keeper blocks to create opening for guide bar.
Quality Saw-Blade Sharpening
A Good Sharpening Service Can Keep Your Carbide Blade Cutting Like New by Matt Ver Steeg
Getting the edge. A good sharpener relies on know-how and sophisticated equipment to produce sharp, long-lasting edges on your blades.
hat a kick it is to unwrap a new saw blade and make those first cuts! But maybe after a few sharpenings, that "new" feeling is gone—the blade just doesn't work the way it used to. Or your cuts may have lost that first velvety smoothness. Maybe the blade just sounds different, or maybe it seems to dull faster than it used to. So you start looking at catalogs again, for something with that brand-new feel.
Things don't have to be that way. A quality blade should cut like new throughout its working life, and this might be measured in decades in a small shop. In this article, I'll show you how to tell when your blades need sharpening, how to find a quality saw-blade sharpener, and what to look for in a properly sharpened blade.
Most woodworkers recognize when a blade is beginning to dull: It gets noisier, the cutting rate slows down, feed pressure increases and cut quality goes out the window. You can also inspect a blade for dullness by shining a flashlight on the top of a tooth. If you see a bright line of reflection on the cutting edge, it's time for a sharpening. Pushing a blade beyond this point will cost you more than the extra cutting is worth, since you'll subject the carbide to heat damage.
Not all sharpening shops produce consistently good results. One of the best ways to find a sharpener is to ask the best cabinet shops in your area who they use. Visit a few sharpeners if you can, and look for clean working conditions, good equipment and people who take obvious pride in their work.
Don't hesitate to ask a few questions before you leave a blade for sharpening.
Here are some things that I'd want to know in advance:
•What kind of grinding wheel is used? You want the results produced by a 400-to 600-grit diamond wheel. A coarse, 120- or 200-grit wheel is faster but gives an inferior edge. (See photos, opposite.) And so-called "green wheels" don't actually sharpen carbide. They merely gouge away the binder that holds the carbide grains in place, leaving the teeth smaller but not much sharper than before. •Does the sharpener use a "flood coolant" while grinding? Better grinding machines Hood the wheel with a special coolant during grinding, producing a clean, bright surface on the carbide. Dry grinding produces burned or discolored teeth and weakens the carbide. •What is the shop's policy on face-grinding? Properly sharpened teeth retain their proportions throughout the life of the blade, as shown in Fig. 2. Excessive face-grinding wastes your carbide and can drastically shorten a blade's life. Because the sides of a tooth taper back from the face (see Fig. I) face-grinding also reduces the blade's side
54 american woodworkfr ▲ june 1995
to da copyrigr clearance in the kerf and may cause overheating. Many blade manufacturers recommend face-grinding only every third or fourth sharpening. •How is the blade cleaned? A good shop will use an ultrasonic cleancr, a chemical bath and plastic brushes or a special blade-polishing machine. The faster, wire-wheel method erodes carbide and makes face-grinding mandatory.
A good sharpener will generally be willing to talk with you briefly and answer your questions. And if he knows you're an educated consumer, he might take extra care with your blade. But in the end, it's the work itself that provides the proof. The real test is to leave a blade for sharpening.
When you get your blade back, here are some results you can readily observe: •Overall appearance. Your blade should be clcan—with all gum, pitch and superficial rust removed. The teeth should be plastic-dippcd for protection. •Fine, precise grinding. The teeth should be clean and bright, with smooth, uninterrupted grind patterns. Even under a hand lens or pocket scope, each tip should appear smooth, not ragged. (See photos, above.) If a tooth looks like it's been groomed with a garden rake, it will break down fast and won't stay "sharp" for long. •Minimum carbide removal. Some sharpeners routinely grind away an excess amount of carbide—sometimes as much as 0.050 in.—to be sure all chips and imperfections are removed in one pass. A good shop takes the time to inspect teeth before grinding, and grinds off no more carbide than necessary. When the sharpener can take 0.004 to 0.012 in. off just the tops of the teeth, he's maximizing the blade's life.
Smoother is better. The tooth on the left shows the fine scratch pattern produced by a 600-grit diamond wheel; the one at right has been scratched deeply by a coarser 200-grit wheel. Deeper scratches weaken the edge and lead to faster dulling. Excessive face-grinding has also changed the tooth's proportions.
•The ultimate test. The final test of a sharpening job is how well the blade performs. If you're satisfied, that's all that really matters. If you're not satisfied, talk with your sharpener and see if he can do anything to improve the blade's performance. And remember to make sure your saw is properly set up and aligned. (Sec AW #39 and #43.) No blade will perform well on a saw that is out of whack.
Between sharpening^, maintain your blade by keeping it clean, especially around the tips, where a buildup of pitch and resin can cause overheating. Scrub the teeth with a soap-and-water solution and a nylon-bristle toothbrush. Then, after drying the blade, spray it with a rust preventative such as Dri-Cote (available from Woodworker's Supply, 1108 N. Glenn Rd., Casper, WY 82601, 800-645-9292) to protect it. A
MATT VER STEEG runs a sharpening service in Iowa and designs carbide-tipped saw blades.
Was this article helpful?
THIS book is one of the series of Handbooks on industrial subjects being published by the Popular Mechanics Company. Like Popular Mechanics Magazine, and like the other books in this series, it is written so you can understand it. The purpose of Popular Mechanics Handbooks is to supply a growing demand for high-class, up-to-date and accurate text-books, suitable for home study as well as for class use, on all mechanical subjects. The textand illustrations, in each instance, have been prepared expressly for this series by well known experts, and revised by the editor of Popular Mechanics.