How do you scribe a large circle without a compass?

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Cabinets & Millwork
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Any radius past a foot or so is beyond a trammel set, and string-and-pencil wanders as the string stretches. A round tabletop or a radius soffit needs an arc struck from a fixed centre with a rigid arm. A blade does exactly that: pin the hook at the centre, hold the pencil at the radius on the blade and walk it round. On the T1 Tomahawk the radius is also a saved number, so the matching part comes off the same figure rather than a re-measure.

How the arc gets struck

T1 hook pins at the centre point
Pencil rides at the radius on the blade
Rigid blade beats a stretching string
T1 saves the radius for the matching part
One pass closes the full circle

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The video finds the centre of a sheet of MDF, taps a pin at that point to catch the hook, then swings the blade around with a pencil held at the radius and strikes a full circle in one pass. The tape is the compass. Nothing else gets set up, and the arc closes where it started.