Has to be a Helix

Discussion in 'FAQs' started by Pitchwife, Mar 26, 2002.

  1. Pitchwife

    Pitchwife Dreamer

    In planning my dream HO layout I have come up against a real problem. I have to raise the elevation aproximately 14 inches and only have a 4'x4' area to do it in. The only solution I have come up with is a helix. I checked out an ad in MR but they were way too big and way too expensive. Has anyone out there ever built one from scratch and has any tips on building one, or any pitfalls to avoide. This will be in a mountain so aesthetics isn't really a factor as long as it gets the job done. Any and all suggestions will be appreciated.
  2. Woodie

    Woodie Active Member

    To Helix, or not to helix........


    I run a 4' * 8' HO layout and have twin loop tracks. the 4' at the ends, is not really enough to get a decent curve, for starters. (That's only 24" radius at the best!) Also, I did some sums for you. 24" radius gives you 150" circumference. (Please check my maths!) Each level will need to rise at least 5". (plus the clearance of supports and roadbed. And a 4' area, will give less than 24" radius, in practice.
    That's close on a 4% grade. Too steep, especially on a sharp curve (24" radius).

    I've got a 4% grade on just a half circle (24" radius) at the 4' end of my layout, and it's a struggle to get anything over 4 passenger coaches up it, let alone 3 - 4 full circles of incline.

    I'd think seriously, before going ahead, given those dimensions you have available.
  3. Gary Pfeil

    Gary Pfeil Active Member

    Clark, I have built a double track helix (24 and 26" radius). The grade is certainly a consideration. I model the 50's, and do not use dome cars, I measured my tallest equipment and found that I could get by with 2 5/8" clearance. The other major factor is the thickness of the roadbed. I used 3/4" plywood. so my total rise per revolution was 3 3/8" This works out to about 2 1/4% grade. Mine has been in operation for a couple years with no problem. Realize however, the trackwork needs to be perfect the first time, you will not be able to relay it later. I had 16" wide 4' long shelves which I cut into 1/4 of a circle. I used a router to remove 3/8" from the top of one end and the bottom of the other end of each 90 degree piece. These were screwed and glued together. I assembled three pieces, then laid track on them (also ran a buss wire and soldered feeds at this point) when finished with track and wiring on the first three sections, I assembled the next three sections and so on. I used pieces of 1x3 to separate the layers as I went. When complete, I ripped 2x4's in half to get 2x2 and these then had slots cut into them (I set my tablesaw blade at 1/2" and made several cuts side by side to obtain a 3/4" wide slot 1/2" deep) The slots were 2 5/8" apart. I then tapped these into place on the 3/4" roadbed and they maintain my clearance as well as serve as a means to hold the helix in place on my benchwork. I should mention that I am no carpenter and my helix isn't pretty, but it works.

  4. Woodie

    Woodie Active Member


    I've just checked the NMRA Standard for clearances. click here

    It suggests 76.2mm (3") from tracktop to min clearance height. Add track height, roadbed, and baseboard to that, for a clearance on each revolution.

    I've "bent" the NMRA standards on a few things. One of them was the height clearance. (well, a mistake actually!). I gave it 3" clearance, but forgot about the cork roadbed and rail height..... KABOOM... One loco I've got, don't go through the tunnell!!
  5. Pitchwife

    Pitchwife Dreamer

    What if I used 1/4" plywood or fiber board for the base and added extra support risers around the circumference? That would give me more clearance and hopefully enough support. If nothing else I may try elevating the lower end some and lowering the upper end so that there wouldn't be as much of a grade. If worse comes to worse I can just make sure that all traffic goes down hill. :D
  6. Woodie

    Woodie Active Member


    A 1/4" plywood sould be fine for support, with lots of support risers, but remember the additional clearance if you use "crossbars" as support risers. Oh... and some room to get your fingers in for derailments/jams etc. Is there any way you can get a larger radius?

    Oh.... and remember "what goes up, must come down... "
    Is your planned layout an "out 'n back" or complete loop... Will you have another helix at the other end? Are you doing a "double track" helix?
  7. Gary Pfeil

    Gary Pfeil Active Member

    Pitchwife, Whatever material you use for the helix roadbed, you will have to allow for splice joints as I don't know how you can avoid having to join pieces together. This, even with your 1/4"plywood, would require another 1/4" splice plate, so now you are at 1/2". I used 3/4" and routed as described above to join, you could save 1/4" using your method, just be sure that you won't have warpage problems. I have never liked using 1/4" plywood for roadbed. I definately wouldn't advise routing half the thickness of 1/4" material as I did with the 3/4". Regarding cheating the NMRA clearances, you certainly want to be aware of exactly what you are limiting yourself to. In my case, the helix is used for interchange between two railroads located on different levels. I wanted, as a minimum, to be able to run standard 50's era freight cars on the helix. No hi cubes on my railroad! so I was able to cheat down to 2 5/8", including the track height. No, I will never be able to run modern stuff if I change my mind, but I can assure you that will never happen. I did buy Accurails auto racks, I can run them on the helix but only without autos on the top deck. As far as Woodie's statement about room to fix derailments, I do not even attempt to rerail equipment that derails(thankfully, it doesn't happen often!). I simply remove the offending piece of equipment from its train, couple the train back together, and resume its run. The problem car is inspected and if ok, returned to its train after exiting the helix. Given that this process, while not really difficult, does interfere with the enjoyment of operating, I recommend you build a helix from good sturdy materials and put the effort into designing it to be dimensionally stable. I repeat my advise about tracklaying on the helix. Using flex track, stagger all rail joints, solder every joiner while last foot or so of flex track is still straight, make sure rail is in cast on spikes, not resting on top of them, so on. You will not get a second chance without dismantling the helix. Going thru the effort of building the helix and having trains constantly derail is going to bum you out. Also remember to be generous with power feeds, although if you have soldered each joint, this shouldn't be a problem. On trackage as hard to work on as a helix, there is no such thing as overkill. Be meticulous in your workmanship once, then don't worry about it anymore!

  8. rockislandmike

    rockislandmike Active Member

    You're gonna want more than 3" if you wanna run doublestacks.
  9. 60103

    60103 Pooh Bah

    Remeber that you don't have to splice the roadbed joints UNDER the roadbed; if you make it wide enough you can do it on TOP, beside the rails.

    On the other hand, I don't know how strong this is.
  10. billk

    billk Active Member

    60103 - If you spice it beside the rails, the splices can be on either the top or bottom without affecting the clearance!
  11. Pitchwife

    Pitchwife Dreamer

    Hey everybody.
    Thanks for all of the great input. (fortunately everything is still on paper and fixes are much easier to make) I did some redesigning and have managed to reduce the height between the levels down to 9 inches which means that there should be 4 1/2" clearance. I also added three inches to the outside diameter making it 51". It may not sound like a lot but every bit helps, and by the way, yes, it is going to be a double track making 1 1/2 revolutions. The other end isn't a problem as there will be 24'+ to gain the needed altitude. As for the supports I thought that I might steal an idea from Trainstyles (www.trainstyles.com). What they do is to drill holes on the outer and inner edges of the helix and run a long threaded shaft through them. Then they use hollow tubes over the bolts between each level to set the clearance and bolt top and bottom to make everything rigid. I'm not sure what they use for the track bed itself, but I'm sure that 3/4 inch plywood would work fine. The ideas for connecting each section together sound really good, almost like tonuge and grove joints.
    Another question I'm not sure about is how much clearance to allow between the tracks. The closer they are the wider the diameter for the inside rail, but I surely don't want two trains interfering with each other. Any thoughts on that?
    Thanks again for all of the great tips. I am feeling more confident about this project all the time.

  12. Gary Pfeil

    Gary Pfeil Active Member

    Assuming 24" radius for the outside track (25 1/2 if you can use all 51") the center to center spacing probably should be 2 1/2". It depends to some extent on the equipment to expect to run on it. I suggest you lay a few feet on a piece of plywood to see what clearance you need. Put your longest passenger car (or 86' freight car) on the outside track, the car with the longest overhang from truck to coupler on the inside track and see what happens with 2 1/4. Say 25" and 22 3/4". If not sufficient, go to 2 1/2.

  13. Woodie

    Woodie Active Member



    The NMRA Standards for track clearances on curves for dual tracks are here

    Go there, and firstly, determine what rollingstock you wish to run (from the list at the top).

    Scroll down to the HO table. Look for your "radius" in inches, and your "rollingstock type". Note how there are no figures for class 1a rollingstock (full length passenger stock) for radius less than 32". NOTE: "Construction or operation of equipment on curves sharper than those listed for its class are neither prohibited nor recommended". In other words, don't do it, but we're not gunna stop ya!
    Refer to the appropriate notes for how to measure the clearances.

    The radius is measured at the track CENTRE of the INNER track. Also allow for the "inner clearance" inside the inner track as well.

    I found this data sheet VERY useful for curves, and most of all, it's pretty correct!

    I again, also "bent" these a little on my dual track curves, and paid for it..... :mad:

    Any trouble interpreting the datasheet, let me know. Yes it did take me a while to work it all out, but I understand it quite well now.
  14. Gary Pfeil

    Gary Pfeil Active Member

    Here I go again, giving bad advise! Or at least contrary to accepted standards. Please be aware that in regard to track spacing, as with previous topic of height clearances, I tend to go my own way. Note I will always specify the type of equipment I use when talking about clearance issues. Just for the record, I run full length passenger cars (Rivarossi) past each other on double track curves of 23 7/8 and 26 1/8. This is 2 1/4" spacing. I don't like it appearance wise, but this is on a helix anyway. My mains are all 30" and 32". These radius are at 2" centers. Again, no problem. I confess I did not check standards before track laying. If you are in a tight space situation, I recommend laying some track on a sheet of plywood and checking clearances as I mentioned above. Longest truck center to center spacing car on outside track, car with longest overhang of body from truck center on inside track, make sure they clear. Keep in mind you need to use longest equipment you will ever want to run. When you have the space, by all means follow the standards.

  15. Woodie

    Woodie Active Member


    Doesn't seem to be any probs with what you are doing, and those clearances seem fine, given your requirements. :)

    The problems I had was making the radius too small in the first place.
    The longest passenger car I run is 27.5cm (13") including couplers. (An 8 car set). These go round my 55cm (22") radius. However, I replaced the bogie mounted couplers with body mounted kadees. They no longer went round that radius, as the body mounted kadee pulled the bogies off the tracks. I had to revert to (replace) the bogies back to the originals. If I was lucky, they would go round the "outer" track, but certainly not the "inner" track. To get the maximum radius into the area I had, I also compromised the track separation. Worked fine until I bought a Bachmann HO doodlebug. The bogies on the doodlebug are mounted far more towards the centre of the car than others, hence the ends "poke out" over the track edges a lot further that the other cars, when rounding the curve. Kaboom. Can't run the doodlebug while the other passenger coaches are on the other track. The other end of the layout, I did adhere to the standards and they only "just miss" when rounding the curves.

    Hence my concern about a tight radius with longer rollingstock, and dual trackage. At the moment, I am quite limited on what I can run, or who's stock I can run on my layout, especially if they have body mounted kadees (on "long" stock and 4 wheel stock) for just the reasons outlined above.
    I built Garahbara with the intention of throwing it out anyway, and I knew I would make mistakes. However, when I do build "the dream", I will be adhering to those standards, so I can run who's/what/when/where/why I like, especially after going to the effort of building "the dream". Given thos dimensions of the rollingstock I run, I'd consider then to be about the longest you can get, hence the concern.
  16. Gary Pfeil

    Gary Pfeil Active Member

    Hi Woodie, That doodlebug truck to truck spacing is a good example of a piece of equipment to use on the inside track for test purposes. With a long passenger car (or 86" flat) on the outside track, one can determine the spacing required. Again, this is only needed if space prevents using the standards. I don't get to hung up on the standards, I noticed on the link you provided it recommended 2 1/2" spacing for 32" radius curve. As I mentioned, I use 2" spacing and long cars (and a doodlebug too!) and have no sideswipping problems. I don't like the look of 2 1/2" spacing. For appearance, I prefer 2" spacing, which I have found over the years is fine as long as the radius of the inside curve is at least 30". Below that you need 2 1/4". And below 26" radius, 2 1/2 is a good idea. I got away with 2 1/4 at 23 7/8 and 26 1/8, but didn't expect to. I really hadn't counted on running passenger equipment there, I just tried it and found I could. I was actually quite surprised. Possibly at higher speeds they wouldn't make it! To all who pay any attention to me on this I say: I am only relating what I have done in situations in which I had no option space wise. I had a clear idea of what I wanted to run and had the equipment on hand to test prior to committing myself. If you must cheat the standard, perform your own test, don't take my word for it!

  17. Pitchwife

    Pitchwife Dreamer

    Your information has proven invaluable. I know that I will be refering back to it again and again when the track meets the road.
    As far as clearance, in a lot that I bought on eBay was a 90' triple deck car carrier. I guess that if I can get enough space for it to pass itself I should be safe with anything that I can put on the rails. Once again it will all be hidden so as long as it works I'll be tickled.
    Consider your brains picked and appreciated.

    Thanks again
  18. marty w.

    marty w. Member

    I assume that the flex track was laid directly on the plywood?

    What is the distance between the level's?

    How did you construct the top level? Plywood and foam? 1'x4", plywood and homasote?

    I'm thinking of adding or starting over with a double deck layout.
    I have room for a 30" max. raduis helix so my grade will be some what less. The building of the helix seems like it will work well and that it will last. I like the idea of using the wood 2x2 for the support of the helix. Someone suggested I use threaded rod and nuts. I do not think that would offer much stability.

  19. Gary Pfeil

    Gary Pfeil Active Member

    Hi Marty, I didn't gave a digital camera back in April when I made those posts, I will take a couple shots tonight and post them. You know what they say about a picture being worth a thousand words. Yes, my track is directly on the plywood. Distance between levels in track length is determined by multiplying the diameter (the radius x 2) by pye(?) I use 3.2 So, for a 26" radius, 26x2=52, 52x3.2=166, 166/12=just under 14'.

  20. marty w.

    marty w. Member

    Thanks Gary,

    Ok check this out.
    30"R with 3.75" rise at 5 laps =
    942.66" of track at 2% with a total rise of 18.75".

    I will use 3/4 plywood with 3" of clearence = 3.75" rise.

    Top deck to be 58" and bottom deck to be 39.25" high.

    How do you do the top deck? Cantilever from wall?
    Width would be kept to 24" max.

    As you can see, I have nothing to do at work today. We are very slow for the month of October.


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