accurately enlarging a hole.....

[al ladd]

I'm interested in hearing how people would reliably concentrically enlarge an existing 1/2" through hole in something like the face of BB plywood or MDF to 3/4" for about half its depth , preferably with only the types of tools the average serious amateur woodworker would own. Tolerance of about .005 -.01"?

[Carl Beckett]

I might put a snug fitting forstner bit in the existing hole. Then tighten on the drill quill. Then clamp the piece in place snug to the table. Then remove the bit and replace with the larger bit.

[glenn bradley]

3167386[/URL]]I might put a snug fitting forstner bit in the existing hole. Then tighten on the drill quill. Then clamp the piece in place snug to the table. Then remove the bit and replace with the larger bit.

This is what I commonly do for alignment in preparation for a secondary operation.

[Bruce Page]

I might put a snug fitting forstner bit in the existing hole. Then tighten on the drill quill. Then clamp the piece in place snug to the table. Then remove the bit and replace with the larger bit.

+1, that’s how I would do it and I’m a retired machinist with a milling machine.
The only thing I would do differently would be to chuck the alignment tool first and then bump the plywood into position, then clamp it down. Either way will work If the plywood piece is small and lightweight.

[Bill Dufour]

Counterbore with pilot that can be removed and exchanged. Common for metal work.
Two days ago I needed a 1/4" pilot so I took a 1/4" bolt and drilled it axially for a 3/16 hole. Cut off the head and cut the short length I needed. Cut and soft soldered a bit of 3/16 rod for a shank and used it. Worked fine. Should really have silver solder or brazed it.
Bill D

Gives you an idea what I am talking about. Stupid Amazon does not mention size.
https://www.amazon.com/HHIP-2007-002...l%2C138&sr=1-4

Ebay now for $25

[Steve Jenkins]

Probably with a rabbiting bit on a router.oops edited because the bearing needed would probably not fit in a1/2” hole

[Jerry Wright]

HF step bit. Self centers in 1/2 hole, them bore to desired depth.

[Steve Eure]

Another way that I was taught is to cover your existing hole with masking tape (painters tape), then take your 1/2" bit,align with your hole, and using the point, make a dimple in the tape. Remove the bit and insert your 3/4" bit. You now have a dimple or small hole to align your larger bit.

[Michael Schuch]

HF step bit. Self centers in 1/2 hole, them bore to desired depth.

Irwin makes a single flute step bit that does an excellent job keeping itself centered. Better than the two flute step bits. I have enlagred holes in saw blades with one without throwing the blade off center.

[Rob Luter]

A few great tips here:

[Rich Engelhardt]

Is it possible to drill the 3/4" part of the hole first?
That would make things a lot easier.

[Michael Schuch]

Probably with a rabbiting bit on a router.oops edited because the bearing needed would probably not fit in a1/2” hole

This is exactly what I was thinking. I have a flush cut bit that would easily fit in a half inch hole and a set of all difference size bearings I can use with it.

[Lee Schierer]

Cut a short piece of 1/2" dowel that fits in the hole. Mark the center of the dowel on one end. Place the dowel in the hole so the marked end is up. Drill the hole larger to the desired depth with the larger forstner bit.

[Bruce Wrenn]

Tolerance of about .005 -.01"?

Your wood can change that much overnight due to humidity changes. It's woodworking, not machining.

[Brian Holcombe]

There is no chance a 1/2” hole is changing by .005-.010” overnight unless it has been cut in green wood. OP is cutting ply and MDF, both materials are reasonably stable.