From the Loftsmith Workshop
Map measurer (opisometer) with km dial for your map scale
Trace a trail or road on a paper map and read the distance straight off the dial in km. The little wheel at the bottom rolls along your route, and the face is marked for 1:25000. Change the wheel size to match a different map scale.
5 parts · 17 g · 44 × 11 × 73 mm
Ask for the sizes you want to tweak, e.g. “make the width adjustable”.
How to print it
Parts
- body · PLA · Floor down, pins upright
44 x 72 x 10 mm, about 7 g, 15 min. Floor, side wall and three 4 mm axle pins in one piece. PLA keeps the pins stiff and the gear spacing true.
- idler gear · PLA · 36-tooth gear down, 12-tooth pinion up
About 2 g, 7 min. Module 0.8 teeth with a chamfered bed edge so elephant's foot does not bind the mesh.
- wheel · PLA · Knurled tread down, pinion up
About 1 g, 6 min. 15.92 mm knurled tread (set by the Wheel diameter slider) over a 12-tooth pinion.
- dial · PLA, cream with green marks · Teeth down, face up
About 4 g, 10 min. 48-tooth gear under a 32 mm dial face with 5 mm bold figures. The raised marks are the top 0.8 mm: use a second AMS slot, or a filament change at that layer.
- lid · PLA, green with cream marks · Flat side down
About 3 g, 8 min. Dial window with an index arrow, a map scale bar and 5 mm scale lettering. The raised marks are the top 0.8 mm in the second colour.
Print settings
- Layer height
- 0.16 mm recommended for the module 0.8 gear teeth (0.2 mm works)
- Walls
- 2 (the stats figure); 3 walls gives about 22 g, 57 min
- Infill
- 15%
- Supports
- None
- Notes
- About 20 g and 51 min at 2 walls/15% for all five parts, including the purge for the second colour (build-report estimate at the default profile; 0.16 mm layers will take longer). Turn on elephant-foot compensation. Two filaments: green body, idler and lid, cream wheel and dial, with the dial and li
Assembly
- Drop the idler gear onto the middle pin, big 36-tooth gear down against the floor.
- Turn the wheel over so its small pinion faces the floor, and slide it onto the pin in the nose. The pinion meshes with the idler's big gear and the knurled tread sticks out past the nose.
- Drop the dial onto the pin in the round head, face up, so its teeth mesh with the idler's small pinion.
- Press the lid straight down onto the two pin tips (wheel and idler) until it sits flat on the wall. The lid ring holds the dial in.
- Zero it: spin the wheel with a fingertip until 0 is under the arrow.
- To measure: hold it upright with the dial facing you, put the wheel on the start of the route and roll along it. Read the distance at the arrow. Rolling to the right counts up; rolling back counts down.
Good to know
- Only the gear ratio, mesh clearance and rolling motion are checked in the engine. Accuracy also depends on the wheel rolling without slipping and on the printed tread diameter. Check before you trust it: at 1:25 000, rolling 200 mm along a ruler should read 5 km.
- If the ruler test is off, set Wheel diameter to the current value x (true distance / reading) and reprint only the dial.
- One dial turn is 600 mm of map at the defaults (15 km at 1:25 000, 30 km at 1:50 000, 60 km at 1:100 000). For longer routes, count the full turns and add 15 km (or 30 or 60 km) for each.
- The lid is held only by a press fit on two 4 mm pin tips; this fit is not checked. If it is loose on your printer, add a drop of glue, which makes it permanent.
- Fine module 0.8 teeth need a well-tuned printer. If the train binds, reprint the wheel and idler with the Axle clearance slider raised toward 0.6 mm.
- The knurled PLA tread may slip on glossy laminated maps. It has not been tested with a TPU tyre.
- PLA softens at about 55 °C. Do not leave it on a car dashboard.
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