By ‘eck. I’m shoving wax in me flange gaps.
Some of the terminology of mould making is quite … interesting
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Category Archives: composite
Composite Fuel Tank #4 – trial part fitted
and I’m a happy bunny. The finish is a little rough, and I can do a little mould polishing to get that, but once the part is in, it will never be seen again, so I’m not going to get all artistic about it.
Prepare to swoon at the fitment …
Top Down – here it is, fitting nicely, stopping about 100mm from the gear lever. There’s a good 10mm clearance all round between the tank and the rest of the transmission tunnel.
Open Wide for the Doctor
This is the view right down the tank into the sump.
Bolt Recess
Here you can see the cut-away area of the part I made to allow me to get a socket in to first insert and then secondly tighten the 1/2″ bolt for the top of the diff cradle.
Tank and Chassis fail to meet
The tank nicely runs under the chassis rail. This is just shy of 10mm. The tank isn’t going anywhere once it’s in, so I’m not stressing this.
Diff Clearance
Again, loads of room here. The diff cradle is held in place with 1/2 inch bushes, so there’s no way can it ever touch. I’ll also be making prop-catchers, so I won’t worry about the prop hitting it. And the tank will be in aramid, so i’m not fussing that.
Topping Out
Here’s the tank the whole area behind it is where the old MG Midget tank used to sit. The black brackets are temporary. I’ll made something rigid out of CF that spans the top of the tank between the cross-members. The tank itself will have m6 male fasteners bonded on to it, so it can be fitted from below.
The last picture demonstrates just how far I’ll be able to move the mass of the tank. It’s forward by 300-400 mm, to the point where it’s now inside the axle line. The aramid tank will have better impact resistance properties than the steel one it replaced, and being in the new place it is in the chassis, will benefit from greater impact resistance. The area behind (at the top of the picture) where the old tank used to hang from will be replaced by a crumple-zone.
And … Attach
These are Big Head fasteners. You basically put a big dollop of the special 2-part epoxy glue no the part (after keying it), push the fastener through, let it set and trust it.
I don’t have a solution for the front of the tank yet – I think I may take a bracket off the prop-catcher I haven’t made yet, or make a top-hat shape, cut a hole in the tank and stick the top-hat to it, but inverted so the top hat makes a recess. Then I can stick a big-head to it (I have some female ones) and bolt through from the other side of the transmission tunnel. It’s going to be … specific.
Composite Fuel Tank #3 – prototype part pulled
Or – Transformers – Fuel Tanks in Disguise!
So, before I make the part out of lovely aramid and carbon I thought I’d do the sensible thing and crack a part out of chopped strand mat first. I wanted to do this for three reasons:
- check the part for fit in the car – if the mould needed a tweak or two, now is the time.
- check the part for fit for the ATL fuel sender – I’d gone to a huge amount of effort to site this so that it reaches to the bottom of the tank.
- fill it full of water to see what the capacity is
Here we have the entire set of parts pulled and trimmed from the mould. As I went along, my trimming got a lot better a lot quicker. I realised it was far easier to scribe the part in the mould for where the trim-line should be, and then to pop it out and trim it. As such, I have a few gaps which have been sorted with how I’m bonding it together (30mm strips of glass, wet laid on).
Now the part is pulled and bonded together, hopefully you get a sense of the size and shape of it.
I managed to bond the whole of the top tank (the top bar of the T shape) internally, but the lower part needs to be bonded externally. I did a reasonable job, but it’s not watertight. It was good practice for when I do the aramid/carbon part.
The entire part weighs just over 2kg, which gives me a saving of 3.7kg over the standard midget tank. It’s a great weight saving, before I even take into account moving the mass about.
Footwell fettling for friends feet – part 2
So, it’s time I completed the write-up of the carbon-fibre footwell, lest alliteration break out o’er the land.
In Footwell Fettling Part 1, I go through how I make the part, and you can find the other footwell posts which are tagged with the footwell tag. I didn’t ever say I was original.
Following on from the sharp-edged part, I then rounded off all the edges using quadrant beading and prepped it for spraying. The process for cutting back and adding the quadrant beading has been gone into at some length in the composite fuel tank section, so I won’t labour it here again.
Here is the part, flatted back, polished and waxed. I waxed it because the wax serves two purposes: performs as a release agent, and gives a shiny surface, filling in all the tiny micro-scratches that come from polishing.
What I’m learning is that you need to add shine on every part of the process in order to get a reasonable shine out of it without major effort at the end.
Here is the part offered up to the fluted sign-board flange. I’ve tried all sorts of methods to get a good straight cut and have settled on a tile shape transferring thingy, and a steady hand with a fresh Stanley knife blade. I’ve tried cutting along steel rules with the Stanley knife, and have found that I get better results with just simply cutting by hand and eye. You can see the green breaker-tape sealing the flanges to each other; resins can’t stick to the tape, so you get a simple seal and don’t have to worry about release agents. Similarly, you can see the moulding wax filling the gaps between the parts and the sign board.
A word of note here – sign-board is far too flimsy on its own to be a flange material, so it needs to be backed up with some form of stiffer board (I use 6mm ply), glued together with hot-glue. Similarly, the ply needs to be glued to the base and part using triangular gussets. Here you can see the whole thing set back at a distance, and get an appreciation of context.
It puts the gel-coat on its skin or it gets the hose again. What you don’t see is me spraying the whole affair with a couple of coats of PVA release agent first. Again,that’s been covered against the footwell tag.
Three layers of 450g CSM backed up and set in poly-resin. You can see how I’ve taped the thermocouple to the part in the oven to avoid over-heating. The part can easily exotherm to 40,50C and if the oven doesn’t sense that, it can add more heat than is needed and the part will over-heat and be trashed. This is also both halves of the mound made together and going in for the final bake.
I’ve split the moulds and you can see a few things. Firstly, the finish looks matte, and this is due to me also adding a chemical release agent on top of the wax to be super sure it was going to come out. From a seasoned mould, this isn’t a problem, but for a green mould that’s a one-off, belt-and-braces is what you need. The arrowed part is where the mould took some of the body-filler from the part with it, so even with all this extra releasing, I still had a mild sticker.
Here are the two mould-halves re-attached to each other. The flanges have been drilled and cross-bolted (M8, because they were handy). The shiny side has been polished by hand quite quickly with Farcela compound, just to demonstrate the difference between the ‘out of the part’ finish, and the final polish before a part gets pulled.
Here is the whole mould backed in breather cloth. Because I’ve split and then reattached the splits, it won’t be easy to get a vacuum tight seal for a pleated bag, so I’ve got to go for an envelope bag. Breather fabric is just a soft, cheap, disposable cloth designed to absorb resin. The red circle shows a part of a corner I didn’t notice wasn’t properly wrapped and this caused a punctured bag. Click here to see a close-up and to see how easy it is to puncture a bag.
I’ve already made the post about laying up the cloth in this youtube video, and next will be the removal and fitting to the car. Believe, me, it’s f’excellent.
DIY Composite Oven
So, every good shed needs an oven. Oh, and a work-bench. Bearing this in mind, it make sense to combine the two, and put it on castors so I can move it about.
I have made the bench deep and that’s for two reasons. Firstly, one needs a lot of room to lay up parts. Secondly that was the quickest way to make it using roofing boards and pressed boards. They’re already pre-cut to a certain size so there was less jig-saw action.
Here it is laid out and on castors. What I didn’t realise is that the roofing boards aren’t remotely stiff on their own so there’s some reinforcing under the floor to hold it all together. Once the sizes are on and the top is on, it will get more rigid.
Sides are on. Top is on. It’s now stiffer, but not fully priapic.
Here’s a perspective of the bench – big innit?
In the true spirit of being an oven, I dismantled an oven I got from ebay for £10. All the wiring and controls get gutted, and it’s a simple wiring job after that. Fans and lights are always on (rather than under control of the controls) and the element itself is under control of the PID controller.
Here is the PID arrangement. Again, £30 from ebay gets you a PID and a very heavy duty solid state relay. The case and assorted bits and pieces came from maplin. You can see two bolts on the front there, where the solid state relay is bolted to the case to act as a bit of a heat-sink if needed. The 3-pin plug on the front is the output power supply for the heating element. I deliberately did it this way in case I then wanted to power something like a convection-air heater or summit else. Up the back of it is a kettle-lead which powers the PID. The kettle-lead is hard-wired into the main power of the oven. If the oven is plugged in, the fans are always on and the PID is powered. You can’t have heat without fans.
The oven now needs king-span to insulate it (sat in the garage gathering dust) and a thorough soak-testing with a fire-extinguisher near by to be sure it works. I don’t think I’ll be leaving it unattended but at least it’s in a shed if there is a fire.