The helix itself is 4.5 turns of 28" radius, rising 4" per turn (width of a 2x4 on edge for spacers, plus 5/8" plywood roadbed), for a slope of (4" / 2•28"•π) 2.7%, which is about average for the entire main line. The roadbed is 4"x24" strips of 5/8" plywood, cut at 22.5° angles at each end. The wider second level deck (not pictured here, yet) is the same idea, but extended to 7.5" width to accomodate a 30.5" radius track on the outside. Spacer blocks are cut from 2x4s, with 45° angles on both ends to make an isosceles trapezoid shape (about 5" on the long side, 1.5" on the short side). You can see how they're laid out in the photo, alternating inside and outside placement. This provides a relatively large support area for the levels above, while still providing plenty of clearance from the 28"-radius track. The only issue I'm mildly concerned about is alignment on the inside edge of the roadbed joints. The outside is nicely supported across both pieces, but the inside is floating, and any warping of the wood would throw it out of alignment. I think I'll simply glue on a splice plate of 1/8" hardboard under the joint to ensure vertical alignment. Even with cork, track, and splice that still leaves 3" of clearance.
Tuesday, November 2, 2010
Construction: Helix (part 1)
The track plan had always included a helix, but I hadn't really planned on putting it in place until later on in the construction process. The track runs from the main yard at one end of the room, eventually to the terminal at the other end, having climed nearly 30" via 3 lengths of the room and 4 loops, but the helix is simply to return from the upper terminal to the hidden staging area (and optionally back to the main yard and/or continuous running). However, I realized that the second loop out coincides with the location of the helix and that at the very least I needed the exact location of the helix determined so that I could lay roadbed for the mainline around it. But I quickly realized that the mainline at that point coincided nicely with the second level of the helix in location, curvature and slope, so I decided to simply double the width of the second-level helix roadbed pieces to have a 3/4-circle of double track.
The helix itself is 4.5 turns of 28" radius, rising 4" per turn (width of a 2x4 on edge for spacers, plus 5/8" plywood roadbed), for a slope of (4" / 2•28"•π) 2.7%, which is about average for the entire main line. The roadbed is 4"x24" strips of 5/8" plywood, cut at 22.5° angles at each end. The wider second level deck (not pictured here, yet) is the same idea, but extended to 7.5" width to accomodate a 30.5" radius track on the outside. Spacer blocks are cut from 2x4s, with 45° angles on both ends to make an isosceles trapezoid shape (about 5" on the long side, 1.5" on the short side). You can see how they're laid out in the photo, alternating inside and outside placement. This provides a relatively large support area for the levels above, while still providing plenty of clearance from the 28"-radius track. The only issue I'm mildly concerned about is alignment on the inside edge of the roadbed joints. The outside is nicely supported across both pieces, but the inside is floating, and any warping of the wood would throw it out of alignment. I think I'll simply glue on a splice plate of 1/8" hardboard under the joint to ensure vertical alignment. Even with cork, track, and splice that still leaves 3" of clearance.
The helix itself is 4.5 turns of 28" radius, rising 4" per turn (width of a 2x4 on edge for spacers, plus 5/8" plywood roadbed), for a slope of (4" / 2•28"•π) 2.7%, which is about average for the entire main line. The roadbed is 4"x24" strips of 5/8" plywood, cut at 22.5° angles at each end. The wider second level deck (not pictured here, yet) is the same idea, but extended to 7.5" width to accomodate a 30.5" radius track on the outside. Spacer blocks are cut from 2x4s, with 45° angles on both ends to make an isosceles trapezoid shape (about 5" on the long side, 1.5" on the short side). You can see how they're laid out in the photo, alternating inside and outside placement. This provides a relatively large support area for the levels above, while still providing plenty of clearance from the 28"-radius track. The only issue I'm mildly concerned about is alignment on the inside edge of the roadbed joints. The outside is nicely supported across both pieces, but the inside is floating, and any warping of the wood would throw it out of alignment. I think I'll simply glue on a splice plate of 1/8" hardboard under the joint to ensure vertical alignment. Even with cork, track, and splice that still leaves 3" of clearance.
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