I’m not the A&O trackwork expert (David is), but on the A&O we seem to use lots of NMRA gages. They are critical for scratch building turnouts, especially for the areas around the frog and along the point rails. They give the “final word” on all dimensions. They work great for code 100, 125 and 148 rail. The only thing they don’t do is hold rail in place while it is still loose. And there never seem to be enough of them when we are working even though I buy another one and toss it in the pile every time I see one.
In years past I’ve seen 3-point gages at Caboose Hobbies in Denver, CO, but at that time I was still an unrepentant HO-scaler and paid no attention to O-scale items. Perhaps P&D Hobby Shop in Michigan can make a recommendation.
One of our track gang, Jackson, wanted rolling gages like the ones he used to hand-lay all the rails on his beautiful HO layout. These were at one time commercially available from a fellow who made them in HO and On3, but not to his knowledge in O. Not only did he want them custom made (as he stared at yours truly who has a Sherline lathe in the basement) but he rejected the first prototype because it wasn’t knurled in the middle! Oy!
I suppose that we may not always know what we are doing (speaking of myself) but we do have fun in the process!
Ahem. Getting back to reality, a primary disadvantage of this design is that they must be made for a specific rail code (100, 125…) and a specific manufacturer (in our case, MicroEngineering.) This is necessary because code refers to a standardized rail height, but the width of the head can and does vary with manufacturer.
The pair with “dimples” on the end were turned for Jeff (another member of the track gang) who uses code 148 rail on the mainline of his layout. The rest in the photo are code 125. Shown are the last of the gages to be made.
On the A&O we have a few for code 125 mainline rail and a pile of them for code 100 sidings and yards. After I made these Jackson showed me his HO gage. The center was turned down in diameter, so that it would work some of the distance between the points and frog of a turnout. *So now he tells me! *
Perhaps you have a modeler friend with a lathe (the Sherline lathe was originally designed in Austrailia.) If so, these are made of 360 brass. The minimum gage is set to 1.254 inches (0.004 more than the NMRA minimum) to be consistent with David’s practice of laying rail close to or at the NMRA minimum gage. The maximum, after fitting a sample of rail we use, offers a few thousandths of an inch play to keep them from binding. That is why they must be made individually for each size of rail.
Another very useful tool is a common modeling T pin.
Here we see T pins temporarily holding rail in “alignment” just after all of us had a big laugh (what’s wrong with this picture?)
The subroadbed is Micore, a mineral product commonly used as the structural core inside office space dividing panels. It readily accepts pins and spikes, but does not hold either as firmly as Homasote.
All the best, and welcome to the A&O forums. Please stay in touch from down under!