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.