Posts Tagged With: Sharpening

Some Thoughts About Flattening Your Tools


Much has been written about sharpening.  I’ve contributed to this mass of sometimes-confusing, often-contradictory literature.  As a frequent instructor on the subject, I have some modest experience with the successes and failures of those learning to tune up their edges.

If any part of sharpening can be called fun, flattening is the least among them.  It is certainly the most time-consuming, and it can be one of the most frustrating aspects, as well.

In earlier posts on my blog, I have recommended that students begin their flattening with a known quantity:  a true, flat reference surface.  Some students listen and take the plunge, purchasing a granite test plate, or one of the more expensive diamond lapping plates, also known to be flat.  Others, for a myriad of reasons, choose to use a piece of glass, or a broken  counter-top.

Many folks believe that these surfaces are fine to use for flattening.  Float glass, in particular, is called the “flattest” glass.  As often as I have looked, I can’t find a definition of “flattest”.  Flatter than what?  The old rippled glass from the late 1700s?  Flatter than a stained glass window?  I just don’t know.  Same for a piece of countertop.  I haven’t found a standard that defines when granite is flat enough to be called a countertop, and if that standard implies true “flatness” the way we need it for sharpening.

I’ve seen folks try to flatten their stones using a small DMT plate, with the long dimension of the DMT held at right angles to their water stones.  If ever there was a sure bet to dish out (or round over) the water stone, that’s it. I’ve had students use all kinds of surfaces as their reference, trusting that these are indeed flat.  Many of these same students are dismayed at the condition of the backs of their tools during the flattening process.

Why does this matter?

It matters because flattening is (at least) one-third of the sharpening process.  The steel from the back of the tool makes up half of the cutting edge.  And creating a true, flat surface on the back of a tool is the only action we can perform to guarantee a tool works the same way, sharpening after sharpening.

It matters even more because of the time you spend with your stones and your tools.  Even a well-manufactured tool takes a while to polish.  A less-expensive tool might take hours.  How frustrating is it to work on the back of a tool, obtain a uniform scratch pattern (one of the telltales that our back is as flat as the abrasive), switch to a finer abrasive, and then discover that you’ve still got a hump or a hollow on the back?  If you make this scary discovery, you are left with few options.  You must make the correction at this point.  All of your previous effort must be corrected, and if you don’t make the correction at this point, all your subsequent work will be wasted.  So you go back, flatten your coarse stone on your reference surface, and try again.

But what it the reference surface itself is the culprit?  What if there is a hollow in it, or a hump?  Then you’re creating the opposite sort of defect in the stone, and your tool will never, ever be flat.

So, back to the beginning of this post.  If you’re using glass, or a counter top, or any other “pretty flat” surface, you’re taking your chances.  It matters not that float glass is “the flattest.”  What matters is how flat your piece of glass, or granite, or steel, or whatever, really is.  Unless you know the answer to this question, you take the chance that all of your efforts at obtaining a flat back will need to be redone.

This is why those of us who sharpen a lot, and teach others to do so – make the recommendations we do.  It isn’t so our students run out and buy something else to clutter the shop.  It’s a lesson most often learned through the painful experience of having to re-flatten tools because we didn’t listen when we should have.

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

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Categories: Woodworking | Tags: , , , , | 2 Comments

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

Grinding by Hand – The Old-Fashioned Way


One of the woodworkers who has shaped some of how I work is James Krenov.  His sensitivity to wood and his approach to harmony in design and construction are elements I try to incorporate into my work.  His respect for tools is another.  His approach to sharpening was straightforward, and not fussy.  When tools needed a new hollow, grinding was often done by hand.   I started using this grinder setup when I got tired of the noise, dust and heat created by the benchtop grinder, and the setup time of a Tormek.  While I still use both of those tools when I need to, I turn to this hand-cranked grinder setup much more frequently.

After much wailing and gnashing of teeth in their editorial meetings, the editors at Fine Woodworking and at Popular Woodworking all decided not to publish this article.  One could speculate that it wasn’t “sexy” enough, or that it didn’t help to sell tools made by their advertisers.  Maybe taking hand tool use to this degree is just boring, Who knows.  But in response to a bunch of requests, mostly from students, but some from the blog, here are plans to my little hand-cranked grinding wheel.

Get the Grinder and Wheel First

Let me say at the outset that there is nothing magical, and nothing cast in stone, about any of the dimensions for this set-up.  To the contrary, it is really important to have both the grinder and wheel available before making any of the parts for this contraption, because the grinder/wheel combination might demand modification from the sizes presented here.  I purchased the grinder on eBay.  You need to ask questions before you buy one sight unseen.  You’ll want to know the maximum wheel size (which you often cannot tell from eBay photos) and how true the arbor runs.  If there’s a lot of runout on the arbor shaft, the wheel will wobble and you will need to correct for that.

When I fabricated this base, I worked off of dimensions from the grinder, rather than from a plan.  The point of all of these “disclaimers” is for you to be careful and think through your own setups before you start cutting materials, because the dimensions might need adjustment.

The Parts

The base is simple: a piece of 3/4″ Baltic birch plywood, 12 inches square.  It would make sense to add a cleat to the bottom so the grinder could be clamped in a vise, but because I travel with this grinder,  it needs to be flexible enough to work on any bench I might encounter.  So I simply clamp it to a bench top using hand clamps or whatever happens to be available.

The Base and the Tool Rest Block

The tool rest block is a laminated block of wood that measures 3-5/8″ x 3-3/8″ x 4-5/8″ before any shaping is done.

The Tool Rest with Pivots

The Tool Rest (top view)

The tool rest is another piece of Baltic birch plywood, cut to 6″ x 3-1/2 “.  The front edge (facing the wheel) is beveled at a 45 degree angle to provide clearance for the wheel.  There is a 1/4″ deep groove cut along the top front edge, precisely parallel to the front edge, in which the tool jig slides.  The width of this groove isn’t terribly important – you’ll cut a piece of 1/4″ MDF to slide in the groove, and you can fit the MDF to the groove fairly easily with a hand plane.

The tool rest pivots on two pieces of 3/4″ Baltic birch plywood that are let into dados cut in the bottom of the tool rest.  The pivots are shaped to fit the pivot point on the tool rest block.  I attach the pivots to the base with a 3/8” carriage bolt, secured with an adjustable handle with a female threaded insert sized to the bolt.

Setup and Use

To use the grinder you will need to square the tool rest to the wheel.  I use an accurate square for this purpose, and periodically check that tools are being ground square.  I square the front edge of the tool rest to the side of the wheel, and once in a while I dress the grinding edge of the wheel so it is square to the sides.

The Finished Assembly

Squaring the Wheel to the Tool Rest

Basic use is straightforward.  Be sure you wear eye protection, but I have not found hearing protection to be at all necessary with this setup-it is quiet, which is very appealing to me.  Rest the tool on the base, and support it on the side with the jig.  Get the wheel started and grind gently.  Using light pressure on the wheel makes it easier to spin, and reduces the risk that you will blue the steel.  Yes, you can burn your tools even with this grinder, so be cautious.   When you feel the steel heating up, give it a rest, or quench it in some water.

The Tool Jig (MDF) In Place on the Tool Rest

The Grinder in Use

Advanced users might grind on this wheel freehand – without the tool jig, just letting the groove in the tool rest guide your fingers.  Grinding freehand permits slight adjustment to an out-of-square condition and also facilitates grinding a slight camber if you want that on a plane iron.  Don’t try this right away – get used to cranking with one hand and guiding the tool (using the tool guide) with your other hand.  Once that’s comfortable, try freehand grinding.

Since I am right-handed, this setup is designed for me to crank with my right hand and grind with my left.  That might sound counter-intuitive, but it works pretty well once you get the hang of it.  Southpaws might want to reverse the orientation of the support block and grinder to permit left-handed cranking.

I’ve produced a fairly accurate SketchUp model of my setup.  Unfortunately this blog does not have the capability for me to simply upload the file for your use.  I’ll be glad to email it to you if you’re interested; just drop me a line at jszens@custombuiltfurniture.com.

Once you’ve got the hollow restored on your chisel or plane iron, you can get to work honing the tool and get back to your project.  If you haven’t read them already, posts that describe the honing proccess begin here.

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

Categories: Sharpening, Woodworking | Tags: , , , , , , , , , | 5 Comments

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