Final fitting of the tub


So, here is everything laid up as a reminder of where this started. I think it’s a good reminder of how far the tub has come, but at the same time it’s also making me think the duratec is photobombing everything in my garage.




Now, here it is in the car:

It’s pretty close to where I want it now, and I’m doing the final fettling. I made this with a positive mould, which has meant the outer surface (that fits to the chassis) isn’t perfectly flat. I’ve had to take it back a little at a time with the flap disk in the appropriate areas to be sure it fits. I developed a methodology to do this after I’d removed the obvious obstructions.

I go around the gap with a feeler gauge set to 0.7m, and look for areas it traps. When I find a trapped area, I set the gauge to 0.05 mm and see if that still sticks, and anywhere it does, I mark with tape (hence the packing tape on the tub at the back top) and take it back about 1mm with a flap disk. I deliberately only mark the jamming points rather than the tight points so I can avoid making gaps unnecessarily larger than they need to be.

Once everything is marked, I lift the tub out (it’s only 13kg, so two adults can easily lift it with fingertips) and do the sanding. When it goes back in it fits a little better. Everywhere is pretty much where I want it, apart from the back where it’s still a little high. Everytime I advance the fit, the back lowers down a bit. I have about 3-4mm left before it’s flush and I’m happy.

This one is a little more difficult to wrap your head around, but it’s the mating surface between the tub (carbon on the right, starting in the top right corner) and the chassis rail. As you can see, the gap is pretty uniform now, and I’m aiming for between 1 and 2mm.

It unfortunately means I’m doing to have to remove some of the powder coat with a flap disk.




Here is the birds eye view. You can just see the lip at the back. I don’t want to just sand it off – I think I can make the tub a better fir before I have to do that.

Then the final act before bonding it in is to have it lacquered and cured. Then I will have an awesome finished product.

Making a vacuum manifold

I suppose your first question is “what are you even on?”,  and your second question, is “why bother?” If you need a vacuum manifold. Well, to answer them in order:

  1. I am on a chair, in my office.
  2. If you want to double bag, or hold down vacuum whist you degas, isolate a catch-pot or pat your head whilst rubbing your tummy, you need a vacuum manifold.

I mentioned making this in the infusion stations post and showed how I’d connected it to my vacuum reservoir, also known as “my old compressor tank”.

Basically, I’d hoped this doodad that I’d wombled off eBay would work (it’s a CO2 gas splitter with valves for the unclicking) and hoped it would fly straight out of the packaging, but it turns out it has non-return valves in, which means it won’t work for vacuum. 

I tested it against my vacuum gauge and it’s great – seals well and holds vacuum both ways.

Here it is, in the vice after I’ve taken it apart to see what gives with the valves, and can I somehow get them out.
They were only turned in with PTFE tape, so were an easy extraction. It’s worth noting that the steel is either polished stainless (probably) or chromed. Either way, the finish was great.

If you look at t’photo ont’ right, you can see the on-return valve, and as I hoped (but didn’t have a clue about before I dismantled it), the housing for the valve (ball on a spring) is a press fit. All I then did was get the right sized drill in there, and started drilling it out. Sure enough, it went pop, and the whole thing turned out.

Here it is, open and ready to go. You can easily see through to the white foam I used as a backing material for the shot.

 And the the detail-obsessed amongst you, here is the spring, cap, o-ring and ball to seal it. Very neat and simple.

Infusion Stations

So, after scrapping my first CF tub, I decided I needed to improve a lot of things (thanks Vic) before I should commit lots of materials for the next tub. First of all was to improve my vacuum management.

What I wanted to achieve was:

  • Make it much easier to route vacuum where i needed it
  • Be 100% sure that I have no leaks in certain parts of the vacuum chain
  • In my case, I want to be sure that everything from the new vacuum manifold inwards was leak proof
  • Prove everything from the manifold to and including the catch-pot was leak-proof
  • have a solid, reliable catch-pot


Firstly, I created a vacuum manifold, printed a bracket and mounted it on to the side of the compressor. The manifold is actually a gas manifold for a caravan gas supply, and I got it new from Ebay for about £30. The manifold itself actually has a non-return valve in each tap assembly, so I had to fettle that. Not a hard job and subject to a different post.



Next I mounted the catch-pot onto the vacuum tank (or an old compressor I repurposed). This was relatively painless – again I printed a bracket. This time it’s the orange thing under the catch-pot. All it is is something that is curved to the tank on one side, and level on the other. Thus I could mount the catch-pot on the level. I bonded it onto the tank with metal-epoxy, and used double-sided tape to stick the pot to the mount. The tape is monster tape – it’s fearsome stuff won’t let go easily. It will let go if I need it to.

Finally the whole thing was piped up (below) and tested.

Once I had this working, I decided I wanted another bench manifold, and made one out of push-to-fit pneumatic connectors. This means I can put my degassing chamber on the bench and not have to connect it directly to the vacuum pump. There’s little time between degassing and infusing, especially if you have 3kg of resin in a bucket – it’ll start exotherming quite quickly. With my manifold setup, i can hold the part under vacuum whist at the same time degassing the resin. Then I just need to connect the feed line to it and I can go.


What you can see here is one branch of the manifold. There’s a t-piece at the bottom, and a valve in the middle. The top is the output. Again, I printed some brackets to give me just the mounting I wanted, and the white bracket in the middle is actually a 15mm hinge-clip for attaching standard poly-pipe when plumbing. They’re £6 for 100, so I bought 100. I have many spares. The top blue bit is the outlet at this part of the manifold. It lets me plug an 8mm pipe straight in to the quick-release connector.

This is the final manifold – the picture isn’t great, but you can see three outlets. It’s set on an old tool-board I used which I didn’t need anymore – far better reuse that (considering it was already bonded to the wall).

All hail Dolphin Glaze for filling holes

So, in feeling around the part, I’ve found a few small undercuts where I’d repaired the gel-coat with more gel-coat. I went around it with my fingers to look for issues, and found a few where the repair I’d done accidentally still went in a little, like a dimple. I’ve started using Dolphin Glaze as filler – it’s really thin and spreads well. It also comes in a squeezy tube so application is easy. I also bought a pack of onion paper for mixing on – wish I’d done it much sooner.   

It’s styrene based though, but because I’m spraying in a barrier gel-coat first, I’m not concerned. 

So, next is to make a 2×2 frame and apply plastic sheet to keep the dust down, and then I’m making cloth templates.

Air in a composite, under the microscope

So, a while back, I was making a trial part for the tub to understand how much resin a 12 layer infusion would take with a 10mm core. I cocked that up, but since then, I’ve also done an excellent infusion for my floor pan, and I wanted to compare the differences in them both for you under the microscope, because I’m that amazing, informative guy.

Pants Infusion – With Lots of Air in

bubblesIn doing the infusion, I inadvertently admitted some air into the infusion, and it ran over the part. Also, I capped the infusion off once complete rather than letting the pump run for ages to try and pull the air out. Now I know better and know it should be under vacuum until it gels off.

So, what you can see here is a scale at 0.1mm per subdividing line. Ignore the 5mm bit. So, these bubbles are anything between 0.1 and 0.5mm wide. Wherever there’s a bubble, there’s a weakness. To the naked eye, they just look like a very fine dot.

Good Infusion, Where I Got It Right

So, this yellow bitch is going on the car. I had infused the resin at 28 degrees, with the mould also at about 30 degrees. I used a brewing mat under the resin to warm it.

no bubble

This time, you can see no air bubbles, and the weave is easy to see. It’s at the same magnification as the part above, but it’s at a different weave. This is 300gsm twill weave (rather than 2/2 twill) but has less threads per twill than above – more tightly woven if you like. I also let the pump run all night to ensure absolutely no spare resin remained in the part. I also have a new technique to ensure there isn’t any air in the original input pipe, when it’s submerged in the epoxy.

Now, I’ve Keyed it!


In laying up the part, I put some strategically placed 1″ strips of peel-ply in where the chassis rails will be when it’s bonded in. Epoxy doesn’t stick to it peel-ply. When I took the part out and tore off the peel ply, I ended up with a nice keyed surface for the adhesive to the chassis. You can see it here. The crappy red fibers are just bits of the peel-ply I can’t get off. It’s incredibly thin nylon but the red threads are only at the edges. I don’t think they will (at all) compromise the quality of the adhesion.


Resin to cloth ratio by weight

IMG_2088.JPGIMG_2087.JPGSo, 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.

Tub nearly finished

so, here is the tub, and here are some of the gaps. The gaps aren’t going to be a problem because all the in the corners need to have a radiused edge. I will be doing this with plasticine and the radius ball. At the end of this I should have really neat lined edges.

Then it’s ready for the mould making process. Actually it’s not, first I need to put all the flanges on in order to actually pu the mould  in this, but it’s nearly there.

I also have some of the polypropylene sheet in the tub which is still a little bit flexible. I’ll be getting in behind that with expanding foam to give it a backing layer to stop it flexing. I will need to cover some of the suspension with release sheet first otherwise the expanding form will stick to it and everything will be an unholy mess. I’m also going to have to take the engine and gearbox out now. I don’t want them to get covered in gelcoat when I start spraying.



Testing Carbon fibre before I commit – Part 1


Some carbon fibre flat pieces were made and tested to see how far they bend for a given load. A load cell was used to measure the force.


So, before I go mad and put several hundred pounds of material into my CF tub, I thought it best that I do some clever investigation into just how does a composite structure bend, yield and break under various loads. So, I made the pieces, tested the pieces, and did some graphs, and came to some conclusions.


8 trial pieces were made of various thicknesses – different cores and layups. Each piece had a few things in common though:

samples 1

  • single layer of 300 gsm aramid for intrusion protection (if it were on the car)
  • this was balanced with a 300 gsm piece on carbon on the opposite layer to the core
  • one layer of 600 gsm either side of the core, and one layer of 200 gsm e-glass either side of the core for a little tolerance and flexibility.


samples 2I could then vary the thicknesses of the cores and extra layers of 600 gsm carbon I wanted to use. I opted for the following core thicknesses:

  • 10mm closed cell foam (CCF)
  • 3mm CCF
  • 6mm (2x 3 layers of 3mm CCF)
  • none


In order to test the bending load, I went to see my good friend Simon at Cornering Force. There are only so many people who like it when you call them at 8pm and say “Hey – do you want to stress test and break some carbon fibre?” After marking up each sample, we then put each on a support, resting on the bed of a mill, and pressed down on it with a load-cell. The load-cell had a 25x50mm contact face. The mill allows us to make vertical adjustments in 0.1mm increments easily, and the load-cell is accurate to the gramme.


The pieces were laid out on one sheet, and infused as one piece, and then cut to size afterwards. The vacuum feed was left on post infusion and for the curing cycle. The resin was degassed. This was to ensure the maximum amount of spare resin was removed until the gel stage. After gelling and the initial cure, they were post-cured at 60C for 12 hours, as per the manufactures instructions. This gave me the maximum strength possible for the sample for the least weight. I decided not to vary curing methods (e.g. length of cure) because a 12 hour, 60C cure is what I can achieve for a part as large as this.

The plan was to work out how much a piece would deflect, how it would yield and fail, and just what were the most significant factors in this – is it core thickness, is it amount of cloth? Did I turn around three times widdershins?

This was also a good opportunity to try a couple of techniques given to me by Vic at Scorpion CDL. I am always astounded at the wealth of technique he has and the quality of work done there.

Lessons Learned

I also had a slight infusion issue, which was the temperature of the resin I infused with. I had it at about 10C which was great for it not going off, but made it too viscous, and meant de-gassing it was a pain. It also meant the infusion was quite slow for such a small part. Further checking says 25C to 30C is a better temperature for this. I should have also wrapped more mesh around the input spiral which would have also alleviated this problem, but that was fixing the wrong problem – get the temperature right – let the resin flow.

Analysis and Conclusions

Coming in the next post.

Vacuum bagging – joy of joys

There’s a great joy in doing a vacuum test on a bag and seeing that it’s held vacuum, before you infuse. That’s what I did last night. Admittedly it dropped somewhat over night, but not enough to cause me issues, especially since I was planning to pop the part in the oven with the pump on anyway.

So, I made a mistake though. When I’d bagged up, I hadn’t actually fitted the tube to the inlet, when I was testing the vacuum, which meant cutting the bag (in the approved manner) to push the tube through and seal it against the silicon connector.

However, fitting the connector and reestablishing vacuum gives me quite a strong leak – either my connector seal isn’t good (unlikely), or the tiny hole I had has been made worse by slacking and reestablishing vacuum – far more likely.

So, I’ll check the seal because that’s quick, otherwise it’s another scrap bag and time to try again. I don’t want to chance infusing over it because there’s already the first half (infusion up to the core) in there and mullering the second half will scrap all that good work already done.


More composite fuel tank updates

This post is really about some of the manufacturing detail I’m going into as I make the part. As I’m sure you know, the sensible route to getting a composite component is:

  1. Make the part you want out of any old stuff so you have to get the right mock-up shape. I’m using kingspan and covering it in glass. I also like kingspan because it sands really well with an orbital sander, and till take bog (body filler) nicely both as a glue and as something to put on the surface when building complicated shapes.
  2. Cover the part in glass so that it is rigid and all the foam is separated away because of course you can’t take a mould straight from foam – they will become one and we all know what happens when two become one.
  3. Where I can, I’m cladding the part in pre-made sheets of 450g chopped strand matt glass which I made on a pane of glass. The reasons are that firstly the sheet made from glass has a reasonable surface finish and secondly it’s a lot less faff to clag this on than wrap the whole thing in glass, set in resin and then flat and polish, flat and polish FOR EVERRRR until I have a sensible surface. Thirdly these sheets, being quite flat, mean I can trust the angles I have them in at so I can reduce the chances of mechanical lock.
  4. Where I can’t clag, I’m putting body filler in, which is great for filling the gaps, but must be recessed slightly back from the overall profile. The filler will then be coated in resin. This is because you can’t go body-filler straight to mould surface – when you pull the part from the mould you will leave the filler behind. So, for the want of a little deft work with an artist’s brush and some resin, I can avoid this.

As ever, this is easiest explained with pictures:

IMG_0064Here is the joint between two panels. Both panels have been cut and bogged down and while the bog is soft a bit of a push allows the bog to squeeze out into the gap, Add deft work with a lolly stick and the gap is scraped out.

You can also see a big gap between the panel and the part. This will be radiused back so I don’t have any right-angles into which I can’t get cloth.

IMG_0062Rivets are handy to stop the panel sliding down the part on the bog. whilst it’s claggy stuff, it still has a propensity to flow. I suppose this is another odd reason why kingspan is so useful – you can stick rivets into it.



IMG_0061Here is the bottom of the tank with the three panels attached. What you can’t easily see is the slight angle the tank tanks to follow the fury transmission tunnel, which is angled.