Posts Tagged With: grinding

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.

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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

Sharpening Class, Part IV – Grinding the Bevel, and the Straight Scoop on Angles


At this point in the sharpening process the back of the tool should be flat and polished.  You shouldn’t see any errant scratches running the long way on the back of the tool – the polished surface should extend from side to side, and run off the end of the tool at the bevel.

Now it’s time to discuss our approach to the beveled face of the tool.

There are two methods for honing the bevel to get it into the same shape as our nicely polished back.  The first approach is to hone it flat – in other words, no grinding.  This technique may appeal to a woodworker with an aversion to the grinding wheel, and there’s no reason why a sharp edge can’t be obtained this way.  It may take you a bit longer to hone, because you’ll be removing more steel.  Changing the angle of the bevel in relation to the back will take much longer than at the wheel – but it can be done.   I’ll discuss the technique later in this post.

Grind Angles

Here are a couple of facts.

  • You own your tools.
  • You can put whatever bevel angle on the tools you choose.
  • The tool manufacturer didn’t know what you would use the tool for when it was fabricated.  Consequently, the grind angle on that tool may or may not be the right one for your work.
  • If you don’t like the results you get from the tool’s bevel, you can change it again.

Most of these little “pearls” come from my own experience, and from teaching sharpening classes to others.  I have found a general reluctance to grind tools, and I’ll be the first to admit it can be scary and intimidating.  I’ve had students who tell me they would rather use a dull tool – or buy a new one – rather than grind.  That fear is the reason you shouldn’t practice grinding bevels on a $50.00 Lie-Nielsen bench chisel or on a valuable antique.  Practice first on the one you’ve used to open paint cans, or buy one at a flea market for $5.00.  If you have replaced hand plane irons, save the old ones for practice.  Get the technique down first, then grab the Lie Nielsen.

There are a lot of books written about sharpening, and a long discussion about the “proper” or “correct” angle at which a tool should be ground.  You’ll often read that the proper grind angle for a tool used in softwoods is about 25 degrees, and about 30 degrees for hardwoods.  That’s all well and good, but what if you use your tools for both?  And what about those softwoods that are harder than some hardwoods, or hardwoods that are softer than some softwoods?

Here’s the reasoning behind varying grind angles.  Think about a razor blade: very acute angle on the edge; very sharp, but not suitable for working with wood.  Why?  Because the edge is too thin, and therefore it’s too frail.  Now think about a chunk of steel with an end that is cut at right angles to the sides.  Picture a piece of bar stock.  Very durable end, right?  Not too likely you’ll  chip that flat end – also not much good as a cutting tool.  The optimal angle for cutting wood is clearly somewhere in between; but at what angle do you find the optimal edge?

That’s the million-dollar question.  Here’s the one rule everyone agrees on: less steel behind the cutting edge makes the edge more delicate than more steel.  Examine a mortise chisel, and you’ll see it is ground at about 45 degrees.  Now look at a paring chisel: that might have a grind angle closer to 20 degrees.  The two tools are used for much different purposes.  That nice sharp paring chisel wouldn’t last too long chopping out a bunch of mortises.  And the big heavy bulk of the mortise chisel won’t give you the fine control to shave off .001″ or .002″ from a tenon.

The “rule” that hardwood tools get a 30̊  bevel is simply aimed at beefing up the steel behind the cutting edge to make it more durable in “harder” woods.  The opposite is true for the 25̊  bevel for softwoods.  We talk a lot more about this in class.

More than anything else, the grind you choose really is a matter of preference that is related to the work you expect the tool to do for you, and how often you care to re-hone.  An angle of 20̊  or 22̊ is fine for your paring chisel.  Most of my bench chisels – and plane irons, for that matter – are ground at about 27̊ or so.  I couldn’t tell you precisely what the angle is.  It’s clearly a compromise between the extra sharpness of a very acute angle, and the durability of a less-acute grind.  In your own shops, experiment a little bit, and don’t be afraid to make changes.  They are, after all, your tools.

Now for the Why.  There are a few reasons to hollow grind your tools, which is what grinding with a wheel is commonly called.  Both are related to simplifying your life.  The first one is simply that when it is time to change the bevel angle on a tool, grinding is the most efficient way to get the job done.  Secondly, honing by hand (which is the way a lot of honing gets done) is a lot surer process when you have the tip and heel of the bevel to register against your abrasive.  Honing a flat-ground chisel or plane iron can be done – but since you have to remove a lot more steel the process takes more time.  Most woodworkers would rather be doing almost anything else than honing a tool, so any technique that reduces honing time counts in the plus column.

Getting the Grind

I use a hand-cranked grinder, a slow speed (1725 rpm) electric bench grinder and a Tormek wet grinder to hollow-grind my tools.  The Tormek turns what started as a 10″ wheel, now probably just under 9″.  The bench grinder turns both an 8″ and a 6″ wheel. I use the 8″ wheel for turning tools, because the hollow is not as deep – leaving more steel behind the edge, and a more durable tool.  The 6″ wheel gives me a nice grind on plane irons and chisels, a little deeper than the 8″, and therefore lasting through one or two more honings.   The rotation speed and composition of the wheel are important for a number of reasons.  The primary reason is heat buildup.  Overheating tool steel destroys the temper, and untempered steel will not hold a cutting edge.  The only way to fix that, short of heat-treating the entire tool, is to carefully grind away the blued steel.   Just what you need, right?  More grinding.  The hand-cranked grinder is nice and slow, plenty safe to use, and keeps me in touch with the process.

For bench tools (chisels and plane irons) I use a 100 grit wheel rather than some of the coarser grits because the scratches are  shallower.  The trade-off is that grinding takes a bit longer, but I figure to make that time up when I hone.  A white wheel is somewhat less prone to heat build-up than the typical grey wheel that comes with many grinders – but make no mistake, a white wheel can blue your tool in short order.  You need to pay attention if you’re dry grinding, or you need to spend considerably more money for a wet grinder.

Let me say up front that the art of grinding is one that doesn’t translate well from the shop (or studio) to a blog, a book, or a magazine article.  So if a lot of the following isn’t entirely clear, don’t fret.  I cover grinding technique thoroughly in my classes; I suspect others do as well.

Once you determine the desired bevel angle, set your tool rest accordingly.  If you use a rest similar to the Veritas® model, you may choose to use it with or without the optional jig.  You can learn to grind free-hand (using a tool rest but no jig) just as easily as learning to hone without the assistance of a jig.  It takes more practice to be sure, but you’ll save a lot of time not fumbling around trying to get the tool set precisely set in the jig.

There are a few keys to successful grinding.  First, know what part of the wheel is actually taking away metal.  If you have trued the stone recently (leaving it a nice, pristine white) you’ll see the white abrasive turning grey or black in the areas it is removing steel from the tool.  This might be one little part of the wheel, or the entire rotating surface.  You can also tell where the cutting is happening from the location of sparks coming over the top of the tool.

Second, aim for a bevel that is made up of a single concave facet.  If you are seeing multiple facets in the bevel, something in your grip is changing, and you’re varying the angle at which the tool passes over the wheel.  Aim for consistent, even and smooth movement across the wheel.  As you check your work, keep your hand position (grip) on the tool consistent.

Third, you don’t need a lot of pressure to grind.  Truthfully, you need very little, if any pressure. Move the tool gently into the rotation of the wheel and let the wheel do the work.  Pressing the steel down on the wheel is a fast way to burn it, drawing out the temper.  As you move the steel from side to side, keep your fingers close enough to the edge being ground to feel for any heat buildup.  If the tool is getting uncomfortably warm, stop grinding and quench the tool in some water or set it down to cool off.

Fourth, you’re usually aiming for an edge that is 90̊  to the sides of the tool.  This is more important on chisels than on plane irons; in fact, plane irons are occasionally ground with a slight camber, and can be adjusted for a true cut when back in the hand plane.

If you are grinding without a jig, hand position plays a key role in getting all of these points coordinated.  Using a jig takes more time (getting the adjustment just right) but eliminates some of the other variables.

There are a few schools of thought about how far down the bevel to grind before you stop.  One view is to grind all the way to the end of the bevel, creating a wire edge on the back.  That way you know you’re done, and you have exposed fresh steel all the way to the edge.  The argument against that technique is twofold.  Part one is a concern with burning the steel, discussed above.  The second concern deals with keeping the edge square to the sides.  Concentrate on keeping the tool square to the grinding wheel, and examine your progress often.  Make adjustments to your grip if necessary, but stop before you grind the edge all the way to one corner or the other.  If you started with a square chisel or iron and you stop before the grind reaches the far edge of the bevel, you’ll finish with a square edge.

Next: Honing the Edge

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

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

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