Monthly Archives: August 2013

Mould Making, and issues

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So, I’m now making the first side panel, which is an intersection of five planes. This is a bit of a step up from my other panels which have been flat.

I have another post to go into the making of the mould but this one is more about the chemistry. As I’ve said to Warren when being frustrated by this before, getting this right is a mixture of talents, namely being a baker, chemist, structural engineer and tailor. He’s got all those skills in spades, and I have few.

So, The mould shape was made from slabs of fibre-board (more on this in another post) clamped to the car and then bonded on the back with glass and poly resin. Then I decided to face the front of it with bog (car body filler) in order to get a reasonable finish.

Now for the trixy bit: epoxy and styrene (the stuff that smells sweet in bog) absolutely don’t mix at all, because the styrene gas breaks down the surface tension in the epoxy and it runs away. Remember this bit for later.

photo copyThe first approach to preparing the surface was to spray tack some release film to it and mould straight off that – it wouldn’t be super shiny and cosmetic but would be very quick to prepare the mould. Spray tack was applied and then release film. Initially it looked lovely and shiny. However, after a few minutes bubbles were appearing under the film, due to styrene gas coming off the part; it was very green at this point. Nadgers.

So, I call Warren and get advice. I don’t have ready access to equipment to spray high-build primer or 2k clear-coat, so the approach I can use is to mix glass microspheres in with the resin to bulk it out and make it easy to sand, then paint it on.

photoand … Disaster

 

 

 

It went off and separated. Three reasons – firstly I didn’t clean the spray-tack off (I assumed epoxy sticks to anything therefore spray-tack can eat my shorts), and secondly didn’t appreciate how sensitive some of this chemistry is. Thirdly it looks like the styrene gas is still bleeding through.

So, how to fix? Go to Warren, sand all the crap off and spray with 2k clear coat.

Job done, and I now have a reasonable mould.

Lessons Learned

  • It takes ages for the poly resin to stop gassing (weeks). Poly is the resin of choice for mould reinforcement though because it’s 20% the price of epoxy
  • it’s a lot of work with an orbital to get that lot off
  • make friends with a local body-shop who can do the spraying as a side-job for beer tokens.
  • It wasn’t necessary to apply the bog to the surface all over, and as thick as I had. All this meant was that I had a mildly uneven, slightly wavy surface. It doesn’t affect the integrity of the part, which fits nicely but it does show up if the sun is bouncing off it and you have a critical eye.

PostScript

I have now pulled a part from this and it fits well. what’s more, it is 546g in weight rather than the original ally panel which is 830g. A saving of 34%. The new part is also way more rigid than the ally. I have a post to follow about the part.

Aramid drilling Haiku

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you think when you work:
fluffy undrillable bitch!
but you need it so
photo
 
 
 
 
It’s very weird drilling through into this stuff. When drilling from the carbon fiber side:
  • firstly there’s there resistance as the drill sits on the outer epoxy layer before it gets through
  • then it’s turning through the two layers of carbon and turns of carbon come out
  • then the drill falls through the adhesive laminate layer really easily (it’s partly air)
  • then the drill hits the aramid and stops dead. It can’t cut its way through, it has to abrade its way through. eventually. The picture above is actually a hole I’ve cleaned up as best I can with a new stanley knife blade, which blunted in no time.

If you try and go through too quickly with something like a pointy grinding stone you introduce too much heat and delaminate the layers.

Still, it’s done now and in:

fluffy aramid

Transmission Tunnel Top Panels

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So, the three ally top panels that constitute the transmission tunnel are next for the carbon fibre, aramad, flat-panel treatment. One is riveted on, and two are bolted into nutserts. I need to go around the nutserts and put a tiny tack in place to remove the risk of them spinning, but that’s another job before the chassis goes off.

In order to give really good impact resistance from inside the tunnel and not risk the panel should there be a stone chip or other underneath, I’ve added two layers of aramid. If I weren’t to be manufacturing composite prop-catchers as well, I would feel secure in just using the two layers of aramid and the other parts of the composite to do the job.

Here is the layup is aramid, aramid, eglass (to add a little flexibility), carbon, carbon for stiffness and pretty facing bling. The pictures follow, before the price breakdown.

laid outHere you can see it all laid out with the aramid on top of the e-glass. I have decided to lay out an entire panel rather than three separate panels, or one panel just the right size, which would have created unnecessary offcuts. I at least have some finished offcuts of a good size that can be reused or sold on ebay.

 

baggedHere we are, fully bagged up and ready to go. The panel is more or less the size of the double-glazing unit I use so there’s no need to pleat the bag – envelope bagging will be fine and for my level of technique it’s quicker as well. The downside is you use a little more resin because the resin will run to all the corners of the bag.

 

infusedNow we’re fully infused, and you can see that the e-glass more or less vanishes. You can see the gaps around the aramid panels. If I were to go for a consistent aramid layer, then you’d get the fluffy edges when the panels were cut which would be visible in the cockpit and not meet the goal of being a cosmetic panel. As such, I’ve allowed a 15mm boundary around each panel for cutting. This is also the width of the metal that it’s mounting onto and means the aramid should fully sit in the exposed space and fill it completely.

 

disaster

And … Disaster … I didn’t spot a couple of stray threads on the panel before I laid it out and they’re now set in there for good. There’s no recovering this panel without making a new panel to bond on top. There’s nothing here that affects the strength with the stray thread, but I will make up a repair panel. Arses.

 

Layer Count Material Width Height Cost
1 2 200g Carbon 600 730 £22.60
2 1 e-Glass 600 730 £1.91
3 2 300g Aramid 130 540 £3.37
4 2 300g Aramid 130 480 £3.00
5 2 300g Aramid 130 320 £2.00
6 1 Peel Ply 650 800 £2.18
7 1 Infusion Spiral 730 £0.31
8 1 Infusion Mesh 650 800 £1.50
9 1 Feed Tube 500 £0.60
10 1 Gun Tape 3000 £1.32
11 300g Resin £6.63
12 1 Vac Bag 1500 1000 £3.72
£45.41

Ouch – I’m £45 in, and can’t use the panels from a cosmetic.sense. I’ll need to make a repair panel.

In order to cost the fina

Stainless, Rubber backed, sprung washers

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sprung washers

Sometimes it’s the little things that matter. I was looking for a clever way of bolting my carbon to the chassis, without having washers bite into the surface and damage the epoxy. Once quick bit of googling and I found these washers.

 

 

As you can see from the washer in the middle, they’re beveled and rubber backed so that when the load is applied, they go flat and the rubber forms a seal. Unexpectedly, I got them from a company specialising in pest deterrent and they’re for attaching anti-pigeon spikes to the sides of buildings and forming a water-tight seal on the way. Perfect for racing cars because they have a M6 hole, are sprung to remove vibration issues, stainless so won’t rust, and water-tight.

The company is PestFix – give them a ring – they’re a nice bunch and got a laugh and were interested in how these were being applied.