Tuesday, January 6, 2015

How sharp is sharp?

Rob Cosman recently posted a video which purports to show why it is worth sharpening planes to 16,000 grit vs. 1,000 grit.  In the end, the only difference he could identify after planing a piece of hard maple was feel: he felt that the 16,000 grit side was ready for finish right off the plane while the 1,000 grit side wasn't.  He also alluded to but did not demonstrate superior performance on figured wood.  That's it.

I use diamond stones followed by honing compound on a leather strop.  Comparisons are difficult and sources differ, but my EZE LAP SF diamond stone is 1200 grit, a bit finer than the coarser waterstone in his test.  The particle size is about 11 microns for the former and 14 microns for the latter.  The 16,000 grit waterstone has a particle size of about 1 micron and produces what is commonly called a mirror finish.  It is apparently about like using green honing compound on a strop or 1 micron diamond paste.

I had several reactions to his test.  First, I think his test may have been a best case for the 16,000 grit waterstone since he took just a few swipes with each plane before feeling the surfaces.  I have read that the 16,000 grit edge will degrade quite quickly and I wonder if the difference between the two edges wouldn't be a lot smaller after even moderate use.  My second reaction was that this isn't much of a difference the way I work.  For a variety of reasons, I normally scrape or sand my surfaces lightly before finishing.  Would the finer stone make a difference if you scrape or sand before finishing?  Third, I am not sure what impact limiting the test to hard maple has.  Fourth, there are a lot of choices in between these two grits and I wonder how they would stack up.  Finally, even if you believe as he does that it is important to hone to a mirror finish, wouldn't the case be limited to the plane you use for final smoothing or for figured wood?  I would certainly not bother on the No. 5 I just used for fitting screen doors.

Thinking about this subject brought to mind a related question, which is this:  if you want to hone to a mirror finish, what is the best medium?  I often feel that I don't gain much by using green honing compound on a leather strop.  Maybe it's for the reasons I have suggested above or maybe it is because the honing is offset by a slight dubbing of the edge, something you read happens quite often.  Given that I won't use waterstones, what might be better ways to hone beyond my SF diamond stone?  I've come up with two alternatives I am going to try.  The first is to use green honing compound on something other than leather, say mdf or a piece of wood planed dead flat, in an effort to avoid dubbing.  The second is to use a steel honing plate and diamond paste, which is available in 6,3 and 1 micron versions.  This is much less expensive than a comparable waterstone, the plate stays very flat and the paste lasts a long time.  Lee Valley suggests that you can use mdf or a flat piece of hardwood for the diamond paste as well, but the steel plate is inexpensive so I don't see any reason not to buy one.

The bottom line for me is that it doesn't take a lot of extra effort to hone to a mirror finish so I might as well do it, so long as I find that the edge doesn't degrade so quickly that it is a waste of time.


  1. Like you, I use diamond plates and green honing compound and when I'm done sharpening a plane, chisel, or knife blade it's got a mirror finish. I'm sure there are occasions I could "sharpen to task" on coarser stones and skip the honing step but I don't have the experience to know which occasion that might be and doing my best sharpening job takes just a couple of minutes at most so why would I stop short of a good job?

    As Paul Sellers has pointed out a lot of very fine woodwork was done by men sharpening their tools by hand on nothing more than a well dished double sided carborundum stone.

  2. Hi Andy,

    Honing compound on mdf is nice. Purists turn their nose up to it but I like it much better than a leather strop for straight edged tools. I still use leather for gouges and knives. I would definitely start there and see if you like it.

    I'll give you a few other options for a final honing - the diamond film that Lee Valley sells being one. The finest film is something crazy like 0.1 micron. They are small, and fragile, but inexpensive, and easy to pull a chisel across to get a final mirror finish. You have to baby them a little, though. I don't think anyone knows how long they truly last because most people inadvertently rip them up long before they stop cutting well. The finest 3M micro abrasive film also works well, and is really cheap. With both of these you'll need a flat surface, and the abrasive film does wear out (but lasts a pretty long time). I have the micro abrasive film on some plate glass and pull them out when I just want to touch something up an not make a mess (still need to build that sharpening station).

    The advantage of these two is that they are a little cleaner than the diamond paste. One reason people gravitate to diamond stones is the lack of mess. No water or excessive oil to deal with (although the diamond film works best with a few drops of oil). The diamond paste is nice but for me it was just one more goopy thing, requiring more paper towels into the trash. I have heard that cast iron is the best medium for diamond paste, where it can better imbed in the pores and require less recharging and maintenance. I had a steel plate that arrived with a big belly on one side and a hollow in the other. Took me forever to get the hollow side something close to flat. The Lee Valley plate should at least save you that.

    I have way too much sharpening crap.

    Good luck,


  3. Andy,

    Some of the most prized natural Japanese waterstones do not give a mirror finish but hone to a haze. Once the edge gets to a finish condition it's the scratch pattern, not the polish that maters. Of course as with all things wood YMMV.


  4. I've got to throw in my 2 cents here. I've been around the sharpening track numerous times and I am now a spectator. I have settled into using my 3 diamond stones, my japanese 8K, and my final step of honing with green compound from Lee Valley as my sharpening method. For all my irons and chisels, etc.
    I don't do micro bevels, polish a nutso mirror finish on anything I sharpen. I instead do something stupid like what does the shaving look like? What does the surface I just planed look like? How does it feel?
    Do you really think a craftsman from the 1800's worried about a mirror finish on this irons? I have seen furniture from this period and I'm happy with how they sharpened thier tools then. I will continue to copy them.

  5. I can remember turning my nose up at honing compound and a strop for fear of the dreaded dubbing effect and I can't help but feel now that it is overstated. Stropping definitely won't work well if you wait too long to touch up the edge and it is something you have to do often. In other words, the tool still have to be sharp to get really sharp. Regardless, I have been using my strop almost exclusively on most of my edge tools for more than a year now and have yet to experience any dubbing effect. I don't deny that it will happen, but if I only have to go back to a stone or grinder to "reset" a bevel once a year and just live by the strop the rest of the time, I'm not going to worry about this mystical dubbing thing.

  6. Since slowly starting to get back into some woodworking, I've been thinking about this.
    The highest grit I use is an 8000 grit Norton. However, I see no point in using that for jack planes and block planes. My other two stones, 1000 and 4000 grit Kings, put a great edge onto just about anything. In most cases I can follow the 4000 with a green strop and be just fine.
    My jointer, smoother, and LN chisels get the 8000 grit treatment. The surface left behind by an iron sharpened to 8000 grit is incredibly smooth. Why would I spend money on another stone?
    I think the best sharpening advice I've ever heard was "do what works for you and ignore everyone else."