Un-blunting – An Existential Crisis in Woodworking:
A year down the line and I can honestly say I don’t miss my waterstones by Derek Jones.
The thought of sharpening has been known to bring about an existential crisis for some woodworkers, and whenever I’m asked about my own regime my answer tends to leave folk more than a little underwhelmed. I’m not that big on sharpening.
You see, our role in the workshop is to make the tools blunt; it’s the only truly predictable outcome of our time spent at the bench, everything else is just a consequence of that outcome. Well, at least that’s the fun way of looking at it; the alternative being to flip this cycle on its head and regard the un-blunting of tools as the objective, which isn’t nearly as much fun. Sharpening for me is the equivalent of a hangover; the price you pay for a good night out, and I want to get it over with as quickly as I can. At the same time I don’t want to be a slouch when it comes to obtaining an appropriate cutting edge on my tools. So to this end, about a year ago, I decided to trade my waterstones in for diamond plates in an attempt to crunch the time and investment involved in un-blunting duties without suffering the loss of edge performance.
It’s a dirty job
Sharpening is a messy business however you do it and whatever medium you use. The problem is that they all require a lubricating fluid to either produce a slurry or to keep the cutting surface live. Not having a dedicated sharpening zone in my workshop or a convenient supply of running water meant that maintaining a permanent water bath for three stones and a flattening plate was problematic to the point where I’d put off the act of un-blunting for as long as possible, or even worse, just grab the next sharp tool!
The inherent flaw with both water and oil stones is the minute you start using them you start throwing bits of them away. Imagine you had a £50 note in your wallet and every time you looked at it you cut a piece off the corner until eventually there was nothing left. A good diamond plate, on the other hand, will not waste away in use.
My choice of plate was the Classic Pro 8in coarse/fine stone from Trend, which comes in a protective wallet with a rubber to help clean the surface after each use, and a non-slip mat. The coarse side of the plate has a 300 grit rating, equal to 50 micron and has a very fast cutting action and will reduce thin blades to dust in no time. It’s so efficient in fact that I’m finding I don’t need to break out the grinder quite as often to establish primary bevels on a lot of blades. The fine side has a 1000 grit rating equal to 15 micron and is ideal for setting secondary bevels. Like a lot of folk, I’ve got a mixed bag of tool steels in my rack that include O1, A2 and PMV-11 and possibly some I’m not sure about; the shocking thing is I cannot detect any difference in time spent un-blunting between the steels. As part of my trial I experimented with working straight off the fine plate with mixed results. Chisels seemed to fare best under this streamlined regime, especially those that are used for more chopping than paring. For all but one plane, a rough semi scrub like No.5, the fine plate was woefully under sharp and was not effective at reducing the wire edge. With the waterstones in moth balls I turned to a ceramic Spyderco fine grade stone for finishing. As good as these stones are, they are narrower than the diamond plates (50mm as opposed to 75mm) and not ideal for wider plane irons. I’ve since moved over to a Shapton Glass Stone HR grit 6000 fine (2.4 micron) and have not looked back.
The pros and cons of diamonds
It’s a known fact that grinding tool steel with diamonds can cause changes in the molecular properties of the steel and generally to its detriment. This only happens when grinding at speed, so unless you are capable of grinding by hand at the equivalent of 6000rpm or more, then it’s hardly an issue. In use a diamond plate behaves differently from other abrasives in that they are not friable, meaning the abrasive compound does not fracture from its substrate and combine with the lubricant and waste material to form a slurry. Although you can use your plate dry and use the rubber to remove the waste filings, it’s better to manage waste material as you work and there are a number of options available in the form of lapping fluids for this purpose. These are designed to prevent the plate from rusting, which is handy for your tools as well. For anything up to the finest plates WD40 can be used as an alternative to lapping fluid, but as it’s a bit of a minestrone mixture of complex chemicals including mineral oil and (allegedly) Vaseline. It’s not as pure as lapping fluid and can form a cushion that’s deeper than the size of the diamonds, preventing the blade from making contact with the abrasive. Plain old tap water works but due to its low surface tension weeps off the plate quickly. Camelia oil and even baby oil are excellent alternatives. Finally, and what’s generally not mentioned about diamond plates, is that they respond better to a lighter touch than a heavy hand. In fact, pushing down harder onto the plate has no effect at all and is a complete waste of energy.
A new diamond plate will cut very quickly. As the act of sharpening is the process of roughing up a surface by decreasing amounts they will leave a coarse scratch pattern on the steel at first and you will generate some spectacular wire edges. This diminishes after a few sessions to be no more harmful than a comparative water or ceramic stone.
How un-blunt do my tools need to be?
I think there’s a definite relation to the level of sharpness you need vs the time spent achieving it. The sharper the edge the quicker it dulls and the sooner you need to return to the sharpening station to restore that edge. Not every tool in the rack needs a mirror shine edge to work. Put smoothing planes and paring chisels on that list and experiment with everything else, as there are far too many variables in the mix to establish a one-stop-shop sharpening regime for all your edge tools.
So after nearly a year of diamond plates, am I happy with the sharpness of my edge tools? Yes. Am I enjoying spending less time un-blunting my tools? Yes. Do I un-blunt more frequently? Yes, and am I making fewer trips to the bathroom? Yes. Do I miss having the dirty trough of water sitting under my bench? No. Do I miss having to flatten three separate stones every time I want to carry out any un-blunting? No. More importantly, am I happy with the sharpness of my edge tools? Yes.