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December 27, 2010

Circular Saw Blades

Circular Saw Blades from General Cutting Tools in Chicago General Cutting Tools, serving Illinois, Iowa, Michigan, Wisconsin and Minnesota has the right saw blade for your application. Freud, Amana, FS Tools, Guhdo, Popular, DeWalt, CMT, Bosch, Diablo, xl-4000, black mamba, rip blade, melamine, non ferrous, scoring, crosscut, panel saw, triple chip, no melt, solid surface, hollow ground, flat top, alternate top bevel, combination, general purpose, cutoff, thin kerf, trim, glue line ripping, miter, framing, decking, dado sets, dado sets with chipper, dial width dado sets, and many others are available from stock for nearly every type of cut.

Wood is a stringy material. If you break a piece of wood, the stringy fibers make it difficult to get a clean break. If you split a piece of wood, the split is clean because the stringy fibers run parallel to the separation. When wood is crosscut (cut across the grain or stringy fibers), a crosscut blade is used. The teeth are designed for crosscutting. Rip blades (for cutting with the grain or fibers) are designed for ripping only. They do not crosscut efficiently. The blade on a table saw is the most important link in the sawing process. It must be sharp and true. Blades should be checked frequently to make sure of this. A saw blade is subjected to extreme forces. Imagine a thin disc with the force of 1-1/2 horsepower at 3,450 rpm applied at the center, and the resistance of 2-inch-thick oak applied at the periphery. There is great power at the center and great resistance at the outer edge. This generates the stress, heat, and vibration that dull the blade. This is why many blades have small slots at their outer edges. These slots allow the blade to expand as the edge heats up. The slots prevent possible blade warpage.

Circular Saw Terms

The cut made by a circular saw blade is called the kerf. The kerf must be slightly larger than the saw-blade thickness. The tooth set or offset is the bend in the teeth. This set allows the blade to cut a kerf that is larger than the blade’s thickness. The teeth on a circular saw blade are set in alternate directions. The gullet is the area behind the cutting edge of the tooth. It carries away the sawdust cut by the tooth. The larger the tooth, the larger the gullet. The hook angle is the angle of the tooth’s cutting edge as it relates to the centerline of the blade. Rip saws usually have a hook angle of about 30 degrees. Crosscut saws usually have a hook angle of about 15 degrees. The greater the hook angle, the bigger the tooth’s bite. Negative hook angles are sometimes used for tough cutting jobs. Some circular saw blades designed to cut used lumber have a negative hook angle. This allows them to cut nails or other metal in the wood. Top clearance is the downward slope of the back of the tooth. This slope keeps the back of the tooth from rubbing on the wood. Without top clearance, the blade cannot cut.

Common Blade Types

Rip Blades
Rip blades have deep gullets and a large hook angle. The tooth’s cutting edge looks like a chisel. It has a straight cutting edge designed to cut with the grain. Rip teeth are usually quite large.

Crosscut Blades
Crosscut blades have smaller teeth than rip blades. The teeth on a crosscut blade come to a point, not an edge. This allows them to cut the stringy fibers in the wood.

Combination Blades
Combination blades are designed for both ripping and crosscutting. They work very well for cutting wood fibers at an angle (miter joints). Some combination blades have teeth that come to a point, but have a rip-tooth profile. Others have a chisel edge and a smaller hook angle. These blades do not produce smooth cuts, but they are well suited to general carpentry on rough construction. Smooth-cutting combination blades are sometimes called novelty combination blades. These blades have both rip and crosscut teeth. Novelty combination blades are preferred for cabinet and furniture work. This is because they cut smoothly with little tear-out.

Hollow-Ground Blades
Hollow-ground blades are blades with no set. The sides of the blade are recessed for clearance in the kerf. Some hollow-ground blades have sides that are recessed all the way to the hub. Others are recessed only part of the way. Blades with partially recessed sides cannot cut thick stock, but are more rigid. Hollow-ground blades cause less splintering and tear-out in the wood they cut. The sides of the blade may burn and accumulate pitch (wood residue) if they are used for heavy cutting instead of finish cutting. Hollow-ground blades work best with very true stock. Most hollow-ground blades have novelty combination teeth. Hollow-ground blades are sometimes called planer blades. This is because the wood is very smooth after being cut. It appears to have been planed.

Plywood Blades
Plywood blades, sometimes called paneling or veneer blades, are designed to cut hardwood plywood with cabinet- or furniture-grade outer veneers. These blades have very fine crosscut teeth with little set. Some of these blades are hollow ground. The fine teeth and small amount of set allow very smooth splinter-free cuts. These blades should be used only when appropriate. Using them for other purposes can ruin them quickly. Certain types of plywood cores (particle or fiber) can dull these blades quickly. Carbide-tipped blades would be a better choice for particle- or fiber-core plywood or other sheet stock. Plywood blades can be useful when you have to resaw solid wood. They have a fine kerf which reduces the amount of wood wasted. In addition, because the teeth are offset, there is little friction during the cut. The small teeth also take a small bite and reduce the chance of kickback. These blades also work well for sawing the lid off a box.

Carbide-Tipped Blades
Carbide-tipped blades have teeth made from small pieces of carbide. The carbide is brazed onto the circular blade. Usually, there is a little set cut in the blade. This is where the carbide is brazed. Most carbide tips are wider than the metal blade, so no set is required. Carbide is much harder than the steel used for conventional blades. Carbide-tipped blades stay sharp five to ten times longer than conventional blades. Because of its hardness, carbide is also quite brittle. Carbide will fracture easily if struck against a hard object. Carbide-tipped blades must be handled with care. Carbide-tipped blades are more expensive than steel blades, but they require much less maintenance. Carbide-tipped blades are preferred for tough materials such as hardboard, plastic laminates, and particleboard. Carbide-tipped blades come in rip, crosscut, combination, hollow-ground, and plywood categories. They do not always resemble their steel counterparts. Usually, the type of teeth, the number of teeth, and the hook angle determine the blade’s function. The teeth may be alternate top bevel, triple chip, rip, cut-off, or combination.

Blade Deflection
A condition in which the circular-saw blade bounces away from the workpiece.

Carbide-Tipped Blade
A blade with teeth made from small pieces of carbide. Carbide-tipped blades are much harder and more brittle than the steel used for conventional blades. They are also more expensive, but require much less maintenance. Carbide-tipped blades come in the following classifications: rip, crosscut, hollow-ground, and plywood.

Coarse Blade
A blade with large teeth, designed for heavy, fast, or less delicate work.

Fine Blade
A blade with small teeth, designed for more delicate work.

Crosscut Blade
A blade that cuts across the grain. Crosscut blades have smaller teeth than rip blades. These teeth come to a point, not an edge.

Footprint (blade)
Amount of blade engaged with the workpiece.

Friction
The amount of resistance caused by contact between the sides of the blade and the saw kerf.

Hollow-Ground Blade (also called Planer Blade)
A blade with no set. The sides of the blade are recessed for clearance in the kerf hollow-ground blades should be used to cut mitres and compound mitres, but not used for heavy ripping.

Kerf
The cut made by a circular-saw”, blade. The kerf must be larger than the saw-blade thickness.

Particleboard
Sheet material made from wood chips or wood particles.

Resins
Material within the wood which can build up on sides of the blade.

Runout
The amount that one surface is not true with another surface, or any deviation from a true orbit.

Rip Blade
A blade with a straight-cutting edge that is designed to cut with the grain. Rip blades have deep gullets and large hook angles.

Tear-out (grain)
When the blade rips or tears out the grain of a workpiece. Tear-out can occur on the back, top, or bottom of a workpiece.

Tooth Set
The bend in the blade’s teeth that allows the blade to cut a kerf that is larger than the blade’s thickness.

BLADES

A dull blade will cause slow, inefficient cutting and an overload on the saw motor. It is a good practice to keep extra blades on hand so that sharp blades are available while the dull ones are being sharpened.  In fact, many lower-priced blades can be replaced with new ones at very little cost over the sharpening price. Hardened gum on the blade will slow down the cutting. This gum can best be removed with trichlorethylene, kerosene or turpentine.

The following types pes of blade can be used with your saw:

  • COMBINATION BLADE—This is the latest-type fast-cutting blade for general service ripping and crosscutting. Each blade carries the correct number of teeth to cut chips rather than scrape sawdust.
  • CHISEL-TOOTH COMBINATION—Chisel-tooth blade edge is specially designed for general-purpose ripping and crosscutting. Fast, smooth cuts. Use of maximum speed in most cutting applications.
  • FRAMING/RIP COMBINATION—A 40-tooth blade for fascia, roofing, siding, sub-flooring, framing, form cutting. Rips, crosscuts, mitres, etc. Gives fast, smooth finishes when cutting with the grain of both soft and hard woods. Popular with users of worm-drive saws.
  • CROSSCUT BLADE—Designed specifically for fast, smooth crosscutting. Makes a smoother cut than the Combination Blade listed above.
  • RIP BLADE—Fast for rip cuts. Minimum binding and better chip clearance given by large teeth.
  • PLYWOOD BLADE—A hollow-ground, hard-chromed surface blade especially de¬signed for exceptionally smooth cuts in plywood.
  • PLANER BLADE—This blade makes both rip and crosscuts. Ideal for interior wood¬work. Hollow ground to produce the finest-possible saw-cut finish.
  • FLOORING BLADE—This is the correct blade to use on jobs when occasional nails may be encountered. Especially useful in cutting through flooring, sawing reclaimed lumber and opening boxes.
  • METAL-CUTTING BLADE—Has teeth shaped and set for cutting aluminum, copper, lead, and other soft metals.
  • FRICTION BLADE—Ideal for cutting corrugated, galvanized sheets and sheet metal up to 16 gauge. Cuts faster, with less dirt, than abrasive disc. Blade is taper-ground for clearance.

Four Popular Saw Blade Tooth Designs

Flat Top Grind (FT).
Generally, or cutting material with grain. Larger gullets on this type blade accept greater chip loads; permit higher feed rates. Excellent for going on either single or multi-rip machines where speed of cut are more important than quality of cut. Teeth with square or flat top shape act as chisels, cutting aerial with chisel-like action. Also serve as rakers to clean out the cuttings or chips.

Triple Chip & Flat Grind (TC&F).
Recommended for cutting brittle and/or hard, abrasive-type materials. Two shapes of teeth—alternate triple-edge and flat top design for dual action Cutting. Triple-edge teeth chip down center of kerf; flat top raker teeth follow to clean out material from both sides. TC&F blades with negative hook angle are also recommended for cutting non-ferrous metals. Negative hook angle prevents climbing: gives you total control over the feed rate.

Alternate Top Bevel Grind (ATB).
For across-the-grain cut¬ting and/or cut-off and trimming operations on undefined grain work. Top bevel shaped teeth sever the material with shearing action alternately left and right. Given a choice, the ATB blade with the higher number of teeth will produce the higher quality of finish cut. Where finish is no con¬cern, select the blade with fewer teeth.

Alternate Top Bevel & Raker (ATB&R).
Excellent for cutting operations both with and/or across the grain. Achieves a fairly high level of quality over wide range of cuts. Two sets of shearing-action alternate left and right top bevel teeth followed by a raking action flat top tooth with large round gullet to facilitate chip removal.

Carbide-Tooth Geometry
The tooth geometry of —bide-tipped blades is designed to improve cut quality. There are four basic tooth 7-figurations used on carbide-tipped blades: alternate top bevel (ATB), alternate top bevel and maker (ATB & Raker), triple chip (TC), and flat top FT). -Alternate top bevel teeth are designed primarily for crosscutting, although they are also used for ripping. When they are used for ripping, feed speed drops somewhat. Alternate top bevel teeth come to a point on alternate sides of the blade. The points cut the edges of the kerf before the middle of the kerf is cut out. This reduces the chance of tear-out. If you plan to do ripping and crosscutting, use a blade with alternate-top-bevel-and-raker teeth. The alternate top-bevel teeth ensure good results when you are crosscutting, and the raker teeth (which have a flat top) clean out the kerf during rip cuts. They actually rake out the chips and increase feed speed.

COMMON BLADE TYPES
The flat top raker tooth is slightly lower than the alternate top bevel teeth. This prevents the raker tooth from causing tear-out during a crosscut. If you experience tear-out when crosscutting with an alternate-top-bevel-and-raker-tooth configuration, it is likely that the points have dulled and the raker teeth are in the same orbit as the alternate top bevel teeth. The triple-chip tooth configuration is designed for cutting plywood, particleboard, and other wood-based sheet stock. One tooth has a flat top, and the next tooth looks like a flat-top tooth with the corners cut off. The tooth with its corners cut off separates the material, and the flat-top tooth planes the sides for a smooth tear-out-free cut. The tooth’s shape resists the abrasive glues and resins in sheet stock. This allows the blade to remain sharp after prolonged cutting of sheet stock. Blades with triple-chip teeth can also be used for cutting solid stock, but generally they are not as efficient as blades with alternate top bevel or alternate-top-bevel-and-raker teeth. Flat-top, carbide-tipped blades have only one function: ripping. Since the wood fibers go the long way in the board, the flat-top tooth will rip the wood smoothly. The quality of the cut is diminished greatly when a flat-top blade is used for crosscutting. Blade Noise Saw blades are not equal in the noise they generate. Blades with laser cuts through them which run parallel with the blade’s rim tend to produce less noise. This is because the noise does not resonate through the blade, but is stopped at each laser cut. Blade noise is a function of the blade design, the saw the blade is mounted on, and the material being cut. When buying blades, inquire about the noise level of the blade when it is coasting, and while it is cutting. Blade dampeners and saw collars can reduce blade noise somewhat. Chip-Limiting Blades Some carbide-tipped blades have a chip-limiting feature. The chip-limiting feature slows the feed speed somewhat because it limits the size of the bite any tooth can take. It also reduces the chance of kickback because each tooth has such a small grip on the wood. The blade’s plate and rim stop the stock from feeding too quickly into the blade. A chip-limiting blade is ideal for beginning woodworkers. They will have better control over the stock and will not be intimidated by the blade. This makes it easier for the beginner to succeed at the table saw. Experts will not notice any difference in blade performance except when power feeding.

Selecting Blades
When you select a saw blade, you reach a series of compromises concerning hook angle, number of teeth, size of gullets, and a number of other design factors. This is why one blade cannot do all things. There are several factors you must consider when selecting a blade. In addition to tooth style and configuration, you must have an understanding of the relationships between the saw, its power and tolerances, the wood, and the type and diameter of saw blade. These all have an influence on friction (blade heat) and feed speed. Friction is a cause of most sawing problems. When you use a fine blade (a blade with many teeth), there are more teeth in the wood during the cut. Since the teeth are smaller, they take a smaller bite. This causes the feed speed to decrease, which means an increase in friction. Increased friction can overwork the motor and cause burning on both edges of the saw kerf. Regardless of how smooth the cut is, burning will ruin its appearance and reduce edge-gluing strength. When the motor is overworked, the tip speed of the blade decreases. This condition increases blade torque and could contribute to a kickback. If you find that the motor is being overworked, go to a coarser blade. All things being equal, a carbide-tipped saw blade will generate more friction than its tool-steel counterpart. This is because the clearance on a tool-steel blade is obtained by bending or offsetting the teeth. This is known as set. The offset teeth touch a small area in the kerf, so there is not much friction. In thick materials, a tool-steel blade might reduce friction enough to improve the cut. Tool-steel blades do not usually produce as high quality a cut as carbide-tipped blades, so they are used as a last resort to reduce friction on a thick cut. For example, a 24-tooth, carbide-tipped blade might burn when making a cut in material. A 24-tooth steel blade would have about one-fourth the friction, so it may handle the cut even on a light-duty table saw. Tool-steel blades are not appropriate for materials such as particleboard and fiber-core plywood. As a guideline, try to keep three to five of the blade’s teeth in the wood during the cut. This will minimize the amount of friction and maximize feed speed. Remember, as the stock gets thicker there are more teeth in the wood. This reduces feed speed, which taxes the saw motor and increases friction. The solution is to replace the blade with a coarser one. If you tilt the saw blade, friction will also in¬crease. For example, if the blade has five teeth in the wood, and you tilt the blade to 45 degrees, there will now be seven teeth in the wood, and the stock will be 1.4 times as thick. This is because the hypotenuse of an isosceles right triangle is about 1.4 times as long as the other legs. To reduce the number of teeth in the wood, some woodworkers will raise the saw blade to full height. While the number of teeth in the wood decreases, the footprint of the blade in the wood is much greater. This increases the chance of a kickback. If the board twists slightly during a rip cut, this will actually cause binding, and possibly a kickback. There is also a much greater chance of injury with the blade at full height. These injuries can be severe, so keep the blade low and use the guard! If the blade has too many teeth to do the job efficiently, change blades. Select a blade with fewer teeth; it will increase feed speed and reduce friction. Table-saw horsepower is also a factor in de¬temining which blade to select. A table saw needs at least 1/2 actual horsepower to cut efficiently. If your saw has less than 1/2 horsepower, consider using a smaller- diameter blade. If you own a 10-inch table saw, consider mounting an 8-inch¬diameter blade on the saw. A smaller blade requires less energy to turn, so there is more energy left to cut wood. The peripheral speed (rim speed) of the blade decreases, so you will be feeding the stock a little slower. Select a coarser blade to compensate for the slower feed speed. A smaller blade will not cut as deeply, but most woodworkers rarely need to use the full depth of the blade. In those rare cases when you do, change to a larger- diameter blade. One additional advantage of the smaller-diameter blade is reduced blade deflection. If the arbor of the saw has a .002 -inch run-out, it will be more obvious at the tip of a 10-inch blade. The farther the tip of the blade is from the run-out, the more noticeable it becomes. Poorly toleranced saws actually work better with a smaller- diameter blade. The following list contains generalizations con¬cerning saw blades. Use this information to help determine which blade to use in a certain situation. Remember, this isgeneralized information. There are always exceptions to the rule.

1. Harder woods require a slower feed rate and develop more heat. Coarser blades or lighter cuts (less depth) increase feed speed.

2. Three to five teeth in the wood are ideal. Softer woods can tolerate more teeth because they have less feed resistance.

3. Smaller-diameter blades require less energy to turn, so there is more energy to cut wood. Smaller blades also run truer because arbor run-out is not as pronounced.

4′. Tool-steel blades generate less friction than carbide-tipped blades. This is because there is less metal contacting the sides of the saw kerf.

5. Tool-steel blades will become dull faster than carbide-tipped blades. Tool-steel blades cannot be used on materials with high-glue contact such as particleboard and fiber-core plywood. The glues in these materials are so hard that they actually take the edge off a tool-steel blade in one cut.

6. If you have two carbide-tipped blades with an equal number of teeth, remember that the blade with the largest gullets (openings in front of the teeth) will cut the fastest.

7. Friction in the saw cut is usually caused by the blade, but it can also be caused by misalignment. Make sure that the fence and blade are parallel to the miter slot. Any misalignment can cause friction. There are ways to determine what is the cause of friction. If both sides of the saw kerf are burned, the blade is too fine. If only the fence side is burned, the fence is probably pinching the stock against the blade. If stock tends to creep along the fence of the miter gauge when you are crosscutting, the blade is not parallel to the miter slots. Check your owner’s manual for alignment specifics.

8. Tilting the blade increases friction. The opera¬tion increases friction by making the cut deeper, engaging more teeth in the wood, and reducing feed speed.

9. Keep the blade no more than 1/4 inch above the work. This will reduce the footprint of the blade in the work and minimize the chance of kickback.

10. For maximum efficiency, use the coarsest blade that produces adequate results.

11. Blades with larger teeth are best for ripping.

12. Use a rip blade when the job is strictly ripping.

13. Small teeth mean a smoother cut and a slower feed rate.

14. Hollow-ground blades and paneling blades should be used only for true, dry, cabinet-grade lumber.

15. Remove high-quality or specialty blades as soon as the job is done.

16. Green lumber and construction lumber require blades with more set than dry hardwood lumber. This is due to the increased moisture content.

17. Never use a dull blade. It is unsafe and produces poor results.

Always analyze the job using the general rules listed and any other information you may have. The time spent changing blades is time well spent. The correct blade does the most efficient and safest job. Dull blades waste time and energy. Trial-and-error experience will help you select the best blade for every job you do. Make note of which blade does the best job. This provides a ready reference for future use.

Some blades have a knock-out arbor hole so that they may be used with more than one size of arbor. Be sure the knock-out is in securely when it must be used. The blade’s arbor hole should just fit the arbor. A sloppy fit means the blade is incorrect for the arbor. Extra knock-outs or spacers can be purchased at most hardware stores. A prick punch may be used to offset metal around the arbor hole. This holds the knock-out in more securely. Knock-outs are frequently removed when the blade is sharpened. Always check the arbor hole after your blades have been sharpened.

Evaluating and Selecting Carbide-Tipped Blades
When selecting a carbide-tipped blade for your saw, select a blade 8-10 inches in diameter with 24 to 60 teeth. For general-duty work, use a 10-inch blade with 40 to 50 alternate-top-bevel or alternate-top-bevel-and-raker teeth. As you become familiar with your saw and the type of work you are doing, select the saw blade best suited to your needs. Buy only what you need; add blades as the job presents itself. Review all information in this section before buying a blade. Not all carbide-tipped blades are equal in quality.

Before buying any blade, look it over and evaluate it carefully. The size of the carbide tips is important. The larger the tips, the more times they can be sharpened, but if they are too long, they can increase blade friction.

Look at the braze joint between the blade and carbide tip. It often indicates blade quality. A quality braze joint will have no voids or pits, and all the braze joints on a blade will be the same size.

Inspect the teeth; they should be ground smooth. The smoother the surface of the carbide, the better the cut. The smoother the carbide, the longer the blade will remain sharp. This is because smooth grinding puts more carbide at the edges of the blade, where cutting occurs. More carbide increases the resistance to wear.

Keep the carbide blade sharp. Use a reliable sharpening service that leaves no coarse grinding marks.

Some lower-quality blades are painted with a silver paint. This makes the blade look like an expensive alloy. In reality, all the paint does is hide the scratches in the carbide tips and the pits in the braze joints. High-quality blades are never painted; the manufacturer is pleased to show you the carbide tips and braze joints.