Hi There;
I’ll try to explain this so it makes sense. I am building a 21" radius helix. I want to use 1x6 pine in an octagon biscuit joined together. My problem is I can’t get my 8 pieces the right length. Is there a formula to figure this out? I don’t want to use plywood because of the extra cost & waste. A 1x6 is actually 5&1/2" wide. My wife & I have been crawling around on the floor with cardboard patterns all afternoon. I sure could use some help.
Tom
Let’s see, you’ll need some semi-serious geometry here. Octagon means 8 pieces. 8 joints.
Each joint will be 1/8th of 360deg. or each side of each joint will be 1/16th of 360deg. 360/8 = 45, so each side will be 22 1/2 deg.
Then we get to circumfrence. 2piR if I remember correctly (piRsquared is area, I think). so 23.141521
131.94 or 132 inches. Divde that by 8 and each section should be about 16 1/2 inches long - in the center. Outside will be longer, inside will be shorter. I’ll leave that for you and a compound miter saw to figure out.
I think that works.
Now, having said that… I highly recommend trying to find some more room for the helix and make it larger. Unless this is N Scale. If it’s HO, a helix of that radius is going to have to have a pretty fierce grade (I make it about 2.6 to 3%) for adequate clearance, and those curves add drag as well, essentially adding “virtual grade” to the helix.
IOW, you may get the helix built but never be able to get anything up it.
I’m hoping this is not an HO helix, because a 21" radius helix will need a nearly 3% grade to get HO clearance between the tiers … and the extra drag of a 21" radius curve will be about +2%, which will make this equivalent to a 5% grade!
Most locos will pull just a few cars up this kind of grade, and since a helix will need to be hidden trackage if you scenic your layout realistically, having a hidden 5% equivalent grade will be an operational headache.
Please tell me this is an N scale helix!
Hi There;
Yes it is in HO. The upper & lower tracks are in the room next door. I am presently using an elevator to get between levels but it is inconvenient to use. So the radius is fixed by the tracks coming through the wall. Jeff thanx for your calculations I’ll give those figures a try. Joe; I used helicalc & came up this;5 turns,16" rise, 3.199" between levels equals 2.4% grade. I run mostly 5-6 car trains. Thanx for your advice I will do a temporary mockup & see how it works.
Tom
Tom,
Measure your tallest car. Add 1 1/2 - 2 inches clearance for fingers if necessary… that’s the spacing between the top of the car and the bottom of the 1x6 - remember, it’s got thickness that has to fit in there as well. So does the track, so make sure you measure while the car is sitting on it too.
I had my CAD software open, so I quickly drew this up. The ends of the boards need to be cut at a 22.5 degree angle. The long side of each segment needs to be 19.1 inches long while the short side needs to be 14.5 inches long. A 21 inch radius track centerline will be 2 inches from the inside of the boards at the joints and 2 inches from the outside edge of the boards at the midpoint of each board.
Tom,
An added problem you may find by using 1x6 pine over plywood is, with such a small radius, once your biscuit joined sections are raised to the spiral configuration, rising of the piece doesn’t keep the same plane and flexing of the unit can stress the joint. Even if the joint holds, cocking can occur. Plywood will twist evenly, pine will not. Also even if you pick clear D select or C or better, the pine could deform by twisting, cupping or bowing. I feel that double layered 3/8" ply w/ alternating splices is the easiest to build and most forgiving. I am a carpenter and love to work w/ clear pine, but I can forsee many headaches in this small helix using it. Also the 22 1/2 degree mitre works in a single plane, you will find that minor adjustments will be needed to compensate for the rise. Not trying to scare you w/ your method, but ply “wood” make life easier.
Hi There;
Wow!! You guys have sure been a lot of help. You’ve given me lots to think about. This is what I like about this forum. Again thanx all.
Tom
TommyR Some of the things you need to consider…What is the longest car you will want to run? I built a 24"r. helix that came out to almost 3% grade. My 4 unit diesel would pull my train up it - 50 cars with metal wheelsets. my freight cars are all 36’ to 40’ because I run '47-‘50 era. However… I cried when I tried to run My Empire Builder up it. Those 85’ cars would not do it, Modern cars won’t either! And they looked like a toy train trying to go there. I ripped it all out in favor of much larger curves…42" to 48" radius. So you have to decide what you are going to run, and, how much room you can get away with. I would reccommend taking the time and effort to do some mockup sections and compare the results. Also remember, if you do a reverse curve leading into the helix, leave at least 12" straight track between the easements. Hope this is helpful. Happy railroading!
Tom:
My helix experience is similar to John’s. I started with a 24" radius helix in HO at a 2.65% grade and my operators hated it. It was always a problem with stalling trains. When I suggested we replace it they had it completely torn out in an afternoon, they were so eager to get rid of it.
I replaced it with a 40" radius helix using a 1.75% grade – and it made a huge difference in how the trains performed going up it.
I call my original helix my “helix from hell” and every chance I get I remind people that a small radius helix will most often be the biggest operational headache you have on your layout. [B)]
Hi There;
Thanx again for all the good advice. I think I will make a temporary mockup on my workbench & see how it works. I run 40’ cars & geared locos pulling log cars. After reading all the good advice my elevator dose’nt look so bad after all. If I can find a way to motorise it & install micro switches to stop it it might the better way to go.(see Pic)
