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Compass Marine How To | all galleries >> Welcome To >> Sealing Deck Penetrations to Prevent Core Rot > Clean Over Sized Hole
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Clean Over Sized Hole

This image shows the 5/16" over sized hole, and the original 1/4" hole on the left. The new bigger hole is just as clean even though there was no "center point" to start the drill with.

At this point I have removed the core with the Dremel and you can see the cavity it created if you blow up the photo and look close.

When using the Dremel to rout the core away make it a practice to insert the head of the bit into the deck before turning it on. Once turned on use the bits shaft as a guide and work your way around the hole moving up and down and around the circumference of the deck hole to clean the core material from the the skins and to make a nice, even, round cavity for the epoxy to seal the deck.. Make a few passes and suck any dust out with a shop vac. It takes all of about 10-20 seconds, per hole, once prepped and ready for it..

Nikon D200
1/60s f/10.0 at 70.0mm iso100 full exif

other sizes: small medium large auto
Ron 24-Apr-2014 12:07
I've just recently started potting about 100 holes. The first two took an hour each to drill out. The problem is the plywood in most of the holes is VERY hard and it tends to gum up the 115 bit. I had to clean the bit with a wire brush 20 to 30 times per hole. To shorten the time, I've come up with two techniques. First, I got a 5/16" forstner bit that I use to pre-drill the hole. I angle the drill to remove as much material as possible. It doesn't gum up like the 115 bit. Second, I run the dremel at a much higher speed than I had been. Now, it takes only about 5 minutes per hole.
Windchaser 16-May-2009 01:15
How much core must remove if I find dampness after drilling a 5/8th inch hole in my cockpit to run instrument cable. This hole is in the center of two holes made when the factory installed the binnacle guard. The moisture seems recent as I have never seen any water after a rainstorm in our back berth which is directly beneath where I drilled the hole.