Regular Derailments At a Turnout


G

GNMT76

Active Member
One Atlas Snap Switch remote control turnout on my small (4' x 6') layout seems to be the cause of regular derailments of my lightly-used, three-year old MTH F3 locomotives when entering the diverging route. I'm still testing the trackage, so the locos are not pulling cars as yet. When following the main route of the turnout, there is never a problem.

I've pinpointed the spot - about a 1/2" area - along points of the turnout where the front trucks of the locos (most often the "A" cab, though the "B" cab also sometimes derails) "skip" and jump the tracks just before entering the diverging route. However, when I run the "A" cab backwards, it almost always remains on the turnout and continues on its way just fine. Nothing on the front of cab "A" or on either end of cab "B" is making any contact with the turnout - or anywhere else on the entire layout.

I've carefully inspected both the turnout and the locos and can see no physical impairments or deformities on either. The rails feel smooth and all lie flat on the cork roadbed. I've tried nailing down the adjoining tracks on both ends of the turnout in different places and distances from the point of derailment to see whether the downward "pressure" they exert in keeping the tracks flat and level has any negative effect, but to no avail. I've even removed those nails altogether, but either way, I get only a brief return to flawless operation before the derailments begin again.

The Tortoise switch machines operating this - and all the other turnouts - move the turnout points fully and completely, as they should. One thought I've had - since the Tortoises were only recently added to the layout - is that the one operating the turnout in question is misaligned beneath the roadbed. Your thoughts on this and other possible causes - and solutions - solicited.
 
If it was working OK before the Tortoise was installed and this problem has occurred since, then the misalignment is the first thing to check and correct and try again.
 
If it only happens with that locomotive at that switch, the probability is that the problem is in the switch.

Does the wire/rod from the tortoise come up between the rails? Could the pin be higher when the switch is set diverging (curved route) and hit the bottom of the truck gear case?

Get an NMRA gauge and check the gauge between the curved stock rail (curved outside rail) and the diverging point, it may be tight.

While you have the gauge out, check the gauge on the wheels of the F unit, they may be a bit off and that switch is the lucky spot that finds it.

Check that the trucks swivel properly on the model.

Is the switch fastened down securely so the Tortise doesn't move the whole switch when it lines the switch?
 
Turnouts cannot sag or be humped partway along them. They must be supported flush along their entire lengths. Learned this the hard way.

For longer framed locomotives, if the engine is moving forward and the front truck derails on a curve or on the diverging route, and if you've checked everything with a gauge (guard rails at the frog are in spec per the NMRA gauge, wheelsets are in gauge, gauge throughout the diverging route is fine between the rails), the problem is probably further back along the locomotive...something that is rolling the frame enough that the front truck's axles are light...being lifted enough that they want to pop out of the rails. It might be a dip where the first joint is, near the points, or it might be elevated track back there, maybe an alignment kink.

As Dave says above, can that front truck pivot freely? How about when you load it by pressing up against the frame...does it still swivel cleanly against its bearing surfaces? Snap switches are fairly sharp, if often necessary. You might find that you need to bend or to scrape material from some underframe component, maybe a stirrup on the shell, to get the truck to rotate just enough to become reliable.
 
Note the track at this turnout beneath the Gondola (picture sourced from this site). are there any like them on yours.

DSCF2599.JPG
 
D&J RailRoad said:
When you say "entering the diverging route" are you refering to the points of the turnout or past the frog?
Click to expand...

The points end, but it could happen entering the other way as well...it just depends on what the rear of the frame is doing as a result of what it's running over.
 
Gentlemen,

Thanks for your suggestions. I'll begin with checking the Tortoise's alignment under the table first, then move on to others as needed. Stay tuned! And the Tortoise wire is not the problem.
 
GNMT76 said:
Toot, some clarification please.
Click to expand...

I thought the picture would have been enough to insult anyone's tracklaying :p:rolleyes:. But this is a common and easily overlooked cause of derailments at turnouts which don't actually relate to the points themselves (there have been some on my club's layout like this). To clarify: Note the dips in the track's rail on one side or the other and opposite a level part on the other. This most usually happens where the tracks joining the turnout's fixed rails are slid into the rail connectors. If the joint dips (insulating joiners are a likely culprit), what happens is the wheels that are on the point track are lifted off the track as the wheels at the other end of the loco/car, drop into the dip at the joiner, the vehicle rocks on the track, twists, and derails. The cure, make sure all the rails on either side of and within the turnout are dead level throughout and beyond in all directions. As Crandell said, a firm LEVEL base throughout, is essential for good turnout operation
 
OK, if you have a torpedo level, you can check how level your track is. Measure across the track to be sure the turnout is not low on one side. Check the moving points to be sure they come up to the fixed rail level. If either of those are low, you will have derailments as the wheels try to grab for rail that isn't there.
 
Your issue may be the Atlas Snapswitch itself. Take a look at the picture below (snagged this from online somewhere). You can see how the main rails have a small cut in that allows the points to sit "into" the main rail. Older snap switches do not have this indent on the main rails and the points simply lean against them. Well, the points can be wide enough that the wheels of the loco, instead of taking the new route, just ride up on top of the point. I've had this same problem on my layout.

Peco%2BSL-8352-5mc.jpg
 
KB02 i believe is on the right track (pun intended). Another problem i have seen with the Atlas switches is, the rivet (pivot point) of the switch can get loose, allowing the rail to bend (Roll) slightly. When this happens, it leaves a slight gap at the switch point. Grab the rail, the one with the rivet (pivot point) and see if it has excessive roll from side to side. I hope that makes since to you. Another thing i have seen, when switched to diverging route the rail with the rivet (pivot) may be out of gauge. I have had to slightly bend (bow) that rail to get it back into gauge.
 
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Gentlemen,

Thank you for your continued feedback and suggestions. Ken, just what is a "torpedo level"? In absence of such or any other level, I laid a 12" metal ruler along all the adjoining tracks and the offending turnout. Everything looks to be lying as level as possible. I even added more track nails in various, nearby spots to see if they made a difference. They did not. If a torpedo level would aid in the assessment, I'll look into it. Would a good hardware store carry them?

Additionally, there are no visible dips or bends in any of the adjoining tracks, in the turnout itself or at the pivot point, and all tracks are securely attached to the ties.

I've run the locos over the offending turnout multiple times this morning at very slow speed and see that the point of derailment is now between the pivot points and the frog. There is also a barely discernible "dip" of the loco's front and rear trucks right at the juncture of the adjoining curved track and the turnout; this may or may be be a contributing factor to the derailments. As a precaution, should I de-solder and then re-join/solder this track and the turnout?

The main rails of this turnout (about nine years old, but very little used to-date) do have the "cuts," or indents, that KB02 referenced. KB02, were you suggesting that these "cuts" could be a cause of derailment or the older turnouts without them?
 
Ken,

Thanks for the "torpedo" photo. It does look like the real thing! I'll look for one at my local Ace Hardware.

Sorry, I have no means of shooting digital photos.
 
Gentlemen,

It looks like the problem is solved! Thanks to Ken's suggestion to get a torpedo level, I did just that and discovered a couple of spots between the beginning of the turnout and the frog that were not level. They weren't off by much, but one very thin shim at each spot and on opposite sides seems to have rectified the situation.

I've run the locos through that turnout now over a dozen times without a single derailment. With earlier attempts trying to fix the problem, the locos successfully negotiated it on no more than three consecutive runs.

And everything looks to be in gauge too - tracks, points, wheels - so thanks for that suggestion as well.

I'm hopeful the problem won't return, but if it does, I'll jump back on board this thread.

Thanks to all for your help and suggestions!
 
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