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R2-D2's dome is a somewhat perplexing item as it's obviously not hemispherical (half a ball) so what shape is it exactly?

That is one of those questions you may ask having seen the Star Wars movies and noticed that the dome looks different in difference scenes and movies. The answer is because it is different, the original was a bit more hemispherical than the latter and some scenes where pure CGI.

One of the main resources for having studied this is the Astromech club which has produced various specs for replicating a droid. The current "elite" aluminium dome is the 300, named because it's approximately 300mm high (well 297mm but hey ho). That actually gives you a good insight as we know that the original dome was 463mm in diameter so it was hemispherical it would be half of that or 231.5mm high. We can conclude then that the dome is egg shaped by 65.5mm or 28.3%.

To save you all the hassle of drawing that I have included a scale JPG dome template here (right click the image and save as to get the full size template). This image will print on three or peices of letter / A4 paper and the crosses are so that you can line up the peices before cutting! The profile has been taken from a laser scan and then compared back. It is within 0.5mm.

Making an R2 dome.

Now I must stress that I have never made a dome in my life (or anything from fibreglass for that matter!!) and spent too many hours looking at aircraft nose cones to see how they are made and anything else round!; after a couple weeks of careful study, I set to work on a FRP (Fibre Reinforced Plastic / Fibreglass) one....

STEP ONE: Making the plug

First you need to make an exact copy of the finished product know as a plug". I used an Ikea Brasa lamp because they are 450mm diameter and hemispherical. On hind sight, this was not such a smart idea as you will see later, however it did work well for the plug. I'd use normal builders plaster if I do it again as it's cheaper and sets quicker.

Below is the beginning of the new dome covered with layers of depron foam board and "hard as nails" tube caulk. The table it's on I made to rotate using a wiper motor from a car and you can see it in detail on my video. It's actually a very useful dome making machine.

Watch the video to see the machine in action and how I got it smooth. Below is the painted and filled plug.

Not a bad hey. (the wife wasn't happy about it being in the kitchen in case you're wondering especially after a coat of cellulose!)

STEP TWO: Making the fibreglass mould

Now I admit that this bit made me nervous as I had invested too much time making the perfect dome so I did a couple of evenings research on mould releases. As it turned out it was enough and it went wrong but I managed to salvage it...

So I followed all the advice I could and gave it eight coats of carnuba wax and then covered it in "gel coat". (you don't need gel coat but everyone else used it so I did!) I waited a few minutes (not long enough as I should have waited perhaps 30) and then applied two lays of 450 gsm fibreglass chopped strand matting and 750g of polyester resin. Despite making a complete mess and covering myself in it all, it actually went on okay so I left it for a few days to firm up. It's easier to do than you might think, you just need gloves, disposable paintbrushes and some mixing tubs. The best tip is to get it all measure out and chopped up first because when it starts to set it goes quick.

Now the eagle eyed will have noticed that I only laid up two layers of 450 matting despite most saying that the mould should be at least twice as thick as the finished dome. Well my theory was that despite the experts advice that when making a 1 piece dome mould, having some flexibility in it will actually help with any tricky release and I was correct as it helped a lot. So two layers is plenty.

Releasing the plug:

Oh dear, well not trusting my instincts to use PVA mould release as well as wax proved a mistake. Just use both whatever anyone says then you know it will come out! I think mine stuck because the cellulose was too fresh (it still smelt). One tip is to wait until all components stop smelling ! before you use them.

Above you can see the Brasa lamp stuck in the mould. Now the reason I said this was a bad idea was because now I have a steel reinforced plug that I need to angle-grind out without breaking the mould!. 2 hours later with a disc cutter and bingo a finsihed fibreglass mould...(and yes that mould is on the living room carpet - the wife was out)

It was actually almost perfect but for a couple of air bubbles which were easily filled. Now we move on to making a finished dome!...

Up next...Dome: Creating a composite fibreglass dome

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