Paul G's post in Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to or raised some questions that I think a lot of us have had at some point about setting up and sharpening the cutting bits on they typical hollowing rig. 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.  

Thanks Vaugn,
I do the same thing as you, only I have the tool handle (boring bar)end slightly higher so when I have a catch it doesn't dig in(self feed). The cutting tip is on center cutting.
Great pictures showing how it works!

Sure, if that is not a problem.

you make it look so easy.  thanks for the fabulous tips.  will have to try this someday. smiley=thumbsup.gif smiley=thumbsup.gif smiley=dankk2.gif smiley=dankk2.gif smiley=dankk2.gif smiley=dankk2.gif smiley=dankk2.gif smiley=dankk2.gif smiley=dankk2.gif smiley=dankk2.gif

Question for you guys already hollowing..

It looks like Vaughn sharpens his to about a 45° angle. In the link Wizzy gave this one  Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to or Stan from Elbo tool he has his grinding table set at 7° below horizontal. What would be the good or bad points between either degree of angle? their both using the burr & no bevel. Could it be that with Vaughn's angle there is no way he would have the bottom of the cutter touch the wood & with Stan's it's a possibility?

These bits are scrapers, so while a 45° bevel is technically sharper, it doesn't help you here because you are presenting the bit to the wood at roughly 90° instead of riding the bevel.
As you mentioned, it is important to have adequate relief so the bottom of the cutter stays clear of the wood.

However, the less relief you have, the longer the bit will stay sharp.
Maybe I should rephrase that and say "The more material you have supporting the edge from underneath, the more durable the edge will be."

For me, 45° is "sharper" than optimal and will cause the blade to dull quicker than it needs to. I generally run 60-70° on my 3/16" bits. I grind the 1/4" bits at 75-80° and grind a secondary bevel at the bottom (like Stan shows in the video).
In a typical HF, the place where the bit is most likely the rub is either at the rim or the base depending on how small of a rim you prefer.
Say the smallest opening you expect to hollow through is a 3/4" hole. You can use a penny (3/4" diameter) to lay your bit on and see what angle would provide the needed relief. You will also want this relief to wrap around the point.
Stan seems to prefer larger HF's so he doesn't need much relief.

Chuck Beland wrote on Apr 4^th, 2009 at 6:45pm:


I just checked, and mine are between 65º and 70º as measured by my little plastic Tormek angle checker thingie. Closer to 70º. That's about 20º off horizontal. Keep in mind that the number of degrees below horizontal will differ, depending on how high the tool rest is, and if the tool is hitting above or below the centerline of the grinding wheel. 

I'd say you should try a few different angles and see which ones seem to work best for you. You may find you want to change grinds for different kinds of wood, or that "one grind fits all". If you're already comfortable using a handled scraper, you might start your hollowing bits at that same angle. Then you can tweak it up or down as you see fit. The only right way is whatever feels best to you.