Routed track banked corner thoughts

[slothead]

Yes, I'm still working on things for my new CNC routed oval. I've been using one of the corner sections from the first botched CNC routing attempt to practice on for when I bank the new corners. That section is now fully banked which I calculate to be about 7 - 8 degrees. While measuring the rise with a level I noticed there is some cupping in the center of the corner.



However, when investigated it doesn't seem to be a problem as shown below by this car having it's guide fully seated in the slot in the center of the corner.



The photo below shows the expected total rise for the backside of the banked corners.



While thinking about how to measure for supports to go under the corner I had a thought. What if rather than cut the supports to size I had a way to 'grow' them in place to the size needed for where they were placed? To accomplish this I'm thinking about fitting empty cardboard tubes (like from the center of a roll of paper towels) under a few places near the outer edge of the track and then fill them with expanding foam from a can. The expanding foam would fill in the tube and then spread out to fill in any remaining gap up to the bottom of the track surface. Once the foam hardens the corner would be fully and reliably supported as though by cement posts. Most of the area under the corner would be a void, but some sort of wall would go around the outside to hide it. A strip of 1 1/2 inch tall PVC moulding mounted on the top will keep cars on the track and billboards above that will keep any cars from launching off the table. This will be most important because the track table will be placed in a corner with 2 sides against walls. The area outside of turn 3 will be basically inaccessible, even with a grabber.

Feedback and comments are welcome.

[mattb]

I think you are thinking thru this too much. I know that's dumb to say, but just cut some supports to go from the inside edge to the outside edge of the track. Use some 1/2 MDF. Make them about 2-3 inches wide. Glue and clamp them to the underside of any part of your track that is not flat on the table. About every 12-18 inches. Use plain white wood glue and be sure to clamp them 8 hours or so. That will keep your track surface good and flat. In the banks, just cut some pie shaped pieces (wedges) to slide in and glue to the supports you have already glued under the track. They will probably vary in height and angle as you progress into and out of the curve. Don't be afraid to use some countersunk screws if need to hole it all together. A couple hours with a saw and some MDF scraps and you can have this done.

[Fast Co.]

When I was building Woodland Trace raceway, I had a similar thought about using expanding foam to fill in under elevations. In the end, though I did as mattb suggested and used plywood and/or mdf cut at an angle to fit underneath the elevated sections of track. I did this for my corkscrew and it worked out very well.

For walls around the track I used hardboard (aka masonite). I had it ripped by the folks at Home Depot into 3 strips of 16". For about $8 I ended up with 3 lengths of 48" each 16" high. You can have it ripped to whatever height you need. Then I temporarily screwed each "wall" to small blocks of wood glued to the underside of the mdf in 2 or three places and used a pencil taped to a small block of wood to draw a line an inch and a half or so above the track surface, removed the wall and cut the pencil line with a jigsaw, sanded the edge slightly, painted it a light grey color, and then permanently installed it. Masonite flexes easily, is very durable and takes latex paint nicely.

[mattb]

And that is a great track.

[Fast Co.]

thanks!

[RichD]

It appears that you want to create banked corners by using wedge shaped supports, if you do that there are bound to be at least some distortion between the supports. If you used a lot of supports that would at least be minimized. The way that banked corners are normally done when you are building a routed track is to do a one piece U shaped turn that is a bit less than 180 degrees. When the legs of the U are pulled together the banking is created. See this: http://www.slotcarracing.org.uk/trackbuild/bking.htm . There is also a small reduction in the radius when you bank the track, a chart for that is included in the article.

[BIG E]

...and that's exactly how the late track master builder Hasse Nilsson built my commercial raceway tracks back in the late 1980s. I couldn't believe how big the flat curved 8 lane section was. Then, with lots of bodies assisting, we all lifted and just followed his instructions until he told us to stop and hold position. He then adjusted his two piece legs (his "patented" design) and started tightening them up. It looked like the bank on a King track... we were all amazed! John Ford was still working with him then, and I believe you can contact him, still living in Texas.

[mattb]

Joe is cutting the corners less than 180 degrees and then pushing the inside until they are 180 degrees and forcing the banking. The moderate banking he wants really won't distort the track surface or the slot very much...

[SpeedyNH]

i can't believe this is this hard. i usually put my wood down first and then rout it. if i can't do that, then i use tabs in the slots to to fit it together and cut the ends to fit. either way, i use a ton of angled wedges across the track under it if i'm building on a flat table base. otherwise, see the Master, Steve Ogilvie track building method.

[slothead]

Another factor I didn't mention above is that with the current plan the track won't have a table top under it. I'm going to make a frame, sort of like how a wall is framed, then turn it horizontal and connect that to the wall on the left side and along the back side. The front and right sides will be held up by legs. Six foot long 1x3 pine boards will span the frame at key places as contact points to support the track. This is a form of the L-girder table used in model railroading and is what I did for my 6'x14' road course.

Here's another view of the outside of the corner. You can just barely see the end of the white 1x2 PVC board attached under the track to limit cupping, and a wedge is under that. But the wedge isn't cut to size and only supports the outer edge of the PVC board. There are 3 'cupping prevention' boards attached to the bottom of the corner section and one support post under the outer end of each would adequately support the track.



Here's a drawing of what I have planned for the frame under the track. This design is for a 12 foot long table but it's now going to be 14 feet long.



The 'boxes' at the left and right sides will be 1 foot wider now and boards C1 & C2 will now be 2x4's. I'm also working on a sub-frame for each corner so they are complete self supported units that just slide onto the table frame and are attached at a few points. I need to do this with the practice corner shown in the photos to finalize the plan.

My plan is still evolving which is why I'm sharing it to help that process. Reading and responding to posts moves me forward a step at a time.

[mattb]

I put some new steps in my garage building where the slot car track is. I have a friend that is a retired building inspector. After seeing them he asked me how I figured it all out. I told him I went to Home depot, bought some sticks and came home and built some steps.

[HO RacePro]

There is no good way to cheat when creating banked curves. You do need to reduce the included angle from a full 180 degrees. Reducing it to 178 or 176 degrees will produce substantial banking when you pull the ends into alignment. And the radius of the curve will be reduced when you form it up. Geometry makes that happen and you can't avoid it.

You need to have straight sections at either end of the banked curve. You pull on them to create the banking, and they also form the transitions onto and off of the banking.

The article RichD cites, above is complete and authoritative. Study it carefully.

If you simply refuse to do the math, the next best thing is to build a model, guessing at the numbers.

I have routinely modeled banked curves as a final check on my designs. I print out a computer model of the curve -- scaled one inch to the foot -- glue it to poster board and cut it out, then try forming it and fastening it to a flat sheet of material. Normally I model the whole track that way. If the model looks good I proceed. If not, I back up, try to figure out what I did wrong, and try again.

Extreme banking is not a good idea. It just isn't. I do not recommend anything over 20 degrees, and 10 degrees is quite a good number for many tracks. More extreme banking can cause issues with cars sliding down the banking or launching on entry.

Don't make the mistake of figuring you can just wedge the curves into shape. Skipping over your homework is a great way to create scrap.

Ed Bianchi

[slothead]

As detailed in other posts going all the way back to early spring when I decided to design a new oval, I checked out a bunch of good resources, did numerous calculations, and did some tests with corner sections cut from stiff paper. For the actual track sections I had Brad Bowman (Brad's Tracks) create the CNC files with 178.5 degree corners. When the lead in and out straights are pressed in to form a 180 degree turn I got the banking you see in post #8 above. It's around 7 - 8 degrees which is what I wanted.

I wasn't shy about doing the math or extensive planning, but if someone else is you needn't be because others have already done the work and will assist you. HRW is a fantastic resource for such things.

All my sections have been CNC routed and cut out and I'm at the building a sub-frame under the corners stage to lock them in place once banked. I'm making the sections downstairs in the barn and will then be moving them upstairs one at a time for assembly into a complete track. Rather than mount the track on a table, the combined sections will form the table.

More pictures soon.

[Mitch58]

I banked every curve at least 5 degrees and the large sweepers are 10 degrees. Works out very well.

[slothead]

Very nice track. I originally wanted 10 degree banking then heard too much banking on an oval can allow cars to run nearly wide open. The 7-ish degree banking I have now seems to be a good compromise that I'm looking forward to.

[HO RacePro]

Ten degrees of bank, and even twenty degrees of bank will not allow cars to run at nearly wide open. At least not without traction magnets or a huge turn radius. Foolhardy racers who try it will be retrieving their cars from the floor, possibly from under furniture.

Reminds me of a story I heard about a slotcar that got so launched. The car couldn't be found, until they smelled it. They found it melting and charring on the side of a hot pot-belly stove, held in place by its magnets.

Ed Bianchi

[Fathead59]

Well Ed , that is one reason not to run with magnets

[32lbking]

Lol!

[slothead]

The track building process has been on hold for nearly 2 weeks due to some minor medical issues - severe bursitis in my left shoulder and lower back pain making it difficult to stand. They are both subsiding now and I hope to get back to work on the corner sections soon. I'm still tweaking some design details on a daily basis trying to account for issues coming up.

One change now that this project is carrying over from summer to autumn is that I'm no longer planning to fully assemble and test it downstairs in the barn before moving it upstairs into the loft where I spend most of my time. Heating season starts the first week of October up here in Maine and it will no longer be ideal to work downstairs in the evening and at night. Now I'm trying to figure out how to fit the new oval in the loft along with the other oval and the road course. The original Shepherd Speedway is 15 years old and has hosted countless laps of racing and the new oval will have to be truly spectacular to warrant the original being dismantled.

I just took a minute to take some photos of the current Shepherd Speedway to formally record how active it's been.