I find the real problem of leaning to sharpen the tools is lost in the fact that it is a skill-just like turning-and it will take time to learn. The good news is that it is very closely related to the skill of woodturning.
At one time every conceivable woodworker learned sharpening skill as part of their activity-whether it be sharpening saw blades, axes, spokeshaves, chisels, or plane irons. Today however, few cabinet or furniture makers sharpen circular or bandsaw blades, planer and joiner knives, router bits or shaper cutters-either these have become throw away's or they are sent to specialty shops. Even the other domain where sharpening was essential to learn-that of carving-has often been replaced by spinning bits and cutters that require no sharpening, just replacement. Alas, the poor woodturner still must learn to sharpen. However there are considerable benefits to be had from learning this skill.
Sharpening is a skill that imitates/mimics woodturning. I mean by that: you take a turning tool and place it on a tool rest, it meets a round object approaching the edge, and you manipulate the cutting edge-sure sounds like what we do as turners. Learn the skill to sharpen and you are learning turning-and vice versa.
What you need if you are frustrated is a similar strategy that is used to learn many different skills: a progression from simple and relatively easy activities to something difficult and more complex. If you think about it, this is how most skills are acquired. If you take up playing the fiddle you don't start with Tshchockiys Violin Concerto as your first task-you probably start with playing notes, then scale, simple tunes and then progress in difficulty at the rate of your learning. The same is true with learning; math, cooking, computers, golf, drawing, driving, sailing, and it should also be true of sharpening turning tools.
The good news to all of this is that leaning those simple tasks first has several benefits: most of those tasks are also foundational-not just easy-and will be the basis for learning the more difficult maneuvers
Success builds on success-it is a far greater sustainer than failure and frustration. I wonder how many folks have quit woodturning over the years because they either could not sharpen the tools or found they spent more time sanding than turning. Working with dull tools is like trying to drive your car with flat tires-it just isn't very satisfying. So, if you are early on in your career as a turner or you are still frustrated about this sharpening thing, bear with me and try this progressive order of learning to sharpening your tools.
To begin with, you can't shape and sharpen your tools by hand. We can certainly hone the tools by hand-but that is only to keep a sharp tool sharp or to regain a small loss of keenness on a cutting type turning tool.
No, power equipment is the order of the day for a host of reasons, not the least of which is the type of tool steels used today. Most turning tools currently being sold are not just higher heat working steels but also higher wear resistant steels. Your grandpappy's Arkansas oil stone is going to have a tough go on a Glaser V-15 tool-or really on most of the English, Canadian, and Australian tools now on the market. And the fact that too many tools need major reshaping from their new condition, we will need some power assist to do the job.
I find that it is not as simple as "anything will work" for a grinder. If you have a 3600-rpm grinder with a 120 grit gray wheel, 1/2" wide and worn down to 4" in diameter-it will be tough sledding. Nor do I find the slow speed water grinders to be my first choice for a grinder, nor a belt or disc sander either. For some strange reason I find that at least 90 % of the turners I know worldwide use a wheel grinder-must be some reason buried there.
Here are my grinder preferences: an 8" dry wheel grinder, with either variable speed or a fixed rate of 1725 (or 1800), rock solid tool rest system, and at least one decent wheel. The 8" wheel offers a lot over smaller and larger wheels: the 8" offers 25% more surface area for each revolution-which means greater efficiency, cooler grinding, and a much longer wear period before replacement. The 10" and greater diameter wheels leave too little of a hollow-grind for me-and I use the concave surface as a two-point honing jig (see honing article).
I prefer the dry wheel as the action is towards me-this allows me to determine from the spark trail a lot of things: where I am grinding, the degree of grinding, and when to stop grinding (sparks just trail over the top of the tool). With a water type grinder the action is away from me and there is no longer a spark trail (those grinders are fantastic for carbon steel tools like plane irons, cabinet makers chisels, scissors and the like-but not a first choice with most turners). I like the slower 1725 speed for a grinder as I aim to remove minimal material, it has a cooler action, and I just find it a more gentle action than a 3600 screamer (those seem to double my mistakes!). We are now seeing two-speed grinders and infinitely adjustable grinders on the market (which will probably be common with most grinders at some point).
If the tool rest assembly is flimsy, I cannot consistently grind my tools nor is it really safe to do so. Place your thumb in the center of the tool rest of your grinder and push down. You should feel virtually zero give-if it feels springy, improve or replace. You can add extra support strapping, build a wooden rest, or purchase one of several after-market accessories rests. Also, the rest should be adjustable both in angle and the ability to slide towards the stone to accommodate for wear as well as keeping the rest close to the stone for safety purposes. Finally a light is a worthwhile accessory to the grinder if one did not come attached to it.
First, work with the widest wheel you can fit to your grinder. In most cases this is 3/4" or 1"-but the wider the better. Next, throw away your gray wheels. Spend a lot or spend a little, but acquire at least one decent wheel to sharpen with.
|It is hard to just look at a wheel and guess its grit size and hardness. Most stones have a code-in this case, the bottom row of numbers. The most important to a turner would be the middle number of 54 (grit size) and which is usually followed by the hardness designation (in this case a "J").|
The wheels I would suggest would be friable aluminum oxide-now in patriotic colors of red (okay, often pink), white, and blue. The word "friable" refers to the ability of the stone to fracture exposing fresh grinding surfaces as you use it (gray wheels usually are not very friable, the cutting particles round over, thus reducing grinding ability and often glazing and generating considerable heat). The color-coding of these wheels make them easy to spot-however, there really is a difference between a $10 wheel and $100 wheel.
My advice: if you have an 8" grinder look for wheels that sell for between $25 and $55 and you'll be fine. Two other critical aspects of the wheels: grit size and hardness. I like to work with two different grits on my grinder. For initial shaping of a tool or any other heavy grinding operation I like to have a 36 or 46 grit wheel. For the actual process of sharpening an edge I prefer either a 60 (the new 54 grits are close enough) or 80 grit. My ideal is a 60 grit on the left side of my grinder (I am right handed, reverse this if you are a lefty) and a 36 grit on the other side.
If you really pushed me I could live with a 24 or 36 grit gray wheel as the roughing stone-I would just be dressing it a lot. And finally, how hard should the stone be? Most stones-but not some of the real cheapys indicate the hardness (see photo xxx). This makes a difference in its friable quality and how well it performs on tougher steels. Stone hardness follows the alphabet scale from soft to hard as you go down the alphabet. Most of the stones commonly found range from H through K. My first choice is a J followed by the K.
|Wheel dressers are essential to the sharpening process. Examples from left to right : gray dressing stick, tee diamond, round diamond, star-wheel, and in the foreground is a boron carbide stick.|
Almost as critical as a good stone is a dresser. These are tools that perform a number of functions: true the wheel to the axis of your grinder, flatten the face of the wheel, remove the build of metal particles, and expose or sharpen the abrasive particles. There are several choices: star-wheel, gray dressing stick, boron carbide stick, and diamond. My suggestion would be the multiple diamond dresser (not a single point) in a round or tee shape. Place it by the grinder and use it to dress the wheels lightly but frequently.
Finally, deal with the hazards associated with tool grinding. One of the greatest hazards is to protect yourself from flying particles, whether they be grit from the wheel or pieces of steel removed in the grinding process. The plastic shields on most grinders are worthless to see through after a while- a full face shield is my first choice followed by goggles. And it should go without saying, only use a grinder with metal shrouds to contain the wheel just in case it shatters into pieces.
Another serious hazard is the dust produced from grinding. I like to think of it as ground up glass-which is not too far off the mark. I know of no turners who use a wet dust collecting system to direct the grinding dust into-but is more common with jewelers and other metal workers. And of course don't direct the dust into your normal wood dust collecting system-think of the drama of sparks and wood dust meeting!
What is most common is to wear a quality respirator, one rated for small particulate matter. And finally, keep the pinch and crush factor to a minimum by always working with the tool rest as close to the wheel as possible.
From my own learning and watching hundreds of students try to learn the sharpening process, I would recommend learning the turning tools in this order:
|Woodturning scraping tools are quite similar to the cabinet maker's scrapers (background, shown with a burnisher). Both types of scrapers usually cut with a burr and both can make use of a burnisher to raise that burr. Turning scrapers obviously are thicker and heavier in weight and come (or can be made into) in a wide array of shapes for specific purposes.|
These are tools, of almost any shape, that are intended primarily to cut with a burr and not rub the bevel on the wood. Yes, I know we violate both of those guidelines from time to time, but that does not help someone who is starting out. Of all the turning tools these are some of the most straight forward to sharpen, very few really struggle with these tools in getting the basic process, and we don't have to be as fussy about shapes, angles, and multi facets on the ground face of the tool.
First rule of all turning tool sharpening: profile the tool first, and then pull a bevel up to meet that profile. For a scraper the shape is determined by the task at hand or personal preference. You will probably discover that the very slight dome on a new "round nose" scraper you just bought isn't very rounded. You may even find you don't use one side of the rounded end, so it may take on the shape of a side ground scraper. Whatever the specific need or your style of turning, shape the tool first.
|One version of a side-cutting scraper.|
Next, rough in the bevel angle. When most of these tools are new I find the bevel to be 80 to even 90 degrees below the cutting edge. I believe this started with the notion that a scraper needs a lot of support under the edge since you don't have the secondary fulcrum of a bevel rubbing tool to add extra support (your tool rest is the primary fulcrum). Unless your scrapers are 1/8" thick, this is a bad notion.
As a matter of fact, if I am using the tool at a scraping angle (with no bevel support) and the bevel inadvertently touches the wood, I can get a catch. I treat the bevels on scrapers as clearance angles, so mine are ground in the window of 45 to 60 degrees. I also don't have to worry about single facets and a hollow grind on the ground bevel: I don't hone the bevel on these tools so it is not as critical as it soon will be. However, grinding uniform bevels on these tools is great practice for all the tools to follow.
The process for sharpening is straight forward. After profiling proceed to grind the bevel to match the profile. If you need some assistance early on in sharpening, set the tool rest angle to that 45-60 degree window. Start at the back of the bevel and progress along the entire cutting edge until sparks just come over the top. I am not looking for a heavy stream of sparks, but even "tracer bullets" that tell me I have reached the cutting surface.
Now being a scraper, the burr that is raised will be my cutting edge at least 90 % of the time. I can use the burr right off of the grinder (especially useful if heavy stock removal is called for) or remove that burr with a flat stone and pull up a new burr with a cabinet maker's burnisher or even the honing stone.
By using one of the other methods I find it easier to produce different types of burrs-some for heavy work, some for fine finishing work. In those cases where the burr is too aggressive for a particular piece of wood (you may feel it "picking" at the wood rather that a smooth leveling action) try scraping with a sharp edge-produced by grinding, then removing the burr on top with a flat honing stone. This is similar to the action of scraping with the edge of a knife or the furniture maker scraping the top of a table with a large piece of broken glass. When you work a sharp edge in a scraping action, it may quickly dull the edge. However for that window of doing fine scraping it may be just the ticket.
Now we come to the tools that start to cause problems for those learning to sharpen. These are tools that will cut with a keen edge and, in most cases, are presented at a cutting angle with the bevel rubbing on the wood. Now we become fussy about angles, uniformly ground bevels, and of course keen edges.
There are several variations of this tool, but the most common will be a rectangular section of steel with the cutting edge in the middle and ground on both sides of the edge. This is a great tool to learn cutting tool sharpening as it has a relatively small area to grind (the edge is usually no greater than 1/4") and the edge is in a flat plane.
|Diamond-section parting tool (profile and angles same as rectangular tool).|
For profiling, make sure the edge is ground straight across, and the included angles are around 25 degrees (see diagram xxx). Fortunately of all the turning tools, these most often come profiled in an acceptable manner-not sharp mind you, but the shaping is normally okay. To sharpen, either set the tool rest at the approximate angle desired, use the edge of the rest as a steady, or use your fingers to adjust the angle.
Start at the back of the bevel (called the "heel"), keep the edge horizontal, and lap from side to side on the wheel until you just see sparks trailing over the top of the cutting edge. Flip the tool over and repeat the same procedure on the other side. Objective is to produce a single facet with a slight hollow grind. If your movements are controlled and steady this all happens; if jerky, uneven, inconsistent, too much pressure, "grind and look" and "grind and look" then things probably won't be so good.
Go slow, be deliberate, leave the tool on the wheel, and use only enough pressure as it takes to keep the tool from bouncing on the rest. I am always surprised how much of grinding and turning is really about feeling your way along rather than seeing.
And in grinding most of the action is on the other side of what you can see. We can help the looking part along-especially when learning the process-by placing our head to the side of the grinder or by the use of a mirror (attributed to a North Carolina turner). In time most of your grinding will be by feel and watching the spark trail to give the additional feedback.
|Until you have a sense of where you are grinding on the tool, it might help to either place you head to the side of the wheel or make use of a small mirror. The mirror allows you to see your placement of the tool on the wheel.|
Fortunately the sharpening of a skew chisel is similar to the parting tool: two ground flat planes that meet to form a cutting edge. The only real difference is in the skewed angle of the cutting end-essentially a clearing and viewing advantage over a straight across chisel.
Again, profile the tool first. For a "traditional" straight across skew I would recommend 70 degrees from point to point. Rather than measuring included angles to measure the steepness of the two ground bevels, I use the thickness of the steel as the reference. Using this method, grind the bevels back to approximately 1.5 times the thickness of the blade.
For the sharpening process, follow these steps: keep the edge horizontal to the face of the wheel, start at the heel and lap back and forth. Continue this process until sparks just trail over the edge. Flip the tool over and repeat the same procedure.
If you have an "oval style" skew (my last choice for a skew) you will find it wants to wobble rather than remain in a flat plane. In that case maintain pressure in the center of the tool with a thumb to essentially lock it into a fixed plane. As an alternative, investigate a grinding jig that locks the darn thing in place.
|Typical grinding of a skew chisel||Using the back edge of the tool rest, the curved skew is pivoted to grind the edge. Using a rotational movement, grind in the area that is roughly parallel to the face of the wheel.|
If you are trying a curved edged skew, simply grind the edge while it is generally parallel to the face of the wheel-which will require a rotational motion that follows the curve of the edge. If the skew plagues you with multiple facets, go ahead and set the tool rest to the suggested bevel angle. Keep the tool flat on the rest and follow the above strategies. I have also had good success just using the front or back edge of the tool rest as a point to slide along for a straight skew or to pivot on while doing a curved edge.
Don't be too bashful in grinding tools. You really can't hurt them, you only shorten them.
By now you may have come up against the problem of bluing the surface of the tool you are grinding. If you have high-carbon steel tools, you have a problem: the steel has now been re-tempered to a hardness that is too soft to hold an edge for woodturning. If you have high speed or high heat working tool steel-no problem. How do you know what kind of steel?
Generally the high carbon tool steels produce a complex, white, bursting spark when placed on the grinding wheel. The high speed steels tend to have individual, orange sparks. Often the manufacturer stamps the handle or steel itself with "HSS" or "High Speed Steel." I have found some inexpensive imported tools stamped with those designations, but sparked like high carbon tools-so be careful.
Here are my suggestions regarding overheating. First, learn to grind with a lightness of hand and movement of tool that does not overwork an area-thereby producing a lot of heat. And, of course, have friable wheels that just grind cooler, and dress the wheel often. If you have carbon steel tools-and some of my old favorites are of that steel-quench in water frequently if you must do some heavy grinding.
If you have high speed tools, don't quench in water: the effect may be too shocky for the steel and possibly produce small fractures at the cutting edge. The high speed steels easily handle temperatures of 700 to 1000 degrees F with no loss of hardness (bluing is around 580 degrees F). If the high speed tools are getting too hot to handle (during heavy grinding), I just place them on a large metal heat sink like a lathe bed and take a short break. The best rule for all steels, is learn to work without generating a lot of excessive heat.
This article originally appeared in the
American Woodturner Fall 2003 Vol 18, No. 3