Posts Tagged With: honing

Secrets of Happy Grinding


To many woodworkers, grinding a bevel on their cutting tools is a task filled with fear and disappointment.  The dangers are many:  poorly shaped bevels, burned steel, edges that are no longer square to the sides of the tool being ground.  In this post, I will offer some suggestions to help correct the most common problems.

Problem:  Bevels with Multiple Facets

One of the most common problems faced by woodworkers who are just learning to grind tools is ending up with many facets in the bevel.  This situation is most often the result of changing the grip on the tool, changing body position during grinding, or a combination of these factors.  The situation can be complicated by the relationship between the grinder, the tool rest, and the wheel mounted on the grinder.  Here is what happens.  During the grinding process, if the wheel is dressed flat across its face, it is cutting all the way across its width, frequently ¾” to 1”.  Because so much of the wheel is in contact with the steel, the slightest change in the angle at which the tool is presented to the wheel results in a new facet.  These miniscule changes can be caused by shifting your balance, stopping the grind to observe your progress, changing hand positions, and a dozen other causes.  Rather than try to control all of the variables (hand position, stance, etc.) I have found it much easier to limit the amount of wheel surface area in contact with the steel.  I do this by creating a very slight crown on the wheel.  To crown the wheel I use a diamond wheel dressing stick (mine is made by Norton) and remove slightly more material from the sides than from the center of the wheel.  The very slight crown provides me with a lot of benefit.  First, I know exactly what part of the wheel is in contact with the tool.  I can see the steel being removed; some of it remains on the wheel in the form of a dark grey streak.  When this streak gets too pronounced I need to re-dress the wheel, because the buildup of steel in the abrasive will slow the grinding process and permit additional heat to build up.  The wheel is becoming clogged in this area.   Second, the grinding is a lot slower, and that leads to much more control over the process.  For many of my sharpening students, this one suggestion is the single most effective change to their sharpening routine, and it clears up a lot of problems.

Problem:  Overheating the Steel

The grinding operation generates a lot of friction, which, of course, can potentially build up a lot of heat in the steel.  Managing heat is an important part of grinding tools safely and effectively.  There are several steps you can take to mitigate grinding’s thermal impact on tools.  Crowning the grinding wheel effectively limits heat buildup, because you are reducing the abrasive surface area in contact with the steel.  Proper hand position is also critical; if your fingers are located close to the edge, you will feel the tool heating up in plenty of time to slow or stop grinding well before the metal turns colors.

Understanding how heat moves is also important to preventing damage.  Heat moves away from its origin.  Some is radiated into the cooler air around the tool, but a lot of it moves within the steel through conduction.  More mass (that is, thicker steel) can “cope” with more heat than thinner steel.  What this means to a tool at the grinding wheel is this:  as the grinding operation moves closer and closer to the thin edge at the end of the bevel, there is less steel available to dissipate the heat.  If the heat has nowhere to go, it builds up, and the steel eventually reaches a temperature where physical changes occur.  These changes manifest themselves visually through a change in color, and physically through a loss of hardness.  When the steel turns blue, it has lost harness, and that area must be removed by additional, more careful grinding.

This situation becomes even more critical as the point of contact between the tool and the wheel approaches the corner of the edge.  In these two areas, there is the least amount of steel available to conduct heat, resulting in a much faster heat buildup and increasing the chances of damaging the steel.  Here are steps you can take to stop grinder-related heat damage:

  • Use a white (aluminum oxide) wheel, or other “friable” wheel.  Friable means that as the abrasive particles at the wheel’s surface dull, they will break off and expose new, sharp abrasive particles.  Sharper abrasives are more effective, reduce friction, and consequently limit the amount of heat buildup.
  • Use a slower grinding speed.  If you don’t already own a grinder, or if you are making one yourself, look for one that turns at 1,725 rpm instead of the more-common 3,450 rpm motors.  Yes, this will slow down the process, but slower is better as you’re getting started.
  • Use NO pressure.  Let the wheel do the work.  Advance the steel to the wheel, but don’t push.  Let the wheel do its job of steel removal while you concentrate on a smooth and easy back-and-forth across the tool rest.
  • Keep the thumb of your weak hand on the steel, near the wheel.  You will feel when heat builds up.  When you do, stop grinding, or dip the tool in some water to cool it off.
  • Pay close attention, and be very careful, as the freshly-ground bevel approaches those thin corners near the tip.  Do not let the tool linger on the wheel in these delicate areas.

Problem:  Out-of-Square Grinding

This is a very common problem for woodworkers just learning to grind tools.   Fortunately, the solution is quite easy, and it’s foolproof.  Simply put, once you have a square end on the tool, never grind all the way to the edge.  Get as close as you dare, but always leave the slightest glimmer of shiny steel from the previous honing.  If the previous edge was square, the new one will be, too.  The down-side to this technique is that your first honing will take just a little longer, because you will have just a bit more steel to remove as you hone,  But the time this takes will easily offset the additional time you spend at the grinder, correcting for an out-of-square edge.

What to do if the tool isn’t square when you start?  Adjust your tool rest so the edge of the tool is presented to the wheel at 90 degrees (rather than your usual grind angle of 25-30 degrees) and carefully grind the tip square to the edges.  Use an accurate combination square to check.  When you’re there, stop, readjust the tool rest to your desired grind angle, and proceed.  You’ll have a blunt tip to the bevel, and as you grind, that blunt edge will slowly disappear.  Go slowly, and check your progress frequently.  Save just a little bit of the bluntness and hone it away.  When you’re done, the tool will be sharp AND square.

Practice Makes Perfect

Just like every other woodworking skill, no one is born knowing how to grind.  It is a skill that can be learned, and once you learn, sharpening becomes so much easier.  No messing with jigs or tool holders; when you need a fresh bevel, you step up to the grinder, take care of business, hone, and go back to work.  All it takes is a little practice, and maybe a lesson from someone who can observe your technique and offer suggestions.  Practice is clearly called for – but don’t practice grinding away an expensive chisel or plane iron.  Buy an old junker at a flea market or garage sale for a dollar, and get your technique down using that tool; save the Hock irons and Lie-Nielsen chisels for after the practice session is complete.

There are probably other problems people have run into at the grinder, but these are the three big ones.  If you have your own stories, leave them here.  I’ll try to address any problems with simple solutions.  If there is a way to mess up a grind, I’ve done it – but I’ve also figured out how to correct most every error.

Categories: Sharpening, Woodworking | Tags: , , , , , , | Leave a comment

Humility, Part II


I finished Krenov’s plane today.

After gently trueing and squaring up the mouth opening, I still needed to remove a small bit of material from one of the inside walls.  That adjustment permitted me to gently tap the plane iron parallel to the mouth opening, allowing the plane to remove the same thickness shaving across the width of the iron.

As I mentioned a few days ago, the iron needed a little touch-up as well.  This was a good opportunity to flatten the water stones in advance of the sharpening process.  I got another smile out of my order of work: Krenov was not a stickler for flattening stones; in fact, his writings would have you believe he was not the least bit obsessive about sharpening.  I believe I have adopted his sensibilities about sharpening.  You sharpen when you need to – when your tools are telling you they need attention.  Beyond that, you keep the tools working productively.  It’s the way I teach, and it’s the way I work.

I looked carefully at the plane iron as I sharpened it.  Krenov used Hock irons in his planes; in fact, Ron Hock’s business (as a maker of fine hand plane irons) got started largely because of Krenov’s CR program and his need for good irons and chip breakers.  The iron in this hand plane is really massive, more like a Japanese hand plane than an Western-style tool.  The back is polished behind the bevel as it should be, but not as high as I would have done it.  The grind angle places the bevel nearly parallel with the sole of the plane.  I didn’t measure it; I should have, I suppose.

As I took the iron to the stones, I wondered if Krenov sharpened it himself.  I doubt it.  Perhaps he ordered enough irons for his plane making that he could convince Hock to flatten, grind and hone them to his wishes.  More likely, he had help from someone at CR or from a former student.  In any case, the thought occurred to me that this was the first time, and most likely the last, that a tool came to me already sharp.  It’s awfully uncommon for that to happen.

After a short sharpening session, the iron is sharp again.  Before I get all the parts back together again, I decide to tune up the wedge a little bit.  The bottom is a bit ragged, and too close to the mouth for shavings to exit easily.  While I’m at it, I thin the bottom so shavings can slide past just a bit easier.

Krenov signed the plane, but you have to look pretty hard to decipher what you’re seeing as his signature.  I’m almost tempted to try a light coat of shellac over the sides of the plane in a modest effort to preserve the marks.  I’m going to use this tool, and I fear that over the years, my hands will gradually erase the signature.  One more time I imagine him laughing at me for the sentiment; this time I’m not sure I care.  (I wouldn’t tell him that I saved his shipping box.  And his newspaper.)

I mentioned that along with the plane he sent a note.  In it, he urges me to adjust gently with the hammer: “Tap, tap, tap, NOT BOOM, BOOM, BOOM.”  With his hand planes, like all wooden planes, subtlety is the key.  You want to adjust them slowly and patiently until they’re set just right.  As long as the humidity doesn’t change too drastically in the shop they’ll stay that way.

Finally everything is back together again, and it’s time for a few passes on the board I keep under my bench just for use when I adjust a hand plane, a piece of sweet cherry I bought from a sawyer in Albany.  I used most of the board for a cabinet (a Krenov-style cabinet, in fact) and I had this short left over piece with a bunch of splits.  So I use that for plane adjusting.  I took a few passes along an edge: the shavings were too thick.  Tap, Tap, tap.  Another few passes, and it’s cutting just a bit heavier on the left.  Tap, tap.  One more tap.

A Krenov Hand Plane

Now it’s dialed in pretty well.  A few more passes.  The shavings are thin enough to read through, and the edge of that sweet cherry board is as smooth as wood ever gets.  The plane is a joy to use, and use it I will.

If I listen closely, I can hear the music.

_______

Jeff Zens owns and operates Custom Built Furniture in Salem, Oregon. He is a frequent woodworking instructor and writer.

Categories: Woodworking | Tags: , , , , | 3 Comments

Sharpening Class, Part VI – Some Final Thoughts


There are as many opinions about the “proper” or correct” path to a sharp edge as there are woodworkers who sharpen.

Not everyone does.  Sharpen, that is.

I have visited enough shops, taken enough classes, and taught enough woodworking students to understand that not everyone pays the same heed to the condition of their edges.  I have also enjoyed enough Eureka! moments during classes to understand that getting (and then using) a sharp edge can be a moment of epiphany for a woodworker.  In a measurable way, woodworking quality begins to change once the owner understands how to obtain that keen edge.

It’s also possible to take things too far.  I read an article in Fine Woodworking several years ago by a pretty well-known contributor to that magazine.  If I recall correctly, he wrote that he’s been known to re-hone an iron after four or five strokes with the hand plane.  Either the wood he was using for that project was terribly abrasive, or the steel in the plane iron was pretty soft, or the grind angle was too severe…whatever the reason, five strokes of a hand plane isn’t getting a lot of work done.

Admittedly, doing good work involves slowing down from the pace we’re often used to working at, either in our shops or in our daily lives.  “Slowing down” is a big reason a lot of woodworkers spend quality time in their shops.  Nonetheless, we often need momentum to carry us through to the end of a project.  Sharpening seems to slow some people down – or so they think.

Slow Down!

The truth is that a dull tool slows you down in a lot of small (and some big) ways.  Dull chisels take more effort to slice through wood, and occasionally slip.  If they slip into your hand, well, they’re still sharp enough to cut, perhaps deeply.  So now you’re bleeding all over the project, reassessing your finishing options – perhaps something to take advantage of the crimson circles with the nicely scalloped edges?  And that dull plane iron is great for building upper body strength at the same time it’s tearing out fibers from your workpiece.

So where’s the happy medium?  For me, it’s pretty easy, now, but it wasn’t always.  To know when it was time to sharpen, I first had to have sharp tools, then learn how they worked.  How they COULD work.  I began asking my tools to do more.  I wanted a surface that didn’t need a lot of sanding.  No sanding at all would be better yet.  Have I mentioned that I hate sanding?  Hate everything about it?

Once I learned that I could expect better results from my tools, I needed to keep them in the condition they needed to be so they could deliver on my demands.  Somewhere along the line, I had a woodworker’s revelation.  As it turns out, doing good work involves a partnership.  You’re only half of the deal; your tools are the other half.  Neither you nor your tools can do work without the other.  Funny realization, isn’t it?  Put your #4 on the workpiece, and then take your hands away.  Watch what happens.  Now, remove the plane, and put your hands on the workpiece.  Move your hands all you want.  Not making much progress?  Probably not.  The magic doesn’t start until your hands give guidance to the steel, which then begins to do work for you.  And for the steel to give good results, you need to maintain it.  I’ve developed this  understanding with my tools.  You should, too.

Listen to them.  They will tell you when they need upkeep.  Your planes won’t sound the same, and they will not leave a clear, glimmering surface behind.  Your chisels will fight you.  They will resist your efforts to push them through wood fibers.  Your scrapers will refuse to take shavings.  They will leave behind sawdust – flour – but not tightly curled shavings of wood.

When they refuse to do the work you ask of them, when they slow down and make you work harder than they are, then it’s time.

Don’t be a slave to honing, but don’t turn a deaf ear to your tools, either.  Pay attention to the messages they send you.  Eventually you will develop a balance between the time you are working and the time you are honing.  Then you will do good work.

_______

Jeff Zens owns and operates Custom Built Furniture in Salem, Oregon. He is a frequent woodworking instructor and writer.

Categories: Sharpening, Woodworking | Tags: , , , , | Leave a comment

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