By the Squares

I do a lot of track design "by the squares", as explained in Track Planning for Realistic Operation by John Armstrong. This is a simple technique for designing by freehand sketch, based on the minimum mainline curve radius. Each square represents the amount of space required to fit a 90° min radius curve with a parallel outer curve at correct centre spacing.

Xtrkcad's Snap Grid makes it very easy to transfer a back-of-dirty-envelope absolute killer plan idea to Xtrkcad.

The trick is to use the square definition to define the Snap grid, then use snap-to-grid in Xtrkcad to locate the main curves from the back-of-envelope design.

Printing out snapshots of the work-in-progress allows lots of alternatives to be explored quickly by pencil, because the grid printed on the snapshot is "by the squares".

Use Snap Grid to define the "Square"

I want to use Roco's 2.1 mm track, with a mainline minimum radius R6 (604.4mm) and track centre spacing of 61.6mm.

For the imperialists out there, this is close to 23 ¹³/₁₆" minimum curve and 2 ⁷/₁₆" track centres.

The square definition gives the side of each square as S = R + 2C, where R is the min radius and C is the track centre spacing. This means each square in my sketch has a side of (604.4 + 2x 61.6)mm which I rounded up to 730mm. So I set the Xtrkcad Snap Grid (View/Change Grid) spacing to 730.0mm.

Now here's the killer step (imho) : I want the subdivisions to represent my track centre spacing, so I can easily align the main curves in my sketch to the Xtrkcad grid. To do this, I need to divide the Snap Grid spacing into the correct number of subdivisions so that each subdivision represents the track centre spacing.

Dividing 730mm by 61.6mm gives me 11.850649, so 12 subdivisions should be OK. Dividing 730mm by 12 tells me each subdivision will be 60.8333mm which is close enough for bush carpentry. The picture shows my final Grid setup.
I don't know how to copy my image to your server !

So what good is all this ?

By-the-squares comes with a number of design templates, that show what can fit into x by y squares (it's a shame John Armstrong's book is out of print, but preloved copies are still around. I got mine through Amazon Germany).

For an area of a given size, translating that area into squares is a fast indicator of what will fit, and what design alternatives are practicable, before the Grandiose Plan Department kicks into gear and ensures the planning process has to include a reality adjustment phase. Conversely, if a specific design feature is an absolute must, by-the-squares indicates what size area is required for a given scale and minimum radius.

Xtrkcad's Snap Grid makes it easy to transfer an original by-the-squares sketch to an Xtrkcad layout. On the sketch, the (minimum radius) outer curves define the limits of the plan-in-progress, the distance between these curves defines how much room there is for features (like yards and stations).

Of course, there will be broader radius curves in places, but to start with it's the minimum radius outer curves that need to be placed. This is because we have defined the Snap Grid to match the context of the minimum-radius outer curves in the sketch.

Place the min-radius outer curves as min-radius circles, use snap-to-grid to place the circles accurately in the context of the squares on the sketch. The broader radius curves get defined by using the parallel track tool set at the correct track centre spacing. Where the sketch has a broad radius curve without a corresponding min-radius curve (for instance, at the angle of an L-shaped segment), a min-radius circle is placed so that the corresponding broad-radius circle will line up correctly against the sketch.

Once all of the sketched curves are placed in Xtrkcad as circles, the snap-to-grid can be turned off and the join tool (with or without easements) is used to join-the-curves-all-together into one-big-happy-track. At this point I usually discover that the features I have sketched are a little ambitious for the available space because my sketched turnouts are not available commercially (or even physically possible).

So it's back to the drawing board, but this time I have a printed snapshot of the Xtrkcad track plan, with the squares all nicely ruled on the printout. Successive refinements of the plan by pencil, with quick exploration of alternatives as bright ideas spring to mind, is as easy as opening another ream of A4.

Of course, the best ideas come to mind when there isn't a snapshot of the plan-in-progress to hand, but by-the-squares people only need a piece of bark and a stick of charcoal to commit the idea before it's lost. And later back in Xtrkcad land that absolutely stunning idea is dead easy to transcribe.


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