To trackday a car it needs a reasonable level of illumination, to communicate your intensions and make yourself more visible in low light conditions. Indicating left, pass me on the right. Hazards flashing, I’ve had a bad day. This is something the Locost has not needed until now, as it has only ever been driven on closed courses with only one car competing at a time.
I already own a set of rear light clusters that I bought almost six years ago when I was initially stockpiling parts. I decided to go with these “hamburger” style rear lights as they mirror the round headlights at the front of the car, that I am also yet to install, and also I could get them with clear LED’s which would keep the car aesthetically pleasing. It also helps that they weren’t cut-off-your-left-leg-and-right-arm expensive.
The easiest and quickest place to mount rear lights on a seven is directly to the rear bodywork. While this could have been done on a Saturday afternoon, with time for a few cups of tea in-between, it would have been almost irreversible and completely illegal for road use if I ever felt like going that way (lights must be a maximum of 100mm from the outer most bodywork). So this left me with only one option which was to mount them on the rear wings. Never one to turn away the opportunity to do something the hardway I decided this would be a great opportunity to make my own light pods, in my own asthetic style- fire up the 3d printer!
First of all, my printers build volume is a measly 150*150*150mm, and would have never been able to print an entire light pod in one go. Also, PLA plastic would have never been a good choice for components like this, given that they will sit in the sun for extended periods of time (damn you 60degC glass transition temperature). These would have had to have been printed in ABS. Printing thin walled ABS shapes is pretty much a no-go without some major warping, so this left me with only one option… a 3d printed mould.
I grew up around fibreglass in all its forms. Quick shabby make-a-mould-out-of-Tupperware fibreglass, and top quality a-thousand-layers-of-wax-and-lots-of-polish fibreglass; this was going to be something in the middle. Because of my limited build volume I opted to design the mould to split into four separate parts. This also meant that releasing the strangely shaped light pod would be relatively straightforward as long as everything was unbolted and persuaded a little; so it was win/win.
After measuring the curvature of the rear arches and the geometry of the lights I frew the mould itself and split it in the X and Y axis. This is a female representation of the lightpod, with the reverse being the actual “male” final piece. Getting a clean striation-free mould surfce was going to be unlikely, and comes with the territory when 3d printing, so I knew I was going to have to sand and polish the final mouldings after they were produced.
I believe these components took between 16 and 19 hours each to print in PLA, which goes to show how awesome my Printrbot Simple Metal is. I’m very happy with my printer setup at the moment, as it’s hugely reliable over a long period of time. Hold on, where’s your RepRap gone Josh? That’s a story for enough time…
The mould was sanded with 200 grit sand paper and given 5 layers of wax. The wax helped to fill in the crevasses between the separate mould pieces and massively helped the release after moulding. In short, this stuff rocks.
Once the mould itself was ready to use the mouldings were made in a fairly simple way. Firstly a layer of White Gel Coat was applied to the mould with a brush. Gel Coat is essentially resin with pigment in, which gives the moulding an outer layer which can be sanded and painted to achieve a nice finish. If the mould is of a high quality the Gel Coat can simply be left as is. I would eventually be painting these moulds so I wasn’t too bothered about the initial surface finish.
Once this had adequately hardened polyester resin was brushed into the back of the Gel Coat and 450gram fibreglass rolled into that (I gave it approximately 4 hours at 10degC, with a 3% mass fraction of catalyst to kick things into gear). The rolling process is important as it helps to remove air bubbles from the structural fibreglass and improves the strength of the composite. It also helps reduce the amount of resin you have to use, as the fibres are pushed tight against the Gel Coat and the resin soaked through. If the whole lot was just brushed on then it would have likely had a higher resin content and been heavier.
This was left for two days to harden and then extracted from the mould. I’m very happy with the final product and its far lighter than I expected it to be. The ‘pods will be glued into the back of the arches and then faired in with filler. The whole lot will then be smoothed and painted; probably glossy battleship grey.
Have you ever tried any Fibreglass work? If not, give it a go! Its actually ver y rewarding and if you take your time with each step you can achieve great results.