About this project
A calibration coupon for bridges. A row of decks spans between pairs of piers at a run of increasing spans, each labelled with its span, so you can print one and find where your machine's bridges start to sag instead of trusting a published figure.
The run
The first bridge has the start span, each bridge after it adds the span step, and the run continues for the number of bridges you ask for: the defaults give six bridges from 10 to 60 mm in 10 mm steps. Deck width, deck thickness, pier width and pier height size the bridges themselves. The plate is derived from the run: wide enough to carry the longest bridge with its label, deep enough for every row.
Piers
Pier width is the anchor length the bridging strands have to land on at each end. Pier height is only the clearance for looking at the underside; keep it low, because the piers are the part of the print that is not measuring anything.
Printer
Layer height does not change the geometry. It feeds the deck-layers readout, so enter the value you will actually print at. The validator refuses a single-layer deck: the first layer is the bridge, and it needs at least one layer on top to close into a surface.
Labels
Each bridge's span is embossed on the plate beside its left pier, so the deck top stays clean for a caliper. Cap height and relief are adjustable; the relief wants at least two layers if the numbers are to survive.
What this prints as
Nothing here predicts the sag. That is the point: how far a bridge goes before the underside turns rough or the strands drop is a property of the machine, the material and the cooling, and the only reliable way to know it is to print the run and look.