sharpening stone properties?

[sumu]

Hello,

Could anyone tell me what is the density of a typical synthetic sharpening stone, like Shapton? Dry and/or wet state density would be nice to know.

Then, are those stones sintered/vitrified or just having some binder to hold them grains together? If there is just some binder, what could it be? It needs to be very low viscosity type for sure.

The reason why I ask this that last weekend I got custody of some sample sacks of classified alumina powers of different types. There is 20 micron, 0,9 micron and 0,2 micron size the smallest. I tried them out as a water slurry on my small granite plates during weekend and they worked quite well, much better than I expected.

Therefore I wonder whether it would be be possible to make some shaped sharpening stones for hollow gouges and other such edges. There might be enough stuff for a full-sized Tormek wet grinder wheel as well, but I think my hand operated jack press is not up to that big squeeze. But maybe a stone of a size of a cigarette box could be done.

Any hints and tips are greatly appreciated :-.

kippis,

sumu

[kman-oz]

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?

[sumu]

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/Industrial%20Products/Alumina.htm
http://www.bladeforums.com/forums/showthread.php?t=370470

kippis,

sumu

[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

[obee60]

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

[sumu]

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

[obee60]

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

[sumu]

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 :D. You must have your own nuclear power plant in your backyard, then.

kippis,

sumu

[obee60]

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:U

[Clinton1]

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.

[kman-oz]

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 :) :2tsup:

[sumu]

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 :-




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 :D.

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 :wink:.

kippis,

sumu

[kman-oz]

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 :)

[Clinton1]

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?

[sumu]

Damn, Clinton and Kman, you are both true W.E. Coyotes! :2tsup:

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 :? :doh:). 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? :2tsup:

kippis,

sumu

[kman-oz]

...you are both true W.E. Coyotes! :2tsup:

I think Super Genius might be over stating things slightly, but I didn't get the 'Master of the Obvious' title for nothing either :D

[Pusser]

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 :-
...


Your English is better than our Finnish!:2tsup:

[sumu]

Thanks Pusser, what a relief :D.

I have decided to improve my lingo hard way, I do not have extra time to attend some classes. And anyway I like to talk with real people about woodworking. By hopping into some native environment and trying to manage there, I wish I would improve my small talk routines. It's a bit tough but refreshing, too. I do not mind to get a bit bruised during the learning experience, for me this is the fastest and most effective way to get in.

This morning I found a piece of thick steel I could use as a mold frame. There is enough of it to make a piston, too. I yet need to find some suitable bottom plate as well, so it seems to be that soon I have a new compression mold :).

kippis,

sumu

[sumu]

Hello,

Things have progressed pretty slowly, but now I have finished the mold and lid.

I was talking with my pal here and he was also interested in taking part of the effort. The original plan changed such that there is now a compression mold having cavity of 330mm x 195mm x 40 mm, and lid with a 16mm deep piston.

The design is aimed to produce one or two stone billets per day, but large-sized product makes two or three separate stones when cutted in half with a wet diamond tile cutter.

It is a cheap mold, made from scrap steel. These kind of molds do not take high pressures, and are not suitable for molding something easily flowing. The structure of the mold has multitude of division surfaces, so pressure will leak out with those materials. But now, when the compound is very stff and not practically flowing but only compacting, it will work. I iterated that I should not exceed mold pressures of 25 MPa, otherwise it would collapse and deform too much. I think that need about 5-15, so it should be good. My shop press is now too weak, so it's used with a 50 ton hydraulic shop press.

It has dismountable frame attached to bottom plate with countersunk bolts. I can dismantle the frame around the product to ensure it's safe removal off the mold. I would guess it's enough if I take off two or three sides of the frame.

The lid has a deck plate and a piston plate, fitting snugly in the frame.

There is a couple of features I would like to highlight. At first, there is extra threaded holes in the edges of the lid deck. The lid will be hard to remove without some kind of method to pull it up, so I ended up using the simplest alternative there is, which are pulling bolts. Supported against the mold frame they should be powerful enough to pull the lid off the mold even when some material had been found it's way between the frame and the piston. I could start opening the mold by dismantling the frame from the mold bottom plate directly, but I think it might be more convenient if the lid is readily removed off the way.

The other feature is in the piston itself. There is four teflon ejectors providing some extra assistance if the piece gets stuck at the piston surface. The cavity bottom will have a release film, but after playing with bringing compound into mold with different methods, I found out that closing the mold might work better if I used just liquid releasing agent preapplied on the piston surface. But if the release agent fails but only some, there is still a change to get the stone off the lid in one piece. The ejectors work in a very simple way, there is just headless allen screws behind the teflon discs.

The mold needs an insert plate or two to reduce the depth of the mold.
In that condition, it makes a billet of 24mm of minimum thickness. I was thinking that about 15mm thickness would be adequate at first, but if things go well and also if I get some more of the powder ceramics of different types, thicker stones would be done, too.

I am going to try out making shaped stones. At first there would be a plastic insert plate (made of POM, for example) where I could mill some hollows and rounds with a router. Might work, don't know yet.

I do not know now, but after reading Jake's article of sharpening blades of moulding planes, it seems to be difficult to do such a thing with just one shaped stone. You would need at least two for different projections, to overcome the clearance problem for sufficient bevel formation. Simpler shapes can be sharpened with one designated stone you can make by yourself.

I'll keep you updated. The aluminium stirrer and it's working parameters in compound making are next in line.

kippis,

sumu

[kman-oz]

Looks like you're getting veru serious about this stuff sumu. When you get some serious product happening you're more than welcome to ship some to me for 'review' if you like :D

[sumu]

Hello kman,


Looks like you're getting veru serious about this stuff sumu. When you get some serious product happening you're more than welcome to ship some to me for 'review' if you like :D

"If p then q", said the old mathematician when standing in queue to the toilet :).

There seems to be quite a line of guys hereabouts intending to have some, so right now I really can't promise anything, sorry :-.

I placed a request to some ceramics suppliers to get some finer and classified abrasive powders. They are making these materials all the time with large air classifier equipment, and the quality is uniform. I wish to receive at least alpha-aluminas of different sizes. I went for 5-15 kilo sample bags.

Anyway, it's just a good start so far. But it seems to get a bit hairy to receive uniform dispersion and compaction for highly filled resin-powder compounds. According to the test compounding experiments, a single impeller mixer providing not much shear is capable to make a dispersion only up to some preliminary level. Premixing this way helps there that the powder dust does not especially puff away that much, but it seems to be that from now on, it must be continued with some other feasible method.

There is so many types of resins, too. I start to think this is going to a bit artistic, so to speak :D.

kippis,

sumu

[kman-oz]

There seems to be quite a line of guys hereabouts intending to have some

Oh, I'm sure there is. :p

I see you becoming the resident Stone Master around here sumu, I wait on the edge of my seat for your next installment:brava

[sumu]

I see you becoming the resident Stone Master around here sumu, I wait on the edge of my seat for your next installment:brava

Waaah!

:)

kippis,

sumu

[sumu]

Right.

I had a chance to make one trial compound today after hours at work. It did not went too well product-wise, but I had some good experiences to be shared.

One thing is now certain: apply any plain metallic mixing head in the powder-resin compound and it will stain the compound right away. The result resembles badly faked Carrara marble :p .

Kman, first of all I'm sorry I do not have pics on the aluminium mixer head, nor Clinton1's suggestion to make a mixer using the compound itself, that one broke down after a few turns, also the coating did not attach the walls properly but flaked off. That was my bad, the primer layer did not work too well.

About the mixing trial: I really did precise calculations for the different vol% ratios for this one trial. I decided to go for higher epoxy ratio to get more better flowing compound, just to see how it would work out. I thought I could return back to original higher fill rate compound after seeing this.

I started with 20 vol% of epoxy resin, and mixed that for a while. There appeared kinda smaller spherical epoxy-alumina clusters within more powderous phase at first, in the same way as in those previous tests. Then I went for 30%, the cluster amount increased and also the maximum size increased, but there were still seemingly powder phase left. It did not dust anymore, so I could do the mixing without lid.

Ok, adding 40 vol% made quite big clusters about the size of finger tip, but still freely rolling in the container and following the impeller rotation. I added 50 vol% and suddenly the cluster spheres consolidated together in a one big heavy chunk banging around in a container, and starting to sweat epoxy.

It's quite a wild feeling, to hold a 4 liter container freehand wherein bounces around about 2,5 kilos of compound trying to follow a mixer head rotating 350 rpm, all this powered by a serious post drill. Ok, time to stop this stage :D.

It formed a big and really stiff chunk of compound I had to take out to the worktable over a plastic film. The compound looked quite bad, there were dark stains all over the chunk when I parted it into pieces. It also sweated epoxy where ever in it I pushed my finger, making the fingerprint moist.

When the impeller had started to spank the chunk around, it finally started to densify it, too. As long as there had been some drier powder portion in the container, it gathered kinda filler-rich release layer on top of the clusters and they "flowed" and followed the rotating mixer. But when it ran out due to just suddenly added-up extra epoxy, it all clogged together. Then the impeller really had a chance to beat the epoxy out of it.

Now when it was a big chunk parted into smaller but as stiff chunks, there were no way how to dissolve those to get some workable dough. With some time it would have been possible, but epoxy was coming to the end of pot life and I had to chop them in as small pieces as I could and stuff them in the mold.

I closed the mold and placed it between heated (100C) plates of hydraulic press, gave 10 tons of squeeze and watched when a lot (but not even the most of ) excess resin just spilled out, carrying some alumina powder making it white. Well, it stopped when starting gelling, and I waited when the resin seemed to be cured, and took the mold off.

Like said, it was proven that this mold does not suit with too liquid phases. Also what was proven that despite one may think that when excess epoxy flows out, it would not homogenize the stuff too and join pieces of compound together seamlessy. First of all, all excess epoxy does not leave the mold. 2nd, no composite homongenizes in a mold only under compression, it really has to be mixed in a evenly distributed dispersion before compacting it.

These lower and higher fill rate regions can be easily seen from the product. The epoxy rich regions are also more shrunken, making stone surface pitted and dimpled. Those can be worked out by intensive truing, but it'll be a serious bout.

What also happened was that the release film attached with these regions very hard. I used this thin polyimide film because it had very nice surface. There probably is a worse choice, but not much, I believe :D. Despite is takes almost 400C heat, it seems to like cured epoxy resins quite much.

I do not know how much there is porosity in a cured stone, but I would think not much. The density implies to about 54 vol% of alumina, 46vol% epoxy. But like seen in the (lousy) pictures, it has fangs and taste for both carbon steel and chrome-vanadium alloyed tool steel.

The stripes are again just single pulls per each, and when I get those surfaces trued, I would think they'll be quite effective. The powder is just 0,9 micron sized, and it makes that special minor slurry with both water and cutting oil. It polishes aggressively although not so soft any more, and you can now also push the edge.

According to The Order of Sharpening, these would do well as the second last stones, preparing the way for 0,5micron or smaller particles for razors.

For DIY home compounding, my guesses at the moment are as follows:

If wished to make harder stone with more resin, start to mix powder to larger amount of epoxy, adding powder gradually up to 40...60 vol%. I have not tried it yet, but I believe that could be done just like people make bread dough. It could turn out that you could really make it as kinda thick dough, and with the aid of spacer rails for even thickness layer, you could use rolling pin or some round smooth tube (plastic film in between) and roll the dough on some smooth surface treated with a release agent. No need for actual compression mold, really, just some kind of open frame to be filled with thick compound and rolled flat and cured. Could work, I'm going to try it out anyway.

If wanted to make softer stone with less resin, mix it with power mixer (maybe with a plastic-coated impeller in a plastic container) and add the resin a bit by bit. You'll get compound resembling almost powder but without dust puffing. Here you would need a real compression mold.

For both purposes, you need to prepare premixed resin-hardener system where pot life at room temperature is long, at least hours. All kinds of mechanical or hand mixing methods will bring heat into compounding process and therefore shorten the potlife.

Basically you can use any chemically inert enough ceramic powder you want, it just needs to be dry enough (enough free of water), too.

Fellas, this is getting too interesting :2tsup:.

kippis,

sumu

[sumu]

Hello,

Time to get this issue updated. (BTW, one (or actually two) of the fine grit alumina stones is about to set sails towards Oz. :wink: )

Here is a couple of pics about soapstone-epoxy stones I made. I got a bag of soapstone powder. Had to play with it, of course :) . The main reason why I made these was to practice mold filling and compacting. These are now pretty good in uniform quality.

These are containing 35 vol% of epoxy and 65 vol% of soapstone powder, making them kinda softish dense and slippery. They are not that effective as the previously presented fine alumina stone is, but are a bit better than natural soapstone is.

The other soapstone has seen some use, the other is not used. These work reasonably with hardened carbon steels and give adequate edge in the end, but are much slower than alumina stones. These stones are also clearly waterstones.

I the pics there is also the current state of the previously reported alumina stone (the dirty white one). I have just used it, and the dirty slurry is still on it. The higher and not so uniformly dispersed epoxy content tends to make it clog a bit, but the surface can be easily renewed with wiping it with mild acidic solution. I am very happy with it's performance.

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I wish to make a wet grinder wheel for my Tormek using soapstone powder. For that I need to finish the wheel mold I have started to work with.

Kippis,

sumu

[sumu]

I'll add up a mixing chart. The calculated ratios are based on the values in materials data sheets.

The purpose of that picture is to suggest some kind of preliminary guideline for the mixing ratios of binder and abrasive powder, in this case especially for high density alumina powder and low-density epoxy system (resin and hardener were mixed before epoxy mixing with alumina). Weight ratios will of course differ if for example alumina is replaced with lower density silicon carbide.

Also that particular epoxy system is by no means any essentially vital choice for binder matrix, not at all. It is just one of the many very low viscosity laminating epoxies having generously long pot life option, so that there is window for compound processing, mold filling, cleaning up the mess etc.

Lower amount of binder means softer stone. Again, stone hardness is yet another matter of taste or application. For me, I have found out for example that 60 micron grit works pretty nicely with 40 vol% of epoxy, 10 micron grit feels good with 30-40 vol% of epoxy and 0.9 micron has been at least interesting with all studied ratios.

Kippis,

sumu

[sumu]

For the 3rd post today in this thread: my updated gear, main methods and some footnotes.

In the 1st pic there is a kitchen utensil called Electrolux Assistant. I picked it up from a flea market. It had some timer switch problem which I fixed just by bypassing it. The speed dial switch is working well, and I'm usually running the device from 2/3 to full speed. This mixer takes and processes about 2 kilo batch at a time if the compound stays free flowing, i.e. has not too high resin content.

It has those twin planetary geared rotating eggbeater style mixer heads which have been better than a single eggbeater head with a vertical post drill. The advantage is mainly in two things:

1. The mixing process is faster because those mixer heads are sweeping almost the entire volume of the bowl while orbiting around the center axle. If the compound starts layering on the bowl walls, I can pat the walls from outside and the layer drops back to the beaters.

2. I can cover the entire bowl and mixer head with a transparent plastic film and tie it with a duct tape. The mixer gearbox protrudes a bit above the bowl edges but it does not matter at all, just let it rub against the film while running.

There is downsides as well. The main problem is that the device is not very powerful. It can be used efficiently with such compounds where resin content is less than 40-45 vol%. If you put that much resin that the entire batch consolidates as a one big chunk, this machine does not tackle it anymore. The compound should remain kinda loose and dryish.

A minor problem is that the beaters do not sweep completely against the bottom of the bowl. I need to stop it at least once after a few minutes (when it has stopped to blow dust), take the mixer head off and scoop the bottom of the bowl with a spatula, kinda turn the compound upside down in the bowl (I'm sorry about my bad english). Then I can attach the mixer head and continue mixing.

Mixing stage lasts usually from about 10 minutes for coarse grit to 15 to 25 minutes for fine grit. Mixing itself causes friction which generates heat in the compound, so it is something to look after. Extra heat shortens the pot life of epoxy but makes the resin viscosity a bit lower as well. With slow hardeners there has been no visible problems with this issue.

Another but minor heating problem might arise with longer mixing sessions when the motor heat is warming up the bowl a bit.

Beater wires have worn some during these sessions, although less than I expected. It seems to be that during mixing there forms a densified and pretty ductile layer of compound covering the wire rake sides, and it looks like it protects the beaters up to some point.

In the 2nd pic I have poured the dryish compound in the mold. This compound has 35 vol% of epoxy. The mold has extra spacer plates on the bottom to decrease the cavity volume down to 15 mm slab thickness when the mold is closed and compressed.

In the 3rd pic I have sleeked the compound with that "doctor blade" in the upper corner. It is made of aluminium. Those cutoffs are supporting against mold edges, and I can slide the doctor blade along the mold. Cutoffs give to the blade about 10mm of depth, so there is 6mm compression travel distance left for the piston of the lid.

The doctor blade should sweep the compound layer surface very carefully. Also while sleeking, the blade should be held in vertical position. If it is in angle while sweeping, the compound layer becomes thicker. There should be no high spots anywhere, not even near the mould edges. I learned this hard way.

In the 4th pic I have placed a piece of PET (polyethylene tereftalate, one of the many polyester plastics) transparent film on top of the compound. You can use printer or copying machine transparents. The film is pretty necessary for two things:

1. It is a foolproof release film. It must be used on both sides of the slab, against the mold bottom and against the lid. Now despite PET can adhere with epoxy quite well especially under compression, you can peel it off the slab quite easily. While peeling, it takes along the thin but tough epoxy skin with the very top layer of the stone.

2. If there is small scratches on the mold surfaces, the existence of this film kinda smoothens them. Very small scratches leave no mark on the slab through the PET film.

You still need to wax the entire mold, it helps a lot in keeping it clean. Remember also that waxed steel molds are quite slippery. Some kind of toe reinforced shoes are a must if working with such things.

In the 5th pic there is the finished slab. It can be cutted into suitable sizes with wet diamond wheel table cutter quite easily. Further shaping of these stones can be done with belt sander, just take care there is a decent dust extraction at hand.


Allright, this is where I have ended up so far. Next I am going to make some shaped stones for chisel gouges and molding planes, and the Tormek wheel mold is also waiting to be finished.

kippis,

sumu