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My question is about sharpening edge tools such as plane irons or chisels.

How do I establish, when looking at a tool, what grit to start the sharpening process on? It's clearly always possible to start on a very coarse grit and work my way up to fine grits and stropping, but in some cases some of that work at the coarser end is unnecessary. How do I figure out when it's OK (and a time saver) to start at, say, 400 grit or 1000 grit?

  • It's essentially a question of how aggressively you want to remove metal. You could technically use 1000 grit for the whole process, but it would take you a LONG, LONG time. Better to do the bulk of the work at your lowest grit, then start stepping up to remove the sanding marks from the previous grits until you reach your target. – Charlie Kilian Sep 27 '16 at 14:47
  • @CharlieKilian yep. I would like to be able to look at the edge and think "yep, I should start at 400" ... but this is the skill I would like to develop and that's what I'm asking for guidance on. – James Youngman Sep 27 '16 at 15:15
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In order to do this without gaining the experience to be able to assess what grit would be a good start, you would have to (I think this is why people are saying you really have to judge it.):

  1. Use a microscope to see the amount of metal that needs to be removed
  2. Know the "depth of cut" of different grade abrasives
  3. Choose the grade of abrasive that would cut as deep as you need material removed.

To gain experience you really just need to do more sharpening. If you are concerned about removing too much material too quickly then start with a fine grit and see if that polishes some parts and leaves scratches or chips untouched. Keep using more coarse grit until the abrasive produces the same size scratches as you're trying to remove. Then start working your way through finer grits to remove the scratches from the previous grit.

As you improve, you'll naturally be able to look at the scratches or chips and know that it looks like you've just finished with 240 or 400 or 80 (gah!) and that's where you should start.

  • 4
    I'll add 2 things: 1. you can judge some of this by feel - but that takes experience too 2. you can use trial and error - start with the finest grade, and if you notice an improvement within a short amount of sharpening time, keep going. If there's no improvement, it means you need to go to a coarser grade. – aaron Sep 27 '16 at 17:50
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    10x magnification is enough if someone wants to visually inspect their wear edges and gauge sharpening progression, so a cheap plastic loupe or a small barrel magnifier are sufficient. – Graphus supports Monica Sep 28 '16 at 7:36
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    Note that the basic principle described here applied to sanding too -- after establishing an even surface (which takes the most work), each finer grade of sandpaper is really being used to remove the scratches from the previous grade and replace them with smaller ones, until you reach a point where the new scratches are too small to matter. – keshlam Sep 29 '16 at 9:32
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How do I establish, when looking at a tool, what grit to start the sharpening process on?

Really you don't need to think about it.

In practice you generally don't need to assess your edge, you can just sharpen the tool "as normal" because it will have blunted approximately equally each time1. This is pretty much the norm for working woodworkers and has been standard workshop practice for maybe the last couple of centuries, so no need to buck the trend :-)

One thing that can help a lot with this is not waiting for your tools to get blunt in the first place.

Little and often
This approach doesn't get stressed enough in sharpening guides, especially today and in online guides. It's common among carvers and some whittlers to keep their tools razor-sharp (literally) by regular 'top-up sharpening', generally by stropping.

Stropping is great for top-up sharpening because it's very fast and effective IF you haven't left it too long, 20-30 seconds to get back to shaving-sharp from a little blunt. So there is a lot to be said for adopting the same policy with plane irons and bench chisels also.

You can of course do the job on stones/plates if you prefer not to strop, but it's a little more difficult to do it as quickly! Still aim to be back at work in under three minutes. Worth bearing in mind also is that it's not always necessary to use your finest stones just because they're there2.

You might find some of these previous Answers useful to read over, in part to keep sharpening distinct from honing in your head (both sharpening tasks but usefully separated sometimes):
Sharpening grits -- naming and selection
What criteria would want me to bevel my chisel in a certain way
How does one aggressively sharpen chisels and plane irons when damaged?


1 This obviously assumes there hasn't been any edge damage, which might happen from a tool being dropped or from contact with a particularly hard knot, where minor folding or chips can occur. In this case you would need to sharpen more aggressively, but this is of course rare in day-to-day woodworking for most of us.

2 We should remember that it was common in the past for there to be a couple of oilstones (sometimes only one!) and maybe a strop to be the sum total of each woodworker's sharpening equipment. The problem these days is that so many of us leisure woodworkers are over-supplied with stones and plates to pick from, especially at the stupidly high end, when all most of us actually need for general honing duties is one combination stone (or individual medium and fine stones) and either a strop or a very fine stone when you need an edge to be more refined, very useful on chisels but with plane irons very much not always necessary.

On a plane iron you can work with an edge straight from 250 grit paper as Paul Sellers has commented on in one or two of his videos, which closely equates with some of the edges achieved in the past..... and we have only to look at old furniture made in workshops from these eras to see what those edges could do, an excellent practical illustration of what is good enough.

  • Very good point about sharpening as appropriate for the task. On the other hand, if you're going for a mirror surface with minimal or no sanding, as in some of the Japanese woodworking styles, you may want a plane sharpened to a finer edge. Tools, and tuning, for the task and how the individual woodworker approaches that task... – keshlam Sep 29 '16 at 9:42
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    I discovered the joys of regular stropping about two weeks ago. I'd just sharpened the chisels, and was really enjoying how easily and well a newly sharpened tool performs. But as work continued, gradually they were becoming more like my "normal" chisels - sharpish, but not the SHARP sharp of a freshly sharpened tool. Everything took a little more effort. Suddenly remembered honing w/ the strop, decided to try it. Holy cow! Back to SHARP sharp in 20 seconds! Suddenly cutting a mortise felt like half the effort it was before. It's a game changer. The strop should simply never be put away. – Charlie Kilian Sep 29 '16 at 15:39
  • @keshlam Yes, lots to be said for only sharpening as much as your work needs. For a scrub plane for example you can go straight from a fairly coarse oilstone without noticing the least impact in cutting performance, and of course the roughness of the edge doesn't matter at all (by extension the same standard can be adopted for a no. 5/jack plane used the traditional way, the iron has a cambered edge and the plane is for hogging off material). Paring chisels on the other hand you always want as sharp as you can get 'em so they can slice like a razor. – Graphus supports Monica Sep 30 '16 at 7:18
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    @CharlieKilian My thoughts exactly. Clearly some woodworkers felt the same in the past as they had the strop on a pull-out shelf just under the workbench surface, protected from dust but ready to be used at a moment's notice. Another thing about stropping for edge maintenance is that if you get really good about doing it regularly it stretches the interval between sharpenings on a stone/plate to weeks or months. – Graphus supports Monica Sep 30 '16 at 7:21
  • "has been standard workshop practice for maybe the last couple of centuries" - I'm pretty sure it's been a while longer than that. "Last couple of millennia" seems closer to the mark (and I wouldn't be surprised if a neolithic woodworker ten millennia ago did the same). – Martin Bonner supports Monica Jun 3 at 7:27
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The basic idea is that you want the grit to make scratches that are finer than the defects you are trying to remove (otherwise the grit will make things worse rather than better), but not a lot finer (otherwise it will take too long).

The only caveat here is that when you are trying to reestablish a main bevel, the relevent "defect" is the layer of metal you are trying to remove (which can be 0.5 or 1mm ).

  • The first sentence of your answer makes a lot of sense (in the context that, at stage N of the honing process, you are mainly eliminating the defects introduced at the coarser stage N-1). However, how, specifically do I choose a grit size? – James Youngman Sep 27 '16 at 15:28
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    @James By running all the grits you have available over a piece of scrap metal and looking at which scratches resemble what you're trying to remove until one day you just remember and don't need to do that any more. It's really not a concrete process. Just pick one and start sharpening, change if the results aren't appropriate. Then you gain experience. Then you'll be fine. Dont over think it. – Jason C Sep 27 '16 at 19:36
  • Or by trying your best guess, and going coarser if it isn't improving fast enough. If you sharpen fairly frequently, or are working on a softer steel, you can start at a higher/finer grade. If you wait longer between sharpening, or are working on a harder steel, you may want a more aggressive starting point. (Note that there's a trade-off here: harder steel stays sharp longer but takes longer to sharpen. Some tool makers explicitly offer two or three different hardnesses so customers can pick the behavior that best fits the way they like to work.) – keshlam Sep 29 '16 at 9:40
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If just the edge needs sharpening, you may be able to start with a relatively fine grain and just work on the micro bevel at the actual edge.

If you need to establish the main bevel, you may need to go with something more aggressive.

If you need to actually repair the edge, or do the initial flattening of the back of a chisel or plane iron, starting at the coarse end of the scale will speed that up.

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Others have covered the looking well, but I find touching is a helpful addition to develop intuition. For example, when sharpening knives I know by running my thumb over the edge sideways if it is 'sharp enough'. A sharp edge will vibrate from your fingerprints - a knife for example will also 'sing' if this is done quickly when sharp. A blunt edge feels slippery by comparison. As far as I can tell the friction increases with sharpness.

  • Welcome to Woodworking. This is interesting information and thank you for sharing your experience, but it does not the question of which grit to use first when sharpening. – Ast Pace Sep 27 '16 at 23:25
  • If comments were persistent, I'd suggest this should be a comment. Since they aren't unless edited into an Answer, and since this is a useful part of "how do I know which grit to use", I am reluctant to make that suggestion and think it can be kept as an Answer. Folks may want to discuss that on the meta area. – keshlam Sep 29 '16 at 9:51
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    Wait, how are comments not persistent? – Charlie Kilian Sep 29 '16 at 15:44
  • You do need 50 rep to leave a comment on other people's posts. – Charlie Kilian Sep 29 '16 at 15:44

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