The most economical, practical, and accurate method of cutting structural and finish lumber is by the use of electric power saws.
In carpentry work, there are many hand cutting operations that can be done with a circular saw. Power tools for carpentry should be selected with care.
Several factors should be considered in selection: cost, upkeep, safety, and labor-saving efficiency.
Our Circular Saw Guide: First, the Basics
The handle is generally located on the top, on the back, or on an angle between the top and back, depending upon the manufacturer. Control of the saw is usually by means of a trigger switch located in the handle and operated by the forefinger of the right hand.
Two adjustment devices are built into the saw. one for the depth of cut adjustment and one that allows for angular adjustment of the blade from zero (90 degrees) to slightly more than 45 degrees.
The graduated angle scale above the thumbscrew clearly shows these settings, as shown in pic 2. A third adjustment is provided through the use of a rip guide. Two small knurled screws on the front of the saw base allow quick installation and adjustment of the rip guide and hold it firmly in position.
The guide is graduated in 1/8-inch increments up to 5 inches.
Aligning the desired width of the rip as graduated on the rip guide, with the rip guide mark on the saw base, ensures a uniform, measured cut. as shown in pic 3 shows the guide set for all/4 inch width of the rip.
Safety guards differ among manufacturers but usually blade guards are provided on the front and bottom of the blade. In the saw illustrated, these are telescoping guards that return to the positions shown through spring action.
One additional feature of the saw illustrated is the kick proof clutch.
This relieves motor strain and possible burnout. It also protects the operator from possible kickback of the saw.
Circular Saw Blade Selection
The selection of the proper circular saw blade ensures the success of the cutting job. Using the right blade contributes to the safety of the operator and the maximum efficiency of the machine. It saves time, expense, and energy.
There are three basic types of blades for the portable electric saw: crosscut, rip, and combination. It is important that the right blade is used for a given job.
A crosscut blade is illustrated in pic 4. A ripsaw blade is shown in pic 4 also. The teeth of a circular saw blade are set (tips of the teeth are bent slightly outward) alternately left and right.
By setting the teeth of the saw, the kerf (saw cut) is slightly wider than the thickness of the blade.
Crosscut teeth are filed to an angle of 75 to 80 degrees producing a knife-edge on the side to which they are set.
The result is that the cutting action resembles that of a knife, slicing fibers of the wood.
The ripsaw blade has flat-faced teeth more like a chisel. It scoops out larger chips than the crosscut.
The combination blade, pic 6, combines features of both the crosscut and ripsaw blades.
It has two outstanding advantages for rough work: it operates on less power and can be sharpened very easily. For special work, special types of blades are available.
Pic 7 shows a planer or miter blade, which is a type of combination blade. It consists of a series of four cutting teeth and one raker tooth.
The cutting teeth resemble crosscut teeth and are set to obtain clearance of the blade. The raker teeth are similar to ripsaw teeth but are not set.
This type of blade makes an especially smooth cut and is very suitable for cutting inside trim. It should be used on dry wood only.
Another special type of blade is called the flooring blade or nail blade. This is ruggedly constructed and designed for use where random nails may be encountered.
They are commonly used for cutting old flooring, reclaimed lumber, and packing cases. Carbide-tipped blades hold a sharp edge longer than regular steel blades. Tungsten- carbide tips brazed onto a hard alloy steel blade give these blades their durability.
They are generally used to cut very hard materials which might rapidly dull the standard steel blade. A final group of special blades are the abrasive cutoff wheels.
They are designed for sawing, slotting, and grooving hard dense material.
There are three types of abrasive cutoff wheels: one for nonferrous metals; one for masonry, brick, stone, tile, concrete, and cinder block; and one for ferrous metals.
Take special care not to twist the saw when cutting with abrasive cutoff wheels.
Although very strong, they are also brittle and can break with dangerous results if the saw is twisted while cutting.
It is also important that the air passages be cleared of dust immediately after using these blades. Metal, concrete, or mortar dust are very abrasive and can severely damage the motor assembly.
Taking Care of Your Circular Saw Blades
To keep blades in good condition, the operator should observe the following precautions.
- Use crosscut saw blades for crosscut work only. Use ripsaw blades for ripsaw work only.
- If the cutting process requires the constant changing of saws, use a combination saw blade.
- Do not use a saw unless there is sufficient set in the teeth to make a saw kerf through which the body of the blade will move freely.
- Do not use a blade after you sense that it is dull, needs setting, or has come in contact with metal.
- Do not twist the saw from a straight line while it is making a cut.
- If a saw becomes cracked, some mechanics drill a small hole through the blade at the end of the crack. This will prevent the crack from extending. However, when the injury it might cause to the operator if it is sprung again is considered, it is better to have the saw ground below the crack or to dispose of the blade.
- If the blade becomes coated with resin from cutting resinous woods, remove it with a little turpentine and fine sandpaper.
How to Change Circular Blades
- Be sure the saw is disconnected from the power source.
- Block the blade by inserting a piece of wood against the teeth at the front of the saw. Then loosen the retaining screw by turning it counterclockwise with the wrench pro¬ vided for the saw.
NOTE: Some saws have (a) a milled flat on the shaft so that it may be held stationary with a second wrench, or (b) a hole in the saw blade and one in the gear housing, through which a nail is inserted, or (c) a built-in blade lock which holds the shaft while the retaining screw is loosened.
- Push the circular guard back until it stops in the open position.
- Remove the retaining screw and clutch spring washer. Lift the old blade from the shaft and slide down through the bottom opening.
- Clean the bearing surface of the collars. Add a film of grease, smoothing it over the bearing surface with the finger.
- Place the new blade on the arbor, making sure the teeth point up at the front of the saw. Add a film of grease around the hole in the blade.
- Place the clutch spring washer in position against the blade. Place the retaining screw in position and tighten by turning clock¬ wise, leaving the clutch spring bowed out slightly. Allow the circular blade guard to swing back in place.
Cutting across the wood grain may be done with the combination blade if smooth¬ ness of the cut is not a factor.
The combination tooth is really a compromise between the ripsaw tooth and the crosscut tooth.
For rough or wet lumber, use the combination blade. Where a smoother cut is required, use the crosscut blade.
How to Perform a Crosscut
- Be sure the work to be cut is solidly supported.
- Adjust the depth of cut so that the blade will extend through the material to be cut to the extent that the gullets of the teeth clear the thickness of the material, as shown in pic 13.
- Be sure the angle-adjustment thumbscrew is set and locked at zero.
- See that the saw guard is in the proper position.
- Plug the saw into the power outlet and make certain the electric cord is properly grounded and is positioned so that it will not become tangled during the sawing operation.
- Grasp the handle firmly with the forefinger ready to operate the starting trigger. Keep the other hand well out of danger.
- Place the front of the saw base on the work so that the guide mark on the front plate and the line of cut are in line. Using a protractor guide to make a square crosscut
- With the blade well clear of the work, start the saw and allow the blade to attain full cutting speed.
- Advance the saw into the wood, following the line of cut with the guide mark. Save the full cutting line. As skill improves, only half the width of the line should be saved. NOTE: Beginners may use a squaring template to guide the saw. After practice, simply use a square to mark the material.
- Guide the saw steadily through the cut. If the saw stalls, do not release the starting trigger but back out the saw until it resumes cutting speed, then continue cutting. A wedge placed in the saw kerf will help prevent the saw’s binding when cutting a wide board. NOTE: If the saw stalls excessively, disconnect the power source and check the blade for dullness or lack of set.
- When the end of the cut is reached, release the trigger switch and allow the blade to follow through as you lift the saw out and away from the work. Twisting the saw as it is removed may score the work.
Cutting with the grain, or ripping, can be done with the combination blade or with the ripping blade. The ripping blade will give a smoother cut. The rip cut is generally more difficult to make than the crosscut because of the length of the cut. Important items to bear in mind when ripping with the portable saw are:
- The board you are ripping must be well supported to prevent sagging.
- The board must be securely held in position.
- The saw blade must not cut into the wrong material.
How to do a Rip Cut
- Insert the rip guide in the frame,
- The guide may be inserted into either side of the frame for wide or narrow widths.
- Proceed as in crosscutting, steps 2 through 11. If the saw kerf seems to close and bind the blade, insert a wedge to open it and give clearance to the blade.
If the ripping is so long that it will be necessary to walk beside the board while cutting, make the following additional preparations before making the cut:
a. Support a 2-inch x 10-inch plank at least as long as the proposed cut, on two horses or other solid foundation at a comfortable height for cutting. b. Place the board to be cut on the 2- inch X 10-inch plank. Allow its edge to
Adjust the rip guide to the desired width by aligning the proper graduation on the guide with the mark on the saw base. Tighten the two thumbscrews to lock the guide in position.
NOTE: If the rip guide contains no graduations, adjust it so that the guide mark on the front plate of the saw aligns with the proposed line of cut. The side of the board against which the guide rides must be straight.
For cuts wider than the scope of the guide, a straight board clamped to the workpiece will serve as a guide.
Project beyond the edge of the plank about 1 inch more than the width of the proposed cut. Tack the board to the plank in this position using nails that will hold securely at each end.
Be sure to have a clear, unobstructed place to walk while pushing the saw along the required length, and see that the saw cord will not become fouled while making the cut.
A bevel cut with the portable electric saw is made in much the same manner as a crosscut. These cuts, however, require the additional adjustment of the angle segment thumbscrew to set the blade at the angle desired. A simple miter cut is actually nothing more than a straight-blade cut made at a 45-degree angle across the board.
A bevel cut is one on which the saw blade is set at the required angle and the cut is made straight across the board.
A compound miter or compound bevel cut is one in which the saw blade is set at the required bevel angle, and the line of cut across the board is also laid out at an angle.
Such cuts are used for ridge cuts of hips, valley jacks, and cripple rafters.
How to Make a Miter Cut
- Layout the line of cut on the material to be cut, using a sliding T bevel, framing square, or protractor to obtain the 45-degree angle.
- An angle gauge may also be used and is the best method. This gauge contains a pro¬ tractor and, when set to the proper angle, provides a guide against which the saw base is pushed as the cut is made.
- Cut as in crosscutting.
How to Make a Bevel Cut
- Loosen the angle segment thumbscrew and rotate the saw frame until the pointer on the angle indicator rests at the desired angle of the bevel. Tighten the thumbscrew securely.
- Adjust the depth of cut so that the saw blade will penetrate the bevel thickness of the material to be cut.
- Proceed to cut as in crosscutting.
NOTE: The bevel thickness will be greater than the straight thickness and it may be necessary, if the blade will not clear the bevel thickness, to make a cut on each side of the wood to cut through it.
If so, reduce the depth of cut to a little more than half of what is ordinarily required.
If a cut must be made on each side of the wood, turn the piece over and maintain the same saw adjustments as with the first cut. Guide the second cut so that the two kerfs will be in line.
How to Make a Compound Bevel Cut
- Layout the line of cut on the material to be cut, using a sliding T bevel, framing square, protractor, or best, an angle gauge.
- Loosen the angle segment thumbscrew, rotate the saw blade to the desired bevel angle as indicated by the pointer, and tighten the thumbscrew securely.
- Adjust the depth of cut so that the blade will penetrate the bevel thickness of the material to be cut. Tighten the depth adjustment knob securely.
- Make a trial cut on scrap lumber and check the accuracy of the bevel angle and the line of cut angle using a protractor or an angle gauge.
- If all adjustments are accurate, proceed to cut as in crosscutting, except the saw should be guided along the outside of the line of cut with reference to the guide mark on the saw base for miter cuts.
Cutting Dadoes, Grooves, and Rabbets
Rabbet and dado cuts with the portable electric saw are made in much the same manner as crosscuts and rip cuts except that the depth adjustment is set so the blade cuts only to the depth of the rabbet or groove desired. A gauge or straightedge is helpful for both types of cuts.
How to Make a Rabbet Cut
NOTE: For edge rabbet cuts (with the grain), use a ripping blade; for end rabbets, use a crosscut blade.
- Mark the required rabbet outlines along the edge and face of the board to be cut.
- Secure the board to be cut on its edge
- Attach the rip guide to the base of the saw and adjust the guide to the depth of the desired rabbet (Picture 20).
- Adjust the depth of cut so it will cut the full width (Picture 20 A) of the desired rabbet.
- Make the cut.
- Now place the board flat with the rabbet outline mark face up. Secure it firmly.
- Set the ripping guide so the blade will follow along the outline mark of the rabbet (C in Pic 21).
- Set the depth of the cut so the blade will cut the full depth of the rabbet (A in Pic 21) and will meet the previous cut.
- Make this second cut. The surplus wood should easily be removed.
Cutting a Pocket
The pocket or interior cut is one that starts and ends within the width or length of a board, floor or wall. When starting this cut, it is necessary to hold the circular blade guard out of the way.
Once the cut is started, the guard stays out of the way without being held.
How to Make a Pocket Cut
NOTE: Since cutting will be done both with and across the grain, a combination blade is best used.
- Mark the area to be cut. Use clean sharp lines and mark exactly to the corners.
- Set up temporary guides along these lines to aid in guiding the saw accurately. Narrow wood strips tacked in position can be used.
- Adjust the depth of cut so the blade will cut through the material only. NOTE: Make sure there are no nails or other obstacles in the cutting paths.
- Push the telescoping guard lever for¬ward so the lower edge of the blade is exposed.
- Starting near a corner limit, tilt the saw forward until the front edge of the blade rests on the surface on the waste side of the line of cut.
- With the blade clear of the material, start the motor and when it has reached full speed, lower the blade into the surface until the base rests on it firmly.
- Advance the saw to the comer. Remove it from the cut, turn it around, and cut in the opposite direction to the corner.
- Proceed in this manner around the other sides of the opening.
NOTE: The circular blade will extend slightly beyond the corner on the top of the work if a full cutout is made. This can be avoided by stopping the cuts when the blade just reaches each comer on the top surface, then finishing the corners with a keyhole or handsaw.
Many types of cuts can be made with the portable electric saw and its standard equipment. With additional accessories, which can be readily attached to the saw frame, and with skill on the part of the operator, this type of saw has the capacity to make any type of cut required by the woodworker.
Special blades such as were described earlier in the unit make possible the cutting of every type of material in modern construction.
Circular saw power rating
The size of a circular saw is determined by the diameter of the blade it uses. Saw sizes range from 4 1/2 inches to 12 inches.
The depth of cuts ranges up to 4 3/8 inches with a 12- inch blade. Horsepower (hp) ratings range from 1/2 hp to 2 1/2 hp.
Most manufacturers report the amperage (amp) rating rather than horsepower. To calculate horsepower, multiply volts by amperes and divide by 746. Seven hundred and forty-six is the number of watts required to do 1 hp of work.
The specifications for the following example are 115 volts ac and 10 amps.
Using the formula, horsepower is calculated as:
volts X amps = j^p 115 x 10 _ i 54 hp 746 746
The result is a rated horsepower of 1 1/2 hp. As new motors and power tools are produced motor ratings will be measured in watts and kilowatts rather than amps or horsepower.
1 hp = 746 watts
Therefore, to convert the above example to the metric equivalent, multiply as follows:
1.54 hp X 746 = 1 148.84 watts per hp
If 1 000 watts equal 1 kilowatt (kW), then
1 148.84 watts = 1.15 kW
The result in metrics is a motor rating of 1.15 kW.
The saw shown in pic 1 is a heavy-duty circular saw. Its universal motor is rated at 12.5 amps and operates on 120 volts ac. The blade is 7 1/4 inches in diameter with a 5/8-inch arbor hole. At 90 degrees, the depth of the cut is 2 7/16 inches.
At a 45- degree angle, it is 1 29/32 inches. No-load or idle speed is 5800 rpm. The machine has precision ball bearings.
The saw is 10 inches long, weighs around 5 pounds, and is double-insulated.
Unlike handsaws, portable power saws cut from the near to the far edge of the work and from the underside of the board up.
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