Just as a reminder, the reader should be reading or at least looking at how to lay track on YouTube. Also, there are excellent articles on street trackage written by Bill Clouser and John T. Derr in the booklet "Traction Guidebook for Model Railroaders" published by Kalmbach Books in 1974.
Three more comments before getting into the curved track. I like a lot of light on the things being worked on. To produce more light on the area being worked on a small desk lamp is used. These come either with an Edison base for an average size screw in bulb or a fluorescent bulb. Chose the one you like best.
My desk lamp on top of the layout.
When using the wooden clothespins to hold work (rails) being soldered, there’s always a chance the wood will start to char. The charring may leave undesirable substances on your work. Always clean this off! It can interfere with glues, paint, etc. If the jaws of a wooden clothespin become too charred toss the clothespin out.
Next, when soldering rail or whatever to the copper clad board being used for street ties be careful not to heat these too much. The copper will come off the board! The gauge of the track may be in question.
Street railways used a different girder rail for curves. This girder rail had a higher back flange for the back of the wheel to rub against. The back flange was higher than the paving and often stuck out of the top of the street. Driving an auto or truck over this rail was difficult but not impossible. I do not know if Clouser had an O scale girder rail for curves.
To mimic the higher back lip of curved girder rail many modelers have used a 0.125” “L” shaped piece of brass soldered to the back of both of the rails involved in the curve. The “L” shape can be hard to bend so the base of the “L” had to be cut or ground out about every 1/8”
I have a surplus supply of 45 year old code 125 rail having a wider head than currently supplied code 125 rail. Therefore, this rail was used on my layout as the running rail in curves. New code 125 rail with a narrower head was used as the interior lip of the flange.
To properly gauge the new code 125 rail being used as the lip or guard rail the code 70 spikes from my track building supplies were 1st inserted on the inside of the running rail. Because the track in mounted on plywood, holes had to be drilled for the insertion of the spikes. The drill was just a few thousands of an inch smaller than the diameter of the spikes. Insertion of the spikes required a pair of pliers. The spikes were spaced about an inch apart.
The red arrow points to a rail joiner. These were installed only in the running rail, never the guard rail. The black heads of the code 70 spikes can be seen. The weight holds down all the rails flat. Solder can be seen on both sides of the running and guard rails.
Using code 125 rail with the 2 different size heads can be seen in the photo above. It looks different, perhaps not like girder rail for curved track but non-the-less not like the girder rail for straight track used in other parts of the layout!
Even with using the code 70 spikes to provide the proper side flangeway, still use an MNRA track gauge to both gauge the running rail but also the size of the flangeway.
Before going further allow me to introduce you to the Precision Scale (PSC) 3-point code 125, O scale track gauge. Currently these are $4.00 each. These were 1st supplied by Kemtron 50-60 years ago. These are a lost wax casting. For this reason, as with any casting, there may be manufacturing irregularities. When 1st removed from the package check the track gauge!
Do not cut off the small sprue on the single rail end of the gauge until you have completed all work on the gauge. This way you'll know you have completed the gauge!
PSC includes a metric screw. I have nothing against metric screws but I decided to drill and tap the mount for the coupler for a 1-72 screw.
If you have 2 of the PSC gauges it’s easy to lay both straight and curves track. For the straight track the gauges are placed on the rails with one gauge facing one direction while the other is placed on the rails facing the other direction. For curved track both gauges should face with the 2 areas to hold the rail on the outside of the curve. This will expand the rail a little for the curve.
Since the gauge is made of brass it's easy to modify the gauge for other size rail. If you do modify the gauge be sure to adequately make it!