Overpass

[Scaleracing]

While an outside loop figure 8 track will create equal lane lengths it will not create equal lanes. However it does tend to create racing where cars are more often side by side racing each other.

Here we race every lane so from the point of view of equal this neutralizes the arguement of a better lane.

The best drivers figure out how to race the track.

On a side note.

While I have little time to post here I supply this Forum to allow a free place for people to help each other in this Hobby.

Not to attack each other or bring up distain for other posters. If you disagree with someone ignore them. Some positive posts would help the Hobby grow.
Toxic comments do not. Continually digging at people and their posting style and opinion got old 10 years ago.

If you can not tolerate or agree with someone else leave them alone, ignore them. But under no circumstance should you post trying to name or shame them. Please I was tired of this 10 years ago let alone now.

I guess there are places where you can attack each other. I do not want that here. It is not clever, funny nor helpful.

Now I need to get back to my Business.

Thank you all for your understanding

[daufderh]

Staying on topic,

Sheets doesn't have it. They're my normal go to for everything but because of the pandemic they're a no go. If I cut the negative space out of 1/2 inch thick MDF will it be flexible enough to do the incline for the overpass? That is assuming I do nothing other than cut the MDF... I didn't think it would be.

So far the best I've found is somebody who would ship it to a location about an hour from here. That'll cost $400ish on top of the materials. If that's the best I can do and 1/2 thick won't flex enough for an overpass, I may scrap the overpass and/or the entire build for now...

[daufderh]

Oh, lost in all the even lane gibber jabber (which I don't care about), I think somebody asked what scale. This is an HO track. It's a digression but I'm curious why that would matter? Seems to me you'd route 1/24, 1/32, or HO all with the same MDF. Just different slot sizes and such...

[NicoRosberg.]

What is your reason for wanting an overpass?

More track in the same space?

[MrFlippant]

Brad uses sintra for his tracks, and they're pretty darn good. Probably a bit more expensive than MDF, though.
As mentioned, some kerf/relief cuts on the bottom of the part being bent will give it more flex. Also, MDF will "creep" over time, which will allow you to bend it a little, then let it rest, then bend it more. The last thing you want to do is bend it A LOT right away.
Do you already have an idea of how much elevation change you want to achieve over a particular distance? Those with experience building tracks might be able to tell you if 1/2" is fine, or if you need to keep looking for 3/8".

[daufderh]

I build tracks for fun. I've never done an overpass so I thought I'd do one this time. I have a 16x6 foot table so with the overpass I was considering something massive, again just for fun. It's that simple. It's for an HO track, beyond that I don't care how high it gets and such. If I had found 3/8 MDF I was planning on some elevation throughout the track aside from the overpass but again, that's just for fun. Really I don't care too much, which is why I'm considering going 1/2 MDF and just doing another flat track.

"some kerf/relief cuts on the bottom of the part being bent will give it more flex". I'll have to google this. I assume you make cuts perpendicular to the where you want it to flex some distance apart at some shallow depth to essentially weaken the board...

Assuming I can find sintra, is routing in it the same as wood? What about gluing the braid down to it? I'm guessing I might need different router bits? And considering for braid to MDF I'm just using wood glue, I assume I'd need something different. How thick do I need? is 3/8 inch still right or do i want to go thinner because its plastic. I haven't found much yet, but what I have found is generally about half that thickness. Keep in mind I'm reasonably good with following directions, no so great coming up with things on my own. But I'm happy to try something new.

[MrFlippant]

16x6 is plenty of distance for some decent elevation changes using 1/2" MDF. As long as you're not making some crazy rally track or a high banked turn, you can have it going up and down over a distance with no major issues or need for undercuts, which you understand correctly.

I don't know if anything special is needed for sintra, which is a brand name of expanded polystyrene. Call around to local plastics suppliers and ask for Sintra, but tell them generic is fine. I might have the specific type of plastic wrong for that. I think it will route just fine using traditional methods used for MDF, but if you're concerned, I'd bet Brad (Brad's Tracks) would be happy to give you some tips.

[Wet Coast Racer]

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

Dave, the only thing I know practically about routing a track is what I learned doing this in 5/8" mdf for a 1/32 scale circuit. 16 x 6 sure sounds like a great opportinity to create something great in HO scale. And it's great to see that you've been at this a while, building other tracks. So let me throw in a few random thoughts, that might actually help you do this!

I think it's great to have some elevation in a circuit, gives it a certain realism. Also, with an overpass/underpass, makes it easier to put the greatest track length on the area you've got. Doesn't matter whether it's a home raceway or a professional venue. I designed mine with a pencil and graph paper, along with some geometry tools from school!

As has been noted, no scale racetrack - whatever the configuration - will produce identical laptimes for the same driver/car/controller combo. But some design of a 'figure 8' is a good step in that direction. Even guys buildiing tracks in gymnasiums with lanes sometimes separated by boulevards can't manage this, let alone the rest of us building tracks in our basements - plastic or routed.

It's important to consider sightlines from the driver's position wherever their controllers plug in. Obviously, the cars are going to briefly disappear as they go through the underpass, and this should be minimized. On large professional circuits like Alan's big 6 & 8 lane courses, some big bad multi-car crashes can happen under the overpass, though that's typically a result of someone losing control of their car coming out of the previous turn. One of the most appealing things about a track that uses elevations is that it can maximize the driver's view of the cars.

Interesting that you'll use magnetic braid. And with HO cars in particular, that must make a huge difference in terms of 'downforce' from their strong magnets. Whether one needs to kerf the track or not to achieve elevations in a short track distance, making quite sudden changes to elevation in a short distance can send slot cars flying into the scenery if they're not 'stuck' to the track - particularly if they need brakes in order to make the next turn.

Final random thought - do you have trucks that you like to race? Might make a difference to the minimum elevation of your overpass/underpass section.

It would sure be good to see if there's anybody out there who might propose a track design for the space you're using, someone who understands how to create a good circuit for the space. The whole beauty of routing a track is that it's your own creation, literally. And the investment in the lumber will be forgotten if you've created something good, eh?

Looking forward to seeing what you come up with!

[RichD]

Sintra is expanded PVC, it can be routed just like you would route MDF. Sintra comes in many colors so you would not have to fuss with painting it. If you are making a track out of MDF and there is even the slightest chance that it might get wet make sure that you paint every surface, including the slots. One of our club tracks had the water line going to a refrigerator passing over it, the line developed a leak and part of the track got soaked. The MDF swelled up or fell apart. The damaged area had to be repaired with Bondo and the slots had to be re-routed.

[HO RacePro]

Let me throw some real-world examples into the discussion...

Several years back a similar discussion motivated me to do some tests elevating 3/8" thick MDF. Inside of 4 feet of run I was easily able to ramp up 3-1/2 inches, starting level and ending level. No pre-forming or other tricks required. The ramp angle was no-way near radical enough to cause an issue with the cars.

IMG_1866.jpeg IMG_1865.jpeg

Similarly, here is a banked curve done without any tricks. The 176-degree curve plus two 24" straights were cut from one sheet of 3/8 inch MDF. The banking was created by pulling the legs of the piece together to make the curve a 180. That made the curve naturally bank. The maximum bank angle is 20-degrees. The outside edge of the curve is 3-1/2 inches higher than the inside edge at the maximum bank. The track is 10-1/2 inches wide. Wedges were added after-the-fact to provide more support, but were not needed to achieve the banking.

IMG_3252.jpeg IMG_3251.jpeg

And here is my most recent track construction, this time in 1/2 inch thick MDF. It is a 1/32 scale track measuring 8 x 13 feet. The eight-foot-long straight under the overpass elevates 5 inches, level-to-level. Again, nothing special was done to achieve that slope. It could be made steeper without any trouble.

IMG_3255.jpeg IMG_3254.jpeg IMG_3253.jpeg

I'll note in passing that the elevated section of that track improves the visibility of the back section, but the overpass does limit the visibility of the straight underneath. It makes it tricky to judge just when to brake for the tight, elevated left corner following.

As far as where to find MDF and what it costs... You won't have much luck shopping at Lowe's or Home Depot. If you are lucky you might find 1/2 inch MDF. You might be able to special order 3/8 inch. But you'll probably have better luck if you can find a shop that caters to the building trades. Again, you may need to special order the stuff, but that shouldn't be an issue. In the United States the Masonite Corporation is the major manufacturer of MDF sheet stock, if your retailer needs a hint.

The last few times I've shopped for 3/8 inch MDF it cost me about US$20 to US$25 per 4 x 8 sheet. It took a few days to get it in stock.

FYI, MDF sheets are typically 49 inches by 97 inches -- one inch oversize from 4 x 8 feet. That little bit of extra material can be useful, especially if your sheet sustains some edge damage in handling.

At one time I had some samples of Sintra to play with. I never attempted to build a track from the stuff. As I recall it cost something like four times what MDF sold for. And being plastic you have to be careful not to overheat it while routing. That's about all I can tell you about it. Anyone who has actually built a track in Sintra is encouraged to share their knowledge here.

Ed Bianchi

[HO RacePro]

On the subject of routed track design...

Alliance Park Cropped.jpeg

This is one of my earliest routed tracks, where I went out of my way to exploit the flexibility of routed track design.

It was hand-routed out of a single sheet of 4 x 8 foot MDF. Almost all of the track has some curvature to it. Even the back straight wanders a little bit, with a reverse curve going into the left corner following. None of the curves are a conventional radius. The largest radius -- if I remember right -- is 32 inches. The tightest radius is 4-1/2 inches.

In other words, you no longer have to have straight straights and integral-segments-of-a-circle curves. In fact your curves do not even have to be circular. Do you want a Monza-style parabolica? How about a four-focus Bezier curve? Or a curve you simply drew freehand? It all works.

What made it possible to have all that curvature was the track was routed using a template, also made from 3/8 inch MDF. The shape of the template can be seen from that of the green infield. While many of the curves needed to be created with a compass, some of them were free-hand shaped using a hand-held belt sander. The advantages of using a template were: one, all of the fussing could be done in creating the template -- including some patching. Once the template was finished using it to rout the actual slots was pretty much brainless. And two, once I had a finished template I could make as many identical tracks as I want. I have sold a number of them.

These days it is very practical to have your track CNC routed. You need to create a DWG or DXF drawing of your track, and that involves having or developing some computer-drawing skills. But once you have that you can send it out for quotes. Any cabinet shop should be able to toss your sketch into their system and pump out a routed and cut-out track. That's what I did to get that 1/32nd scale track made for me, shown in my previous post.

Ed Bianchi

[daufderh]

At this point I suspect I'm going to use 1/2" MDF. I can actually get that at Lowes/Home Depot. Home Depot use to be able to special order 3/8" but tha cannot any longer. I can't find anything locally and as you can imagine shipping a 4x8 sheet of MDF costs a lot more than the MDF itself. Given that 1/2 inch can support the overpass, I think I'll play around it once I have it. The trick of course will be to to give it enough time to get up to the height I need. That's the case with 3/8" too, but its probably a bit more important with 1/2" since it bends less.

I'm open to any/all track designs that'll fit on a 16x6 foot table. I've been looking around and have some ideas but I'm happy to see more. Usually I find something I like and then tweak it a bit. Especially if what I found was in plastic track, Then I change the curve radius' and such...

If I don't do an overpass I may do something like Ed's above. I'd elevate the back half so its sort of leaning towards the drivers. I have wireless controllers so there's a lot of flexibility there. My main concern really is cars crashing in the middle of the table. They'll be hard to reach as 6 feet is right on the edge of what can be leaned over and grabbed... This track is probably going to be 3 lanes because I already have a lot of sensor setups for 3 lanes, but I may do 4 depending on the layout I choose. The nice thing about 3 is that it makes it easier to keep the turn radius' farther away from the hair pin turn.

[noddaz]

Interesting track discussion here. Can you run the cut overpass sections of MDF through a planer to achieve the thickness you want?

Build the flat sections in 1/2" and make the transitions and overpass 3/8" if:
A) You can plane (?) MDF
2) The overpass sections will fit through the planer

I hope this helps. Otherwise just disregard this with my other useless ramblings.


I am BACK! I just Googled "MDF through a planer". It can be done. Creates a boatload of bad for you dust. And is hard on the planer knives.

Scott

[daufderh]

I'm pretty limited on tools. I don't have access to a planer. Basically I have a router and whatever Home Depot will do (which is just cut to size). I can cut the negatives with the router and that allows me to do the overpass, but I can't do much more. I still haven't gotten the MDF but when I do the plan is to see if I can do the overpass in 1/2 inch or not. It seems like I should be able to based on this post so we'll see.

[HO RacePro]

Daufderh,

I really think you are too concerned about fabricating the overpass. If you are at all flexible in track design you should have no trouble creating the ramps needed to achieve your desired elevation. MDF is quite flexible. It is also cheap enough that if you do overstress it and break it -- very unlikely -- you can replace the broken piece without also breaking the bank.

Take another look at the photos I posted above. Everything was done by simply routing and cutting out the track sections 'on the flat' and using a very reasonable amount of force to bend them. At the extreme you can bend the MDF a bit, give it a few days to relax, then bend it some more. I've never had to do that, but it is possible.

Here is another one of my tracks. It is a 4 x 16 foot layout with an overpass, in 3/8 inch thick MDF. I don't remember how much clearance it has, but certainly way more than enough for HO. The track also includes a banked turn, shown in the foreground.

ECHORR Race Beers Track.jpg

The overpass includes a bit of twist, which gave the elevated curves a bit of banking. That twist also reduces the stress necessary to create the overpass elevation. Note that the track sections are cut-out. All that green stuff is paint on the 3/4 inch plywood supporting the track.

This track, by the way, is on permanent display at the "America On Wheels" museum in Allentown Pennsylvania USA. The photo was taken during the annual ECHORR race there.

Ed Bianchi