I couldn't find (NMRA S-7 clearance) Z scale clearance dimensions in inches. Below is a page from the NMRA site that has AAR plate B, plate E and plate F dimensions in feet and inches. I'm sure that z scale clearances can be calculated from that. Keep in mind that these clearances are for straight track. http://www.nmra.org/standards/sandrp/gauge.html Here is an quote from the page: I know you were probably looking for exact dimensions, but I hope this helps.
I had made my tunnels to the earlier standard and then got some Gundersuns. I ended up about 4 scale feet short. So now my tunnels are up to 26' to the ground from 22'. .
Thanks guys! I had already been over the NMRA pages. Here's the S7 page. NMRA - S-7 Clearances. You have to add track height to the "H" dimension, and then a fudge factor. I'm writing an article on grades and crossovers and was looking for the clearance manufacturers use in their portals. I"m finding a lot of inconsistency out there, and some people even say that they've bought portals that turned out to have insufficient clearance for modern diesels and cars. Like Jeff, they had to raise them. One thing I really found curious... on the Hornby forum I was told that a major manufacturer of OO scale portals uses 8 cm... which is 3.14 inches. The NMRA site talks about 3.5 inches for HO (because its "H" dimension is 3 inches). So it is common in England to have shorter portals for a larger scale. I'm using 3.75 inches in my table for OO. LOL I find Jeff's response interesting because 26' scale feet works out to just over 1.4 inches. And the Chooch Enterprises tunnel portals I've bought in N scale are 1.75 inches. Best!
That's because British prototypes are much smaller, with dimensions closer to US three-footers than modern standard gauge equipment.
Great thread! I know this is Z Scale and I have no intention of hijacking your thread, but I had real problems in HO scale until I learned that the NMRA gauge is also perfect for ensuring my 85' passenger cars will make it through the portal. Joe
No official tunnel portals on my layout currently, but I believe my previous layout had the track top to portal opening of 23 feet. I know my briddes are 23 feet. I model steam and things were smaller then. Today with all the doublestacks and stuff you should be okay at 27 feet. Remember that a precasted portal in Z on a 195mm or sharper curve could be problematic for cars over 75 feet. Locos too. Cheers, Jim CCRR
Jim you are right. My tunnel is on a curve, so I had to raise it even thought it was design for double stacks. There is rubbing of tunnel due to the tilting of the cars.
Okay... based on manufactured piers and portals I could measure, what people have told me on forums, and my own gut-feel fudge factors, I've made my table of clearances and the grade runs you need for them. It's a graphic in this article: Model Train Track Grades and Your Maximum Grade You have to click on a link to make the table readable. About.com doesn't let us embed HTML tables in our articles at this time. This is a beginner's primer on grades. Any and all feedback is appreciated.
For Z scale you should put some tracks in place and roll your longest car between two posts and check for clearence to your specific requirements. If your tunnel portal is on a tight curve it will require more space than if it is on a tangent piece of track. I have a MTL Gunderson car only for checking clearances. I was using Marklin passenger cars for this but the Gunderson car is very tall. If you are using very short radius Z scale track you must also take into consideration the overhang from the inside wall of the passenger car taking the short cut through the curve. If you want diagrams for prototype trains I found a web page showing Great Northern specs by Ben Ringnalda. Great Northern Empire - Then and Now
