Thread: sharpening stone properties?

I remember seing someone else using these in a wax based crayon style honing compound then applying it to shaped timber for sharpening. Might be a lot simpler and more efficient perhaps?

Hello Kman,

Yes, a portion of powders will be mixed in some suitable soft wax binder, to be used with felt wheels. I did a small survey, and those true PCM-waxes could be one possible candidates, like those paraffins offered by Rubitherm GmbH here: http://www.rubitherm.com/english/index.htm They might yield a bit hard wax compound when combined with powders, so it is possible that some liquid paraffin should be added to soften the end product.

Plain water slurry seems to dry out a bit too easy to maintain it's consistency. Basic machinist's cutting fluid is better. I haven't tried dishwashing medium in a water solution yet, but with 0,2 micron particles, I think there is need for some kind of surfactant.

But I think it would be fun to check out making hard stones as well. I have some edge tools working seemingly better if there is no significant microbevel. I think wooden substrate might be too soft especially when wax softens it up even more. Smooth and round steel bar works better, you can make them into specific radius with a metal lathe. But still I'd like to try out making hard stones as well. My wife uses that kind of no-microbevel edges when cutting leather, rubber, weaves, felts and cardboard templates for her textile hobbies. Those are often homemade HSS tools, small knives and such. Some are made of quite hard tempered M42 and my wife likes to use them.

The main problems are still the resin binder type and fill rate. I would like to make as educated guess as possible beforehand. I think I can mix them evenly although if it appeared to be very low volume content of resin. There is some open porosity needed in the stone (to ensure particle release and to maintain some amount of fluid) , so it will not need ultra-high compression pressures. Therefore a quite lightweight and simple aluminium mold could work, just for making a few stones. I mean, it can't be too complicated when making single stones. Mass production is probably something else, process tools wear rate and quality control of raw materials and end product must be a drag sometimes.

By the way, I found some info on alumina powders and sharpening stones. Might be useful .

http://www.metallographic.com/Indust...ts/Alumina.htm
http://www.bladeforums.com/forums/sh...d.php?t=370470

kippis,

sumu

Hello,

I made one test slab using 0,9 micron alumina particles and low viscosity epoxy system. The unfortunate thing in this project is that I do not know the brand or manufacturer of this lot of alumina powder. There were only the result report of particle size distribution measurements.

I made a simple aluminium frame mould of 120 mm x 60 mm x 30mm (depth) with detachable bottom (screws) and with a tight fit compressive piston (30 mm depth, explained later) lid, cutted and placed suitable pieces of a potato chip package, one in the bottom of the mould and one to be placed between the piston and the cake in the mould.

I mixed about 80 vol% of alumina and 20 vol% of premixed epoxy system in a plastic cup with a rigid steel spatula. The epoxy was SP Prime 20 LV, + Slow Hardener, resin and hardener mixed together right before mixing with alumina.

I started at first with a 10 vol% of epoxy, but it seemed to be impossible with these methods, so I had to increase the amount of epoxy up to 20 vol%. I wore a long raincoat, dust mask, rubber gloves and glasses all the time. I'd say protection is now a must, these are nano-sized particles I was messing with.

In the beginning, I had to turn the spatula in a cup very carefully, otherwise it blew a cloud right against my face. But after a 15-20 minutes or so, it started to wet enough so there were no intense dust clouds anymore. The mixed compound looked like the same as slightly wet clay, not really flowing anywhere but if pushed with a fingertip, you could kinda smoothen the touchpoint as with slightly wet clay.

I applied the compound in the mold, filling the cavity evenly and calandering the top as smooth surface. Then I closed it with a piston lid and used my shop jack press to compress the cake. I used about 5 tons of the press capacity, making about 7 MPa, or 70 bar pressure level in the mould. (There is really no precise info on actual mould pressure, because the compound was of really poorly flowing type. There might have been uneven pressure distribution just because of that feature. If the stone suddenly cracks especially during soaking in honing fluid, it would be an evidence of such a thing.)

I left the mold there under pressure for overnight. Next morning I placed the yet unopened mold in the heating cabinet at 80 C for 6 hours.

When removing the bottom plate of mould, the piston movement is long enough (30mm) to push it out of the mould frame. The pressure is evenly distributed and the hardened slab will not break during removal. It just slides out from the frame and drops off easily, because there is that piece of potato chip bag as releasing film.

The result is in the pics (sorry again about their poor quality). Like said, the actual slab was twice as big. I cutted it in half, and this one is tested with water. The other half will be tested with cutting oil.

In the second pic, there is just two laps of that 16mm berg chisel (hardened carbon steel), the first one is just one straight pull and the other is that curved one. No overlapping pulls, just two single pulls. I pressed the edge against the stone firmly, but not particulary strongly.

This artificial stone is very soft. It seems to dent easily if the edge digs in. Therefore I have been testing it as pulling the blades like done with a strop, or like in side-sharpening manner by hand.

There seems to be minor formation of actual slurry. I assume the releasing single particles and particle agglomerates are sinking soon back in the stone surface with the steel debris they are carrying. The steel debris seems to be tacking slightly, but comes off clean and rapidly when reconditioning the stone surface on glass plate, using almost invisible layer of water-alumina mixture I made and reserved for this purpose.

Because I have very limited experience on waterstones, I must ask if this kind of result was expectable? Despite it's quite fine texture regarding particle size and dispersion, it seems to hog out hardened steel like some etch. I am slightly amazed, but like said, I have no previous experience on these kind of stones whatsoever .

I do not know what I have here, but it seems to polish hardened carbon steels and tool steels very quickly. It makes a sharp edge, but I feel I have no such control over it as with diamond stones, scary mirka or with buffing wheels. Whatever you guys might have to say about this, any comments and critics will help and are welcome.

kippis,

sumu

That's interesting Suma. When you talk about alumina, are you refering to the powder produced from bauxite and used to manufacture aluminium?

I ask because I work in the aluminium smelting industry and we have no end of problems with the abrasive nature of alumina cutting through the pipes in our dense phase systems.
Cheers.......obee

Hello obee60,

I am here using the term "alumina" in nominating aluminium oxide.

I am not any kind of professional in ceramics manufacturing processes, but according to the (a bit vague) information I received with the lot, I believe this particular alumina is calcined alumina formed at very high temperatures, like over 700 C for gamma-alumina or so.

Below that temperature level, I have understood that aluminium hydroxides and other aluminium compounds are relatively soft and non-abrasive by nature. I would think aluminium extrusion or molding processes do not require that high process temps where aluminium hydroxide would be freed of crystalline water completely, or am I right?

Whether it is gamma-alumina or delta-alumina or alpha-alumina, unfortunately I do not really know that. I hope it is stabilized alpha-alumina, because then it would not form back to softer hydroxides very rapidly when coming in contact with water and mechanical rubbing.

So far seems to work, though .

kippis,

sumu

sumu, some interesting facts on alumina, as used for aluminium manufacturing process.
Alumina (aluminium oxide, or Al2O3) is a white powder produced from bauxite ores (iron alumino silicate). As pure alumina, it contains 52.9 per cent aluminium. About 90 per cent of world production is as raw material for the manufacture of aluminium with the balance used to produce aluminium chemicals.

In 2000, Australia mined 50 million tonnes of bauxite to produce 15 million tonnes of alumina representing 32 per cent of world production of which 80 per cent was exported. World production in 2000 was 48million tonnes projected to increase to 83.5 million tonnes in 2020.
Electricity consumption for alumina is around 260kWh per tonne implying a cost of 8 per cent of market value. For aluminium metal, requiring 14 000kWh per tonne (say 140 gigajoules of gas per tonne), the cost is around 45 per cent.
Alumina can also be used to prepare special calcines that may include low soda (0.2%Na2O) and high surface area (50m2/gm) for specialist applications such as insulators for batteries.
Fused alumina is a granular material with a melting point of around 2 500°C and a hardness of 9 on the Mohs scale. It is used in a range of refractory bricks and monoliths and as abbrasive.
I work for Portland Aluminium. We produce approx 350,000T of hight grade aluminium ingot per annum, all exported.
Cheers......obee

Hello obee60, thanks about that information flash .

Unbelieveable amount of electricity needed to prepare a tonne of aluminium metal, no wonder they like to recycle beer cans and used up fighter planes back into circulation.

14 000 kWh x 350 000 T makes quite a big spark . You must have your own nuclear power plant in your backyard, then.

kippis,

sumu

Suma,
The amount of power we use is staggering. We run approx 320,000 amps at around 7 volts.
We've got 408 pots and when we bring a new pot (refurbished) online, we use aluminium plates approx 1" thick as a fuse. When power is applied it cuts straight through the plate. It sounds and looks like a lightning strike. I've seen a number of people lose their balance if they aren't expecting it.

Yes we are probably greedy power users, but I guess when you weigh that against us being the state of Victoria's largest exporter and a major employer in the region - it helps justify the power usage.
We are also benchmark around the world for power use efficiency and emissions.

obee

Sumu,
Thats very interesting and I'll re-read your posts and try to get my head around it.
A great experiment... looking forward to seeing you progress this.

Originally Posted by sumu

This artificial stone is very soft. It seems to dent easily if the edge digs in. ...

There seems to be minor formation of actual slurry. ...

Because I have very limited experience on waterstones, I must ask if this kind of result was expectable? Despite it's quite fine texture regarding particle size and dispersion, it seems to hog out hardened steel like some etch. I am slightly amazed, but like said, I have no previous experience on these kind of stones whatsoever .

I do not know what I have here, but it seems to polish hardened carbon steels and tool steels very quickly. It makes a sharp edge, but I feel I have no such control over it as with diamond stones, scary mirka or with buffing wheels. Whatever you guys might have to say about this, any comments and critics will help and are welcome.

Sounds to me like you've produced a very soft fast cutting stone, sounds very interesting! The second pic tends to support this thinking in that a) the stones surfaces may deform slightly to match the bevel face, and b) the loose binding is allowing good slurry formation and exposure of new cutting particles.

The typical hardness is one of the things I don't like about fine water stones. Firstly it's very difficult to get sufficient water penetration to act as an on-going lubricant and the stone gets blocked up easily, and secondly the very fine binding makes it easy to get your tool stuck on the surface.

A loosley bound stone like this might be really handy, the downside is the wear rate and flattening required. If you have a fair amount of the stuff to play with perhaps try a higher quantity of binder per volume. Too much and it will end up like glass of course, but it sounds to me like you're at the soft end of the scale at the moment.

Great work sumu! I look forward to future results eagerly

Thanks guys

Clinton1, sorry my english is still a bit messy and stumbling, not really up to the things I try to explain there. Please bear with me, I'm trying, really

Originally Posted by kman-oz

The typical hardness is one of the things I don't like about fine water stones. Firstly it's very difficult to get sufficient water penetration to act as an on-going lubricant and the stone gets blocked up easily, and secondly the very fine binding makes it easy to get your tool stuck on the surface.

I have now experienced that smaller water droplets are vanishing off the stone surface much faster than just by via evaporation. So it must take in some water, and therefore it has open surface porosity up to some level.

It kinda clogs in such a way that it collects visible metal residues at least on the very surface. This happens quite immendiately. But, seems to be I can polish that 16 mm wide bevel having about 25 degree bevel angle at least about 4 to 6 times. Then I think I need to recondition the surface.

The surface is blackened by the metal residues after the first polish, but I can keep on going those extra 3 to 5 times without reconditioning the stone surface, so there must be some invisibe microscopic layer of particles still active.

On the other hand, reconditioning is very easy task. I have not experienced yet any significant hollowing of the surface. I think it's behaviour just forces the sharpener to maintain it's flatness.

Like said, for maintaining the flatness I have used the same type of particles on the glass plate with small amount of water. Takes so far about 5 to 10 minutes to clean it up back to reasonable clean surface. It really does not need to be snow white, it works the same way even with still slightly stained surface.

I really wonder if cutting oil will make a difference. I think water may be kinda unable to bind the metal residues so that the residue and the releasing particles would be more loose, and that way oil would extend the reconditioning cycle.

If you have a fair amount of the stuff to play with perhaps try a higher quantity of binder per volume. Too much and it will end up like glass of course, but it sounds to me like you're at the soft end of the scale at the moment.

I believe you are right here. It seems to be even too soft and greedy. If I make a mistake when pulling the edge, there clearly occurs a formation of too steep microbevel. Compared to this, even the bench grinder powered running rigid felt wheel is hard .

For now, I have powder for approximately four different types of compounds, but I have intention to get more of it. I think I need to upgrade the mold as made of steel, too, because it would be just more rigid. I think that 7 MPa mold pressure might be close to the truth, but perhaps a bit higher mold pressure would make more dense stone, too. Let's say the aim is currently at 10-15 MPa for the second manufacturing test. For this, I think I need to somehow ensure better importing of compound in the mold cavity. Like said, it does not flow very well, therefore the mold cavity filling might be an important task, I believe.

But the most difficult task will undoubtly be the mixing stage of binder and powder. Seems to be I can't use even hardened steel mixing heads, those will wear and leave metal residues in the slab. While rusting, steel debris has a nasty tendency to expand greatly, and if there is evenly distributed amount of rusting iron residue inside the stone, it may get a bit fragile just because of this. I mean, it is not sintered, but just cured with a very small quantity of binder. And it's porous, too. Dunno.

I need some kind of mixing head made of either superaustenitic steel (like the spatula was), wear resistant ceramic layer coated mixing tool or made of some wear resistant plastic or rubber. I think that rotor type of mixer, running in the closed lid container could be reasonable low cost method to make compound for one stone at a time. I think I'll use the stationary post drill as mixer engine, then drill a tight fit hole through the lid of a plastic mixing can for the mixing rotor shaft and let it spin there in the compound for a while with additional shaking of the can.

One thing to be considered is the binder type, too. It should be of very low viscosity type, able to wet small alumina particles and strong and tough enough, to produce rigid enough sharpening stone after curing cycle. I believe I can't use epoxy viscosity cutters like xylene or acetone here, it should contain all reactive components. I also want it's pH to become near neutral, also I don not want to use too toxic chemicals.

It would be a real drag if there would exist a requirement for minimum porosity. It would be then a pretty impossible task to accomplish at home shop. But because there is now as an essential requirement to receive a porous slab, all this sounds really feasible . I do not need to worry about air bubbles captured inside because I am not applying especially high mold pressure during compression, and if I come up with a good method of applying compound in the mold, I believe throughout degassing of the cake is not especially needed here.

Still, quite a lot of things to be considered. I wonder what kind of things I have missed here, but if some new problem rears it's ugly head, I'm optimistic I could solve it and get rid of it. That's what I do for a living anyway .

This will take some time now, to make a new steel mold and gathering up some practical info on mixing and binders. I do not want to waste that alumina powder sample, it seems to be powerful stuff.

But I promise to keep you guys updated .

kippis,

sumu

Regarding the mixing tool, I don't see any reason why you can't use aluminium. Aluminium Oxide particles will be abraded from the surface, but so what? Aluminium doesn't expand when it oxidise either.... no problem

Sumu,
I think its my use of English that caused the confusion!
I'm re-reading this as it is fascinating and well outside what I know.

Can the stirrer be made from the resin you use?

Damn, Clinton and Kman, you are both true W.E. Coyotes!

Of course, both solutions will do perfectly, indeed. How I did not come to think of those? ( Eh, and even Obee60 talked about their aluminium smelter, too ). But guys, things are to be solved, not worried about. Yes! Yay!

This made a couple things a lot cheaper and way more available. I have loads of suitable aluminium stock usable as a mixer head. I can make different types to see which one suits the best.

Then I can really make a coating of the same resin filled with some alumina powder in the inner walls of the otherwise suitable steel can I have here. When cured, it will be a wear resistant layer and if abraded, it becomes one with a stone. Anyway it can be cleaned as well with a solvent and it sticks there.

Thanks guys! Greenies, right?

kippis,

sumu