Dedeco does it

Dedeco A/0 Thin discs are .009" and do a great job.

The link is for the 100-count box.

There's also a 25-count box, but as shipping is a bit hefty ($12-$13 if I remember), and as you'll break about 5 of them before you get used to using them, you might as well get the 100 right off the bat.

Here's a photo comparing the regular Dremel "Ultra Thin" cut-off disc [top] with the Dedeco .009" thin [bottom]:

Very thin, very fragile, but very very good.

Do what the prototype does.

Make the frog and closure rails as separate items, then fix them down with as close a gap as you wish, within reason.

The prototype has lots of great ideas for modeling railroads. After all they have been at it for almost 200 years.

The prototype has lots of

Great point. now, just as soon as I can get that super cheap/free land from the government I need, I'm in business!

I've tried gapping as andy suggested, but I never was able to constantly set my gaps at a proper distance. In the end, I found Tim's suggestion to work the best and cleanest for me.

Always fill the gap

But Professor

But Professor, 

The gaps cut on turnout as shown in the pictures above and on fastrack built turnouts can not your #2 happen.  The rail is solder to PC ties and each side of the gap.  There is no opportunity  for "joint creep" or "closing up" since the rail is soldered in place first and then the gap is cut after the turnout is constructed.

JKTrains

Why cut the corner?

Note: Dremels typically cut installed rail at a slight angle

While this looks like a great way to cut gaps, note that the body of the Dremel is out of the picture, stage right.

So if the drill body is a much larger diameter than the cutting disk, the chuck end is pointed downwards. Rarely a problem, except maybe visually, unless there is some grit or uneveness on the roadbed, and the gap is very fine. Then there is a slight risk of it invisibly closing the gap by pressure from underneath.

There is no "proper" mechanical gap size, since it's for electrical isolation. 0.001" will work. Whatever click you can enjoy/tolerate is just fine. Just make sure it stays aligned, especially if on the outside of curved rails and it isn't so small it won't be closed by expansion.

gap filling

Probably a turnout built on pc ties will not move.  Those manufactured by various track manufacturers are on plastic ties WILL move.  I've moved them when connecting more track to the frog end.  They move quite easily.

As a general practice I cut gaps in all turnouts.  Thin gaps are filled with paper and wider gaps filled with plastic, both are held in place with ACC and cleaned up to match the rail profile after setting up.

Over the years I have gone to a zona saw for a very narrow gap. I think this improves appearance over the Dremel cut gaps.  Yes, it's a pain in the (insert your choice of anatomy location here) to cut them on a finished turnout.

Terry

The o.p. doesn't mention what type of turnouts he is using.

I would agree with Prof_Klyzer.  Why take a chance with an unfilled gap.  If you are talking about cutting gaps on a r-t-r turnout, always fill the gap because the rails are free to move.  I have seen solder joints fail.  I've seen rials expand enough to close gaps (I've heard all of the formulas put forth to "prove" that rail expansion isn't enough to be significant-hogwash).  We had a set up in a mall under sky lights where there was not enough clearance in joiner tracks set the night before.  The mall was enclosed and climate controlled, and the temp never got warm enough to be uncomfortable where the sun was shining in.  I don't believe that we had an hour to hour humidity change to cause the wood in the modules to swell or contract, but over the course of one day as the sun moved, each section of layout that was in the sun expanded and kinked, so that we spent most of the day removing and shortening joiner tracks to keep trains running on the layout.  The bottom line is that if you don't fill gaps with some sort of insulator, you have opened the door to Mr Murphy, and when Mr Murphy has an open door, he runs in.

Don't underestimate expansion force.

Russ makes a very good point, and it leads into another not often realized factor. The expansion force of rail is very easy to underestimate.

But you can get a good idea if you visualize clamping down a yard length of rail in a bench top vice, grabbing the other end hard with a pair of strong grips, and imagine pulling hard to spring the rail 1/16" longer! Most of  us are not at all strong enough to do that

So even filled gaps should be wide enough, and filled with soft enough material, that they can still accommodate the worst expected rail expansion. Otherwise, it the ends are too firmly fixed,  the expansion is going to go somewhere else (usually sideways) instead! Just think how easily you could do that with the same pulling force and the grips.

Razor saw

I use a thin fine tooth razor saw to cut through rail for electrical gapping purposes. I've tried the Dremel (angle, too big a gap), and rail nippers (don't even ask...) and the razor saw made the smallest gap - which I promptly filled with thin styrene and ACC that I filed to shape.

Small gaps

Small gaps can close as the rail expands with temperature. I once had a layout in a glass atrium at an exhibition, several gaps closed up and I had to re-cut them. I now always fill gaps with styrene. If you do that before painting the rail the gap is almost invisible. I originally used black styrene, but found white shows up less. I cut them with a cut off disc, a larger diameter allows squarer cuts. I then glue in a strip of styrene with acc. After drying I cut it to the rail profile with a knife.

Mike Ruby

Gap filling

Expansion

The coefficient of thermal expansion for most metals is in the 7-10 parts per million (ppm) per degree F.

On the high side one foot of rail will expand 12" x 10ppm x 20 for a 20 degree rise, 0.0024" or 2.4 thousandths of an inch over a temp change of 20 degrees.  Doesn't take much track to close a narrow gap.

Add in sun loading and the temp change can probably be much higher--think of a black steering wheel sitting in the sun even with the windows down.

Even the prototype has problems with sun kinked rail.

Terry

Filling and Filing Gap

On my RR the track must operate flawlessly, so cutting, filing and filling the gap must happen.  Generally I cut the gap with a Dremel cut off disk.  Once you are skilled at doing this, you can cut the gap with a series of light passes which will NOT melt the plastic ties of commercial turnouts.  The rail may still move, however, so at that point you may need to adjust the rail back into gauge.  Once complete, several passes with a mill file will help bevel the cut edges a bit so that the wheel flanges will not snag the cut.  At this point the trains will operate flawlessly as long as the gap doesn't close.  Which is why you must fill the gap.

As for filling the gap, I find inserting, gluing, and then filing down plastic strips quite tedious.  Fiding a plastic strip that actually matches the gap frustrates me to no end.  So, years ago I tried squirting a bit of white glue into the gap.  It works great.  It does not fill the gap to the top, but it does prevent the rail from moving into contact with the frog.  If I need to change something (like readjusting the rail), I can dig out the white glue after hitting it with a bit of water.  Aesthetically it is not perfect.  But filling the gap with white glue does the job for me.

Dedeco does it

I use a Micro-Mark jeweler's saw with a super fine blade, cutting the frog gaps before the turnout is laid on the layout. I'm just now entering the summer season, but with refrigeration air conditioning I don't expect the train room temperature to exceed 78 degrees F.

All of the turnouts I have assembled so far were built (and the gaps cut) this winter and early spring, when the train room temperature might have been as low as 68 degrees F.

On page 17-5 here:  http://cp.literature.agilent.com/litweb/pdf/05517-90143.pdf the coefficient of thermal expansion of nickel silver is given as around 9.3ppm/F degree. In this context, 9.3ppm means a one meter length of nickel silver rail will expand 0.093mm from winter to summer in my train room. While this might sound like enough to close my super thin gaps, I am taking heart in the idea that the stock rails are also expanding this much, helping to maintain the gaps as cut.

The gaps for power management districts, being in both rails, are another question. I used a relatively large diameter diamond-impregnated metal disc to cut those gaps. The disc measures about 0.6mm in thickness, and when you add my unsteadiness while manipulating the Dremel tool to cut the gaps, the resulting gaps are close to, if not exceeding, 1mm wide, measured today with the windows open and the temperature about 76 degrees F.

The longest rails adjacent to these "uber" gaps are (or will be as construction moves ahead) about 3m long. The temperature in the train room will have to exceed 110 degrees F for the uber gaps to close, ignoring the relative expansion effects of the sound board/birch plywood base and sawn plywood benchwork (I made "lumber" out of the plywood, and used this lumber to build the benchwork.)

The super fine jeweler's saw blade measures about 0.19 - 0.20mm thick. A randomly selected frog gap measures about 0.17 - 0.18mm wide. Taking worst cases, an 8 F degree temperature change causes a 0.02mm gap closing on an installed turnout. So, about 68 F degree change will possibly close the remaining gap. 68 plus the existing 76 is a scorching 144 F degrees (about 62 C degrees - still scorching!) I doubt I will be trying to operate my layout under those conditions.

But, the benchwork will be expanding about 4 times more rapidly than the rails, so it looks like the gaps will be opening, not closing with increasing temperatures. Apparently my train room will have to get very uncomfortably cold before the gaps start to close up...

Bottom line? I am enjoying the very fine gaps that result at the frogs from using my jeweler's saw. And I'm wishing that my hand was more steady, to minimize the size of the uber gaps at the power management boundaries...

Regards

Chuck Lee

Roadbed expansion

Don't forget the roadbed has a thermal expansion coefficient of 20-30ppm, depending on the material so the roadbed will expand more than the nickle silver rail for the same temperature.   Roadbed has more mass so it will take more time to get to the same temperature as the rail.

Terry

What works

There's a lotta ways to do a specific thing in this hobby.  Some are expensive in time, some expensive in money.

Just because some book says "this is the way to do it" is no reason not to try something in a way that appeals to you and your skill set.  Try what you read here and use what works for you, but remember some of the others when you get in a tight spot.

Terry

Thank you to all

cutting rail gaps with cutoff wheels

It is a pain to use a standard Dremel to cut rail gaps, especially where the body of the Dremel tool hits scenery or structures. I've found it very helpful to use the Dremel right-angle attachment when cutting rail gaps. This allows me to position the body of the tool vertically, where the cord is more easily held out of the way, and the much smaller diameter of the right angle assembly allows a cutoff wheel to cut a perfectly square gap in the rail.

I always fill my gaps, no matter what. It is simply amazing the force expanding rail will generate due to temperature variations. Sooner or later, the rail WILL move and close the gap. It only takes a few seconds and once the filler is painted and weathered a bit it is virtually invisible.

Available any where else?

I use the Dremel flex shaft

Filling rail gaps with gray ABS plastic

Great point. now, just as

Technically, the land wasn't free.  The railroads had to give the government reduced rates for the next 100 years.