Wayne Roderick, 3rd Division, PNR, NMRA (life)

07/01/98 rev 06/10/09

At the heart of Malfunction Junction (MFJ) lies a piece of trackwork in HO scale, built with code 70 rail that had to be rebuilt twice over to attain the reliability needed. A double slip switch, sometimes called a puzzle switch, connects the main line and drill tracks to both receiving/departure tracks. We originally copied the design from commercial HO scale switchs only to find it a disaster in spite of very carefull attention to NMRA standards.

double-slip switch

One of our visitors one night pointed out a magazine photo of the prototype in Chicago Union Station trackage and we discovered the key to success. The "store bought" model switches have two frogs in the center that allow a wheelset to go anywhere it pleases! Most wheel sets will faithfully continue in the original direction, but every once in a while one of them will skew a bit, pick the point of the frog and on the ground we go. This is intolerable! Perhaps those prototype engineers knew how to keep them on the track.

Here is a better photo at an unknown location, perhaps European as I don't recognize the signal or switch machines. The mystery photo of the slip is at Broad St. Station on the Pennsy! The oddball signal is a "pedestal" signal and is, in effect, a two-headed position light dwarf- courtesy Jim Duncan 06/10/09

11/30/04 Still not convinced that a successful double-slip switch MUST have moveable points in the frog? Perhaps, it's an ego thing, defending your decision that wasted good money on that solid frog contraption? We understand & sympathize- sigh.

Here's a couple more pix that our support group sent to help convince you.



Faulty double slip switch

We started over again providing switchable points in place of the frogs, and it was entirely successful.

Effective double slip switch

Move your eyeballs to the far edge of the screen (or printout) and look down a track that is aligned. You'll see solid iron right down thru all the mess in the middle, just like the steel wheel sees it.


Rummaging through my older MRs, I found an article TERMINAL TURNOUTS by Boomer Pete (MR May '46). I was eleven then, and the mag' only cost twenty-five cents :-) Been at the hobby for quite a spell. A picture of SPs Los Angeles yard again shows pictures with points instead of frogs.

Quoting from our author "Of course, you don't like slip switches. Neither do I. They're nasty things and cause a lot of trouble. So far I've found only two real uses for them, the first use is to save space where quarters are very, very cramped. The second use is to build one -if you've got the patience- just to prove you can do it."

Fifty plus years later, what he says is still true- so don't use one if you can avoid it and if you must do the prove-it-thing, then build it right. The prototype folks were cramped for space in urban passenger yards and they proved that you could make them work. For us modelers, it's lots easier today with proper size rail and printed circuit board ties. For goodness sake don't buy a piece of troublesome, improperly built junk just cause it looks impressive.


The first requirement is that you know how to build high quality switches (or turnouts if you prefer that non-railroad term). I really would advise you to not start with a double slip switch. If you're not experienced, then download the NMRA standards S3 and S4 ,buy some three point track guages (3 of 'em), the NMRA standards guage, a solder iron and some 63/37 fine solder, some pc ties and get experienced. Most folks that I've encouraged to try it, swear they'd never buy a switch again. There have been a number of good articles in the hobby magazines over the years to guide you and it's not my intent to repeat that information here. My guru was Ed Stimpson Jr. I met him in Salt Lake City when they had a great club layout at the fairgrounds and he showed me the secrets of success using pc (printed circuit board) ties. Ed later published an article "Maintenance-free turnouts" in May '78 MR, for all the rest of the world. I will assume you meet this requirement and we'll go on to extend the techniques for the TSL double-slip switch.


Throw figure 1 far away. That's how NOT to build it!

In Figure 2 I've used color to help identify rail pieces without a lot of text and tags. The black sections are curved, the cyan sections are straight, and the red sections are movable points. The green shows ties spaced at five per inch and can be used as a scale. The yellow shows some detail of the machinery to move the points. This area is expanded in the following Figure 3 and of course everything is mirror imaged to all four quadrants of the switch.

Expanded details, double slip switch

figure 3

The diagrams pretty well tell all except for a few hints and kinks that I might add to your switch building bag of tricks.

SOLDER TRICKS: Use high quality electronic grade, 63% tin solder, Don't trust the flux in the core- it comes too late to be very effective on tiny joints. Get some of that corrosive (zinc chloride) liquid flux from a welding supply store, the acid kind that they tell you not to use on electric stuff. It's clear, like water and washes away easily. Put a tiny drop on the joint before you touch the iron and/or solder to it. Use it on any rail joint including wire connections. Dilute and wash the corrosive flux away with a toothbrush and water, then use a sponge to soak it up- Do this twice, else things turn green :-( . On ballasted track, I find that a tiny drop can be washed into the ballast without sponging..

It's nasty stuff, so use common sense safety measures to keep it out of your eyes.

PIVOT POINT: At the junction of a point piece (red) and a closure rail (cyan), at ties 4-5 and 6-7, I use one half of a conventional rail joiner. It's soldered to the closure rail and slightly spread out so the point rail can move freely in it. The base of the point rail is feathered and rounded a bit to ease the action. It'll slip out easily, but we'll soon fix that.

SPIDER: There is no throw bar between pairs of points- instead each point is linked by a piece of .015" springy music wire to a .055" rotating vertical rod coming up through the road bed- lets call it a spider for lack of a better name. Each spider, it takes four of them, throws three points. The mechanism below is arranged to rotate the spiders vertical rod about 30 degrees. The rod is sleeved in a piece of 1/16" brass (K&S) tubing cemented into the road bed and at the top it's bent 90 degrees, and clipped about 3/32" long, where it solders to the three .015" horizontal throw rods (spider legs). This virtually eliminates critical adjustments and holds each of the three points firmly, but independantly against its stock rail.

The .015" spider legs are connected to the points simply be bending the end down 90 degrees (do spiders have feet?- ours walk on their tippy toes) and dropping into the hole of a tab made from .005" brass sheet and soldered under the base of the rail. The point is now captive, but easily removable. The tabs are between the ties 4-5 and 10-11. Additional tabs are soldered to the points at ties 1-2 and freely slip under the stock rails to insure that the points will not tend to rise up. Note that this spider assembly is easily removable for bench construction (and reconstruction 'til you get it right).

UNDERSIDE: On the underside, after smooth action of the spider has been assured, oil the steel rod and brass sleeve to keep solder out, then wipe the rod clean below the sleeve. A short length of 1/16" brass tube is slipped on and soldered to the rotating rod to restrict vertical motion. A crank arm is then soldered onto the rod and linked to the switch machine with conventional techniques. I like to use solder, 'cause it can be heated and wiped clean, permitting the spider to be lifted out as one unit, as well as permitting adjustments with the touch of the solder iron. Clamping devices don't anchor well on the music wire because its too hard to bite into.

The two spiders on each end of the switch are linked underneath with an insulated piece, I used a scrap of nylon from a wire tie, so that six points move in unison to select the route at one end of the switch. Both rods rotate in the same direction and are driven by one switch machine. The control is simple- just select the route into the switch and then select the route out- two machines and two controls.

ELECTRICAL: It's amazingly simple. Gaps are cut in the closure rails between pc ties 14-15, the location is in a green circle. Everything on the top half of the diagram (call it North) is connected to the North (black) stock rail and every thing on the bottom of the diagram (call it South) is connected to the South stock rail. The pc ties 0-15 have to have the copper layer cut in the middle to electrically separate the North and South sections.

FAILURES: Ours had one solder joint fail in twenty plus years, and its slapped around with a pair of those big thumpin' rotary machines. Let me know how yours goes together now and please advise again in 2020 on the reliability ;-)

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