This article, based on one by Roger Lloyd, discusses creating a helix using straight sheets of plywood with cuts at the correct angle so that they fit together.
In cell B1, enter number of sectors in a half circle e.g. 4 or 6 In cell B2 , enter inside radius less allowance for clearance e.g. for an inside track radius of 750mm (centreline), you may enter 725 In cell B3, enter outside radius plus clearance e.g. 900 plus 25 = 925 The results are shown below Cell B4 is the cutting angle for a mitre drop saw Cell B5 is the length of the inside face. You will need to add your desired overlap e.g. 100mm Cell B6 is the length of the outside face. Again add your overlap.
The Helix on the Layout
For a larger view click here. The drawing below of 4 tracks using close to what your tracks would be i.e. 750 radius for inside track and 900mm radius for outside track.
The blue circles show the clearance line. In the top half, are drawn 6 sectors using the formula and the lower half using 4 sectors. The red lines indicate the overlap which are drawn at 100mm.
More or Less Sectors
The advantage of fewer sectors is less joining. The advantage of more sectors is that the strips are narrower thus using less plywood.