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Curved diamond crossings for the M&N RR - Part 5


There are another four posts related to this one, each describing a part of the construction of a custom diamond crossing in N Scale for my test layout, the Mitchieville and Natalieburg Railroad.

Part 1: Making accurate drawings of the N Scale curved diamond crossing from digital photographs of the layout.

Part 2: Installing the ties for the diamond crossing using the drawings and putting the first few rails in place.

Part 3: Installing and testing the remaining live rails.

Part 4: Installing the guard rails.

Installing the diamond

This is our starting point for this session. Sixteen of the twenty rail pieces in the crossing have been shaped, cut and secured in place leaving the diamond itself as the last rail related task.


In this post, I’ll install the diamond and fine tune the wheel paths.

Laying in the diamond

The diamond is really just four guard rails made from four pieces of pre-curved rail. They have to be set in place 25 thousandths of an inch from the live rails.

First, cut the one of the short diamond rails a little longer than needed and sand into length and ends to shape. Test fit the diamond guard rail then tack and secure in place. I tacked this one in place and checked clearances and alignment and ran a truck through several times both ways. Make sure to leave room at the frog where the other guard rail meets this one. The gaps look too big initially. If they look like normal flangeway spacing at the frog, you’ll run out of room when the adjoining rail is put in position and have to do some fancy filing to make it all work, maybe.


Cut, shape and tack in place the opposite short diamond rail. It is an easy process now to cut and sand the other two diamond rails to fit against the ends of the two diamond rails already tacked in place. I tacked the remaining diamond rails in place and then soldered the ends together after very carefully checking clearances and test running a truck through the crossing several times in each direction before moving to the next solder job.


Put plenty of flux on the tie so the solder will flow readily between the rail base and the copper cladding on the tie to make a strong joint between the rail base and the tie. Solder the joints of the diamond guard rails to make them strong.


All four diamond rails in place. Ain’t she pretty!!

Fine tuning

A thing of beauty, maybe, but does it work?! We are basically relying on good alignment of all rails during the construction to result in good operation. If something is out of tolerance at this point in the construction, it’s pretty difficult to go back and change it. Even a few thousands of an inch can cause rough and/or unreliable operation through the crossing, especially at the frogs. If you’ve done a perfect job, there’s no need to do any filing or sanding.

I had a few spots that were less than perfect so I lightly sanded the tops of the rail heads using a disposable nail file to clear away any solder or roughness. I also filed and polished the tops and insides of the running rails and guard rails using a thin flexible file. I contemplated using a piece of 0.015” thick styrene with wet and dry glued to it or wrapped around it to follow the rail path along the curves but didn’t need to do this in the end.

Double check solder joints on all PCB ties. During the sanding of the tops of the frogs, I had one tie break loose. All the while as you are filing and sanding, run trucks back and forth in both directions on both legs to check clearance. I used an old toothbrush to keep the wheel paths clear before running the truck through. Sometimes a bump only occurs in one direction. Hold the truck and twist it so the wheel flanges are pushing against the inside edges of the rails as you push it through each leg. Any tendency for the flange to catch and ride up will show up whereas it may not from just rolling the trucks through.

Here’s the finished diamond with all rails in place and fully tuned!


Next steps

To make the diamond compatible with DCC operation, two of the frogs need to be isolated. I’m off to Boston for a few days and when I get back, I’ll cut and fill the gaps according to the electrical diagram.


Part 4: Installing the guard rails.

Part 6: Preparation for wiring



Reader Comments (2)

Thanks for posting this. I have the exact same situation on my 0 scale layout. Very helpful. Sincerely,

October 31, 2007 | Unregistered CommenterChristopher Smith

Thanks Christopher. Send some pics if you can.

- Steve

October 31, 2007 | Registered CommenterSteve Cox

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