Boring with Expansive Bits

Irwin Expansive Bit

Expansive bits are great boring holes of variable widths, especially greater than 1 inch. They come with adjustable cutters that extend and retract. Many models come with two cutters, one that can cut a hole up to 1 3/4 inch diameter and the second cutter can cut up to 3 inches diameter. The cutters have gradations on them to help set the proper size hole to be bored. The gradations of some of these bits are approximations, so boring test holes is a must. On mine, they happen to be quite accurate.


To bore holes this large you will need plenty of muscle and a very good, sturdy brace, the great the sweep, the better. Do not use an antique 200 year old wooden brace. The likelihood of it snapping is high. In my book stand article, I needed to bore 1 3/8 inch diameter hole in the base. I didn’t think it would turn out to be heavy work. Well, lets just say I got a work out, but hey that hand tool woodworking.

To set the bit, line up the gradation marks with the mark on the main body of the bit. Be sure to bore a test hole first in some scrap to make sure your hole size is accurate. When you’re satisfied, bore the real thing.

With a bit of care, this can almost be as accurate as a drill.

2 thoughts on “Boring with Expansive Bits

  1. Hi Salko. I recall telling you earlier this year that I had a poor result using the expansive bit. The hole was off-center and very rough. But more recently, I had greater success. I used it to bore out the waste in a saw handle. I clamped a backer board to my workpiece so that I could bore all the way through, rather than come from both sides, which is very hard to do with one of these bits.


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