Here’s a brief video I’ve done showing the tub pattern part as it stands now. All the shapes are right and the flanges are on. I wanted to show the flanges, as well as how I support them.
Tub Pattern Video
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Category Archives: tub
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.
Brackets made
I’ve welded the brackets to hold the underfloor bracing on and tacked them onto the chassis. They only need two tacks. I don’t want them to be any stronger than something that can be taken off with a chisel.
First attempt at filleting with plasticine
Here is the first attempt at a fillet. I appreciate that it doesn’t look much from this distance (so there’s a close-up to follow). I’ve been using a 1″ ball and liquid wax dissolved in styrene as a lubricant. It helps if the plasticine is nice and warm and soft before one rolls it into a sausage and shoves it in.
However, I’ve got to stop now for a couple of reasons:
- the wooden frame supporting the polypropylene has come away from the chassis – the adhesive holding it together came away today. This is a bit frustrating. What it means is that the base isn’t as accurate as it should be, and isn’t as supported as it should be, meaning things may shift under the plasticine.
- I realised there’s still a little sanding to be done on the tunnel part to make it fit perfectly to the chassis. This is going to throw a load of dust about which will settle into the plasticine and contaminate the finish.
This is the filleted edge up close and again, it’s not easy to judge the finish. However, this is at the bottom of the tub and most of it will be covered by seat, so whilst I want the best finish I can make, I’m not going to get het up on making it perfect. I can always do a little post-finishing on the mould or even the part if the urge gets me.
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.
Down the drivers site of the tub
Fairly pleased with this, ready for the back to go on (not sure how yet 🙂 )
Notes on applying Meguiar’s No 16 Wax
So, again, thanks to Vic, I’ve started applying wax to the transmission tunnel in order to both give it a decent shine and put a layer of release in there. The wax won’t be the only release agent I will use – i will also spray a healthy coat of PVA on there as well. When the whole thing is blue, it’s safe 🙂
The wax is Meguiar’s No16 paste wax, and is great stuff. It’s a lot thinner than the mould release wax I have used in the past, which took some polishing off with a micro-fibre cloth. This time, I have started using a red polishing head on my rotary polisher, and that’s making light work of buffing it. It should do considering it’s on a nice large flat surface.
Lessons Learned
- Put it on thinly – if you clag it on you just spend more time polishing it off, wasting wax. A nice thin coat means the polisher can whiz over it and bring out the shine all the quicker
- speed setting on the polisher is between 3 and 4
- it takes a while to dry and glaze over – I left it overnight which isn’t the norm at all, and it was 5C in the garage. This, I think, is a reflection on my operating conditions rather than the wax
Tunnel gets its first coat of wax…
Look at that shine. I did that flaring back with wet and dry. Now the wax goes on.
Testing Carbon Fibre before I commit – Part 2
So, here is the raw results file:
I’ve kept it there in the spirit of honesty, but the following distilled data into the graph is what really matters:
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.
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.
Testing Carbon fibre before I commit – Part 1
Abstract
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.
Introduction
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.
Method
8 trial pieces were made of various thicknesses – different cores and layups. Each piece had a few things in common though:
- 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.
I 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.
Manufacture
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.