Potential Problems With Atlas HO Code 100 Snap-Track Turnouts

Several weeks ago, Mark Grecco alarmed about a potential problem with Atlas HO Code 100 Snap-Track turnouts with part numbers 850, 851, 860 and 861. The issue is because of the wrong geometry specifications form the Atlas catalogs, where these turnouts are listed with 20 degree branches, while the real track pieces, measured by Mark are with 15 degree branches.

It is not uncommon the data in the catalogs to be wrong, but in this particular case it is possible that these parts are changed (replaced) with new ones while the part numbers are still the same. As we cannot be sure that this assumption is true, I decided to keep the old spec in the Atlas-HO-100 SCARM library and to add the new 15-degree parts with the numbers 850/15, 851/15, 860/15 and 861/15 with the next update of SCARM.

These turnouts are labelled as “MS L” and “MS R” for the manual switches and “RS L” and “RS R” for the remote switches in the tracks selection panel. The updated turnouts will be marked as “MS L/15″, “MS R/15″, “RS L/15″ and “RS R/15″ respectively and will be positioned below the group of existing ones.

If you already have Atlas 850, 851, 860 or 861 turnouts, you will need to check the degree of the branch in order to know which part numbers in SCARM to use. To do that, attach two 10-degree curves #835 to the branch followed by a straight as showed on the picture below.

• If the straight from the branch is parallel with the straight part of the turnout, it is a 20-degree switch – use 850, 851, 860 and 861 parts in SCARM track plan.

• If the straight from the branch is going to cross the straight part of the turnout (as in the picture above), it is a 15-degree switch – use 850/15, 851/15, 860/15 and 861/15 parts in SCARM track plan.

It is also a good idea to check in your local model train store to see what kind of these tracks they have on stock before start planning a layout in SCARM, if you intend to use Atlas HO code 100 Snap-Tracks.

Updated SCARM library for Atlas HO code 100 Snap-Track system is provided in the links below as a ZIP archive. Download and unzip it and then copy the .lib file into the Lib folder of SCARM (usually C:/Program Files/SCARM).

The new updated library is included by default in the program starting from SCARM v.0.9.21.

I am really sorry if this mismatch between Atlas catalog data and the real tracks caused problems to any of you. And finally, I want to thank to Marc Grecco for the information and measurements of the turnouts that he shared with us.

Updated library

10 thoughts on “Potential Problems With Atlas HO Code 100 Snap-Track Turnouts

  1. Gracias por todo tu trabajo y tiempo empleado en la programacion de SCRAM con gusto puedo aportarte ideas si te parece prudente que lo haga ya que al usar el programa se va ocurriendo nuevas funciones o problemas normales de programacion
    Desde Argentina, Buenos Aires Edgar

  2. There is another problem about Atlas snap switches. I recently (Jan. 2016) bought two right and two left remote snap switches #850 and #851 and found they were not quite as described. According to Atlas’s published description, if you put a #835 10-degree curve on the end of the curved segment of a snap switch, the result should be the same as a normal 30-degree 18-inch-radius curve plus a 1 1/2-inch straight extension. On the ones I bought, the straight extension required would be only 1 1/4 inch: that is, the tracks diverge 1/4 inch sooner than the Atlas documentation says they do! This of course means also that the outer end of the curved segment is also 1/4 inch away from where it should be according to the documentation. I don’t know whether there were older versions of these switches that agreed with the published description. (By the way, the ones I bought have the full 20 degrees of curvature, not the 15 that you discuss here.)

  3. Actually they are not a 15 degree switch either. Using a 15 degree section of curved track does not create a parallel line either. It is actually somewhere between 15 and 20. Closer to 15.

  4. Atlas has made a lot of different turnouts through the years. Some of the earliest snap-switches had a 20-degree 18-inch radius for the diverging route, others have a 15-degree segment, then there is a #4 switch (actually #4.5) which is 12.5-degree divergence (like a conventional switch, not with a uniform radius) as I recall. I don’t know all the part numbers off the top of my head. Sometimes, if you are using older secondhand switches, you may need to measure them yourself to be sure what the geometry is.

    Atlas also made a curved switch with (according to the instructions sheet) curves of 18-inch radius and 22-inch radius, both of 30-degree curvature. I would like to see these included in the SCARM track library, but their geometry is somehow fudged and doesn’t match the actual switch when I use the prescribed numbers to create custom pieces and overlap them into a switch configuration.

  5. Hello Ace,

    The wrong turnouts were from a defective batch, that was recalled from the model train shops. However, some of these switches were already sold.

    Currently, Atlas has only #595 & #596 curved switches. There may be another curved switches and other turnouts produced before, but I have no geometry info about them and cannot include such pieces in the current libraries.

  6. Hello,

    I have tested my Atlas Snap-Switches as shown above and all of them have a 20 degree radius. I bought all of mine used at a model train show for really cheap and so I have no idea how old they might be. They appear to be pretty old, as some of their switch motors are broken and the rails are heavily tarnished. Does anyone know which radius (15 or 20) describes the current production Atlas Snap-Switch?

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