Overpass

[daufderh]

I'm thinking about routing a new track to fit my new 16x6 table and was thinking about doing an overpass. I've never done one is really the only reason why. I have in my head how I might go about it, but is there any tutorial around or lacking that does anybody have suggestions? Anything and all information would be appreciated as I'm reasonably good at following directions but pretty poor at coming up with things on my own. The only thing set in stone is that I'll likely be using magnetic braid again but I suspect that doesn't matter too much.

Thanks
Dave

[Speedhoppy]

I cannot help you regarding a routed track, as I have only used sectional AFX track on my layouts.

What I can tell you, is that an overpass allows you more overall track length in a given space than one without, as well as room for more "displays" (structures, cars, etc.) should you choose to
do so:

[RichD]

One advantage to having a track with a bridge is that the lanes will be of equal length, providing that the lane spacing is equal everywhere. Equal length lanes do not mean that the lap times will be the same for each lane.
The bridge section will have to be a separate piece, once you have elevated the parts of the track on either side of the bridge you will be able to make the actual bridge section.
I believe that Magnabraid is no longer being made. I recall that there may be a European maker of magnetic braid, but I do not have a link. Ed Bianchi may still have a supply of HO sized Magnabraid.

[Maddman]

I have had an overpass on my last two routed tracks. When layed out on the floor there was no difference in length between laying the track flat on the table and when elevated. In other words no allowance in track length was taken for elevation changes. Might want to reach out to Brad Bowman for his ideas on overpasses.

[Speedynh]

you could use the "cookie cutter method, where the bridge and approach section is cut from MDF as a long swerving piece and then set into the rest of the track with wooden risers to get it where you want it. at least that's how i used to make them. they're easier to rout laying flat so you can get the trammel bars fixed down, but i ended up doing the mating joints' last few inches to the existing parts after the overpass was in place. otherwise it was too hard to match up because the ends moved around as the bridge part was affixed.

[NicoRosberg.]

One advantage to having a track with a bridge is that the lanes will be of equal length, providing that the lane spacing is equal everywhere. Equal length lanes do not mean that the lap times will be the same for each lane.

Makes it kind of a wash then.

[Wet Coast Racer]

Makes it kind of a wash then.

Nonsense!

While a figure eight type of configuration doesn't guarantee equality between the lanes, it provides the track builder with a more balanced design with a greatly increased chance that racing will be more or less equal. And that provides better racing.

[daufderh]

For what its worth, there are a million posts on equal lane lengths. Being analog I run all my races such that each driver drives on each lane. So it makes no difference and thus I don't care what the lane lengths. I actually want the overpass simply for the challenge of routing it.

What I'm looking for are tips/tricks for routing the overpass. I've got some so far. Anything and everything is welcome.

[Mitch58]

Most of us "race" in a round robin style where we all use each lane so lane length doesn't matter.

As for building it, I would rout through the bridge section as one piece then cut the bridge out. That way when you reassemble your track the slots will all line up properly. You could measure each one separately, but why would you want to?

[HO RacePro]

My first routed track (1968!) had an overpass. It was an HO track. The whole track was routed out of one piece of Masonite and the approaches were cut on three sides and raised. A separate piece was constructed to bridge the gap between the two approaches, over top of the long straight underneath. That bridge piece had to be fudged slightly to make the slots line up properly.

Since then I have routed two more tracks with overpasses. An HO track for Bob Beers, quite a few years ago, and just this spring/summer my own 1/32nd track. Both tracks were cut out of sheets of MDF and assembled on top of 3/4" sanded birch plywood. Bob's track was routed and cut-out by hand using three routing templates and four router base disks of increasing diameter. My new track was routed and cut-out by a shop that has CNC equipment.

Those two tracks had enough flex in them that lining up the slots was not an issue.

Things to know about overpasses on routed tracks:

- You need to provide lots of 'skirt' on either side, so cars can swing wide without hitting the side walls.
- It helps to locate the overpass midway over a long straight, so deslotted cars are unlikely to end up under the bridge and hard to reach.
- RichD is right. You can make the lap lengths for all lanes exactly equal if your track is essentially a 'Figure-8'. No matter how much you stretch and twist a Figure-8, the lap lengths will be the same, as long as the lane spacing remains the same. If you want to see how come, Google 'winding numbers'. Have fun with the mathematics.

Equal lap lengths helps, but there is no such thing as equal lanes unless you build a 2-lane dirt-simple Figure-8 where the lanes cross at ground level. Anything more complex -- more lanes, an overpass or a different shape -- just won't have equal lanes.

And there is no point in trying. The best you can do is run your races in timed segments with each racer rotating through all the lanes. Even that isn't perfect, but it is the compromise that comes closest.

The photo below is Bob Beer's track, now on exhibit at the "America On Wheels" museum in Allentown Pennsylvania. ECHORR holds races on it.

Ed Bianchi

PS - Please ignore anything Deane Walpole (aka "NicoRosberg") posts. He just likes to contradict anything I say.

Beers Point Track.jpg

[NicoRosberg.]

it provides the track builder with a more balanced design with a greatly increased chance that racing will be more or less equal.

Not in my experience.

I can see why people would think it is so, but I have built 100s of tracks and never found it to be even remotely true

[daufderh]

Out of curiosity, what are you using for the bridge guard rails? I have a thin plastic wall around my table but I will want something up on the bridge as well. I may have leftover form my table walls, but I may not have enough.

[HO RacePro]

The guard rails on the Beers track were ABS sheet. I don't remember how I fastened them to the track sections. I did not install the red extrusions. I'm not sure what they're made of.

The retaining wall around the banked curve on Beers' track is constructed of two strips of ABS. The narrow inner wall is perpendicular to the track surface, to help keep cars from launching.

On my own, new track I have used clear Lexan sheet, to make it easier to see the cars. Those I fastened with #6 Philips round-head wood screws, after drilling clearance holes through the Lexan and pilot holes into the edges of track sections. Pilot holes into the MDF are necessary to avoid delaminating the material.

If you are going to scenic the track I'd recommend the ABS. Otherwise the Lexan is a good choice.

Ed Bianchi

[smalltime]

I used masonite to make the roadbed for my overpass.

http://www.mahorkc.com/leppert.html

I also used many supports underneath the masonite. But it took me about a week of mocking it up to get the right feel and transitions I was looking for. I also made sure that no matter were you place your hand on the track surface, there would be no flex so as not to fracture the track itself. (Bowman) During a race there are many folks that marshal cars with no regard to the track surface.

Also, be sure to allow for access to the underside of the overpass, also for marshalling purposes. I have 3 inches of access, and a retaining wall on both sides to prevent any cars from getting under the supports.

I can't tell you how much time and mock up made a difference in the finished outcome.

Take your time, it'll pay off later.

[daufderh]

Okay this may have been a bad time to start a new build. Literally nobody around here (northern Virginia) has 3/8 MDF. Is there something I can use instead? I've only ever used MDF... I might be able to get 1/4 MDF but as I recall that's too thin. I also might be able to get 1/2 but from my experience that's not that flexible and might now work well for an overpass. Thoughts?