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Making Whetstones

The following was written for The Windrow magazine (and then judiciously edited), of which the March 2016 issue has just been released. Contact Simon Fairlie to subscribe to this very informative publication.

 

For all whetstones, regardless of whether they are synthetic or natural, there are a number of factors that determine, together, how they perform:

  • Size of the particles that make up the stone. Sand, for example, by definition, refers to particles that fall within a size range of 1/16th of a mm to 2mm, so in theory sandstones at either end of this range can be comprised of particles that differ in size by a factor of 32.
  • Shape of the particles. Stones made of particles of similar sizes can differ markedly in whether they behave like a coarse or a fine stone, because of the way the particles are shaped (smooth or sharp).
  • The configuration of the particles. Again, stones made of particles of similar sizes can differ markedly in whether they behave like a coarse or a fine stone, because of the way the particles are ‘clumped’ or not clumped. Particles can be clumped due to some bond between them such that they behave like a larger particle or, as in natural metamorphic stones, they may be partially fused by pressure and/or heat (in which case it becomes a matter of distinction about whether the particle size has actually changed). Most natural whetstones are sedimentary rock, but not all.
  • Hardness of the particles. A particle of diamond 1mm in size will continue to grind steel far longer than a particle of relatively soft sand of the same size. Sand can be comprised of a variety of particles, so one sandstone may have harder particles than another.
  • Strength of the substrate/bond between the particles, or between the clumps of particles. A soft bond will result in fresh particles being exposed faster, so will likely result in a more aggressive cut. A bond that is overly soft will result in the entire stone breaking easily.
  • Consistency/regularity of the composition. For example, a very nice, fine sandstone may be rendered far less useful if it’s peppered with large chunks of quartz.

The interplay between these factors can be confounding. For example, a stone with relatively hard, large particles and a relatively hard bond is likely to give a very aggressive cut for some time, but having a harder bond, the particles may wear down and start to behave far less aggressively as the rough edges of the particles are worn off, while a stone with softer, smaller particles and a soft bond may continue to behave more aggressively than the first stone because fresh, sharp points are continually being applied to the steel. This is why I consider a stone’s “grit” rating – which refers to the particle size alone – to be a rather unhelpful measure for natural stones (as opposed to synthetic stones, where all the factors can be controlled in manufacture, so that it is possible to compare apples to apples). Perhaps a whetstone boffin could create something like a natural whetstone ‘cut rating’ (to supersede ‘grit rating’), which would refer to the effect a stone has (which is what we’re ultimately concerned with) on a standard grade of steel after a standard number of hours, to allow for particle and bond hardness, as well as the size and shape of the particle, to have a role in determining the end result.

In addition to the above factors, there are “wildcards” that can be added into the mix, as occurs in natural Coticule. This stone has garnets in it which will roll around in the slurry to smooth the steel more, which adds a very different kind of finish and also gives a wide variety of aggressiveness depending on whether the stone is used with a thick or thin slurry or none at all. For the purposes of scythe sharpening, though, a slurry is not likely to come into play since most field honing is done quickly.

Finding the stone

So how does one go about choosing a suitable whetstone? My answer is that beyond just looking at it with a loupe and rubbing it with your thumb to see how ‘toothy’ and soft it feels, you can’t, really – you really need to test it over time. Henk Bos gave a simple test which will at least tell you whether your stone has any hope of performing adequately, and that is to try it on the back of a stainless steel spoon – if it marks or polishes the spoon, it’s worth pursuing.

It’s also worth noting that I’m yet to find a sedimentary rock that is completely useless for any honing purpose. Pretty much any sedimentary rock will do something to steel, it’s just a question of what minimum level of effectiveness you are prepared to accept. Even metamorphic stones that can be polished up like marble will do something to steel, if the stone is not polished and left reasonably rough.

This discussion, though, is about financial viability, so the minimum level of effectiveness needs to be quite high. My main issue in stone selection with this in mind was hardness of the bond; any stone that a customer will be happy to pay for needs to be reasonably hard (at least you would expect so – I personally am unimpressed with the durability of the Bregenzer, despite its cutting effectiveness) so that it won’t break or get whittled away too quickly. The first whetstone I made (with an angle grinder and standard masonry cutting wheel) from sandstone sourced on the farm, was a brilliant performer as a coarse stone, except that the stone was removed faster than the steel from the blade, and it ended up simply breaking in half in my hand after some dozen or two dozen uses. This level of softness was typical for most sandstone I was able to find, even after haunting several stonemasons locally and interstate.

hard-shardThe sandstone we eventually located is extremely hard – as can be seen in this picture, it’s possible to mechanically slice off quite thin slivers of the stone without it breaking. While the longer-lasting stone makes it a more attractive proposition for buyers and therefore more likely to be financially viable (I’m assuming here that my scythe-wielding audience would not be interested selling stones with planned obsolescence to promote their own ‘financial viability’), it also creates a bigger financial burden on the manufacturer in terms of getting the stone cut; a standard masonry wheel would be chewed away into nothing before making many cuts into hard sandstone, so it calls for specialised gear.

Finding the kit

So, at this point we had a ute-load of really hard sandstone and no means of cutting it effectively. I did cut a couple for ourselves to confirm that the sandstone would be effective as a whetstone, with an angle grinder and a diamond cutting wheel, but even this was terribly slow going and not at all safe. I contacted a number of stonemasons to enquire about having the stone ‘roughed out’ to the basic canoe shape, so I could finish them with a grinder. Some never replied, one agreed to do a proof of concept and never did, another wasn’t really equipped to do the job, and another was fully equipped and quoted $154 per hour for their time (all costs here will be in AUD – at time of writing the AUD is worth 0.48 GBP and $0.73 USD). I couldn’t imagine any of our customers being willing to bear that cost.

The kind of block saws that I wanted to use to do the job safely – with a table that slides into the saw blade – had a starting retail price of around $1500, with the really good ones being in the range of $4000.  Second-hand gear became interesting. Used hand-held concrete demolition saws were available on online auctions for $200-$400 – not ideal, but a big step up from an angle grinder. Used table-style block saws were available for around for $600-$1200, and I got as far as making enquiries about these and looking at the costs involved in bringing one in from interstate.

We ended up securing a used table-style block saw with a 400mm diamond blade, and another small tile saw, for $100 from our University’s Geology department, which was looking to upgrade its equipment. Brand-name blades themselves retail at $300. It’s an old saw, and the closest contemporary model I’ve been able to find online is a Husqvarna 400mm brick saw which retails at $1800. Universities are great.

I was now able to rough out my canoe shapes safely and relatively quickly (but only relatively – when I’m cutting blocks the blade only cuts about 1mm per second), and I now needed some more effective grinding gear. I found some marble grinding cups in Klingspor’s range, and these work very well – they seemed quite pricey at $13 each wholesale, but I ordered six and I am still using the first one, having made thirty stones. A google search for “klingspor supra c16r” will find these accessories.

On top of these expenses, there’s electricity (which I haven’t attempted to price yet) and safety gear such as a good quality particulate mask (silicosis is a very real risk when cutting or grinding stone – less so with the table saw as it uses running water to keep the blade wet which also stops the dust flying), visor, earmuffs, and gloves.

Does it pay?

We are able to sell these stones – at $40 each – faster than I’m able to make them with my available time. The raw material costs us nothing except $30 per annum for a prospecting licence and fuel and time to retrieve the sandstone from where it’s hiding. Based on the last batch I produced, I retrospectively guesstimated that it takes about 16 minutes to rough out one whetstone (by cutting large blocks into whetstone-width slabs, then marking the slabs with canoe shapes and cutting outside the lines) and another 15 minutes to grind it into its final shape. So about half an hour’s time, electricity, consumables (diamond blade – eventually – and the grinding cups), wear and tear on $100 worth (or $1800 worth, depending on how you look at it) of machinery, and safety gear that I already owned – for $40. In short, this item is about the only thing in our catalogue that we’re really making any money on. If we were dealing with a large deposit of sandstone (as in, a rockface) it may be faster or slower than collecting manageable-sized rocks as we are currently – depending on how the rockface sheared. It’s also quite likely we could be charging more – one scythe retailer has whetstones listed at $45USD, which is $62AUD at time of writing, and we have whetstone reviews with high praise from Peter and Ashley Vido.

And this, of course, is an important point – what the customer is willing to pay based on an item’s perceived worth. I am trying to value-add: by creating a beautifully-shaped stone; one which is thicker in both widths than most other stones and so will last longer; one that has rounded honing edges to better match the curved blade, rather than dead-flat edges as in the Rozsutec, and; one which is much stronger than, say, the Bregenzer. Our customers also place value on the fact that we made it ourselves – they tell us so.

In addition to what the customer is willing to pay, viability is also entangled with what else you have to do with your time. I can do IT work for $80 an hour, so going to the effort I do to create a whetstone for quite a bit less (all things considered) than that is not, strictly speaking, financially viable, even though it’s the biggest profit item we carry. But sometimes it helps keep me sane (and sometimes it doesn’t). There are also “bad days” where it takes 4 hours to make two stones because the stones I first spent time cutting prove to be inappropriate for the application.

Presumably the abandoned whetstone quarries in countries with manufacturing histories, like the UK, would provide a more certain source of good quality stone; as far as I’m aware, no natural scythe whetstones have been manufactured on scale in Australia – like most ‘specialised’ gear, they’d have been brought in from the mother-country or elsewhere. [errata… following on from my ‘find’ of an old Tasmanian-made whetstone, Steve Leppold has since pointed me in the direction of a relative wealth of information regarding Tasmania’s own history of whetstone production; it seems we were more self-sufficient than I had thought].

Ceramic stones

ceramicsI should also mention our ceramic stones. One story related in Henk Bos’ work – of an older gent flipping his dinner plate to sharpen a kitchen knife on the unglazed base – inspired me to approach my next door neighbour, a potter, to discuss making whetstones. We’ve been offering these on our website for a little over a year now, and we’ve sold nearly 60 of them in that time (more than any other stone we’ve stocked to date so far). They cost us $24 and I was very particular in telling the potter to make it worth his while when he worked out a price. We sell them for $35 (but I do dress these on a grinder too, so there’s time involved there). So even this approach (which is producing something that sits somewhere between natural and synthetic) is arguably financially viable, depending, again, on what the buyer is willing to pay – which, in the absence of other options, is likely to be quite a lot.

I would certainly encourage individual mowers to have a go at creating their own whetstones, though. Spending a couple of hours creating one with basic tools may not be financially viable in terms of what else you could be doing with your time (as compared to buying one from a scythe supplier), but it’s not a bad way to spend part of a weekend, and it’s immensely satisfying to hone a blade with a whetstone you’ve made yourself. Grab a stainless steel teaspoon and start testing rocks. Just be sure to use all the right safety gear and be very aware that anything that cuts rock will cut you much, much faster.

Another tip Mr Bos gave me personally was that you can soak a strip of softwood in linseed oil and then roll it around in sand. When it dries, you have a quite an effective improvised ‘whetstick’ – not as good as a whetstone, but a lot easier to make when times are tough.

Happy honing!

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