How I Set Up and Sharpen Captive Hollowing Tools
by Vaughn McMillan ©

There are probably a bazillion ways it can be done, but I figured I'd show how I do it, right or wrong. I'm not trying to describe the whole hollowing process, just how I set up and sharpen the cutting bits.

First, I make sure the cutting edge is exactly on the centerline of the piece. I almost always start my hollowing with a Forstner bit to give me room to work and a place for the initial shavings to go. The point of the bit leaves a nice hole that's exactly at centerline, so it makes a handy reference for setting the tool rest height to get the cutter centered. In this picture, I've already hollowed most of this piece, but you can still see a little dot that's the sign last of the drill bit. To the left of the dot, you can see the top edge of the cutter. To the right of the hole, you can see a scratch that I made with the cutter to draw a line, showing the exact plane that it's traveling. (The lathe was turned off, of course.) You can see the line runs straight to the center hole, showing it's lined up just right.

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The cutting tip acts as a small scraper. It's sharpened at the same angle as all my scrapers. It doesn't ride the bevel, but cuts with a burr, just like a scraper. Here's a picture of the cutter touching the surface of the wood. It's the same on the inside, just harder to photograph...

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The question has also come up regarding how far the tool rest should be from the opening of the piece. I usually try to keep it around 1/2" to 3/4" away. I want it as close as reasonably possible, but not so close my hand hits the piece while holding the boring bar. For scale, this is a 1/2" boring bar...

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As I mentioned, I sharpen the cutters the same as my handled scrapers. To make it easier to see in the pictures, I used a 3/8" cutter. The 1/4" cutter is done exactly the same way, it's just smaller.

This poorly-focused picture shows the angle at which the tool rest is set on the grinder...

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I simply sweep the cutter in an arc, following (or forming) the curve I want in the tip. I hold the cutter down close to the grinding wheel, and sweep the other end in arc as I grind. You'll notice the curved scratches in the tool rest on my grinder. That's from sharpening hollowing bits and bowl scrapers. Here are a couple views.

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And one more shot, showing the angle of the grind stays the same as the bit is swept through the radius...

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I didn't take any photographs, but I sharpen the teardrop scrapers in the same way, and at the same angle.

Like I said, this is by no means the only (or best) way to set up and sharpen these bits, but it's what works for me. I hope this helps.


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