Tuesday, May 27, 2014

How do you know when your tools are sharp?

The necessity of having a sharp chisel or plane iron with which to do your work is almost universally recognized (a very rare thing in the world of woodworking!). Sure, you can muddle through a job with half-sharp tools, but sooner or later a dull-ish tool will negatively impact your work (or your finger!) as you try to force the tool to do work for which it is not prepared.

I won't engage in the ad nauseum debate over sharpening systems or the use of honing guides that is so prevalent in the woodworking media as a whole. That topic has been beat to death and resurrected so many times that I seriously consider packing a zombie apocalypse bug-out bag every time I venture to an online forum. Pick a system, learn it, use it. I use oil stones freehand because that works for me. It might work for you. It might not. End of topic.

The faces of the sharpening thread apocalypse
My concern here today is knowing when your tool is sharp enough for woodwork. With all the discussion of which system to buy, to what level must a tool be honed, and what stone can I buy to make my edges better (remember, its the archer not the arrow...), there is very little attention paid to the idea of knowing when a tool is actually sharp enough to do the job.With a simple tool like a chisel, it is no big deal to finish honing, try the tool on your work piece, and rework the edge if necessary. However, with a plane, it can be a real pain to sharpen the iron, reassemble the tool, set the iron, and then test the tool only to find out that the edge needs more work. What is a woodworker to do?

My solution to this problem is to obtain a piece of the softest, nastiest white pine you can find. With this wood, the faces and edges are stupidly easy to plane and pare cleanly, but the end grain can be a challenge. The wood is so soft that it simply tears out ahead of a dull-ish tool rather than being cut cleanly, as you can see the following pictures of my sharpening test block after a few cuts with a dull W. Butcher chisel. Please note that this chisel will still shave the hair on my arm and will take a fingernail shaving, two of the much-bandied-about ways to test an edge.

This will not be a good edge for woodwork.

Torn up early wood. 
As you can see, there is significant tearing of the soft early wood in this piece of white pine. This chisel is not currently sharp enough for fine work, but it is sharp enough to cause a serious injury to the user should the chisel be forced to do work, based on the equation Dull Edge x Force = Blood. No exceptions. It gets all of us at one point or another.

It doesn't have any chips in the edge, as I caught this edge before it started to degrade, so it will not need serious attention. After less than 30 seconds of honing on my translucent Arkansas (not an endorsement of a sharpening system, this is just what I use) and about 5 swipes on a strop, this is the same chisel cutting the same piece of pine. Note that the cut is clean as a whistle with no torn up early wood. The effort required to make this cut was virtually non-existent; the chisel wants to do the job!

This is much better.
So, no matter what you use to sharpen your tools. I encourage you to try the "paring end grain white pine" test on a chisel that you consider to be sharp. I've never found a chisel or plane iron which passed this test and then failed to do good work for me in my actual workpiece.

9 comments:

  1. Very much the best and only test that matter most, can it cut wood cleanly! Never cease to amazed me about all the other ways to test an edge on your own body parts, yikes...

    Bob Demers

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    1. True enough Bob! They call bare arms "Galoot Pattern Baldness" over on the Old Tools List from all the guys who shave their arms while testing. I don't like doing that, as intentionally sending an edge careening towards my arm bothers me for some reason...

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  2. Replies
    1. Thanks Wiktor! Would you like to cross-post this on wkfinetools.com?

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  3. Yes, I was thinking about it. It fits well to what I am trying to do. Will work on it tonight and let you know.

    Best, WK

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    1. Sounds good. I think you have my email address, so just shoot me an email if you move forward.

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  4. Yep, if you want to check do so on the medium you will be working with. Worryingly I draw my thumb across the edge to test!

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  5. Zach, I have gotten much better at sharpening with practice and a few accessories but still can't seem to get to that "scary" sharp. I don't know where my process is lacking I have watched a bunch of utube videos. The 16000 grit stone used by some is just not in my arsenal, I go up to 8000. The debate over secondary bevels and polishing the entire back or just the working section is just fun to read. Any pointers would be greatly appreciated.

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    1. Pat, it's difficult to diagnose sharpening issues from a distance. For the vast majority of woodworking tasks, an 8,000 grit stone will be more than sufficient. The important thing to remember is that you should try to raise a burr with each stone in your process before moving to the next stone. If you aren't raising a burr, you aren't sharpening all the way to the convergence of the bevel and the back, i.e. you aren't doing anything to the edge. Raise your burr, get rid of it on your finest stone. Repeat for each stone in your arsenal until you get to your finish stone, which may not raise much of burr (but you should still be able to feel it). Maybe a couple of swipes on a strop, and you should be good to go.

      If you have further questions, feel free to email me through my business website, www.theeatoncountyjoinery.com. I hope to hear from you.

      Zach

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