Simple Tip on enlarging an already cut hole too large for a drill bit.

We purchased a newer style multi-purpose transducer that is a slightly larger diameter than the old one. This presented a problem of increasing the size of the opening in the through hull. Last thing I wanted was not to have a snug fit around the transducer caused by irregular filing and grinding.

My solution so as not to lose that perfectly round shape was to select a hole saw to the size of the old hole. I then picked the right size saw to fit over the old one but with washers between so the old saw blades made first contact and lined up the second blade for a perfect cut hole. It took a bit of "fiddling" to get the two matched up and secured tightly but was more than worth the effort.

It worked like a charm!!

Never thought of that idea!
That's a good one.

Brilliant! Now if I can only remember this when I run across the situation.

What a great idea! Thanks for the tip (although I hope I never need it...)

Thanks for that!

Very Nice!

Thanks for posting.

Here is a similar trick for a situation where you can't access the clean original hole.

I needed to drill a larger hole for a new transducer where the existing flush mount transducer fitting was still bonded into the hull.

You drive the correct size tapered softwood plug (like the one in the background of the first picture) tightly into the fitting from the outside.
Cut it off close to flush to the hull.
Mark the center for the pilot bit and drill with the larger hole saw.

Mark

Enlarging a hole.

Fellers, In all honesty unless the correct placement of a new hole is incredibly critical, you might consider what i did years ago when enlarging a hole in the hull for my new raw water engine intake. Ericson in their obtuse wisdom, fitted our boat with a 1/2" gate valve, clearly not the proper type and size for a 3/4"seacock, the smallest seacock available. I removed the old brass gate valve inside and bronze mushroom fitting from the outside (was on the hard of course) revealing the old, small hole. In order to make the new bigger hole, I simply rested the bottom of my hole saw in the bottom of the old small hole and drilled away. The resultant crescent shaped scrap of glass was near wafer-like in thickness and the new hole was good to go in mere seconds, wham, bam, thank you ma'am. No wood plugs were harmed in the making of this new hole. I defy anyone visiting our boat today to notice that the 3/4" seacock is slightly out of kilter relative to the original hole, photo attached. Remember, always have fun with your boat, Glyn Judson, The Dawn Treader, E31 hull #55, Marina del Rey CA

Holed up so to speak.

Leslie, Good point my friend and you reminded me of one critical part that I left out. I started the new, bigger hole by positioning the saw at about a 45° angle to the existing smaller hole but still resting it in the bottom of that hole. Then by slowly reducing that angle, the cutting is minimal and a groove begins to form in the glass which steadies the saw and keeps it from chattering all over the place. And that's how I did it. Thanks for jogging my memory regarding critical that detail, Glyn

Glyn Judson said:

Leslie, Good point my friend and you reminded me of one critical part that I left out. I started the new, bigger hole by positioning the saw at about a 45° angle to the existing smaller hole but still resting it in the bottom of that hole. Then by slowly reducing that angle, the cutting is minimal and a groove begins to form in the glass which steadies the saw and keeps it from chattering all over the place. And that's how I did it. Thanks for jogging my memory regarding critical that detail, Glyn

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Angling the start sounds like a very good idea. If I can't rig up the hole saw - in hole saw, I'll try angling. But it will probably still skitter for me . Thanks.

https://www.mcmaster.com/#hole-saw-enlarging-guides/=1c3qjj6

Just saw this at McMaster Carr.

bigd14 said:

https://www.mcmaster.com/#hole-saw-enlarging-guides/=1c3qjj6

Just saw this at McMaster Carr.

Click to expand...

Definitely going to order one! ...That way I probably won't have to ever drill one again

I like how they reversed the smaller saw as well. The extended shank makes it a breeze instead of the "fiddling" I had to do.

THANKS for the keen eye and sharing with us!

I did a similar move the other day.....Had to enlarge a 2" hole to a 4" hole in a lawn "irrigation valve cover box." I steadied the plastic valve box by hand against a 2X6, and drilled the pilot hole into the wood to anchor the 4" hole saw. I tipped the hole saw back-and-forth so it was only cutting one edge at a time. Worked like a charm until the sawblade bit into a thickened plastic rib. The shock from the blade instantly stopping felt like it almost cracked my wrist. Next time I'll do this kind of work in a vice.

Kenneth K said:

I did a similar move the other day.....Had to enlarge a 2" hole to a 4" hole in a lawn "irrigation valve cover box." I steadied the plastic valve box by hand against a 2X6, and drilled the pilot hole into the wood to anchor the 4" hole saw. I tipped the hole saw back-and-forth so it was only cutting one edge at a time. Worked like a charm until the sawblade bit into a thickened plastic rib. The shock from the blade instantly stopping felt like it almost cracked my wrist. Next time I'll do this kind of work in a vice.

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Hi Ken, ...YIKES!!! Going to keep that bit of self learning advise in my memory banks for sure!!

Anytime we work with tools, one should keep "O'Toole's Law" in mind. (O'Toole was the one who wisely said "Murphy" was an optimist!)

-fair winds!

Enlarging holes

kapnkd said:

We purchased a newer style multi-purpose transducer that is a slightly larger diameter than the old one. This presented a problem of increasing the size of the opening in the through hull. Last thing I wanted was not to have a snug fit around the transducer caused by irregular filing and grinding.

My solution so as not to lose that perfectly round shape was to select a hole saw to the size of the old hole. I then picked the right size saw to fit over the old one but with washers between so the old saw blades made first contact and lined up the second blade for a perfect cut hole. It took a bit of "fiddling" to get the two matched up and secured tightly but was more than worth the effort.

It worked like a charm!!

View attachment 23941

Click to expand...

A similar idea is to use a damage control plug. Tapered to fit the existing hole. Mark the center, and drill it to fit the guide pin (drill bit) of the hole saw. Cost effective compared to McMaster Carr.

Vagabond39 said:

A similar idea is to use a damage control plug. Tapered to fit the existing hole. Mark the center, and drill it to fit the guide pin (drill bit) of the hole saw. Cost effective compared to McMaster Carr.

Click to expand...

Good point Bob,

I'm probably still going to get one anyway as I can see using it for other non-boat projects as well.