How to best enlarge a hole cut with a hole saw

rogerbum

I need to enlarge a roughly 1" hole through the aft cabin bulk head by about 0.25" to install a different fitting for the raw water wash down system. I have the appropriate size hole saws but since there's already a smaller hole there, the pilot bit (which centers the hole saw) has nothing to guide it. I'm wondering if there's an easy "trick" to solve this problem.

dutch123 · Posted: Mon Jun 11, 2012 6:42 pm Post subject:

Glue in a plug,wait till tomorrow, drill new hole! Thumbs Up

Physalia · Posted: Mon Jun 11, 2012 6:46 pm Post subject:

Rogerbum,

With some holesaws it is possible to thread more than one holesaw onto the threaded mandrel at once. Put the 1 1/4" holesaw on first and then the 1" holesaw inside that. You may have to use some washers so that the inside blade protrudes out further so that it can act as the centering guide for the larger holesaw. Hope this works for you as it has for me in the past!

beermanPDX · Posted: Mon Jun 11, 2012 7:09 pm Post subject:

Drill your 1-1/4" hole in a piece of scrap wood. This becomes your guide when you center it over the 1" hole. Ideally you'd clamp the guide to the bulkhead. But if that's not easy to do, you may be able to hold it there by hand long enough to get the hole saw started.

TyBoo · Posted: Mon Jun 11, 2012 7:44 pm Post subject:

A round plug is the simplest but it has to fit. One that is cut with the original hole saw will be a bit small. If you can secure a piece of plywood to the wall inside the hole and use a longer pilot, that will work. Have you computer sciences son print a template to find exact center. (Or eyeball it like like us K-12 guys do, but then I am a little off center myself).

On the other hand, that is only 1/8" material to be removed. You probably spent more time reading these replies than it would take to enlarge it with a half-round rasp. Also, you can buy rotary cutters to turn in a drill motor that will shave the ID.

Adeline · Posted: Mon Jun 11, 2012 7:54 pm Post subject:

Enlarge Holes With The Starrett Oops Arbor

Click image

tomherrick · Guest

Looks to me like the multi-sized hole saw would be the easiest trick. What I do is to simply screw a scrap of plywood with a pilot hole to the back side of the hole - making sure the screws are well within the new saw diameter. Then use the proper sized hole saw and pilot arbor to fix the goof. I don't want to say how experienced I am with this method...

thataway · Posted: Mon Jun 11, 2012 8:34 pm Post subject:

I have done this type of cut with a rotary rasp in a drill (as TyBoo suggests). Also there is the drum type of sander--Most often use the 1/2" drum in the Dremel tool for this type of cut. If larger hole only needs a small amount I have a 2" sleeve sander for the drill. 1/8" is not much to take off. It is easy to tape around the hole, and mark off what you need to take off.

rogerbum · Posted: Mon Jun 11, 2012 8:42 pm Post subject:

Adeline · Posted: Mon Jun 11, 2012 9:00 pm Post subject:

rogerbum · Posted: Mon Jun 11, 2012 10:53 pm Post subject:

By the way - THANKS Gary! (I forgot to type that on the last post).

Physalia · Posted: Mon Jun 11, 2012 11:14 pm Post subject:

You aare very welcome! Glad it worked for you. @