Figure 8 components

[Craig]

We've got a 14'x6' large scale layout under our HO layout. I'm giving my sons each a large scale train of the own. I'd like to add a 13'x5' oval inside of the 14'x6', and another inside of the 13'x5'. Since the inner most oval will be smallest, I thought I'd try to make it more interesting. Can anyone tell me off hand what components are necessary to achieve a figure 8 using the Bachmann 90º crossing? I'd also like to know the overall dimension of the basic figure 8 track plan. Of course it will be 4' wide. I'm wondering by what amount I will be able to elongate it. Thanks for any tips guys.

Craig

[Joe Satnik]

Dear Craig,

As close as I can measure on the screen, the actual crossing portion of the 90 degree crossing is 3-1/2" long. <-Error!: Hunt measured 11-7/8"


Dear Terry T. (or others that own a 90 degree crossing),

Please measure to the nearest 1/16th inch the rail top length of the G 90 degree crossing. 

Thanks in advance. 


Back to Craig,

Bachmann G curves try to imitate LGB 1100 series R1 curves, which are 1200mm diameter (=23-5/8" radius).   

A natural 23-5/8" radius 90 degree figure 8 would need ~18" long straights (times 4 legs) between a ~12"  long crossing and the 9 curves on each side (= 18 total). 

If you wanted to expand along the length in both directions, you would neet to cut two of your curves into 4 half curves, or buy 4 LGB 11020 half curves. 

If expanding along the length in only one direction, cut one curve into two half curves, or buy 2 LGB half curves.

I have new Bachmann G curves and straights to sell (set breakup).  If interested, joebarb"AT"wwt"DOT"net. 

Hope this helps.

Sincerely,

Joe Satnik   

[Craig]

Joe,

Thank for your reply. I've emailed you about your track, btw.

I wanted to know the basic figure 8 dimensions because I'd like to do something along the lines of my crude illustration, and I need to know the maximum lenght (and thus, how many more straights I need) the red sections will be. I have 13 linear feet to work with, less the basic figure 8.




Obviously the layout in the illustration exceeds my 13' space constraints, but you get the picture. It should be possible to create the above diagram without modifying any track.

[Joe Satnik]

Dear Craig,

The base length of the natural figure 8 in my example above is 114" to the track centerline.  Because of the Big Hauler 4-6-0 cowcatcher overhang, though, you must add at least 3-1/2 to each side of the track centerline. 

So, "fence to fence" or "wall to wall", you would need 7 more inches, or 121" total clearance for the base figure 8 

But,

You would also have to be aware of underhang clearance on curves for the middle of long cars on the next oval out.

I haven't specifically measured it, but have found through experience making concentric ovals out of Bachmann R1 track, that if you have 1-1/2 more straights on each of the 4 sides of the next oval out, you will avoid overhang/underhang crashes between the Big Hauler cowcatchers and (long) passenger cars.

You said:  "It should be possible to create the above diagram without modifying any track."

Sorry, not true.  Bachmann curves are 30 degrees each, with no half-curves available.   

With the 90 degree crossing, you need to turn 45 degrees between the crossing leg straights and the expansion straights. 

This requires a normal curve plus a half curve (30 degrees + 15 degrees = 45 degrees). 

Even if you bought LGB (solid rail) half curves, you would have to remove the black blades that fit inside the hollow Bachmann rails. 

Your statement could be true if Bachmann made a 60 degree G crossing.  (Natural for figure 8s using 30 degree curves and expansion straights.)  They have chosen, however,  to put their efforts into locomotives, not track geometry, hence the mis-matched 90 degree crossing.<- Error! Turns out the 90 degree crossing with the included half straights is perfectly matched for the non-expandable figure 8.  My apologies.

Hope this helps.

Sincerely,

Joe Satnik

               

[Craig]

"Sorry, not true.  Bachmann curves are 30 degrees each, with no half-curves available."

Now that's disappointing. It makes me wonder why Bachmann sells the crossing. Still, cutting two curved sections in half to obtain four 1/2 sections isn't beyond my ability, or that of my power mitre saw. Thanks a bundle for the info, Joe.

Craig

[Craig]

Joe,

At your convenience, please check your e-mail. my e-mail address is broncomaniac and hotmail is the domain I use. Thanks.

Regards,
Craig

[andyb]

Just as an exercise I've had a go at drawing up possible layouts using the dimensions you've given, without cutting the curves (I reckon it is possible to construct an offset '8' figure but you may still have to cut the straights either side of the crossing to fit), see below:



Just to see how much room the standard 8 takes up I drew that first and then extended it by adding a passing siding at one end - you can purchase Bachmann turnouts separately - with the addition of some isolators you might just be able to fit two short trains on the layout and run them alternately (depends on the lengths of your locomotives and stock of course...)

Sadly, in this configuration, this doesn't give you any room to place the outer oval unless you can widen the board by say 12"?

But an interesting exercise in geometry...

Best regards

Andy

[Joe Satnik]

Dear Andy,

Nice diagram.  What program did you use to generate it?

How wide and long is the green tabletop shown?

Here's a no-cut G figure 8 recipe, though not expandable along the length as Craig had asked for:

Recipe deleted as crossing length was in error.  See recipe below.

Hope this helps. 

Sincerely,

Joe Satnik

[andyb]

Dear Andy,
Nice diagram.  What program did you use to generate it?
How wide and long is the green tabletop shown?
..
Joe Satnik

Thanks Joe - I used CorelDraw! v9 using a 12mm to the foot grid .

The green area is scaled at 13' x 5' to the edges but I don't believe this would give adequate clearance to add the outer oval and stay within the 14' x 6' specified.

Hope this helps?

Andy

[Craig]

Thanks to Andy and Joe for the additional helpful responses.

[Craig]

Joe,

I've acquired a 90º crossing and have experimented a little with your suggestions. I believe Bachmann should publish the formula you used to implement their crossing. I also feel Bachmann should market a "kit" to convert the small ovals they sell with their big Haulers into a figure-8. Your "no-cut G figure 8 recipe" would do nicely.

Thanks much,
Craig

[Joe Satnik]

Dear Craig,

Thanks for the kind words.

The next track to release should be a half curve, 

or a 60 degree crossing (of a specific useful length for R1 curves),

or both.

(60 degree figure 8s don't need the half curves.)

Offering half straights separate from the 90 degree crossing would be great.

A 30 degree crossing (of a specific useful length for R1 curves) would allow shorter length figure 8s. 

Half curves would allow expansion along the length of the 30 degree figure 8, in the same manner as they would help the 90 degree figure 8. 

Hope this helps.     

Sincerely,

Joe Satnik

   

[Alex Butner]

If I build a figure without modifications, will it work? I'm talking about a crossover, four straights and twelve curves. Will that work?

[Joe Satnik]

Dear Alex,

With a 90 degree crossing, you would need 9 Bachmann G curves per side, X2 sides = 18 curves total.

360 - crossing degrees = curve degrees per side.

Example,

360 - 90 = 270 degrees.

270 / 30 degrees per curve = 9 curves per side. 

I haven't added the extra crossing length to my old recipe yet. 

Tomorrow, perhaps.

Sincerely,

Joe Satnik

[Craig]

If I build a figure without modifications, will it work? I'm talking about a crossover, four straights and twelve curves. Will that work?

Without adding three more curves on each loop, you're just splitting a circle in half. There's no way for the ends to meet in the middle. As I've discovered, you can't  use the Bachmann crossing even if you do add six more curves. Joe Satnik has provided a list of the necessary materials, some of which (four half-straights) come with the crossing, to create a reasonably fluid figure-8. As Joe pointed out, his "kit" results in less than a half inch error over 64 inches. I think most of us can live with that tolerance.