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post #1 of 18 Old 12-24-2012 Thread Starter
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Enlarging hole in hull

I'm changing out a thru-hull and need to increase the size of the existing hole in the hull from 1" to 1 1/8". A twist drill bit seems ideal for this application, but bits in that size are hard to find and expensive when you do (especially for a one-time use item). I feel like a a hole saw or a forstner bit would be hard to keep centered and straight in an existing hole and a spade bit I imagine would be a total disaster going through solid FG. Anyone have any ideas or tips for doing this?

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post #2 of 18 Old 12-24-2012
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Re: Enlarging hole in hull

Can you get a peice of lumber on the inside to stay in place which will allow the arbour of a hole saw to bite to something and keep from wandering?
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post #3 of 18 Old 12-24-2012
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Re: Enlarging hole in hull

A twist drill can also grab something fierce when doing an incremental enlargement like that, yanking the drill from your hand and breaking your thumb.

Hole saw with block of wood. Once you are in 1/8" the guide is not needed.

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post #4 of 18 Old 12-24-2012
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Re: Enlarging hole in hull

Hole saw is the ticket. Block on the outside and a longer pilot bit works for me if drilling from inside. I prefer drilling from inside. Prevents unintended consequences better even if it's abut awkward. Or if you like having tools, and foresee this being a repeated activity buy an oopsie arbor. Let's you use a smaller hole saw as the pilot bit. Usual cost around 8$ endlessly helpful. Especially in thick curved awkward areas.
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Last edited by Jgbrown; 12-24-2012 at 08:47 AM.
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post #5 of 18 Old 12-24-2012
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Re: Enlarging hole in hull

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Originally Posted by Jgbrown View Post
Hole saw is the ticket. ... if you like having tools, and foresee this being a repeated activity buy an oopsie arbor. .
In case anyone else was wondering....



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Re: Enlarging hole in hull

I've used a piece of wood as a guide for the larger hole saw. Use a piece of 2X and drill the diameter of the existing hole then put the cut out on the pilot bit with the larger hole saw.

Edit: Oooh, I think I need one of those oopsie arbors:-))

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Re: Enlarging hole in hull

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Originally Posted by jrd22 View Post
I've used a piece of wood as a guide for the larger hole saw. Use a piece of 2X and drill the diameter of the existing hole then put the cut out on the pilot bit with the larger hole saw.

Edit: Oooh, I think I need one of those oopsie arbors:-))
John, I've done similar many times.. the only place the 'oops' arbor won't work is if you need to realign or slightly move the hole center.. that CAN be done with a predrilled template as you suggest.

Another thing I've been able to do is to clamp the drill into one of those portable drill press thingies, spin the drill around, stand on the base and position the hole saw that way.. but that requires a decent surface to work on.

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post #8 of 18 Old 12-24-2012
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Re: Enlarging hole in hull

pound in a thru hull plug and redrill.
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Re: Enlarging hole in hull

Thanks for the ideas all. I like the idea of the oops arbor and I could definitely see it being a useful addition to my toolbox. The plug and redrill option also sounds like a good one.

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post #10 of 18 Old 12-24-2012
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Re: Enlarging hole in hull

Why not a grinding bit in a dremel... and just open the hole up...?

From a 1" to a 1 1/8" is only a 1/16" all around... hardly worth the effort for plug and redrill or the cost of an "oops" bit which may not take up the minor difference anyway...

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