I used R1 and R2. R1 is the down slope, and R2 is the up. I would have used R2 and 3, but I barely have the space in the eaves for the helix the size it is, R3 would ahve made it far too big to fit. If you have the space, go for R3, as it will lower the gra:dient
Measuring from the floor to the exit point is innacurate, as the helix sits on a 1.5x1.5inch pine batten, which was to keep it nice and solid (and it works well too
) A better way of measuring is from the surface of the first deck, to the surface of the last deck. That measures 20cm.
The thickness is 12mm, but I seem to have shot myself in the foot, as the thickness of the material has a direct impact on the possible gradient. B&Q did 6mm MDF sheet the right size, but nowhere had it in stock. I had to settle for the 12mm stuff. Also beware as the size of MDF big enough for the cuts are huge, (1x2m) and need to be cut in store, unless you have a van to take it home.
I marked out the MDF sheet with abit of plastic, a nail and a pen, drawing two perfect circles and nailed the two bits of MDF together with the nailgun. I then cut the discs out with a jigsaw, just carefuly following the line. After that, I cut a slit in the two giant polo mints, so i could spread it out. I joined the three peices of MDF together using 'mending plates' and bolts. It takes a fair ammount of force to get the two ends to meet up, as the MDFs stiffness trys to keep them apart. With a bit of gentle pursuasion you can get it to fit and the join to be pretty smooth.
I did calculate the slope and I hoped it would be 1:50 but rather unfortunatly due to the thickness of the MDF and other unknown factors, it has ended up as 1:33, which, unfortunatly is too steep for my Class 101 DMU, which is the only train that will be going up and down this helix.
The good thing about this design is that the threaded rods allow complete adjustability. You are restricted only by the height of the trains you intend to send up the helix, in my case the highest is a little BR steamer. Its about 68-70mm. You need to calculate the height of each rod at all 5 points (there is four, but the first point counts as two as the track passes through it twice). In my case it was 0 to begin with, then the deck at each point was 1.75cm higher than the last (if that makes sense).
Its pretty easy really...