Building the dome - Part 2

Saturday 7 April

Change of plan - fibreglass dome instead of styrene

My original plan was to vacuum form a styrene dome over the original polystyrene one that I had made. I started making the polystyrene dome slightly smaller in diameter to allow for the thickness of the vacuum formed styrene shell which would be formed over the outside. Unfortunately, by the time I had plastered the polystyrene dome it ended up full size. This means that a vacuum formed dome would end up too big for the body so I have had to change plan and use the polystyrene dome as a plug from which to make a fibreglass mould and then a replica fibreglass dome the same size as the polystyrene one.

Preparing the plug

Now that the polystyrene dome will be used as a plug for a fibreglass mould, I need to prepare it as follows:

1. Attach it to a flat base
2. Paint the dome
3. Cut and polish with various graded of wet and dry paper up to 2000 grit
4. Polish again with a fine cut and polish paste
5. Apply ten coats of mould release wax
6. Apply coat of PVA mould release.

I thought this first step would be a good opportunity to test some aluminium look spray paint to see if the finish will be suitable for the final dome. I figure it is better to do this now than on the final dome where I may need to sand it off.

Dome plug prepared for fibre glassing.

I was not very happy with the aluminium look spray paint as it came out a bit darker than I would have liked. The photo above doesn't do it justice as in the photo it has ten layers of mould release wax and a coat of PVA mould release as well (also my prep was a bit poor so there are a couple of blotches in the finish)

Dome again with white gel coat ready to apply fibreglass

Building the frame - Part 2

Saturday 17 March

Made use of the jig again to cut the top plate - will use it again for the middle ring as well. I think I will also try to arrange the partial rings in one or more circles for cutting so I can do them all at one using the jig again.
I copied the detail from the full size Senna frame templates printout again using carbon paper.

Top and Bottom plates

Have also cut out all of the uprights today. The two main supports are completed but the rest of the uprights need to have their slots cut out - Will do this tomorrow as today is a beautiful day and I need to enjoy some it it with my family.

Very exciting moment - enough uprights to support the dome (have actually cut them all out but took this photo after the first few were done as I couldn't wait to see R2 take shape. 

Sunday 18 March

Had a false start today. I started using the circle slot jig to cut the slots in the uprights was was not aboe to hold them in place firmly while routing the slots. The spin of the router moved the ply to one side and resulted in diagonal slots. This cost me one of my uprights so I had to cut a new one. Also made up a jig specifically for this task out of some scraps - including the wasted upright.

Jig for cutting slots in uprights. The piece being cut is the longer horizontal piece in the foreground. The smaller horizontal piece is a stopper for the router. The vertical piece (the wasted upright) is the guide for the router.

Have now finished cutting the frame and everything lines up but I need to sand or file out some of the slots for a perfect fit. All in all - a good productive weekend..

All pieces cut and in place (not yet fixed in place)

Building the frame - Part 1

Sunday 11 March

I didn't plan on starting the frame this soon as I am still in the middle of plastering the dome. The weather is cold at the moment and the plaster seems to be taking forever to dry - I need something else to do so the frame seemed like a good option.

My frame will be made from plywood and based on the Senna frame templates. I say "based on" because I have to make some adjustments due to plywood here (in New Zealand) only being available in metric sizes.
The Senna frame is based on half and three-quarter inch ply. I will be using 17mm instead of three-quarter inch ply (19mm), and 12mm instead of half inch ply (12.7mm).

Base plate

I had two copies of the template printed full size - I will keep one copy for reference (and to admire); the other copy I have cut into pieces like sewing pattern - I will use this for marking up the plywood.

Base plate cut out (outline only). With template taped in place so I can mark the plywood  using carbon paper ready for for the routing. 

Here is the base plate with the carbon paper markings

I stopped here for a while because, while I was studying the frame templates, I was trying to decide how best to cut the slots. After sleeping on it I decided that I would make a jig for the router that will pivot about the centre of the plate and clamp to the outside of the plate, and allow me to quickly rotate around this, the top plate, and the rings, while cutting grooves and slots at just the correct length and angle (always towards the centre).

Monday 12 March

My jig for cutting the slots in base plate, top plate, and rings

Friday 16 March

Completed base plate

Have finally cut out the base plate. The jig worked really well but I had to move the pivot point 6mm as I had measured to the centre of the router and not the edge of the 12mm bit. Using the jig it only took a few minutes to cut out the slots and a couple of hours to do the rest without a jig.
Made a couple of mistakes (see repair at position 4 o'clock ) but the 10 slots are all OK.
Decided to cut the  four clearance hollows (as positions 12, 4, 6, and 10 o'clock) all the way through - according to specs (Senna frame prints by M Hendricks) the thickness of ply that needs to remain in these areas is between 0.02" and 0.03" (0.5mm and 0.75mm). I initially cut them like that but the remaining ply was so thin and fragile that a couple of them just fell apart as I was cutting them. I think this will be OK as the vacuum formed underbelly should cover this.