Posts Tagged With: Woodworking instruction

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 surface (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.  Surface plates are precision instruments.  Glass and polished granite are not.

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 do know this:  glass does not need to be flat to do its job, only clear and somewhat resistant to breakage.  Countertops are polished to a point of high gloss, but not tested for flatness.  That characteristic is not needed to hold up a pot of spaghetti.

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 must it be 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.


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

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

Finishing for Non-Finishers, Part IV

Now we’re ready to do final assembly operations for the project.

Before you begin, I recommend that you do some serious housekeeping around your bench or your assembly area, if you have a separate spot. If you are like a lot of woodworkers, you might have a tool or two on your bench, along with some sawdust or shavings from your hand plane or scraper. Right now is the time to get all of the debris left over from your milling and smoothing operations cleaned up. Put away all of the tools, vacuum the bench top and the floor. You’re at the point in the project where significant care should be taken to maintain the surfaces you’ve worked hard to create. This additional care during assembly will pay off when you begin applying a finish.

Get your hands on some carpet remnants or a quilted moving blanket to cover your bench or assembly table. Even with a clean bench top, project components can (and do) slip out of your hands and a collision with a hard bench top can ding an edge or round a corner. A bit of padding on your work surface will help prevent damage.

Careful Clamping is Key

Clamping components together is a staple of the glue-up and assembly processes. But clamps can damage components if they’re not carefully applied, and if a big bar clamp slips or slides into your work, you have repair work ahead.

I  use four kinds of clamps in my shop. I have a lot of pipe clamps with Jorgensen heads. The nice thing about pipe clamps is the ability to change clamp length by moving the heads to different length pipe.  Over the years I have epoxied small squares of 1/4″ MDF with rounded edges to the faces of both clamp components,  rounded edges facing the component to be glued up. I have found that it is considerably easier to attach these clamping blocks or pads to the clamp than it is to struggle with loose clamping blocks, the clamps, the glue bottle, and the components. The alternative, which I did for a few years, is to tape clamping blocks to the components before gluing up. Eventually I wised up.  Here’s an image:

MDF pads epoxied to clamp fixtures

The second kind of clamp I use is a Bessey K-body in varying bar lengths. I like the performance of these clamps, but they are expensive, and limited by the length of the bar. I have not found the pads to mar or discolor surfaces, but if I am applying them to relatively soft woods, I will use a clamping block where needed.

The third clamp style is a Jorgensen F clamp, either the heavy-duty or “3700” style clamps.  I don’t use the light duty clamps for glue-ups because there is too much flex in the bar.  The heavy-duty style does an acceptable job in the right circumstances, with one caution: the factory-applied orange clamping pads will stain the work if they are left in place too long.  Some time ago, I removed these clamping pads and replaced them with MDF pads similar to those pictured above.  In my shop, the “3700” clamps are mostly utility clamps, and see limited duty during glue-ups.

The fourth and final style clamp is a wooden handscrew. These “old-fashioned” clamps can exert a tremendous amount of clamping pressure, and are really quite useful in the right application. They are limited by the size of the jaw opening, and so are not suitable for large-scale glue-ups.

There is at least one trait common to all of these clamps: they must be kept clean.  Furniture assembly is messy business.  Glue gets squeezed out of joints and panels, and some of it is going to find its way to your clamps.  Clean it off as soon as the glue-up is complete.  The drop you miss today will be the one that gets pressed into the surface of your next glue-up.  How do I know this?  If you’re clamping panels using pipe or bar clamps, it is sometimes helpful to put a short piece of masking tape on the bar or pipe directly below the joint being glued.  That way, squeeze-out can be easily removed when the glue-up is complete.

A Last Look and Some Housekeeping

Once the project is completely glued together, do a careful inspection of every surface. You’re looking for any errant glue squeeze-out, as well as any damage or marking caused by the clamps. The best way to look for these assembly remnants is with strong light from a window or from a set of halogen lamps on a stand. You want the light raking off the surface at a low angle and bouncing into your eyes. Take your time and look at every surface and joint. If you find glue use a scraper, a sharp chisel, or a dental pick to remove it. If you notice marks from the clamps, a light sanding or a touch-up with your scraper or hand plane should clean things up. Use care when manipulating the project to preserve all of the surface preparation work you have done. Keep the project on the moving blanket or carpet remnant as much as possible.

I like to clean the finishing area of the shop the night before I plan to apply finish. I will vacuum floors and work surfaces, and also vacuum the project. I also turn off the ceiling fans so that any bit of airborne dust have the chance to settle out of the air. I save the tack cloth for just before the first coat of finish goes on.

Now is the time to get out the project cutoffs mentioned earlier in this series. They should have been planed, scraped or sanded (or all of the above) just like the project components were. They should be vacuumed to clean up what dust has accumulated since you produced them.

In the next post we’ll start applying finish to the sample boards and evaluating the results.

Previous Posts in this Series:

Finishing for Non-Finishers, Part I
Finishing for Non-Finishers, Part II
Finishing for Non-Finishers, Part III


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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