From previous posts I learned that a ceramic stone can get blunt and needed to be resurfaced. I do not have a ceramic stone but I have several ceramic rods. I have not idea of the original purpose of them, I bought them from ebay several years ago. I do not use them for sharpening for two reasons: first their grit is too coarse and second they are not aggressive. They do cut metal and leave black trace indicating metal removal but times less than a Sharpal sharpening ceramic rod which is my favorite sharpening tool. I decided to improve the rods abrasiveness, bought a diamond block and spent about 20 minutes rubbing one rod on the block. To my surprise there were not any visible effect! I tried different grits of the diamond block, initially used low pressure then increased it and nothing helps! The rod's ceramic materials feels too strong for the diamond block! What should I do to get the result?
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Ceramic Rod resurfacing
- Thread starter Barmaley
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I have resurfaced some ceramic stones with automotive wet/dry sandpaper, about 400-800 grit. That will allow you to get more surface coverage as the diamond block is only going to touch one part of the rod at a time. Some diamond stones will also not survive against ceramics and all you will do is knock off the diamonds. All that said, without knowing what sort of ceramic rods you have, they may well be as you say, too course and not aggressive, they may have been intended only for burnishing which only works on softer blades, or they may simply just be not very good quality, and not worth your time.
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I've used diamond hones to resurface sintered ceramics. The dust produced is minimal and extremely fine, and won't easily be seen when you're doing this dry. Even less so, if the ceramic is white or off-white in color. One way to better see how much is coming off is to do all of the rubbing with the rod & diamond hone immersed in a pan of water. The ceramic swarf coming off will collect at the bottom of the pan used to hold the water. Water will also help keep the swarf from collecting on the diamond hone.
BTW, I was actually doing the same thing yesterday, on the bottom of a ceramic (porcelain) coffee mug I dropped in the sink & broke a couple days ago. I'd already broken one of those a year or two ago and repurposed it for light touch-up honing for simple stainless, such as in kitchen knives. It works pretty well for that. After breaking the 2nd mug, I experimented with a cheap Harbor Freight diamond hone (180-grit, as rated) to alter the surface of the unglazed ceramic ring at the bottom of the mug. The dust coming off the mug was almost unnoticeable - but I periodically wiped the mug and the hone against my blue jeans and could see the smudge of light-colored dust on the denim. Not a lot there - but it's there. A much harder alumina ceramic made for sharpening will grind much slower, even on diamond. So the dust generated will be minimal - not much needs to be removed to alter how the surface of the hone cuts.
And resurfacing a round ceramic rod implies a very narrow contact area between the diamond and the ceramic. So the accumulation of ceramic swarf generated will be that much less in proportion.
BTW, I was actually doing the same thing yesterday, on the bottom of a ceramic (porcelain) coffee mug I dropped in the sink & broke a couple days ago. I'd already broken one of those a year or two ago and repurposed it for light touch-up honing for simple stainless, such as in kitchen knives. It works pretty well for that. After breaking the 2nd mug, I experimented with a cheap Harbor Freight diamond hone (180-grit, as rated) to alter the surface of the unglazed ceramic ring at the bottom of the mug. The dust coming off the mug was almost unnoticeable - but I periodically wiped the mug and the hone against my blue jeans and could see the smudge of light-colored dust on the denim. Not a lot there - but it's there. A much harder alumina ceramic made for sharpening will grind much slower, even on diamond. So the dust generated will be minimal - not much needs to be removed to alter how the surface of the hone cuts.
And resurfacing a round ceramic rod implies a very narrow contact area between the diamond and the ceramic. So the accumulation of ceramic swarf generated will be that much less in proportion.
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Another thought:
- If you're not sure what the original design purpose was, for the rods you're resurfacing...
- And you're seeing they're not aggressive at metal removal, even as coarse as they seem to be...
It may just be that the rods are of a composition that's not very pure, i.e., not containing a high percentage of alumina. Very high-quality alumina sharpening hones might be 99% alumina, for example. The inexpensive ones might've been made to suit a different purpose other than for sharpening, such as for heat resistance, chemical resistance (lab use). There are inexpensive ceramic 'stirring rods' made for stirring molten metal in lab settings, for example - clearly, extreme heat resistance is the priority there, instead of abrasive properties. Some of those rods also are touted for the ceramic's nonconductivity (electrically), as used for stirring induction-melted metals. Whatever alumina grit might be there, it might not be shaped for cutting steel - many grades of alumina grit are roundish or blocky, and others are more jagged like edged cutting tools. Some inexpensive ceramics can be OK for simple light honing, whether they were made for it or not. But a lot of other inexpensive ones may not function well at all for that purpose. It's basically a toss-up as to what you're getting and what it'll do as compared to your expectations.
- If you're not sure what the original design purpose was, for the rods you're resurfacing...
- And you're seeing they're not aggressive at metal removal, even as coarse as they seem to be...
It may just be that the rods are of a composition that's not very pure, i.e., not containing a high percentage of alumina. Very high-quality alumina sharpening hones might be 99% alumina, for example. The inexpensive ones might've been made to suit a different purpose other than for sharpening, such as for heat resistance, chemical resistance (lab use). There are inexpensive ceramic 'stirring rods' made for stirring molten metal in lab settings, for example - clearly, extreme heat resistance is the priority there, instead of abrasive properties. Some of those rods also are touted for the ceramic's nonconductivity (electrically), as used for stirring induction-melted metals. Whatever alumina grit might be there, it might not be shaped for cutting steel - many grades of alumina grit are roundish or blocky, and others are more jagged like edged cutting tools. Some inexpensive ceramics can be OK for simple light honing, whether they were made for it or not. But a lot of other inexpensive ones may not function well at all for that purpose. It's basically a toss-up as to what you're getting and what it'll do as compared to your expectations.
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I think that is exactly the root of the problem since the round rod and flat diamond block to not fit well! What is the automotive sandpaper? Is it diamond based? Where to get some? I used before Silicon Carbide sandpaper on the same rods and it just made them very smooth and bold. Before the treatment the grit was not aggressive and too coarse but after the SiC paper it became close to a glass surface and the result was very disappointing.
The rods were definitely not designed as sharpeners but so hard that they easily scratch glass, steel etc. If I could figure out how to condition them to become abrasive they may be very useful.
David,
As always your answers are very informative. Could you please help me to resolve my misconception about sintered ceramic structure. I may understand that before baking the alumina grit may play a role but after the stone became blunt and was resurfaces it seems to me that the grit does not play a role any more since during the baking the ceramic particles became melted together and diamond abrasive rather cuts through the body of ceramic mass than breaks away grains like in vitrified stones.
I was looking at websites of different ceramic manufacturers and it looks like 99% and higher purity is not hard to get and still is very cheap. At the same time hardness if alumina is the same for a wide range of purity (look at https://www.insaco.com/designers-guide/)
One of the reasons I am trying to experiment with ceramic tiles machining is that I am trying to make a specific size stone to fit my sharpening tool with I did for myself. My theory is that if I can get reasonably suitable tile (porcelain or ceramic whatever is better) I can cut a piece with a diamond saw and then to flatten the back side.
I am not concern about seeing the ceramic swarf coming off the rod as with the results. I did not see any abrasiveness on the rod. It seems that the diamond block (I also used Harbor Fright one) did not scratch the rod at all at the first glance.
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The grit in the rod can vary in so many ways. Assuming it is alumina, even that by itself can vary in its percentage of the total makeup, shape, toughness (resistance to fracture), friability (how easily it breaks down to smaller pieces), etc. Any of those factors can be engineered to either emphasize certain traits or to minimize them, to suit specific end-use needs - including prioritizing low cost. A grit intended for sharpening, specifically, would then be engineered for shape (sharp edges), hardness and toughness (for strength in holding its cutting edge shape, resistance to fracture and for longer-term durability). The fact you're not seeing much abrasiveness in the result, no matter what you've tried with it, suggests that either the shape, hardness, toughness or friability, or any combination of those factors, are affecting the result. Whatever new crisp cutting edges might be created by resurfacing may not be strong enough, not tough enough or just too friable to hold up and maintain a crisp cutting edge for abrading the steel, or abrading as aggressively as you might expect.
And as mentioned before, even high-quality sintered ceramic may not respond so well to abrasive sanding anyway. SiC sandpaper was mentioned - I've tried that on known quality sharpening hones (like Lansky, Spyderco and Fallkniven) with the results you saw, with the surface becoming overly polished & glassy and losing a lot of aggression in how it cuts the steel. The friability of SiC grit in particular, as used with sandpaper, means it will break down to much smaller grit size very quickly - this is a known limitation with SiC wet/dry paper. And because it breaks down so fast, its finished result will ALWAYS trend toward more polished, the longer a piece of it is used - the paper needs to be replaced frequently to maintain the same level of sanding aggression. And even diamond itself needs to be very coarse in relation to the target grit performance of the result, or it will also tend to make the result too polished with a big loss in aggression (I've tried this too).
And as mentioned before, even high-quality sintered ceramic may not respond so well to abrasive sanding anyway. SiC sandpaper was mentioned - I've tried that on known quality sharpening hones (like Lansky, Spyderco and Fallkniven) with the results you saw, with the surface becoming overly polished & glassy and losing a lot of aggression in how it cuts the steel. The friability of SiC grit in particular, as used with sandpaper, means it will break down to much smaller grit size very quickly - this is a known limitation with SiC wet/dry paper. And because it breaks down so fast, its finished result will ALWAYS trend toward more polished, the longer a piece of it is used - the paper needs to be replaced frequently to maintain the same level of sanding aggression. And even diamond itself needs to be very coarse in relation to the target grit performance of the result, or it will also tend to make the result too polished with a big loss in aggression (I've tried this too).
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It would be a great idea unless we consider the fact that I have two rods of Sharpal brand ( highly recommend since it is really aggressive and at the same time rated at 3000 grit) as well as several sticks if Idahone replacement sticks in both medium and fine. But the most important buying rods eliminates fun of this hobby. Frankly saying I can send my knives for sharpening but again - what would I do in the free time? My wife complains that our knives too sharp and I have hard time chasing around the house to find another knife which needs sharpening LOL.
I am trying to learn where I can harvest right type if ceramic material and how to treat it to convert to sharpening stone. For my specific liking I prefer longer stones and I am thinking on cutting a piece of a tile 12" long to resurface it to become a sharpening stone. For now I am using my rods to do the honing of kitchen knives but something tells me that a flat stone can do a better job that a rounded rod.
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For what it's worth - just throwing this in for consideration...
For me, a flat 8" x 2" medium-grit stone (320-400 range - compare to a Norton India Fine stone) is more useful for first setting new edges on kitchen knives - all that extra surface area on the stone, along with the appropriate grit size, made of the right abrasive material for the work, speeds up the grinding. Once that's done though, I use rods like honing steels or triangular ceramics to touch them up. Takes maybe 5 passes or less per side on something like a Spyderco Sharpmaker's triangular rod (1/2" x 7") - I use the corners of the rod for that. I also have a smaller Lanksy triangular ceramic that I sometimes use in that capacity and it works very well (and for maybe $10 - $15 spent, at that). After an edge is set to good geometry and fully apexed, a small but effective ceramic hone is perfectly proportional to the small amount of touch-up work needed to maintain that edge. A large stone with lots of surface area isn't really needed for such light work.
Chances are, even a large piece of ceramic floor tile isn't going to grind a new edge very quickly - and some tiles might have trouble cutting cutlery steel at all. This perspective is just based on the things I've tried with improvised 'stones' like that, in ceramic floor tiles or kitchen tiles for countertops and such. And the grinding limitations are almost entirely about the composition of the tile, and less about the size or the surface prep. If the material itself struggles to cut the steel, it creates other issues like extremely heavy burring and also limits how refined an edge can be made using them. This differs from high-quality ceramics made for sharpening, in that the good ones will cut the steel much, much more cleanly without burring issues and take an edge to a much higher level of refinement.
It's fun to try these things out to see what works and maybe figure out where an improvised tool might fit in a larger sharpening scheme. For the most part, such tools will be limited to use as burnishers or aligners of edges that're already relatively sharp. And they'll sometimes abrade a little bit of steel away for some refinement. But in the end, if you're looking to get the job done more efficiently, and with likely better results, you'll always do better with a stone that was actually engineered for the job. Using a material that wasn't engineered with sharpening steel in mind, and trying to convert it for use as such, will usually be disappointing.
David, I use 90% the same technique which you just described. The main difference is that I use Crystolon instead of India. I made a DYI machine specifically designed to use a full size stone to set the the edge and I I set it at 10.5 degrees per side. I use a ceramic steel style rod to set the final micro bevel. This there the problem starts. I can not come up with an elegant way to make a convenient set up to use the rod in a machine. However, if I use free hand rod sharpening I am getting a convex edge which will require an angle setting in a machine every two weeks. on the other hand I discovered that if I use a machine two very light passes set the mini bevel what after a loaded paper strop the knife is getting tomato sharp again. I cook a lot and with my experience I found that after about 30 minutes of curing and chopping a knife needs a touch up to keep it in the shape as I like it to be. I made a mini jig to keep it handy in my kitchen but I can not figure out the right way to set a rod to provide an exact angle and been convenient to use. I do not know if all what I said here makes sense to you guys but I think if I can get a proper strip of flat ceramic in about 2000 grit it can completely conclude my sharpening cycle. All those ideas are not urgent or too important since I can my knives to a working shape, all I am trying to do is to make the process more elegant. If finding a proper ceramic material or machining it to a proper grit, aggressiveness and flatness will prove to be too challenging I will simply continue to use my favorite ceramic steel free hand.
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For a microbevel like you describe, I've just done maybe one or two extremely light passes per side on the corner of a triangular ceramic rod. In the case of the Spyderco Sharpmaker ceramics I use, I do use them in the Sharpmaker's base - usually at the 40° setting (20° per side), but occasionally at the narrower 30° (15° per side) setting for edges I've set at narrower geometry (like 25° inclusive or lower). Doing it that way in an absolute minimum of passes, it negates any significant issues with convexing at the apex and the edge will stay much crisper. It's just enough to make the apex narrower, stronger and more stable without any noticeable rounding-off issues at the edge. The more passes it takes to make a microbevel, the trickier it gets to do it cleanly when done freehand. I sometimes do the same with a small Lansky triangular ceramic - but I use that one held in one hand while honing the edge with the other hand. Done that way, I usually try to keep the number of passes at just one per side to minimize any deviation in held angle.