Dannyboy6:
Thanks for the link to the helix calculator. Wonderful tool!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Here's a calclulation tool that I posted to our NMRA Division website:http://michiana-nmra.org/resources.html
Keep in mind that what works for a table top type application on top of a grid won't necessarily work when cut into 4" wide pieces for cookie cutter (or helix deck) subroadbed. You can put 1/4" ply on top of a 2x4 grid with cross members every 16" and that will work fine. But cut that 1/4" ply into 4" wide strips and support it every 16" and it will eventually sag like the wires between telephone poles.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
The reason I was asking is that I used 3/8" ply for my existing benchwork, which may or may not be re-usable (2'x4' sections on most of it). I was thinking of using 3/8" ply but that would require more frequent support.
BMMECNYCIs there a structural reason for using 1/2" ply (or 1/2" of ply) or is it just used to keep the numbers simple
It's more about the subroadbed sagging than it is structural integrity. I think 1/2" is generally accepted by most model railroaders as the minimum requirement to prevent sagging between risers over time.
I have heard of helix decks that were made from a sandwich of two pieces of 1/8" tempered hardboard. I suppose that with enough risers it would probably work.
Is there a structural reason for using 1/2" ply (or 1/2" of ply) or is it just used to keep the numbers simple?
hon30critterI noticed that Jeff is only using 3" risers and there still seems to be lots of clearance. I'd have to check my caboose smoke stacks though.
My risers are 2 3/4". I also found my caboose stacks to be the highest point on any of my rolling stock.
One other thing I did differently than the linked video is that I laminated two layers of 1/4" ply with staggered joints rather than using 1/2" for the deck.
BMMECNYC, Dave and any other interested parties,
I have a PDF on techniques I used when building my helix. I tried to get the most out of the helix. Mine is a double helix with staging, several runarounds and wyes at the top and bottom. Send me a PM if you are interested.
Guy
see stuff at: the Willoughby Line Site
Steve:
When I click on your link I get a message saying the folder is not yet public. Do I need to do something else?
Thanks
Central Gulf:
Thanks for the links to the videos.
I noticed that Jeff is only using 3" risers and there still seems to be lots of clearance. I'd have to check my caboose smoke stacks though.
Just in case anyone interested in building a helix hasn't seen these videos by Jeff Johnson. They are based on an article he had in the April 2008 MRR. Johnson is a professional journalist and videographer. His presentation is excellent.
https://www.youtube.com/watch?v=ZdrXH--f41Y
https://www.youtube.com/watch?v=gZzdID42q9M
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=565927
Here is an excell program I have been working on.
Steve
I built a 30/32.5" radius helix using a 3.25" space block with 1/2 inch plywood. It has worked great for the last decade or so. I haven't found the need to reach inside to re-rail cars and the locos like the gentler grade.
BMMECNYC.75" for the fingers/support for the subroadbed
Definately lose the cork.
If you build the helix like most of us have, there will be no sub-roadbed support over the rails. Support is usually provided with blocks on the edges of the sub-roadbed.
Finger space is optional. It may necessary if you want to be able to fix a derailment, but if you are willing to work a little harder or settle for extraction, maybe not. I'll bet that with an inch of finger space, you'll still end up extracting way more often than fixing.
My experience is that derailments happen when something changes, like at a turnout or a change in direction or grade. If you take care in construction, the helix is actually one of the least likely spots for a derailment. I won't say it won't happen, just that it is more likely to happen elsewhere. This makes the choice of extraction a little easier to make.
I haven't had a derailment in my helix yet, but I have done some testing and find that a derailed car is easily removed with an index finger on each end of car. It is operationally disruptive, but I'm willing to live with this in order to reduce the grade.
BTW, if you do a little looking, you'll find a lot helix builders used 1/2" plywood and 3 1/2" spacers between levels for 4" railhead to railhead. One of the first helix articles (might have been Jim Hediger) did it this way and a lot of folks followed that lead. The 3 1/2" spacer comes from cutting blocks from 1x4 which is 3 1/2" across - very convenient.
BroadwayLion The tunnel does NOT have to accomodate a fully extended pantograph. You can not get into Penn Station that way. ...
The tunnel does NOT have to accomodate a fully extended pantograph. You can not get into Penn Station that way. ...
My layout, and probably his, does not have Penn Station. I don't have wire, and I am not inclined to build a ramp to lower my pantograph so that it can enter a tunnel portal from the outside. Even so, my point was that the person looking for minimum helix separation had better consider the height of his tallest item of rolling stock.
BroadwayLion ROAR
ROAR
Indeed. I did that when I learned that lesson.
gregc you also need to leave room for fingers if something derails
you also need to leave room for fingers if something derails
So a good rule of thumb (or I guess finger) would be Subroadbed depth+roadbed+track+NMRA guage+fingerspace/support for subroadbed=Distance between railheads.
Assuming .5" Plywood + .1875" (3/16") Cork + .165" (Atlas Code 100 or 83 flex) + 3.007" (NMRA Mark IVb measured with a Starrett Dial Caliper) + .75" for the fingers/support for the subroadbed = 4.60" between railheads.
Loose the cork: 4.422"
Loose cork and skimp on plywood (3/8" vs 1/2"): 4.297"
Am I missing something?
Note: Tallest piece of rolling stock is 2.70" (heavy duty flatcar with oversize load shipment). Have several other cars with depressed centers carrying various other types of oversized loads. The railroad line (MEC mountain division) the helix is being used to connect to the rest of the layout (Portland Terminal Co) was used for oversized loads due to having no tunnels (also kind of a problem, but not one that is unsolvable).
greg - Philadelphia & Reading / Reading
The tunnel does NOT have to accomodate a fully extended pantograph. You can not get into Penn Station that way. The wire decends before the the tunnel, and then enters the tunnel where the pan is almost all the way down to the roof.
You can do this by having a gradually decenting roof to your tunnel (helix) which will gently lower the pantograph.
Better yet, string wire over your your entire layout : )
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Treat the helix as a circle and use the formula for the circumference of a circle to get the distance traveled at the centerline of the tracks on the helix. Then, impart the grade you feel you need and you'll get the rise over the run by using the formula for figuring grades and height changes. That's what I did, and I was bang-on.
Just don't forget to factor the thicknesses of your sub-roadbed material, be it plywood or something else, and the rail heights of the rails and ties sitting on the roadbed, if you use roadbed. I don't use roadbed in my helices, but if you do, subtract that from your separation to get your clearance.
My highest item is the pantograph, fully extended, on my Trix GG1. Learned that the hard way, but earlier, thank goodness.
x by y times z2 etc. LIONS do NOT do That!
Look at the picture.
The helix MUST start where the helix must start. It must end where it must end. It MUST have enough clearance for trains to fit in the helix, and the diameter of the helix id dictated by the size of the table.
It has to do what it has to do.
About the only wiggle room you have is the diameter of the helix shich can be free standing or overlap the table on an extension of some sort. These tables, and thus the helix are 5' across. (former ping-pong tables).
LIONS are optional.
The table in the lower left is a 4" high 2' x 6' "mini-table" which sits on top of the ping-pong table. The top of the helix ends on another "mini-table" that is about 2" high and 2' x 6' and is supported by such supports as necessary to support it. LION uses lots of these "mini-tables" around the layout. It makes construction much easier.
Dave,
The chart shows railhead separations starting from 1 5/8" as a minimum for N working its way up from there to 2.5" then, .5" increments up to 6". I am looking to keep the grade a shallow as possible in a 7' diameter circle, preferably less than 7'. I understand the forces involved with curves on a grade. I have been using Model Railroad System locomotive pull calculator (does grades and curves as well). I realize that I need to maximize my curve radius as much as possible and minimize the grade.
Greg,
Those are handy charts. I had not yet considered benchwork thickness. I will likely use 3/8" ply if I can get away with it.
there are other considerations such as "Effective slope caused by curves" that are discussed in an earlier thread
http://cs.trains.com/mrr/f/11/p/221186/2444394.aspx#2444394
Hi BMMECNYC:
I don't think the grades in the chart will translate very well for helicies.
The chart shows minimum clearances for the crossover, and I believe it is based on standard height rolling stock. Minimum clearances are OK when you can reach in to get at the rolling stock easily from either side of the bridge in the event of a derailment. That is the scenario I believe the chart is based on. However, if you suffer a derailment in a helix where there is no extra space to reach into to recover a train, then you are inviting problems. From a theoretical perspective minimum clearances will work fine. Unfortunately we are dealing with reality when a train derails in the middle of your helix. Theoretically, you could fish a derailed locomotive out of a helix with only 1/4" of spare room, but how much damage are you going to do to the locomotive in the process?
I'm guessing that you are trying to figure out how to fit a helix into a limited space. Correct? I told myself for years that I could do exactly that. Finally, reality kicked in and I increased the radii from 26" to 30". That made a big difference in the clearances between each level and it reduced the grade to about 2.1%. Just don't tell my wife how much more garage space the layout is going to occupy as a result of the change!
Cheers!
Having read through Track Planning for Realistic Operation (John Armstrong), I have a question. Is the grade separation chart on page 83 accurate for a helix as well. Or will the grades be slightly more or less?
Edit: I should have mentioned 3rd edition as well as the chapter (6), last page before chapter 7 if that helps anyone with different editions.