23 replies to this topic

[Paul's Slots]

I have been building tracks now for about 35 years now, the most asked question that I get asked is, how do you get that bank....well I will show you the picture of the bank that I just pulled and you can ask any question that you would like....so here it is.....Paul of Moose Comp

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[Paul's Slots]

Here's some update pics.....125 ft 30o bank.

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[Rob G]

Here's some update pics.....125 ft 30o bank.

Ok,, so how do you  do it ? Route it flat for 176 Degrees then pull the ends together?

How do you control the bank angle?

[Paul's Slots]

Hey there, ok, in this case I'm pulling the front straight in line with the back straight, my radius is 5.5 ft ....I measure with the center of your radius, 180o then what ever the bank degrees you want ..in this case 30o so 150o then cut from the center line out to the 150o mark.....cut with straigtht edge and a router....router toward the edge you want to get rid of ...then put on your legs route the grove and the braid landing so as to where your track will get flat, then start walking the two straights together until they are paraelle with each other, and the bank will be at 30o......Paul

[Mike Wurn]

Still a little confused here. Are you saying you cut the curve ends at 150 degrees of arc, than attach the straights to the arc ends, then route the grooves and the braid lands?

[Dennis David]

Sounds like he routes the grooves first then attaches the straights then bends the straights together until they are parallel.not sure if that's an actual 30 degree banking but it should work.

[Paul's Slots]

Hey guys, sorry about not getting back, but here I go again........you put the straights on both sides, that gives you enough lenght to bend the bank......now you got the sides on start routing....route all the lanes and if your using braid route the braid landings as well......now that all the lanes are routed start closing the two straights together, nice and easy now! And adjust the legs as you go....this will give the track support...and there will be a bank.

[Paul's Slots]

Well, after two heart attacks, I'm just about ready to start routing, this will be at my house, hoping to get it done by summer, it is 85ft and 14sets of banking, nine corners. I hope to be racing D3 and some hard plastic...hope you enjoy the post, regards Paul

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[Pappy]

You do nice work, Paul. 

[Steve Ogilvie]

There is a math formula that I use to make a banked turn that uses a few simple methods :

1) do a proper scale drawing so you get an exact idea of your corners diameter and radius and degrees around .Draw your corners at the dimensions you want them to be , not what you think they will end up at .Make sure you allow room for sidewalls .

2)The circumference of a corner stays the same banked or flat .For example : A 96"(8'diam) circle has a circumf. of 96 times PI = 301.592 . Divide by 360 and this gives you inches per degree , in this case .83775 etc .Multiply this number times the amount of corner degrees  and you have your outer circumference .Always use a calculator and do not round off till your final result .

3) To make a banked corner you increase the radius that you cut it at .Use degree number desired press cosine on your calculator and divide that number into your radius .On a TI 30XA calc press  48-:-10COS=48.74 so set your circle cutter at an outside radius of 48.75 for a 10 degree bank .Which is pretty extreme for an 8' turn on an 8 lane track but easy with a 6 or 4 lane track .The bigger the inside hole of the circle , the more bank you can do .

[Mach9]

A question for Paul or Steve. Are you saying for a track with parallel straights, that you cut the turn 1 degree short (I always called it "back cutting") for every 1 degree of bank that you want? It's been 20+ years since I've built a banked track. But I seem to remember that we had to back cut the turn about 2 1/2 degrees for every degree of desired banking. Although that seem now like a lot. I most certainly could be wrong. It's been a long time and my memory is terrible. I didn't have any kind of formula for it. It was just a trial and error type of deal. I remember cutting miniature sections of track out of construction paper on the kitchen table. Thanks. Nice work Paul!

[Steve Ogilvie]

I don't back cut to make a bank .All I do is increase the radius when I cut the corner with a radius cutter .The circumference is measured and marked after the outer cut is made . I use the formulas above to get the dimensions .Back cutting a corner will give you a bank , but you will not be able to accurately predict the finished dimensions .In my thread on building home tracks , there are diagrams of the tools that you can make yourself to do this . After you cut and assemble the corner and put some straights on , you will see that the straights are splayed out just like they would be if you had back cut .The advantage is the accuracy , being able to route the track quickly in large chunks at once and better designs .Take a look at the first track pictured and imagine how much nicer it would look if the inner corner were snuggled right up to the walls of the banked turn .The track would be slightly longer and it would not have the hole for cars to fall in to .

[Mach9]

I think I'm starting to grasp it a little. So you're saying for a 180 deg. turn with parallel straights, you still cut your turn 180 deg, but make the diameter/radius larger according to your formula (which is WAYYY over my head), and when you pull it up, your straights will still be parallel? Do I have it right? The part of the formula where you arrive at "x" of inches per degree I can do. When you get to the cosine part, I'm totally lost.

[MattD]

If you cut a turn 180 degrees, it doesn't matter how big or small the radius is, if you pull a bank into a flat 180 degree turn, the straights cannot be parallel. Either I am not understanding what you guys mean, or my math training is lacking. Clarify this if possible.

When you say you "back cut" a corner, I think of cutting slots crossways on the bottom side of the track.
. This makes the corner flex easy and is how I banked turns years ago.

[Steve Ogilvie]

When you make the radius you cut the track at bigger , you are making a bigger circle .But you are marking and cutting the circumference that corresponds to the circle that you want that is smaller, in this case 8' diameter 180 degrees  . So a 180 degree 10 degree banked corner with a cut radius of 48 3/4" with a flat measured and marked  circumference (you measure the circle with a tape measure after the outside is cut ) of 150.8 " will pull up in to an 8' diameter 10degree banked turn and the straights will be parallel when measured outside to outside .Keep in mind the formulas do not take in to account the thickness of the board and the bend will not come out to exactly 10 degrees but it will be close enough .It is also next to impossible to bend a bank without the inside hole cut out .I always use a cutter with an inside and outside radius pin .You cut the inside of the turn from line to line after the outside of the turn is cut measured and marked .I will try to draw a diagram to make it all a little easier to understand .Back cutting is just taking some degrees off a 180 degree corner so the straights will be splayed out and can be pulled in to make a bank .It is not an accurate way to do things , but it does work .

[Steve Ogilvie]

The Texas Instruments calculator I mention is only about 20 dollars .Get one and you can see all you have to do is press a few buttons to figure the radius for a banked curve .It is also great for doing banking and your taxes !

[Mach9]

Ok. I think I have it now. Will be getting the correct calculator. If I understand it right, the final flat cut on the turn piece will still be something less than 180 deg. as Matt suggests.

   Matt, When I use the term "back cutting", I'm not talking about grooving the underside of the track. I'm talking about cutting a given turn something less than its intended angle, so when you do pull it together, it forms a bank. I could be using the the wrong terminology. Grooving the back of the surface or inner walls in some cases I always called "skinning". Again, that's just the terms that I use. Not saying they're correct. Thanks for the explanations!!!!!!!!!!!!!!!!!

[MattD]

I still am not real clear on Steves' process. In my mind, a finished curve that is going to be 180 degrees and banked with the straights parallel when it is completed, must have the following requirements; the flat routed curve must be less than 180 degrees before it is pulled into the banked form, the curve must be a larger diameter when flat than the desired final diameter. Maybe we are all talking about the same thing with different terminology. Same old thing, making something easy complicated!!

[Steve Ogilvie]

Yes , when you cut out the corner using my methods it will be less than 180 degrees as measured flat and will have a bigger diameter when flat .In this case , the amount less than 180 degrees is irrelevant .If you have done all your calculations right and cut the the corner accurately , when you bend it up it will be an 8' diameter banked turn with paralell straights .This method works for all diameters and amount of corners .That is how we can put a whole track together flat (with two sections still apart), route the whole thing and bend it up and bolt it together and have it fit perfectly .On a hillclimb for instance ,we would first build and route part of the drivers straight and deadman .Then take the deadman off the piece of drivers straight and build and route the rest of the track .That area becomes the closing area after the track gets bent up . 

[MSwiss]

Steve,

How do you calculate something like the Big Bank, where the degree of banking varies quite a bit?

[MSwiss]

When you say you "back cut" a corner, I think of cutting slots crossways on the bottom side of the track.
. This makes the corner flex easy and is how I banked turns years ago.

I relieved, on the bottom, all the turns on my King.
 
I used a 1" diameter, round, router bit.
 

Not a lot of contrast, but the relief routing under my finger.
 

I did quite a bit of the straightaways, also, so they would twist, and I could go from the right hand, 12 degree max banking, in the Deadman, to the left hand, 17 degree max banking , in the Finger.

 

This view gives a much better idea how much that short straight twists.

 

[Steve Ogilvie]

All turns are figured out the same way .My early kings were cut out as a 30 degree bank 14' diameter turn all the way around .They turned out pretty good but I was not happy with how hard it was to get the main straight( and back straight especially) really smooth .So I started cutting these banks with 3 distinct radiuses , varying the amount of banking out over three pieces of the corner .Depending on what the track was going to be used for ,a 15 degree cut on the entry piece and exit piece with the bigger middle piece cut at 30 degrees made it easier to keep the main fairly flat and smooth and the back straight easier to transition to the deadman . And  a 14 foot turn only needs about 5 degrees  for most cars to go flat out on anyway . For a track like Lee Roberts that was meant to break records , I did the bank at 30 entry 20 mid 15 exit and then you lived with a tilted main straight . I cut the finger bank with 2 radiuses and the donuts were cut with 3 radiuses .All with the goal to force a car to take a corner "set" as soon as possible on entry to a corner and have it exit still holding the set with less banking coming out to set it up properly for the next curve . Our kings had banks that varied between 12 and 14 feet wide depending on size and style of track .

[Steve Ogilvie]

Mike : How thick is the board you used ?

[MSwiss]

1/2".

I drew where the slots are, on the bottom, and obviously avoided routing in those areas.