This is NOT a new sharpening thread...but...

[Patrick Chase]

As I have posted quite a few times before I am a grinder convert. I fought the idea for years, trying all sorts of stones, natural, ceramic, diamond....For me in the final analysis the larger jobs require many more strokes across some sort of abrasive surface. I am not so young any more and my hands are much more sensitive to all the abrasives and fine metal they make. I use an electric grinder so I can get the job done, on the PDQ, and get back to working wood.

In my opinion using grinders has more to offer than just removing metal faster. I finally experimented with the whole concept of hollow grinding and find it a much better method of sharpening for me. I don't like to have to hunt for and set a jig when I want to sharpen. Hollow ground edges are very easy to hone by hand without a jig. The edge naturally registers against the two sides of the hollow, removing most of the guess work/rocking when touching up an edge after it gets a little dull. Most of the time a few passes on medium and extra fine 2x8" Spyderco stones and I am back at work. The Spydercos are very hard which translates into not needing to flatten them. They do not require water. I love this system as it is much quicker, less messy, very easy to do by hand without any sort of jig.

For me a workable grinder set up changed the whole way I sharpen, making the whole system less complicated and easier to do, well worth any negligible cost vs stones IMHO. I like CBN wheels. I understand that many consider them needless expense. For me having an abrasive surface that will grind as fast and cool as a CBN wheel which will also probably out last me is worth the cost, saving time, effort, worry, every time I need to sharpen. In my experience a grinder solves more sharpening scenarios than any other device, more than several stones. I wish I had followed the lead of guys like David Weaver and Derek Cohen years ago.

Same here - that's why the first line in my first reply to the OP was "the obvious answer here is a bench grinder".

Interestingly the stone-vs-sandpaper tradeoffs carry over to power-assisted sharpening, except now they're called "grinding wheels" and "sanding belts/discs" respectively. The bottom line is about the same too: Sanding belts/discs are convenient (no dressing etc) but wheels are hard to beat for cost per sharpening.

[george wilson]

I'll say it again: If you invest in a diamond stone and a coarse and a fine Spyderco ceramic stone,you will not have to spend another dime for a very long time.

And,if you want a diamond stone for cheap as dirt,go on Ebay and find the Chinese guy who sells 6" diameter diamond impregnated lapidary disks for $9.00 each. If you can get by without the rectangular shaped diamond stone,these disks are nickel plated matrix based,and are just a good as any other diamond coated stone. They are 1/16" thick steel,and they are FLAT. I have a horizontal/vertical 200 RPM diamond grinder. I paid $250.00 for a wheel for it before I discovered the cheap Chinese discs. These cheap discs can be had anywhere from coarse to 2000 or 3000 grit(Can't recall how fine they go). A bit of alteration,and they work fine on my grinder. But YOU can use them for hand honing just as they are.

I strop on a piece of MDF with LV green buffing compound. I keep the MDF strop where it can't get grit or shop dust particles floating around and getting on it.

[Mike Holbrook]

I apparently missed the Chinese lapidary disk information when George posted it before, great to know about that alternative, will check it out. I have a couple pieces of MDF, and green compound I picked up after reading another of George's posts. I find that they work well for me too. I plan to try a little diamond paste on one of the MDF blocks to see if I like it vs green compound and an extra fine Spyderco. The MDF blocks with some sort of compound may work faster and polish better than a Spyderco extra fine stone. When I was a kid my cousin and I would grind fine sand into soft wood and use it to sharpen rough tools with, which is sort of similar in function.

[Patrick Chase]

I'll say it again: If you invest in a diamond stone and a coarse and a fine Spyderco ceramic stone,you will not have to spend another dime for a very long time.

And,if you want a diamond stone for cheap as dirt,go on Ebay and find the Chinese guy who sells 6" diameter diamond impregnated lapidary disks for $9.00 each. If you can get by without the rectangular shaped diamond stone,these disks are nickel plated matrix based,and are just a good as any other diamond coated stone. They are 1/16" thick steel,and they are FLAT. I have a horizontal/vertical 200 RPM diamond grinder. I paid $250.00 for a wheel for it before I discovered the cheap Chinese discs. These cheap discs can be had anywhere from coarse to 2000 or 3000 grit(Can't recall how fine they go). A bit of alteration,and they work fine on my grinder. But YOU can use them for hand honing just as they are.

I strop on a piece of MDF with LV green buffing compound. I keep the MDF strop where it can't get grit or shop dust particles floating around and getting on it.

Do you happen to know if those Chinese disks are mono- or polycrystalline?

I personally don't like diamond plates with nickel-bonded particles due to scratch [non]uniformity. Almost every plate I've ever used seems to have some "outlier" particles that leave deep scratches, even after break-in. From looking at SEM shots other have posted and based on my knowledge of the processes involved I suspect that this issue is more a function of the bonding process than of the abrasives themselves. A polycrystalline plate won't last as long but might be better in that regard since the "sore thumb" particles would tend to break down quickly, and at the price you cite life wouldn't be such a concern anyway.

I've had very good experiences with diamond lapping films (3M 661X/668X) and pastes. The adhesive bonding process for the films seems to achieve very good uniformity without any break-in, and the pastes are basically as good as the substrate you use them on (mild steel in my case - I take my plates to the machine shop down the road for regrinding whenever they start to go out of flat, which isn't often). I've had very good luck with some of the cheap polycrystalline diamond pastes that you can find on Amazon - you don't need the robustness of monocrystalline diamonds for that, and in that sense DMT/Norton/etc pastes are overkill.

[george wilson]

I like the bonded plates just fine,and haven't noticed any scratches from larger particles. Your mileage may vary. They ARE CHINESE,remember. I prefer to not use paste. I have several tubes,but they get wiped off the rotating plate,and I don't like turning diamonds loose around my precision machinery. Using them by hand motion only is different.

Patrick,you are lucky to be able to go to a machine shop and get small things ground. Here,they only seem interested in fat government contracts,and charge an arm and a leg for work. Fortunately,back in the early 70's I began to assemble my own machine shop.I hadn't had access to lathes and mills since the 50's. I ought to hang out a sign that says "The Poor Man's Machine Shop". It would be legal where I live. Except I know I'd only get badly rusted farm machinery parts to work on! No fun in that!!

[Ray Selinger]

What is a CBN wheel? This is a good discussion, I have quite a number of used and fleamarket chisels that need that first reshaping. I think the shaping is more correct term than sharpening.

[Patrick Chase]

What is a CBN wheel? This is a good discussion, I have quite a number of used and fleamarket chisels that need that first reshaping. I think the shaping is more correct term than sharpening.

Cubic Boron Nitride. It's crystallographically similar to diamond, but with Boron and Nitrogen atoms instead of Carbon. It's a hair softer than diamond but has much better life when grinding HSS at very high temperatures (700C and above).

Because of its suitability for bulk production grinding of HSS it's widely available in grinding wheels, and that makes it a reasonable choice for woodworkers even though diamond wheels would be slightly better for the less intensive grinding we do.

[Mike Holbrook]

Ray, Patrick answered your question quite well. I will just add that woodturners have been using CBN wheels for sharpening turning tools, often HSS or other hard steels, for a long time now. Turners dull tools fast and most report that they just can't wear CBN wheels out. Another major bonus of CBN wheels is they run much cooler than other grinding materials preventing most over heating scenarios. For "flat" woodworkers these wheels should outlast several friable stone wheels. As stone wheels decompose they can put a good deal of dust in the air, not to mention that they can break, which is why many use the very large washers on the outside of thinner stones. Although the stone wheels are certainly less expensive one might make the argument that over the long haul the CBN wheel may make up for the initially higher price in longevity, safety, easy care...

[Patrick Chase]

Ray, Patrick answered your question quite well. I will just add that woodturners have been using CBN wheels for sharpening turning tools, often HSS or other hard steels, for a long time now. Turners dull tools fast and most report that they just can't wear CBN wheels out. Another major bonus of CBN wheels is they run much cooler than other grinding materials preventing most over heating scenarios. For "flat" woodworkers these wheels should outlast several friable stone wheels. As stone wheels decompose they can put a good deal of dust in the air, not to mention that they can break, which is why many use the very large washers on the outside of thinner stones. Although the stone wheels are certainly less expensive one might make the argument that over the long haul the CBN wheel may make up for the initially higher price in longevity, safety, easy care...

Mike's absolutely right about heat. More broadly, there are two key metrics that matter to flat woodworkers:

- Grinding efficiency. This measures how much of the power used during grinding is spent removing material versus heating the workpiece. Note however that the efficiency itself varies with grinding rate (generally the faster you go the more efficient, for reasons I'll get to later), so you also need to worry about...

- Absolute rate of heat release. This measures how slowly you can dissipate power into the workpiece while grinding it.

CBN does very well on both metrics. I saw a paper a while back that showed that for production grinding of HSS, CBN wheels are about 3X more efficient than traditional Aluminum-Oxide wheels, and my own experience with lower-speed/temperature work is consistent with that. CBN also runs cool in absolute terms because the sharp abrasives particles cut with very little pressure - you can therefore manage tool temperature by simply using a light touch on the wheel.

The other common choices are friable aluminum-oxide (AlOx) wheels and seeded gel (SG) wheels.

Friable AlOx wheels cut hard tool steels quickly for precisely the same reason as waterstones - they maintain sharpness by releasing grit particles before they can dull or break down. The fact that they continuously expose fresh particles makes friable AlOx wheels both efficient and cool in absolute terms, though not as good as CBN in either respect. They also wear/dish quickly and have to be trued fairly often, again just like waterstones.

SG wheels include some percentage of particles made of an Al-Oxide ceramic, that exposes fresh, sharp edges as it breaks down instead of dulling. The catch is that you have to apply a fair amount of pressure to get those SG particles to break down - if you grind too lightly then the wheel just dulls and glazes and is no better than a conventional AlOx wheel of the same hardness. SG wheels therefore have good efficiency at high grinding pressures, but lower efficiency when used with a light touch. In terms of the metrics I described above they're efficient when used as intended, but not particularly cool-running in absolute terms. In practice you can get around this limitation by either grinding in bursts or by using a low-speed grinder (which allows you to use more pressure without burning the tool). Note that the requirement for relatively high grinding pressure is a property of the SG particles themselves rather than the binder, so softer wheels like the I-grade ones at TFWW only help inasmuch as they make an SG wheel behave more like a friable one, which sort of defeats the point of SG.

FWIW up until about a year ago I used SG wheels, and managed heat by applying pressure in bursts and by using a half-speed grinder. While I hadn't burned a tool in many years with that setup, I now use CBN wheels. They're a LOT more user-friendly.

[Jim Koepke]

I have quite a number of used and fleamarket chisels that need that first reshaping. I think the shaping is more correct term than sharpening.

Most of the time when I have had an old chisel that needs reshaping the back needs a lot of work.

It is difficult for me to imagine having success flattening the back with a bench grinder without doing something that was a major NO, NO when I was taught to use a bench grinder.

Have times and wisdom changed about using the side of a grinding wheel?

I do know having the hollow ground bevel a bench grinder provides is a major help to free hand sharpening. I have been able to free hand without a hollow grind.

For me working the back is easy with abrasive paper on a piece of granite or my flat disk power sharpening system.

jtk

[Patrick Chase]

Most of the time when I have had an old chisel that needs reshaping the back needs a lot of work.

It is difficult for me to imagine having success flattening the back with a bench grinder without doing something that was a major NO, NO when I was taught to use a bench grinder.

Have times and wisdom changed about using the side of a grinding wheel?

You certainly don't want to do that with a conventional vitrified wheel. CBN and diamond wheels are different in that they're turned out of a single chunk of steel so the usual disintegration concerns don't apply. You can even get some with extended sides for exactly this sort of work.

[Mike Holbrook]

Great information Patrick, thanks for providing a better explanation of what is actually happening with CBN abrasive vs other alternatives. My use of CBN wheels has lead me to the same conclusions. I learned early that they cut very well with lighter pressure, simultaneously dramatically reducing the heat produced by removing steel at a relatively rapid rate. It has seemed to me that the grinding pressure /speed necessary to keep heat down while grinding with a CBN wheel is just the speed I find works for making straight, reliable hollow grinds for radiuses etc. by hand.

Jim, I happen to have a CBN wheel that has abrasive on about a 1" band around both sides. I will do a little experimenting with an old chisel to see if I can do flat grinding with that part of the wheel. The challenge I found in doing that on a Tormek wheel is the part of the wheel next to the arbor is rotating faster than the edge 10" from the arbor. Logic would suggest that the speed difference on a 1" band on the outside of a 8" wheel moving at a slow speed might not be as great.

[Ray Selinger]

I wish I heard about CBN before I replaced the wheels on the my two grinders, with soft AO. One is used with the metal lathe the other the wood lathe. Since both are 3450s and bigger at 7" and 8", I chickened out and I ended up using wet/dry to correct my earlier freehand sharpening. The Veil tool rest didn't angle up to 25, so it would have been freehand. The paper was painfully slow and I didn't mess up that badly. There has to be a better way. The fleamarket chisels are very different story.

[Patrick Chase]

I wish I heard about CBN before I replaced the wheels on the my two grinders, with soft AO.

I wouldn't worry about it. A lot of people here use CBN wheels and are vocal about how great they are (as I was above), but IMO CBN wheels remain a luxury item as opposed to a must have. Soft AO wheels (vitrified grade H bond or thereabouts) get the job done very nicely and aren't all that demanding in terms of user technique. Just keep the pressure light, rest the tool whenever it gets warm (I shoot for "never uncomfortable to touch, even at the tip"), and dress/true them when needed.

[Derek Cohen]

What is a CBN wheel? This is a good discussion, I have quite a number of used and fleamarket chisels that need that first reshaping. I think the shaping is more correct term than sharpening.

Hi Ray

I posted this article here about a year ago, and updated it a few months later: http://www.inthewoodshop.com/Woodwor...ningSetUp.html

There are illustrations of the wheels and how I use them (others will do so differently, with much success - in other words, lots of room for variation). There are a couple of links to suppliers, as well as tips what to watch out for.

Regards from Perth

Derek