I have two helixes (helices?) on my layout. Both of them are used to get branch lines from the main level down to shadow box switching areas. This will chronicle the construction of the second helix, A helix with two tracks. One track is the French Creek Branch, an active switching branch, and the other is the Main Line connection to Reading Outer Station, a staging area for passenger trains.
Design
The helix was required to get the French Creek Branch down to the St. Peters switching areas on a lower level. I also decided I could use it to get passenger trains down to a staging yard, since they did not terminate at Birdsboro, but went on into Reading. After a couple iterations of design I realized that I could make my passenger staging yard into another shadow box of Reading Outer Station, since it had a train shed and I could replicate the train shed as the top of the shadow box.
As a result the helix was designed to be double track, but they were separate lines. In order to avoid a diamond crossing at the top, both tracks were extended beyond the helix and and additional loop was added to make the inner loop become the outer loop. That oriented the two tracks in and out of the helix in the correct orientation to provide the maximum versatility to the helix.
The orientation had the added advantage that it allowed me to configure the lower level tracks for normal operation, a reverse loop to turn passenger trains and a continuous running connection.
I used a spreadsheet to evaluate various combinations of grade, turn separation and number of turns. Because I am using 1900 era equipment I could make the vertical separation a bit tighter than a 1950’s or a modern modeler could. on the flip side, because I am modeling with 1900 era engines, I couldn’t have a very steep grade.
The radius was pretty much set by the space. I first calculated what grade and total climb would be with various turn separations. Since my entrance and exit were not going to be right above each other I used a fractional number of turns.
I made the total climb a little less than I wanted because I would need extra room on the top and bottom for the vertical curves to get from the helix grade to level.
I used 2 1/4″ track centers because my equipment is short, if I was using modern equipment, I might have gone with 2 1/2″ centers. I then allowed an extra 3/4 in on the outside of the clearance lines to attach the spacers between the turns. I drew a roadbed section on 1/8″ hard board for a quarter turn and then cut that out. That was used as a template to layout out the actual roadbed on 1/2″ plywood.
I used code 100 flex track because I had a bunch of it and there was no need to worry about looks since it was going to be hidden.
Prep
Before I could actually start on the helix, I needed to prep the walls by installing the backdrop that would be behind the track next to the helix. I put 1×4’s on the wall to space the 1/8″ hardboard away from the wall. I could have just painted the wall or attached the hardboard directly to the wall, however I found in other areas that later I wanted to run wires up above the backdrop for various things and attaching the backdrop to the wall doesn’t allow that.
I used minimal screws in the backdrop, using construction adhesive to attach the backdrop to the 1×4’s and screws to hold the backdrop in place while the adhesive set. I then removed the screws to give a much smaller hole to fill.
After the backdrop as attached and secured, the joints and holes were filled and sanded. I gave it 3 coats of sky color paint and then painted the tree line on the backdrop.
This was much easier to do without the helix and benchwork in the way.
Construction
I built the helix using 1/2″ plywood with spacers between each level. I reviewed You Tube and saw several methods, I combined the methods that I preferred into my helix.
The benchwork frame was built under the corner out of 1×4’s with 2×2 legs. L girder type construction was used with one “L” attached to the walls.
I began with a base, which was a flat ring of plywood. While that isn’t absolutely necessary, I decided that having a flat base would allow me to level or adjust the height of the helix relative to the rest of the layout more easily.
I used a spread sheet to calculate the height of the risers for the first turn and cut them using a table saw. I also cut the spacers to be used between each turn of the helix (the blocks on the right). The size of the risers and spacers depends on the radius, grade and vertical spacing of the individual helix. I started the helix 1/2″ above the base so I would have room for the vertical curve out of the helix.
I glued the base risers to the base. You may notice that the helix is not in its final position since its under construction That’s the reason I used the base, so I could move the helix around to position it and turn it to facilitate construction and alignment. Look for the position of the “long” riser on the right side to see the rotation.
The roadbed (and base) where arcs of 1/2″ plywood and the roadbed pieces on the first level were cut so the joints fell between the risers. I used splice plates between the pieces. The joints are at the clamps. The joints on the first turn are glued. The roadbed is secured to the risers by screws at the outer edges of the roadbed.
Track was installed as I went up the helix. Once the first turn of roadbed was complete track was laid up that turn. Center lines were drawn on the roadbed pieces using curve templates cut from 1/8″ hardboard. The track is secured using screws. Originally I used a flat head screw and a small washer and later I converted to a pan head screw (after I finally found the right size, #6 x 1/2″, at a hardware store ). I did that because is disaster strikes, I can unscrew the screws and remove the track or adjust any kinks later.
After the track is laid, I start adding spacer blocks glued to the roadbed. They are spaced about every 8 inches, spaced to match the arcs of roadbed. There should be a spacer centered under the end of each piece of roadbed.
Here is the start of the second level. The roadbed on the second (and higher) turns is screwed to the spacer blocks after the glue dries. As each turn is attached, track is laid on that turn. Note also that the helix has been turn to more closely align with its final position
The basic helix completed. Originally it was supposed to have an additional turn by I re-evaluated the track design and eliminated one turn, adding grade to the visible trackage instead.
The unique thing about this helix is that to make all the connections work, the “inside” track needed to be the “outside” track at the at the top. Originally that was going to be a diamond crossing, but by adjusting the grades I could put the top turn as a single track helix and bring it up and over, eliminating the crossing and a traffic conflict in a hidden area.
The problem was that this additional turn would be less of a rise so a different grade. To accomplish that I added additional risers on the outside of the helix. 1×3’s were used as the riser and a cleat of 1/2″ plywood attached. The cleat would be screwed to the outside of the spacer blocks.
Final positioning
After all the helix turns were added, the helix could be rotated to final alignment. I then elevated the helix to final position using blocks under the base and then attaching risers.
The risers are circled.
The last step is connecting the helix to the rest of the layout and test running it.