CBN Wheel Grit for 'Flat' Woodworkers

[Hasin Haroon]

Hi All

I have been wishing to switch hollow grinding my chisels and blades for some time now. Now that Lee Valley carries CBN wheels, they are readily accessible and I am ready to make the switch. I will be using the grinder primarily to reshape bevels (a lot of my vintage tools have been sharpened at way too steep a bevel), and remove nicks and chips from blades before sharpening on my water stones. I will be using a 1 hp slow speed grinder (1720 RPM). While I do some turning, I am mostly a regular woodworker, and will use the wheels accordingly. I use a mix of O1, A2 and PMV 11.

My options are 80 grit or 180 grit, flat wheels. Is the 80 too aggressive (leave scratches too deep that will take a while to hone out) or is the 180 too slow? I'm hoping those of you who use these wheels will be able to suggest the best one for my purposes. I've looked at past posts on CBN wheels, and while a lot of the merits and issues have been discussed, the relative utility of the different grits hasn't been touched on much.

Thanks!

[Malcolm Schweizer]

If you are only going to use it to grind hollows, and you have other methods of establishing the edge, I'd go with the 80 grit. If your sharpening methods are limited, the 180 will take a little longer, but leave a finer edge which means less work for the next steps. I personally have a Tormek and I'm thinking about getting a CBN or diamond wheel for it, but the next steps would be the Tormek wheel and then water or oil stones to finish. I'm probably going to go for a coarser grit. I wish Lee Valley had these in 10" so they match the profile of the Tormek.

[Chet R Parks]

Malcolm, You can get the Tormek style (10 x 2) CBN at Woodturners Wonders for $180 plus shipping. Sorry if you already new this.
Chet

[Todd Stock]

80 grit 8" diameter by 1" wide radiused wheel works much like a traditionally dressed SG grinding wheel, except cooler and - of course - no dressing dust. Tools for Working Wood has them. The Veritas supports work well for hand-held work, but fixed shop-made supports are easy to do as well. Bevel established with a coarse diamond stone with a few swipes and finished with an 8000 water stone goes quickly. With more time spent, an India for the bevel and natural oilstones to polish gets the same edge.

Re: Tormek...finally sold mine after 15 years for more than I paid for it...too slow to fit in the work flow. Running side by side with a low speed grinder & CBN wheel combo, the Tormek sat unused by students and the other luthiers that visit the shop. With the new diamond or the 10" CBN, I suspect the Tormek would speed up a bit, but doubt it's anything close to what I see with the low speed grinder and 80 grit wheel.

[Hasin Haroon]

Thanks Malcolm and Todd. Looks like I have two votes for the 80 grit CBN Wheel. I have ceramic waterstones in 1000, 4000 and 8000 grit. From what I read, the 180 grit is very aggressive, so I was worried the scratches from the 80 grit would be too deep and take too long to hone out (and a big reason to go CBN for me is the speed).

[Frederick Skelly]

Hasin, I use a 120 grit CBN. I like it a lot. It cuts well without leaving deep scratches. I suspect that 180 would be too fine a grit for just reshaping my bevels.

Fred

[Edit: Thanks Vincent. Your experience with the 180 is useful information.]

[Vincent Tai]

I have a 180 and 220 wheel. Both are very fast and the 220 leaves a nice finish. Both are faster than a 80 grit white wheel. The 80 grit CBN wheel must be really really fast. I'm thinking of getting an 80 grit or even 60 grit but that'll be for heavy shaping for me. 180 leaves a nice surface while being pretty quick at resetting bevels or grinding past nicks. Only reason I'm looking for anything coarser is because I have to grind a brand new bevel on chisels or irons I make so thats a decent chunk of steel to grind away. Still done easily with a 180 but it gets beyond 10-15 min on wider irons or when doing shaping. Below's a chisel that I made from some O1 scrap and shaped on a bench grinder with a 180 CBN wheel. Took about 30-40 min I think; and there was a decent amount steel to grind away. If you do get the 80 grit LV CBN wheel let us know how you like it; I really like Ken's CBN wheel from Woodturner's Wonder's but being able to get wheels with a run to LV is a major plus. I don't think you'll have trouble with getting a nice edge from an 80 grit wheel because its very easy to grind very accurately with CBN wheels; even if you have to take a few extra passes on your first stone you'll still have pretty tiny bevel landings. I remember Derek's writeup on CBN wheels saying that from what he could tell the 180 grit was nearly as fast as the 80 and provided a smoother finish. If theres a pre-existing bevel of sorts it should be rather fast to establish the new hollow ground bevel with a 180 wheel. I recently had a 1" PMV-11 chisel slam (with full force of a mallet) into a surface it wasn't suppose to. Took about 25-30 secs for 99% of the damage to be ground away. Another half minute and I was good to go sharpen. It's when grinding a bevel from scratch I long for the extra muscle of coarser wheels.
IMG_1634.jpgIMG_4218.JPGIMG_1636.jpgIMG_1603.jpg

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[brian zawatsky]

I have CBN wheels in 180 grit and 600 grit which came from Ken at Woodturners Wonders. I bought them specifically for grinding bowl and spindle gouges (I was bit by the bowl turning bug a few years ago). 180 is plenty fast enough for me when re-establishing a hollow grind on plane irons. CBN cuts very fast, I think you have a high potential for wasting a lot of steel with an 80 grit wheel. Just my .02

[Todd Stock]

Coarser wheels are generally going to cut faster and cooler than finer grit wheels, but leave a rougher finish. For turners, that matters, because some tools are used directly off the grinding wheel, so going to a finer wheel makes sense. For flat blades like chisels and plane blades, the wheel forms the ground primary bevel, and the honed secondary bevel is formed with a much finer grit stone (e.g., my 325 DuoSharp diamond stone)...so the concern with having to work out deep, coarse scratches from an 80 grit wheel is not something we have to worry about because we never hone the primary bevel. One of the reasons why I prefer the CBN 80 grit/1725 rpm grinder is the speed that something like a 2" framing chisel can be reground without much in the way of concern with overheating, and things move along a lot faster than with conventional wheels, but slow enough to control the tool.

I've also not found that over-grinding is a valid concern with flat work...grinding stops once the honed bevel is removed, and the tool goes a long time between grindings because on most tools...I'll run the honed bevel out to 1/2 the ground bevel's width before heading back to the wheel.

[Patrick Chase]

A few thoughts:

When we dry-grind woodworking tools on conventional wheels we're limited by heat, not cutting rate. We spend so much time pausing, dipping, using ultra-light pressure, or otherwise avoiding heating that we're not working anywhere near the limits of any of our wheels. Our choice of grit for such wheels is therefore largely a matter of which wheel will heat the tool least while getting the job done.

With conventional wheels the dominant heat contribution is from friction, and that's basically the same per wheel revolution regardless of grit. In other words, 10 revolutions of an 80# AlOx wheel heats the tool basically the same amount as 10 revolutions of a 180# AlOx wheel. The 80# wheel can finish any given job in less revolutions because it removes more material per turn, and that means that the 80# wheel will dissipate less total heat into the tool to get any given job done. This is why we typically use coarse-grit conventional wheels.

CBN wheels are very different, in that the sharp diamond points cut so efficiently that friction is no longer the dominant source of heating. I've seen one study showing ~1/5th of the frictional heating for CBN vs AlOx at any given speed/grit/pressure setting. This in turn means that you can work efficiently (without undue time spent paused/dipping/etc) with a higher-grit wheel when using CBN than you can with Alumina.

To put this in concrete terms, I mostly use 80# AlOx wheels ("white" or "blue"/3X), but I use 180# or even 350# with CBN. I have an 80# CBN wheel but seldom use it. The higher-grit wheels are more than fast enough, barely heat my tools, and provide a better finish and more gradual/controlled material removal.

[Derek Cohen]

I am coming in a little late here ... away in New Zealand at present, trampling around the forests.

I have 80 and 180 grit wheels. THe 180 grit is used 90 % of the time.

The importance of a smoother grit lies in the way the hollow is finished. I grind to the very edge of the blade. The 180 grit leaves fewer serrations than the 80 grit. The 80 grit is faster to grind, but for general use, the 180 grit is plenty fast. The 80 grit is reserved for when grinding a lot of metal.

The smoother edge off the 180 means that it is possible to go straight to a Medium Spyderco (or 6000 Sigma) before finishing on a UF Spyderco. This creates a micro bevel that will stay micro a long time. Equals faster sharpening.

220 grit is too fine for flat grinding. It will create more noticable heat, which is not a good thing. The 180 grit, with light pressure, remains lukewarm.

Regards from Auckland

Derek

[Vincent Tai]

I am coming in a little late here ... away in New Zealand at present, trampling around the forests.

I have 80 and 180 grit wheels. THe 180 grit is used 90 % of the time.

The importance of a smoother grit lies in the way the hollow is finished. I grind to the very edge of the blade. The 180 grit leaves fewer serrations than the 80 grit. The 80 grit is faster to grind, but for general use, the 180 grit is plenty fast. The 80 grit is reserved for when grinding a lot of metal.

The smoother edge off the 180 means that it is possible to go straight to a Medium Spyderco (or 6000 Sigma) before finishing on a UF Spyderco. This creates a micro bevel that will stay micro a long time. Equals faster sharpening.

220 grit is too fine for flat grinding. It will create more noticable heat, which is not a good thing. The 180 grit, with light pressure, remains lukewarm.

Regards from Auckland

Derek

Interesting that you found 220 too fine. I used my 220 wheel exclusively for a few months when I first got my wheels because I only have one tool rest. I found it very acceptable for flat woodworking tools and even ground some bevels from scratch on 1/8” thick small plane irons. For grinding away the inevitably largened micro bevels I found that no dipping in water was needed, lukewarm like 180 wheel use. For grinding new bevels I dipped once or twice. I have a habit of keeping my fingers dangerously close to the edge and wheel, and dip well before the any uncomfortable heat levels occur. I have a habit of dipping even at that lukewarm level that tools stay at for a few minutes on a 180 CBN wheel. Saunas would laugh at the temps I dip at. When I started getting my head around how cool CBN wheels run I started moving my fingers further away for most of the grinding. I spent a lot of time in high school a few years ago standing at a bench grinder. On one particular day I logged a total of nearly three hours. There were many forgotten and unused or abused hand tools in the shop (the ones that were used daily were also abused) and my teacher was trusting enough to let me have a go at them. There was literally rows of unused Stanley No5s in a storage room rescued from their destination to the grave. Other high schools that were putting an end to their shop programs had handtools lined up for the gallows and a few sensible teachers liberated them and had them stored for years and years in my HS. I was careful from the very first iron I tried on, and never did any water at edge sizzling nonsense. I dipped so frequently the iron would be room temp and I’d dip it. Every time I inspected progress I dipped. It’s such a habit I don’t find a bothersome when I have to dip 2-4 times grinding a shallower bevel on a tool with a steeper established bevel when using the 220 CBN wheel. The 180 is certainly a better wheel for heavier work and versatility but I’m glad I have a 220 wheel. I suppose I may be used to dipping so often that once or twice with a 220 CBN wheel was/is heavenly to me. Just need to get another tool rest so I can use both easily.

Cheers,
Vincent

[John K Jordan]

Hasin,

My experience:

I have four CBN wheels mounted to sharpen lathe tools. I have also used them on chisels and other non-lathe tools. I have 80 grit, 220, and 600 grit on 8" bench grinders and a 1200 grit on a Tormek (and a 600 grit Tormek wheel on the shelf). I had a 320 grit wheel on a bench grinder but I sold it and got the 220 since it was close to the 600 grit. All of my wheels are flat across the face with square "corners" and a 1" flat down the sides. I tried one with the radiused edges but didn't like it.

Sharpening_small.jpg

I rarely use the 80 grit and only for major resharpening of fairly large and thick HSS tools, but not for sharpening. For example, I shaped these negative rake scrapers from 10v Thompson stock, 3/4" and 1" wide - they started out as square end tools so I hand to remove a LOT of metal.

scrapers_neg_rake.jpg

For every thing but major reshaping (for all sharpening) I use the finer wheels. I can easily do less aggressive shaping on the 220 grit wheel and even the 600 grit. Both leave a better surface than the 80, of course. I'm surprised at how quickly even the 600 grit wheel will remove metal for minor bevel changes for even relatively wide bevels on skew chisels. I use the 1200 grit wheel on the Tormek for my spindle gouges and a few other tools - it turns so slowly it removes very little metal but still sharpens quickly and I love the edge it gives for turning tools. If I rated the wheels I have by the amount of use they would be in this order: 600, 1200, 80, 220. Although I think the 220 grit is a good multi-use wheel I rarely use it since the 600 does such a good job.

However, if I had just one wheel I would get a 220 or maybe even a 320, aggressive enough for some shaping and fine enough for most sharpening.

Do you know anyone nearby who has a CBN wheel you can try? I've had several people come to my shop to try mine. A lot of woodturners use them so one possibility of finding someone is to contact a woodturning club. It seems that woodturners, like other woodworkers, love to share.

Another possibility is to call Ken Rizza at Woodturners Wonders and ask him. He may have feedback from customers with similar needs, may know someone near you, or may even be able to work a deal to let you "audition" a wheel, perhaps a used one - I don't know if he would do this but it doesn't hurt to ask.

Be advised that a new CBN wheel will cut much more aggressively than one that is "broken in". Apparently the electro depositing method leaves random sharp bits of CBN gains proud of the surface. After some hours of use the corners of these must be knocked off and the wheel settles down to it's long term state.

Reed Grey (Robo Hippy) has an article on CBN wheels you might find interesting, from the perspective of a woodturner who mostly makes bowls: http://www.robohippy.net/featured-article/

JKJ

[Rob Lee]

Hi Hasin -

I would recommend the 180 grit - it's not really that much slower, and will yield a better finish for moving on to final honing.

While turners have been early adapters of CBN wheels - they have been slower to penetrate the "flat" world. Derek was kind enough to run me through his set-up when I was in Australia, and he's really worked through his workflow with CBN. Not only has he been using them for years, he's worked through various grits and styles as well.

I'd be happy to arrange a session at the Edmonton store, where you could bring in some blades or chisels, and give each wheel a try. Just mail me directly at rlee@leevalley.com to set it up. In any event - we are always happy to take back products that don't meet your expectation.

Cheers -

Rob

[Hasin Haroon]

Vincent, I am also quite accustomed to dunking my tools more often than is necessary to prevent heat build up when grinding (unless I've spent a few hours at the grinder, those last chisels may lose their temper). Also, that's a very nice looking chisel. You should share photos of the other tools you've made.