On 02/07/2020 15:23, TimW wrote:
On 02/07/2020 13:41, Thomas Prufer wrote:
Given: plywood, jigsaw
wanted: circular bit of plywood, diameters 60-80 cm, small hole in the
middle is
OK.

Yeah: "make a jig", i.e. an arm with the wanted radius, attached to
the jigsaw
base, screw middle down and cut around.

But: I seem to recall there's a catch there somewhere, or a best way
of doing
this, in positioning the radius arm with respect to the blade. Should
the radius
arm attach to the jigsaw a) ahead of the blade, b) exactly off to the
side of
the blade, or c) further back from the jigsaw blade?


A holesaw will leave you a circular bit of ply:
https://www.screwfix.com/c/tools/holesaws/cat5920018
TW


He wants 600-800 mm.

In answer to the OP, the blade needs to be at 90 degrees to the radius.
As others have said, you might want two radius arms, to hold the jigsaw
steady. But it's easier just to use a rectangular piece of ply with a
hole at one end for the pivot?