I need and surface finished. Then I can make the right mould.