How do you scribe a circle with no compass?
The circle needs to be 300 mm across. Your compass tops out at 150 and is in a drawer somewhere.
Applies to
- Process
- Layout and marking
- Materials
- Card, board, sheet goods
- Setup
- Zip tie, pen or pencil, a pin or nail at the centre
- Best for
- Circles bigger than your compass
Why it matters
A trammel is just a fixed distance between a centre point and a marker. Anything that holds that distance works, and a zip tie holds it well because it doesn't stretch much.
The failure mode of a string compass is stretch. Nylon strap is stiffer than string, so the circle stays round.
What good looks like
- The radius doesn't change as you go around — check it at four points
- The pen stays at a constant angle to the surface
- The circle closes back on where it started
How to apply it
- Pin one end of the tie at the centre point.
- Fix the pen at the radius you want, measuring from the centre pin to the pen tip.
- Keep the tie taut and the pen upright, and swing the full circle.
- Check where it closes — if it misses, the radius moved.
Exceptions & tradeoffs
Anything precise wants a real trammel or a router circle jig. This is for marking, not for machining.
Leaning the pen changes the effective radius. Keep it upright the whole way round.
Common mistakes
- Measuring the radius to the end of the tie instead of the pen tipCentre pin to pen tip. That's the radius
- Letting the tie go slack on the far sideConstant tension, or you get an egg
Using a zip tie with a pen as an improvised compass to scribe a circle — 60 Zip Tie Life Hacks ↗ at 2:30.
Summarized and independently edited by Start Here. The source is a rapid-fire compilation, so the steps and cautions here are ours — the creator shows the move, not the procedure.