It has been a while since I updated the progress made with the spline helix so here is where I am now. 11 November. Added Oval Helix Virtual Grade estimations/calculations used for this project.
Over the last couple of months, the 4th turn/level section was added, cork roadbed and track were installed, electrical feeders added for that turn/level, and the track tested by running some engines as shown by movies in a couple of my previous installments. Next, I worked on the last turn/level section (#5) which will be the entrance to the helix/exit to the main level of the layout. First, I had to rearrange the support risers on my helix build table to accommodate the exit/entry interface to the main layout level.
I kept the same 2% grade on the 5th turn/level so the bottom of the spline would be at 48" from the floor at the planned joint with the main level (not yet built).
As of 9 November, the last turn section has been added, the cork roadbed as been installed, and the rest of the threaded rods have been installed. There are 16 sets of threaded 1/4" rods (32 total) and 324 each of the 1/4" nuts, lock washers, and flat washers.
The two pictures below show the overall helix with the 5th turn/level added and the cork roadbed installed. These pictures also show the entry/exit to the main level from two perspectives. Note that the helix was placed in the middle of the building's floor for ease of construction and will be moved back to its permanent location when completed. I also made the 5th turn/section longer than needed since it is easier to cut rather than to add.
Remember, that the helix is built in sections and joined using a #10 or #20 biscuit. Also, I have not been able to solve the problem of the spline roadbed wanting to curve inward at the joint. Because of that, I moved the joint from near a curve to the straight section just before the curve on both the 4th and 5th sections. It still did the same thing, i.e., the spline wants to curve inward. The only thing that I could think of is that the glue drying process must be causing the spline to have some kind of memory of the curve even when it was screwed down in the straight section where the section begins being built. The pictures below show top and side views of a good example of the issue, which is easily solvable.
Adjustments to the alignment are fixed by adding some screw eyes on either side of the joint and then tightening the requisite number of nuts, lock washers, and flat washers until fixed. The pictures below show both a top and side view of the solution.I've done it twice and I am satisfied that it works good enough. Remember, I do not glue the biscuit joints, as they are only used for initial alignment of the two sections.
While I was crawling around under the table, I decided to add some supports for the legs. The pictures below show the base table from both a front and back perspective. When the helix is moved back to its permanent location, I will enter from the front only.
After this helix is completed, I will begin work on the staging yard which is on the lower level. I have also been researching how to support the main level of the layout which will be above the lower staging yard and join into the 5th turn/level of the helix. I have settled on 24" heavy duty double track shelving brackets as shown in the picture below. The idea came from several articles found during internet searches but mainly from following the construction of Cliff Powers' HO Mississippi, Alabama & Gulf Railroad over a couple of years. I felt that the shelf brackets were a better choice, albeit more expensive, than supporting the main level with legs down to the yard level which I felt would get in the way. The other advantage is that the main level could be built in sections on a workbench and then placed on the brackets and screwed down. His website, http://magnoliaroute.com/magnolia_route_001.htm,has some great ideas for construction and I thank him for posting them for everyone to see. He certainly gave me some ideas that I will put to use.
11 November additions.
Virtual Grade Calculations for N-Scale Oval Helix (in case someone is interested). First a couple of pictures to set the stage.
The basic formula for calculating virtual grade for a helix (found on the internet a couple of years ago that indicated that it was based upon the ruling grade discussions on pp 82-83 in John Armstrong’s book Track Planning for Realistic Operation (third edition) ) that I modified for the N-scale oval helix is: (virtual) grade = compensation + clearance / length of 1 loop or grade in N-scale in percent = (16 * Cl + 20) / R. Also, remember that the curve adds resistance, thus a compensation factor is required.
First calculate the estimation of circumference of the oval helix. Note, the oval helix circumference has to be estimated since it is essentially an ellipse. This gives you a number to compare to the virtual circumference calculation, where the length of the straight sections is added, to see if you are close. Next calculate the virtual circumference. My assumption in this calculation is that the addition of the straight sections create a virtual radius. Finally, calculate the virtual grade, first using the actual radius and then using the virtual radius. The virtual radius is then used to calculate the final virtual grade (VG2). Note, that the actual as built measured grade was determined to be ~1.9 to 2% using a Micro-Mark analog gradient tool. I believe that these calculations are close enough to be a good estimation of the virtual grade as a planning tool.
Thank you for the interest shown and don't hesitate to ask questions.
