Tip for using hole saws and other large hole makers

[sweensdv]

+1, I agree. A good circle cutter, AKA 'fly cutter' (not a cheap one) does cut a clean hole, and if operated at slow speeds runs very smooth. Either a single or twin cutter will work.

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+2 The key is slow speeds and not applying too much downward pressure. Slow and easy will give you excellent results everytime.

[LCHIEN]

The planning for that type of an enlargement procedure does take some planning from the start. Once you get past the forstner stage, and run the first rabbet depth, it has to be high enough to accommodate the bearing of the flush trim. Then you need a landing for either the rabbet bearing and the flush trim bearing. The last run may have to be done with a flush trim with the bearing on the top. Whether you can access the backside of the subject piece may also play into the planning.

Some of the enlargement holes may not be accessible to a router, or a drill press. JMO.

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well, yes there are some restrictions on the rabbet bit/flush trim bit method of enlarging holes.

I would generally characterize it as being suitable for about 1/2" to 1" thick material, since rabbet bits general won't cut more than 3/4" deep and flush trim bits don't go but about 1" or 1-1/2 inch deep. Top or bottom bearing won't matter much but for flipping the piece. I always have done this on a router table.

I suppose you could go 1-1/2 thick material making rabbets on both sides.
and then using a 1-1/2" flush trim bit (I think these are readily available in that length) knock off the middle protrusion.

Bearing Landing is not much of a problem - the walls are always straight when starting the rabbet bit step, and you should leave 1/4" of the new diameter for the flush trim to ride.

I would think this would be tough to apply to a blind hole (one that did not go through the wood), the rabbet step would be possible if there was enough clearance for the bearing attachment but then you'd need a real short flush trim bit since the you'd have to use a bottom bearing (terminology refers to handheld use, as usual for bits) to ride the new diameter but the cutting edge could not be longer than the step to the bottom. Not that it couldn't be specially made but I've never seen a 1/4" or 1/2" cutting length flush trim bit.

[cabinetman]

Bearing Landing is not much of a problem - the walls are always straight when starting the rabbet bit step, and you should leave 1/4" of the new diameter for the flush trim to ride.

The walls are straight, but they have to be tall enough for the next bearing.

I would think this would be tough to apply to a blind hole (one that did not go through the wood), the rabbet step would be possible if there was enough clearance for the bearing attachment but then you'd need a real short flush trim bit since the you'd have to use a bottom bearing (terminology refers to handheld use, as usual for bits) to ride the new diameter but the cutting edge could not be longer than the step to the bottom. Not that it couldn't be specially made but I've never seen a 1/4" or 1/2" cutting length flush trim bit.

A short cutting length would be needed for a blind hole. Here is a pattern bit, with a 1/2" cutting length. It's the first one on the chart.

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[Mr__Bill]

Sometimes you want to enlarge a hole with a hole saw. With no stock in the middle for the guide drill to drill into it's a problem. If you cut a hole in a thin piece of scrap and then place it where you want the larger hole you can guide the hole saw from the outside rather than by the guide/piloit bit. This is also the way to cut a plug without the center piloit hole in it. Using the same trick put the hole saw into a drill press and drill through a thick, 2" pice of hard wood, then use this to drill a hole perpendictular on a surface where the drill press can't reach. Clamp the guide in place and use the true hole to guide your hole saw stright into the wood.

As Loring said, whenever possable the sawdust releif hole saves the hole saw from burning.

Bill