Fast Tracks

Cutting Those Pesky Gaps!

By Tim Warris (This newsletter was originally published on February 1, 2004)

Every hand built turnout needs isolation gaps to electrically isolate the frog from the rest of the turnout. Without them there would be a dead short in the turnout.

Commercial ready-to-run turnouts provide isolation by using an all-plastic frog, or by using the switch points to route power to the frog. This not only leaves a very unsightly gap in the switch points, but also relies on the points to route power to the closure rails and the frog, which can be a constant source of trouble.

Hand constructed turnouts or crossings on the other hand need to have the isolation gaps manually cut into the rail. There are a couple of ways to do this.


Why I Hate Dentists

The simplest and most common method of cutting isolation gaps is to use a cut-off disk with a Dremel Moto-Tool.






There are two types of cut-off disks that you can use. The first is a ceramic disk; a very thin cutting wheel that will cut a clean, discrete gap. The downside to using this type of wheel is that they are VERY fragile and will break very easily. Twist the wheel even slightly while cutting the gap and BOOM! It will explode! So safety glasses and great care are essential.

Personally I prefer to use ceramic wheels, as I like the thin gap and the smaller diameter of the wheels are less likely to nick the stock rails. Fortunately they are sold in packages of 25, so blowing up a few wheels is not hugely expensive!

The second cutting wheel option is a fiberglass reinforced cut- off disk. These wheels are very durable and long lasting, and short of taking a hammer to them, very resistant to breaking.

The downside to fiberglass wheels is that they are a bit thicker than the ceramic disks and are usually only available in larger diameters.

Fiberglass wheels do work well for larger scales (HO and up), but in scales where there isn't much space between the rails, like N or narrow gauges, cutting gaps on a finished turnout can pose a bit of a challenge. Dual gauge turnouts are even more of a problem as the rails are very close together, which can prevent your from using a cut-off wheel at all. I have several times "nicked" the guardrails while trying to cut the gaps for the frog with fiberglass wheels.


Why I Like Jewelers

So for these types of turnouts there is a third method - the Jewelers Saw.


We offer these on our site here.

This nifty little tool is very handy for all aspects of model work, but are particularly useful for cutting isolation gaps. By opening one end of the saw the blade can be passed through the ties to cut the rails at the frog, even in the tightest of spots!

The completed trackwork is mounted into a vise, clamping onto the ties sticking out on the side of the rail. After threading the blade through the ties, start cutting with a long even stroke until the blade bites into the rail a bit, and then short back and forth strokes. Rail being very soft will cut quickly and cleanly. You might break the odd blade, this is not unusual as they are very small and fragile, after cutting a few gaps you will get a feel for how much pressure to apply.



This is one of the handiest methods I have found yet to cut the gaps in tight spots. Of course this will only work with a "bench built" turnout, like the turnouts and crossings produced in a Fast Tracks fixture (shameless promotion!)

Once the gap is cut, carefully inspect the gap for any burrs that might be crossing the gap, as these will cause a difficult to find short in the turnout.

A video documenting this process can be found on our main site here.

This requires a high speed connection. If you have a slower connection, a smaller version is available here.

A through collection of videos is available on our site here.

- Tim

----------------------------------------
Have a question or comment about this issue of the Fast Tracks newsletter? Then post a reply! I will be happy to respond to any posts. - Tim

Probably a lot of us like the disk when cutting gaps, problem is the fibreglas reenforced one is to big and too thick. the smaller disk is thin enough but fragile. but most of us would like something thinner and more robust. Well micro mark has the answer.

Check out the saw blades made out of stainless steel that mount on mandrels that fit dremel or sear units. They are very thin, thinner than the fragile disk we normally use, and very sharp, the diameter is very small too,
Now heres the hitch, the diameter, (you get two sizes) is so small that you'll have to use either the 90 degree angle converter for the dremel or the shaft unit. control is very good, the blade cuts very cleanly.

It may have other uses that I haven't explored yet.

Rob de rebel
Custom track builder

_________________
Cheers!

Tim Warris
Fast Tracks
http://www.fast-tracks.net
service@fast-tracks.net

_________________
"Life is about learning"

The link aren't showing up right now so these may be what your talking about. I use Dedeco ultra .009" wheels:
http://www.dedeco.com/cart/products.asp?grouping_id=96

I cut from the bottom so not to nick the surrounding rails.

Hello Sambear,
No these are the second gaps past the point of the frog, the ones on the two exit rails.
If you leave those rails connected to the frog, the frog powers the exit rails of the turnout.

There are three advantages to this:

1. It uncomplicates the wiring. put two insulated rail joiners (I use four) on the exit rails (for signaling reasons) Now the you don't have to run two feeders to the dead rails past the turnout. This area has no clearance for trains. So why have the gaps there?

2. It makes the turnout stronger, why? because now there aren't any breaks (gaps) on the two exit rails.

3. It eliminates having to cut that pesky gap in the turnout just past the frog, (where fast tracks has the two ties) Your gaps would ordinarily go between the two ties, and on the second tie, (towards the ends of the turnout) you have to gap the pc tie otherwise you'll have a short.

If your having trouble following me pull up one of the templates, and look at the turnout. The first gaps are in the two rails just before the rail pinch before the point of the frog. The second gaps are past the frog right inbetween the two pc ties. The pc tie gap is the second of those pc ties going in the direction of the exit of the turnout.

Rob

For cutting gaps I have found the diamond Dremel wheel to be much thinner than the regular cutting wheels. The diamond wheels are more expensive at around $15 at Home Depot but for me they are well worth it.

_________________

Proxxon sells (diamond coated) disks (at the bottom of the page) of 0,6 mm thick

_________________
Paul Bender

Everybody can shovel, firing is an art


Firing this train was more fun then hard labor © R. de Water