Thread: Hollow-Grinding Hand Tools on a CBN Wheel

I suppose another potential solution would be an extremely narrow, maybe 1/8" or 1/4" CBN wheel. Are these out there?

Cheers,
Luke

Wheel does not need to be crowned to produce a hollow grind Cabinet makers have been hollow grinding on flat wheels for a couple of hundred years at least
I have been hollow grinding for 50 years and have never used a crowned wheel, in fact if the wheel was crowned I would dress it to bring it back to a flat condition.

I am in the same boat as china as to why you want a crowned wheel when the natural way of the wheel gives you a hollow ground tool.

Or are you shaping the tool differently

I'm with the others on this, I dress my wheel nice and flat before grinding.

I'm with you Luke with regards to crowning the wheel for freehand sharpening. I always found it easier to put the cutter to a single point on the wheel rather than trying to line up the entire cutter bevel with the face of the wheel. However, I recently had the opportunity to sharpen a woodturning skew chisel using a CBN wheel and a decent tool rest. It worked phenomenally well. I could slide the chisel left and right over the wheel knowing that it didn't matter how many passes I made, the CBN wheel face will remain flat and true unlike the AlOx wheels which wear away almost instantly leaving high and low spots.

The hollow comes from it being a wheel instead of a flat stone.
If you're trying to get the actual edge of the blade concave (can't think of why you'd want to though), I'm sure a diamond wheel dresser will make the wheel whatever shape you want it

Thanks fellas.

I'm not 100% sure everyone understands what I'm talking about with crowning the wheel, maybe?

Or maybe it's my definition of hollow-grinding. I'm not just talking about general grinding on a wheel. I'm talking specifically about deliberately removing material from the bevel between the cutting edge and the heel of the bevel WITHOUT actually grinding anything off of either the edge or the heel.

I just find it far easier to direct and fine tune the grind with a crowned wheel. As Kuffy said, you aim for a single point instead of having to have the bevel aligned with the entire width of the wheel. It reduces the chance of messing up and nicking the actual cutting edge.

I know that the reason the hollow is created is because of the roundness of the wheel. If you imagine a 1.5" wide plane iron and you're trying to grind it on a perfectly flat wheel, even if it's perfectly aligned across the wheel you will still wear it unevenly as you move it back and forth and the middle gets more wheel time than the edges, whereas with a crowned wheel you can take a bit off here and there until it's nice and eve.

Crowning a wheel is very commonly done by users of single bevel hand tools (Garret Hack, Christopher Schwarz) and has been for a while I presume. As indicated here, however, it's not for everyone.

But it is for me!

So is anyone aware of someone who will make one?

Cheers,
Luke

Try at a saw doctor. We've had the bore on a wheel enlarged to a custom size at our local saw doctor, they could probably dress it with a slight crown as well.

Originally Posted by Luke Maddux

Thanks fellas.

I'm not 100% sure everyone understands what I'm talking about with crowning the wheel, maybe?

Or maybe it's my definition of hollow-grinding. I'm not just talking about general grinding on a wheel. I'm talking specifically about deliberately removing material from the bevel between the cutting edge and the heel of the bevel WITHOUT actually grinding anything off of either the edge or the heel.

I just find it far easier to direct and fine tune the grind with a crowned wheel. As Kuffy said, you aim for a single point instead of having to have the bevel aligned with the entire width of the wheel. It reduces the chance of messing up and nicking the actual cutting edge.

I know that the reason the hollow is created is because of the roundness of the wheel. If you imagine a 1.5" wide plane iron and you're trying to grind it on a perfectly flat wheel, even if it's perfectly aligned across the wheel you will still wear it unevenly as you move it back and forth and the middle gets more wheel time than the edges, whereas with a crowned wheel you can take a bit off here and there until it's nice and eve.

Crowning a wheel is very commonly done by users of single bevel hand tools (Garret Hack, Christopher Schwarz) and has been for a while I presume. As indicated here, however, it's not for everyone.

But it is for me!

So is anyone aware of someone who will make one?

Cheers,
Luke

Luke, how much experience have you with the CBN wheel?

I've been hollow grinding with wide and flat 80- and 180 grit wheels for over a year (see my write up here). Prior to this I used a white Norton 38 grit wheel that I cambered, as per Joel Moskowitz' article in FWW many years ago. I used it this way for many years. The camber on the white wheel was necessary as one moved the blade to reduce the heat (not let it build up in one spot for long). However, the CBN wheels grind so fast and so cool that you can hold the blade flat against the wheel and create the entire camber in one hit if it is a blade narrower than the wheel, or in two hits if it is a blade wider than the wheel. In other words, the camber is no longer needed.

Regards from Perth

Derek

The comment above about just laying the tool on a single spot of the grinding wheel is what I prefer, too. The heat buildup is small compared to other wheels, and slow to occur unless you're heavy handed.

Many of the wheels have a wrap around radius that's probably a 3/16th radius or something. You can bias a tool to the left or right of the wheel if you want to create a smaller contact point, or go around the rest more and use that radius itself.

Also, you're using a grinder with two wheels, presumably. A cambered abrasive wheel can go on the other wheel. You won't end up using it often, but it is useful for things like rough grinding while toolmaking (where putting wear with soft steel on a CBN wheel might not be that advisable).

Derek: I have zero experience with CBN wheels.

I'm just really, really over the mess associated with AlOx. It's something I want to eliminate from my workshop permanently, and I view CBN as the fix.

I've done a bit of research and I am considering a CBN "cutoff" wheel. They make them in sizes all the way down to 0.144". I feel like with this on one side and a larger, maybe 1.25" flat CBN wheel on the other, I could handle pretty much everything from hollow and round moulding plane blades to 3/4" bowl gouges, and I would have the option of at least trying Derek's method of grinding on the flat wheel if I needed to.

Any thoughts on that kind of setup?