Trackwork - Wye turnarounds

[Anonymous]

Hi you All,

I have a question about "wye" turnouts and tight radii.

My reference is John Armstrong's "Track Planning..." book.

I'm planning a little branch line for 1920's short equipment only running at slow speeds; I'm diligently laying out a wye turnaround using proper substitution radii etc. and am generally keeping to a minimum curvature of 18" radius...space is at a premium.

The RCR of a #2 wye is listed as 15", and John cautions against using turnouts w/ an RCR of any less than the minimum radius which intended equipment can handle. I note, e.g., that the minimum radius for a Bowser 442 Atlantic is 18", and even for a 040 Dockside, 18" min is recommended though the specs say 15" r. is doable.

Because space is very tight, I want to use the #2 wye turnouts for my wye turnaround, and since the RCR of the #2 wye is 15", it seems reasonable to just maintain that 15" radius between the turnouts.

My question is: In practice, can #2 wyes be used w/ equipment rated for 18" min. radius curves?..and, can I get away with continuing the 15" radius between them?

If not, how can #2 wye's ever be used?

Humbly,

Fred

[IRONROOSTER]

Use #2 wyes with 15" radius curve. If you need 18" radius you can make your own with a curved frog and both legs curving 18". This is what Atlas does with the diverging leg of their snap switch, which is why it has no number. In general less than 18" is considered very sharp in HO. Since most manufacturers don't list below 18", you'll probably have to do some trial and error to see what will get around 15" or less. The NMRA's site recommends 4 wheel locomotives and cars no longer than 40' http://www.nmra.org/standards/rp-11.html for 14" curves. You can use longer cars with truck mounted couplers.

The other thing is to use a larger wye turnout. BK Enterprises, http://www.troutcreekeng.com/bkho.html makes a 2 1/2 wye in several rail sizes. You have to spike it down yourself, but that shouldn't be too hard and it's only a little larger than a #2. If you're using code 83, Walthers lists a 2 1/2 for Wathers Shinohara track. PECO and Atlas have wyes also, but the Walthers' site doesn't say anything about size or radius.

If you hand lay your track, you can widen the gauge a little bit on the curves and in the trunouts. Again you are in trial and error territory here. The NMRA standard http://www.nmra.org/standards/S-3_2ScaleTrackwork.html calls for HO standard gauge to be between .649" and .672", so you could go at least the .672".

Enjoy
Paul

[chateauricher]

Fred,

Are you working with HO or N-scale ?

As Paul states above, 15" or 18" are very tight curves for HO; however, they are not bad for N-scale.

[Anonymous]

Timothy, I'm in HO all the way...I'm aware that 18" r. is extremely tight; as I first mentioned, this is only being used on a little branch line run which will only be used by the very shortest of locomotives and rolling stock; operationally this wye turnaround is pretty important. Though I'm constrained to work within a small area for the entire layout, elsewhere my standard is generously-easemented 22" rad. curves (most of which are either in tunnels or behind backdrops so at least I don't have to look at them).

[Derailedtoosoon]

According to Walthers 2003 catalog, their #2-½ wye 946-890 matches a #5 turnout.
Total length is 7-3/16” Points to Frog is 3-19/32” Frog angle is 22 degrees, 54 minutes.
If that will not pass a 4-8-2, my layout is not going to work! [:I]

[Anonymous]

Remember that a wye does not need to be a neat little three point diamond. Look at the Atlas HO track planning guide, they show several vareations that you might be able to use in the space you have but with larger turnouts. Do you want to turn the entire train? Just turn the engine and run it around the train? Turn the engine and one or two passenger cars?

Back when I was playing with the Atlas track planner and trying to model the real CG&P trackage I had 4 of the things. It is much easer when you know what you need them to do.

[fwright]

A #2 wye has the same curvature as a traditional #4 turnout curved leg - it's 2 of them put together which doubles the angle (and halves the number). The Atlas Custom-Line #3 wye turnout has exactly the same curvature as their #6 turnout; as derailedtoosoon points out, the Walters #2.5 wye has the same curvature as their #5 turnout.

Although the #4 turnout and #2 wye has an RCR of 15in, it is only for a very short distance. The impact of the 15in radius for a length of slightly less than 2.5 inches is not as much of a problem as one might think because only wheelbases less than 2.5 inches (about 17 scale feet) "feel" that radius. Most rigid wheelbases that short can handle a 15inch radius in HO anyway. The problem for larger rigid wheel bases is the effective radius of a #4 turnout, which is fairly tight, too. The curved part of the turnout turns over 15 degrees in a distance of just over 5 inches. This what the longer rigid wheelbase "feels".

Overall, a true #4 is on the tight side for use with 18in radius. It is close to being, or would actually be the most critical curve where 18 inches is the minimum radius. This is why Atlas actually uses a 4.5 frog angle on their #4 Custom Line turnouts, and 18 inch radius on their Snap Switches. The 4.5 turnout actually works well with up to about 22 inch radius. Of course, a #2.5 or #3 wye is gentler still, and takes up very little more space.

Long answer to your first question is yes, a true #2 wye or #4 turnout will generally work with equipment rated for 18inch minimum radius. Long wheelbase steam engines and longer cars that struggle with 18in radius curves are going to struggle with the #2 wyes, too.

Have you considered hand-laying the track in the wye? You can decide for yourself (draw it right on your soft pine or Homasote roadbed prior to laying track) what radius curves you will accept and use.

To answer your second question, when you use 15in radius curves between the turnouts, then your minimum radius becomes 15 inches because the entire length of the car or locomotive is on the 15in radius at one time.

As far as what equipment can be used on 15inch radius, there are several forums and modelers that have done some research. The tables I have seen list manufacturer's minimum (when available), commonly accepted minimum without major modifications, and the best anybody has achieved with the modifications required to achieve. Most manufacturers no longer bother testing below 18inch radius in HO, even though their equipment might be quite capable of less.

In general, smaller 8 wheel diesels, 40ft cars, and steam engines up to 4-6-0 (where the driver wheelbase is not spread too far) will take 15inch radius curves. Small 2-8-0s (especially with blind middle drivers) can often work, as can many 50ft passenger and freight cars. Upper end equipment having more details which will limit truck swing may have more problems, and require some modification to work on 15in curves.

If you are going to use 15in radius curves, I recommend using a portable test track oval of 15inradius Snap Track (can even be temporarily set up on the floor or a table!) for checking for yourself. If you are buying ready-to-run locomotives or cars from your LHS (not many locomotive kits are still being produced but that's another story), then perhaps you can arrange to try it on your test track, and return it if it doesn't work.

The above is just some hints I have learned should you choose 15 inch radius curves. You can have reliable and pleasurable operation in this situation. But don't construe this as a general recommendation for curves that tight. Using 15 inch (or any minimum radius for that matter) curves should be a matter of informed choice, based on your desires and priorities. Space available, desired track arrangements, equipment preferences, priority of appearances on curves vs track layout features, and time for tinkering with track and equipment (more required for tight curves) are all factors to be considered.