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How to cut out a large round hole

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What is the issue?
Cutting out a hole larger than the largest hole saw fitting, can be daunting. It is very difficult to hand cut with a jigsaw unless it is very large.

Why address this?
In time you will come across a piece of work that the aperture of a particular hole saw will not be able to deal with, or it is a corner piece that the hole saw is not capable of achieving.

How to address this?
Boats use portholes extensively and round holes are often required for outlets. All that is required is a flat length of mild steel to make a jig and use it to carve out the hole.

Cutting a large round hole
Photo: Michael Harpur
Drill two ¼ inch holes next to each other, as close as possible, at one end of the rod, on either side of the axis of the rod. Measure the length of the desired radius from the intersection of the centre point of both holes and the steel bars axial line. Drill a hole at that point to provide the fulcrum for the jig. Drill a hole in the centre of the area you wish to cut out and bolt the jig in place at the fulcrum. Run the drill through one of the ¼ inch holes.

Move the slot on one hole then peg it. Now run the drill through the other hole. Continue to rotate, peg and drill until a round hole is cut. Finish off with a coping saw and rasp if necessary and sand.

Ideal for cutting out porthols
Photo: Phil Dolby via CC BY 2.0

With thanks to:
Michael Harpur, Yacht Obsession.

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