Cutting a semi-circular hole in the deck off edge of existing hole

[Stefanojo]

Long title, I know. I'm replacing my windlass. And I have to make a little semi-circular cut out on the edge of the existing hole for the windlass to accommodate the chain counter sensor. Any ideas on the best way to do that?

[Ron Hill]

Steve : I'd try a narrow blade saber saw.

A thought

[Noah]

I agree with saber saw. You can get long blades. However, be careful you keep saw and blade at a 90 degree angle all the way through the cut, as the long blades can get pretty bendy. Another option is you can drill out some of the cut first and then use saw to shape the remaining radius.

[waughoo]

I would find a hole saw that matches the diameter of the semicircle you want to cut out.  Drill a hole in a suare of plywood (3/4 would be my recomendation) with that hole somewhere near the center.  You probably want the size of plywood to be about 12 to 16" square so you can stand on it.

Mark out where you want that semicircle cut out on the deck, lay the board with the hole over the mark on the deck and line the hole in the plywood up with your mark on the deck.  If it is a smooth portion of deck, double sided mounting tape can be used to hold the board still. If it is over non skid, you'll want to find that rubber mat used to hold carpet still placed under the board as the tape may not be rnough to keep it still on nonskid.

Chuck up your hole saw with the centering bit retracted below the teeth of the hole saw.  Put the hole saw into your cut out in the board till it touches the deck then back up just a wee bit and start the drill, and make your cut.  The board will act as a guide and give you a nice clean cut out!

The jig saw will also work, but just won't be as clean of a deck cut out.  The jig saw will cant as you make the arc of the semicircle and you'll end up with a cut that is at an angle through the deck.

[Craig Illman]

Agree with Alex

Craig

[Ron Hill]

Steve : Which ever you try, You're going to probably have some filing to do with a narrow half-round file!!

A thought

[Stefanojo]

And...we have a hole!  Took a suggestion from another board and used a Dremel side cutting tool. Just long enough. Finished it with a Dremel drum sander. Super easy. Not perfect, but close enough. Now to seal it and put this project to bed

Thanks for all your suggestions. This is a great group!


Steve