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.

The tub is out of the mould

So, it’s been a while since I posted, but a lot has been achieved, and there are videos below to share the love. So, the tub has been infused, it’s been extracted, the peel ply and infusion mesh have been dragged off the back (that was a sweaty day), it’s been partially fitted and baked.

I’ve got three videos below to show what happened. There’s the infusion setup, followed by the resin going in, and finally the lovely tub once it’s out.

The infusion setup

The actual Infusion going in

The Tub out of the mould – ta-daaaaa

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).

Aramid floor tray is in

Here’s the floor tray, all nicely bonded in.

IMG_3334Here’s the floor-tray all nicely bonded in. You can see on the right of the picture how the floor-tray now replaces the cross-member I removed. I put several extra layers in there as well to pass even more force forward (than the 6 layers of 300gsm that’s already in there).

There’s also extra reinforcement, like a lardy-blokes truss, to take engine mounts if I decide to do that.

So Mark – tell us how you did it

IMG_3316 2

 

Here’s the part as it came out of the mould – all sharp edges and over-sized. Next job was to put it on the car – mark it up and trim it. That’s the boring bit and I don’t have any photos to document.

 

 

IMG_3324This is the chassis before the part is bonded to it. It had been blasted before powder coating, and I used the right high-temp non residue leaving breaker-tape to mask off the mating areas. The blasting heaves a fantastic key. I was worried originally that the tape wouldn’t make a brilliant barrier to rust after coating but it’s worked out fine. The reason being, the coating forms a seal against the tape so there’s nothing to get in – no air or moisture so no rust.

I marked the part up after clamping it down, and drilled for rivets. The rivets were just soft-ally headed ones to provide clamping force rather than to be anything structural.

 

IMG_3319

 

Here I am as Clampy-McClamp-Face. I had every surface clamped before I drilled rivet-holes. If you drill-rivet as you go along the part, it starts to creep and your holes don’t line up. Clamping the entire thing before drilling keeps the accuracy.

 

 

IMG_3325Here’s a close-up of the rivet holes – I’m pretty pleased with how accurately the holes line up. Structurally it’s not really important, but attention to detail matters.

 

 

 

 

 

 

img_3327

One post-trimming, bonded, riveted part in place. I used an epoxy two-part adhesive. It’s the slightly flexible stuff for parts under a lot of vibration.

Once the adhesive set (24 hours for full cure at 20C) it feels rock-solid.

 

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!

keying

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.

 

How much will my tub weigh?

So, based on the sketch I made on the white board (below), I need to calculate just how heavy the tub will be. The main reason I need to calculate this is to be sure the 19kg I’ve taken out by chopping out all that steel and removing the ally panels isn’t then replaced by even more carbon.

 

 

IMG_1007.JPG

 

 

 

 

 

 

 

Method

I made a trial part, consisting of:

  • 4 * 600gsm carbon (2 above the core, 2 below)
  • 2 * 200gsm e-glass (1 above the core, one below)
  • 1 * 300 gsm aramid (on the bottom, facing the tarmac)
  • 1 * 300 gsm carbon (on the top, to look pretty)
  • 1 * 10mm thick closed cell foam for the core (in the middle)

The layup is symmetrical around the core, apart from the aramid on the bottom and the facing carbon on the top. I have discounted the weight of clear gel-coat applied to the finished part (assume 1kg at the end).

The part measured approximately 103mm * 204mm, and weighed 130g. This meant a unit weight of 0.006 g/mm2.

From this, I fed the dimensions of the panels above into my CAD package. Given a surface extruded to 1mm depth, it will tell me the mass of the panel, to a bazillion decimal places.

Conclusion

Part count Unit Weight Total Weight Running Total
Tunnel Side 2 2.37 4.74 4.74
Tunnel Top 1 1.16 1.16 5.9
Back 2 1.0375 2.075 7.975
Base 2 2.7 5.4 13.375

So, if I go for this, the new tub will weigh 6 kg less than the original steel work.

Assumptions

  • 10mm closed cell foam is used uniformly. This won’t be the case – the sides do not need a 10m core – I will probably go for a 3mm core.
  • the base, back and top of the tunnel need to be strong in bending load, the sides need to be strong in lateral load. As such, I can use a thinner (or even no core) for the sides. I think I will save 1kg there.

Trying out some new products

So, I was taking a wander around East-Coast Fibreglass because I needed more 100gsm chopped strand map to act as the first layer when laying up to prevent print-through in a mould. I came across something called Finishline Polyester Veil. What you’d normally do is put a layer of 100gsm chopped strand mat down first, and let that go off. Then put your heavy 450 down afterwards.

This stuff, being a felt doesn’t need a binder (to hold the chopped strands together) which means (apparently) it has a better chemical grip on the gel-coat. Then, once it’s set, you can put the final 4 layers of 450gsm down. Hopefully this will give me a great finish and is really cheap. I have had print-through before, so I know not to let this happen.

Then I discovered that Marbocoat do a release agent called Fastcote, which you wipe on and it leaves a shiny release surface. I called them today and it is good for epoxy. Fantastic. Everything that contributes to a nice surface finish is welcome.

I will test it first before I use it, I think.

 

Testing Carbon Fibre before I commit – Part 2

So, here is the raw results file:

raw data

I’ve kept it there in the spirit of honesty, but the following distilled data into the graph is what really matters:

new graph

 

So the numbers that matter are those on top of the line – each of those is the number of KG force required to deflect the part by a given distance. You can correlate the colour to the number to the data in the top chart (click through for details)

Finally, there is the density/deflection ratio, which would show the ideal performing part if absolute strength wasn’t the most desired outcome.

density

Conclusions

There is a trade-off between core and layers, which is what would be expected. What actually surprised me the most was the difference a core makes.

The top line has two variables set – 4 layers of CF (rather than 2), and a 10mm core, rather than the yellow line, which is 4 layers and a 6mm core. The third highest line is the darker blue line, which is 2 layers and a 10mm core.

So, it’s layers over core but again, there’s a trade-off. The red line is 4 layers over a 3mm core, and you can see it yielded really quickly at 3mm with a very low amount of force (well, 98kg of force). Without doing any statistical analysis, I am observing that each 3mm of core seems to give me an extra 100kg of resistive force before yielding. However, I don’t know how far that scales.

Finally, you can see that there are a selection of flat lines near the bottom, and they are parts made without core. The seem to bend a lot and not yield. For my purposes though, they’re not suitable. Parts 6 and 7 (four and two layers), deflected up to 7mm without yielding, but weren’t much use to me.

As the thicker parts started to yield, we could actually hear them crack (quietly). I’m assuming that’s the fibres snapping. As such, the moment it starts to happen the part is compromised.