Enlarging drilled holes

[Greg Magone]

I drilled 10 holes in oak using a Forstener bit to mate with dowels. Hole diameter is 1.25 inches. Turns out, hole is slightly too small of diameter and dowels do not fit in. (Yes, I did a test cut in softwood and the dowels fit fine. For some reason the finished hole size is a bit too small in oak.)

I'm wondering how I can enlarge the hole diameter or shrink the dowel diameter so I can get a good mate. I can redrill using a spade bit, but I'm concerned this will not be safe and potentially result in injury or damage to the oak board. I don't think I can sand the 1.25 inch hole larger evenly and don't think that I can sand the dowel evenly smaller.

So, I'm a bit stuck. Redrilling seems to be the best option if I can figure out how to do it safely.

[Jerry Miner]

If you can get the correct-size hole in a scrap of wood, you can clamp the scrap over your existing hole and use a router and "pattern cutting" or "top bearing flush cutter" bit (two names for the same bit) to make the existing hole match the new hole.

Option B: cut a slot in the end of the dowel with a bandsaw or fine-tooth handsaw, just shy of the penetration depth of the dowel.

[Dan Hintz]

If you can get the correct-size hole in a scrap of wood, you can clamp the scrap over your existing hole...

No need for a router. Use the proper size forstner bit to cut a hole in a scrap piece. Mount the scrap piece over the existing smaller hole and use the scrap piece as a guide. Works like a charm.

[Lee Schierer]

What you are encountering is not unusual. When boring in soft wood you get more tear out on the sides that you will with hardwood. If you don't need much material removed, a spindle sander can enlarge your holes.

[pat warner]

Reamers will do it safely & "roundly". But do you have a chuck big enough & are you willing to spend for a one time deal?
The routing idea sounds like the most economical.

[Dick Strauss]

Greg,
Another option is to have a local woodturner take just a bit off your spindles if necessary (it should take him/her just a few minutes each). I have found that dowels are not always sized properly and can vary from one to another within the same batch. For example, if I measure 6 "half inch dowels" I may get readings from 0.450 to 0.510".

One thing that you may have already done is to round over the end of the dowel very slightly to help it get started in the hole easier.

Good luck!

[Matt Day]

I'd make the dowels smaller. Put them on a lathe and use sandpaper to slowly reduce th diameter. Or make a metal plate with the correct size hole and knock the dowels through (a la LN dowel plate).

[Peter Quinn]

Sounds to me like you are pretty close to a fit, not off by a whole drill size? At that diameter they don't make drills that go up in increments of thousands like machinist bits do, so you are probably not going to find the correct sized bit. I'm guessing the dowels are store bought, like closed rod material or similar? Problem is probably the dowels not made to tight tolerances. I'm thinking either you adjust the dowels or you adjust the holes. If you have a lathe or one of those drill press mini lathe attachments and some sandpaper it's a pretty simple thing to skinny the dowels down a bit. If not files or some cylinder hones might work to expand the holes just a bit.

http://www.amazon.com/31-8mm-Flex-Ho.../dp/B002T09ICU

[glenn bradley]

How tight is too tight? Put a caliper on the dowel and in the hole. Are we talking a few thou or are we talking 64ths?

[ian maybury]

I wouldn't try to use a spade bit without the point into wood and the work being well anchored under a press either.

Dowels are often not very round, or to a given diameter - best to do plenty of checking first as if that's the case it's possibly the dowelling/rod that's the problem. Turning some up might indeed be easier than re-boring your holes.

What's possible on the holes depends quite a bit on how you are drilling - into a clamped down workpiece under a press, or using a hand held drill. The latter is a handful with a big forstner at the best of times anyway - best with a centre drill fitted. The same size guide block Dan describes is a good idea too. The problem with a forstner may be to get the right size if you have already used one that's nominally correct.

I've been known to cut a circular plug and glue it in a misplaced hole using a thick super glue (miter bonder etc) with an activator - then go again. Works fine with forstners.

A flush cutting drum sander might be an alternative to a router: http://www.highlandwoodworking.com/r...1diameter.aspx Hard to keep it round or square except under a press or on a spindle though.

A simple engineering style fly cutter (cheap and widely available from DIY/light machining supply places) makes it possible to start with a slightly undersize hole, and then work up to whatever you need, but the work needs to be well located and tightly clamped down under a drill press or mill drill. e.g. http://www.warco.co.uk/fly-cutters/2...-38-shank.html Make sure you grind enough clearance angle on the tip.

[Bill Orbine]

Rasp the dowels.....

[Mike Schuch]

I have a cheap set of Silver and Deming drill bits from harbor freight that I use for situations like you have. You will probably not be able to find one that is just the little bit bigger size that you will need.



I have only used my adjustable reamer set on metal... I have never tried them on wood...

[Dan Hahr]

If it will fit in the softwood hole, it will fit in the hardwood one. Get a bigger hammer and pound it in. Unless it is too delicate; then just use some sand paper or scraper to trim it down a bit.
Dan

[Brian Jarnell]

Definitely more than one way to skin a cat

[Brad Patch]

I drilled 10 holes in oak using a Forstener bit to mate with dowels. Hole diameter is 1.25 inches. Turns out, hole is slightly too small of diameter and dowels do not fit in. (Yes, I did a test cut in softwood and the dowels fit fine. For some reason the finished hole size is a bit too small in oak.)

I'm wondering how I can enlarge the hole diameter or shrink the dowel diameter so I can get a good mate. I can redrill using a spade bit, but I'm concerned this will not be safe and potentially result in injury or damage to the oak board. I don't think I can sand the 1.25 inch hole larger evenly and don't think that I can sand the dowel evenly smaller.

So, I'm a bit stuck. Redrilling seems to be the best option if I can figure out how to do it safely.

Trying to enlarge the hole is probably not a good option. Previous suggestions could work but some would be time consuming, expensive or down right dangerous if using a spade bit. Use whatever method is available to you to reduce the size of the dowels.