Dumb Woodworking Question of the Day: How do I enlarge a through-deck hole?...

[TimScearce]

I need to enlard a 3" hole in my teak covered plywood deck to about 3 1/2". The hole will accomodate a dorade vent to replace on I lost overboard recently :(

The hole is currently in a varnished base that is attached to the surface of the deck.

My apologies if this is an obvious question. I'm still learning...

Thanks,

Tim

[NormMessinger]

Well, there are many ways, no doubt, so I'll start with the first one that comes to mind:

Put a plug in the hole so you will have something to center a 3-1/2" hole saw and drill it out.

Since you say "about" perhaps if you are comfortable with using one, you can use a jig saw.

Next:

[Gresham CA]

If you can put two hole saw blades on your chuck, use a 3" blade(it acts as the pilot) and a 3 1/2" blade. If not, and you can get below decks, back it with a piece of wood and use the 3" saw blade and bit to get your pilot hole and finish with your 3 1/2" saw. Nothing to it. smile.gif

[ 08-05-2003, 02:56 PM: Message edited by: Gresham CA ]

[Sam F]

There are probably 10 ways to do this. Here are two:
Draw a correct circle and cut it out carefully with a sabre saw. I've done this sort of thing and it's rather more difficult to make a neat hole than it looks
or
Plug the hole with a block (really tight friction fit + hot melt glue, or screwed in from the back but be sure to miss the saw!, or what ever works in your situation). Position a 3.5" hole saw in the exact center and have at it. This will make a very neat hole but it is a bit of work to install the blocking (could be a dowel if a large one is available) in the original hole.

[Mike Vogdes]

One way would be to fill the existing 3" hole with a piece 3/4" plywood cut with a 3" holesaw, shim and epoxy in place so your deck is once again a flat even surface, then when the epoxy kicks go ahead a cut a new hole with a 3-1/2" holesaw.

[Bruce Hooke]

Two additional thoughts:

1. If you haven't already (and you probably have) check below the deck to make sure that enlarging the hole won't cause you to run into any deck beams or other obstructions.

2. Is the varnished ring big enough to be able to handle having the hole in it enlarged? If not then of course you may need to make a new ring. If you are unsure of the reliablity of the procedure for enlarging the hole then you may want to remove the varnished ring and expand the hole in it seperately.

[Scott Rosen]

I'd follow Norm's advice. You don't even need to fuss with getting the plug flush or the pilot bit centered, as long as the 3.5" hole is completely outside of the 3" one. I'm assuming you're using a Lenox type (http://www.coastaltool.com/cgi-bin/SoftCart.exe/a/ab/leno/holesaw.htm?L+coastest+kdjg7834ffb3efb3+1060118762 ) hole saw.

[Mike Vogdes]

I would be as acurate as possible with the pilot hole, there is only 1/4" tolorence between a 3" and 3-1/2" hole using a holesaw..

[NormMessinger]

If two hole cutters will fit on one mandrel, I like Charles' idea. Slap two cutters togeather and bob's yer uncle.

I learn somethin' most every day.

[Gerald]

Cut a 3 1/2 hole in a board. Slap the board on the surface you want to cut and use the hole in the board as your guide.
Gerald Niffenegger

[Gary E]

Tim,

I am going to assume that someone who would ask this question here dose not have a drill motor as large as would be required to drive a 3 1/2 in hole saw..cuz ifin ya did, you would know how, ya need a giant drill motor..

So for a simple solution, find a tin can, peanut butter jar or anything else that is the diameter you want.. draw the circle where ya want it and go at it with the jig saw.. finish up with a rasp and then a sanding drum in your drill motor...

Good luck
G

[Gresham CA]

Norm,

I've done it before and it works like a charm.

Gary,

I did it with an 18 volt battery drill. Granted it had to work, but it did work and didn't burn anything up.

[TimScearce]

You guys rock!

Thanks for all the great advice. I'll have a go at it and try to post a pic with the final results.

Thanks again!

Tim

[Nicholas Carey]

Any fasteners in the way of the hole?

If there aren't, cut a 3-1/2 hole in a piece of masonite or plywood to make a template.

Trace the shape of the hold on the deck, rough it out with a jigsaw. Then tack down the masonite template with double stick carpet tape or hot melt glue. and finish it with your routah with a bearing guided pattern bit mounted

http://www.cmtusa.com/store/catimg/811B.jpg

Smooth as glass.

[John B]

if you use the hole saw , drill from both top and bottom. If you drill all the way through from the top say , chances are you'll get edge break out inside the boat.

[doorstop]

What Gerald said, cut your correct size hole in a piece of scrap, tack, nail or screw it where you want the hole and you won't need to worry about the pilot bit..... I used to replace a lot of dor locks this way, luckily I could just clamp the piece in place though. A very quick, simple little job....

[Ex-Oceangoddess]

Quickest and easiest way I've found is simply tack a piece of scrap ply at least 1/2" bigger than the hole you want to end up with, centered on the existing hole, and drill away. All you need is something to keep the pilot drill bit in the proper place - doesn't need to be actually IN the old hole.

[ken mcclure]

Or make a template and use a router with a spiral cutting bit. The template needs to be bigger by the size of the collar on the router.