Figure Eights on Different Curve Radii

[keesu]

Hey, All

I'm new to this hobby and have a question about figuring out how to make basic layouts. Circles are a cinch, as are ovals, but figure eights never cease to confuse me.  I'd appreciate it if one of you could explain which track parts I need to make a figure eight using 26" curve track.  I've tried to do it on AnyRail but to no avail.  I had no trouble at all with figure eights using 18" and 22", but 26" has me stumped. 

Sorry for the rookie question, but we all have to start somewhere.  Maybe I need to take a geometry course!

Keith

[Doneldon]

Keith-

It's not quite as easy as just specifying a curve radius. You also need to decide how long and wide you want your figure eight to be.

You can add straight track sections in the middles of the end curves to make the arrangement wider or leave them out and have an overall width of about 54-55 inches, plus a couple of inches for a safety allowance at the edges. Adding the straights on the ends will change the geometry of the straights you'll need to get to the middle of your layout and the angle of the crossing.

You can also end your curves just barely beyond the point of 180^o curvature and then run straight tracks until you get to the place where you'll need a crossing. This will give you a layout of maximum length. (Well, not exactly - you can also add straights right at the 180^o points which will lengthen your layout to whatever total length you want.) If you run the curves farther around you'll use fewer straights between the ends of the curves and the crossing, and the crossing angle will shift in proportion to how far you run those curves.

It might be best if you tell us the actual size layout you hope to finish with and then we should be able to give you the information you want. Without those outside dimensions, there are literally thousands of possible figure eights using 26-inch curves. Incidentally, please let me congratulate you on your decision to go to a moderate curvature rather than trying to jam your figure eight into the smallest possible footprint with tight curves like 18- or 22-inch radius.

                                                                                                                                     -- D

[jward]

the 26r and larger radii will be problematic if you want to use a crossing with your figure 8.     the 26r and above are 18 degree sections. as such, they only match up with the 90 degree crossing and nothing else. if you want to use the 60 degree crossing, you'll have to use the 12 or 6 degree curves (35.5r I believe) to match the crossing angle. the other angles  won't work.

I would suggest that  if you want to do a figure 8 using the larger radii, that you consider an over and under type plan. it would be a good time to learn to use the grade tool in anyrail.

[Joe Satnik]

Dear Keith,

I'm not sure why Anyrail didn't work for you with the 90 degree crossing.    

To expand on jward's post,

crossing - straight(s) - half fitter curve* - regular curves - full fitter curve*- regular curves - half fitter curve* - straight(s) - return to crossing

*Note:  Choose either 1 full fitter curve in center, or 2 half fitter curves next to the straights.

Half fitters are calculated to put the track joints of the curves on the main compass points, which help if you want to expand the Figure-8.

26"R - 18 degree regular curves:

90 degree crossing: full fitter = 18 degrees (= a full regular curve), half fitters = 9 degrees (doesn't exist).

60 degree crossing: full fitter = 12 degrees, half fitters = 6 degrees.

45 degree crossing: full fitter = 27 degrees (doesn't exist) half fitters = 13.5 degrees (doesn't exist).

30 degree crossing: full fitter = 6 degrees, half fitters = 3 degrees (doesn't exist).

Throw the fitter curve(s) at AnyRail and massage the lengths of the straights (both straights equal in length with each other) until it fits/works.  

Hope this helps.

Sincerely,

Joe Satnik

Edit:  Added (= a full regular curve)

[Joe Satnik]

Dear All,

With 90 degree (and ONLY 90 degree) Figure-8's:

The length of each of the four straight legs = curve radius - half the crossing length.

According to AnyRail, the 90 degree crossing is 2" long. 

In the 26" radius case, = 26" - (2"/2) = 26" - 1" = 25".  (You will see that AnyRail lays this out perfectly.)

Your mission, should you decide to accept it, is to figure out which combination of E-Z Track straights and fitter straights = 25" ( x 4 legs)

in the most cost effective manner. 

AnyRail will also show you how long and wide this monster will be. 

AnyRail numbers are calculated to the center-line of the track.

Don't forget to add 3-1/2" to 4" to the AnyRail's overall length and overall width

to cover loco and car overhang.   

For comparison, try the 30 degree crossing - full fitter combo.  Straight legs are much shorter in that case. 

Hope this helps.

Sincerely,

Joe Satnik

[keesu]

Hey, Folks

First off, I want to say that you guys amaze me with your awesome amount of knowledge and analytical ability.  I'm afraid a lot of it is wasted on me, however.  I can only say that I'm trying to make the smallest figure eight possible using 26" track, smallest meaning both in terms of length and width. 

I tried Joe's suggestion about cobbling together 25" of straights but to no avail.  I feel as though I've tried hundreds of combinations using AnyRail, so I think I'm just going to buy a bunch of track and see if a little hands-on activity will yield better results. 

Thanks for the accolades, D, regarding my choice of 26" curves, but it's really of matter of not being able to run the passenger cars I want given that most of them require a minimum 24" curvature.

Keith
 

[Joe Satnik]

k,

Try 9,9,3,2,2 inches to add up to a 25" straight leg.

Try 15 curves (26"R) each side to add up to 270 degrees. 

Have you figured out how to rotate a connected group of track pieces on AnyRail?

Joe

[jward]

for the tightest possible figure 8 you will have to elevate the track to pass over itself in an over and under configuration.  by doing so, the degrees of curvature become irrelevant.

[Joe Satnik]

Jeff,

An up and over configuration using only curves (the shortest possible Figure-8) would give you S-curves, which don't work well with long passenger cars. 

Keith,

What is the length of your longest passenger car or loco? (Info needed to avoid S-curve problems.)

The shortest length level Figure-8 in HO E-Z Track with a 26" Radius would use the 30 degree crossing. 

It is possible to adapt in another brand of crossing (with less than 30 degrees), but then the straight length between the opposing curves could get too short to avoid opposing curve (S-curve) problems. 

The other brand also has 24" Radius curves available, which would save you another 8" off the overall length of your table.

Try the E-Z Track 30 degree crossing - full fitter combo on AnyRail:

In the order shown:

Connect together (9) 26"R - 18 deg. curves, (1) 35.5"R - 6 deg. curve, (9) 26"R - 18 deg. curves. 

This should form a huge "Letter C". 

Throw down a 30 degree crossing near the gap in the "C", then try various straight fitter length pairs (one each leg of the crossing) til it fits.

To disconnect a joint in AnyRail, left-click on the joint (it should highlight), then left-click on "Disconnect" in tool bar above.  You can then move the disconnected piece away.

Hope this helps.

Sincerely,

Joe Satnik