Materials for Constructing the Spline Helix
Jim,
Thanks for your comments. My answer will be long and may provide more details than you wanted. Remember, the construction of the spline helix began in April and was completed in November. Much of what I describe below was why it took so long to get to the end because I adjusted techniques along the way if I found that they did not work. The last section of roadbed added to the helix was built in about a quarter of the time that the first section took. I guess that was my learning curve.
On my previous layout, I was going to add a deck bridge that would have to use a curve of spline roadbed (3 pieces of 1/2" high 1/8" thick hardboard) that I did build but did not use because I had to dismantle that layout. But after a year and a half of sitting in my garage in Central Texas, the section of spline was still in the same shape as the day I made it. That made me want to look at using spline for the next layout. I then made the decision to try to use spline to build the helix.
However, several issues had to be solved before beginning construction: first, it was easy to determine that the helix could not be built continuous because of the gluey mess plus the cleanup of the rough top and bottom after gluing as well as how would you add the track and cork roadbed if it was built that way; second, since it could not be built continuous, then could it be built in sections and then populated with cork and track before adding the next section? The answer was yes. Since I was familiar with using biscuits for joining sections of cabinets, I did some testing and determined that biscuits could be used to align each successive section; third, if it was to be built in sections, how was the helix to be supported, i.e., by wood supports or threaded rod? The one problem that wood supports create is that they would require a wider cross section of spline so that there was sufficient clearance room between the wood spacers and the tracks so there would not be any interference with the operation of the trains. (Note: Jeff Johnston has a video on Youtube on how to build a helix using the wood spacers that I viewed several times) If I used that technique, then I would have to make my radii smaller since I was constrained to exactly 48 inches width of the finished helix support table. This was to ensure that the aisle width remained 36 inches between the helix table and the 48 inch wide peninsula in the center of the train room. I decided on using threaded rods because I really liked their ability to be adjusted but I could not figure out how to attach them to the side of the spline roadbed. I then came upon an article that used screw eyes to hold threaded rod externally from a section of plywood or dimensional lumber and that gave me the idea to use the screw eyes. After a couple of trips to the local hardware stores, I settled on 2 foot long 1/4 inch threaded rod and determined that a particular screw eye (roughly 3/8 inch opening with about a 1 inch long thread) that I found at Ace Hardware would be tight enough but have a little bit of play in case it was not lined up just right. By the way all of the holes for the screw eyes are predrilled; and fourth and the most important, how to maintain a constant 2% grade on the helix. To do this, I needed to dedicate a large table to build each section with risers placed along the route that established the 2% grade from start to finish of each section. I already had a 4 foot x 8 foot table built from 1/2 inch plywood that I used for assembling cabinets that could be used for this purpose. I laid out the helix on the table and began construction.
During the construction process, I cleaned out our Ace Hardware of all of the packages of screw eyes that I used plus I had to special order some more. Other hardware stores had screw eyes but they were different enough that they would not work. I bought the associated nuts, washers, and lock washers by the hundreds from several different stores. The 1/8 inch thick hardboard, some of which was made by masonite and some by someone else (?) was readily available at local stores. I looked at possibly using a thicker hardboard so I would have to cut less strips but decided that the 1/8 inch was the best to use for N-scale. If you are building in HO or larger scale, then the thicker hardboards should be fine.
One of the problems (I think that I described several in my blogs over the six months) that I never really solved is the hardboard spline wanting to curve inward at the ends. Each section was built to be about 16 feet long, plus or minus, in length. I then cut the ends in the overlapping straight section and made the biscuit cut for joining the section to the previous section. Apparently, the gluing process gives the spline some memory of the previous curve and it wants to continue that curve inward. I have clamped each section differently each time and nothing has worked, so on a couple of sections, I have added some external short sections of threaded rod along the outside and inside of the spline to force it straight. That seems to work. When I get around to building the second helix that I need, maybe I will try a different technique.
Don't forget to watch for any sale on the three inch clamps. I found a sale on a Home Depot where they were on sale for $.99. I had about a dozen before the sale and now I have somewhere between 73-83 of them. You need a lot of them to do spline efficiently. Early on, I used a lot of my cabinet making clamps (you can see them in the various pictures over the project). After the second section was built, I determined that if I built the outer radius to about 12-14 splines and then built the inside radius that I could use the 3 inch clamps until the last 2-3 splines were put into the middle of the 24 wide sections. Then I would use the larger clamps as the last splines were added to the middle. I found that each time that splines were glued that I could wait about 1 to 1 1/2 hours and then do the next section without having the previous splines glued together coming loose from each other. If I did not say it anywhere else, I recommend yellow glue which I buy by the gallon. I think that I used about two gallons of glue for the project.
Please let me know if this is what you were interested in or if I missed the mark. I would be glad to provide more details if you are interested.
Thanks again,
John Tanzillo
