Circular saw

How it works

An electric motor turns a shaft that carries the blade, either directly or through gearing. Michel’s 1922 patent application describes the arrangement: a motor with a handle and a switch, a housing at the front carrying a shaft, a toothed rotary cutter on that shaft driven through gears from the armature shaft, and a plate over the upper edge of the cutter that serves as a guard.

The shoe, also called the base plate, rests on the surface being cut and sets how far the blade projects below it. In Michel’s patent an adjustable guide arm with a pivoting foot determined both the depth of cut and the angle of the blade. In current saws a depth lever slides the shoe up and down and a bevel lever tilts it, and DEWALT’s manual says the blade should project far enough to expose one half of a tooth below the material.

A spring-loaded lower guard covers the part of the blade below the shoe and is pushed back by the work as the cut advances. Wodack and Haas described such a guard in 1926: when the saw was withdrawn from the work and held by its handle, the guard swung by gravity to hang beside the projecting part of the blade. Because the blade teeth move upward through the material at the shoe, any splintering occurs on the face that is up during the cut.

Anatomy

Motor housing and handle: Michel’s 1922 drawing shows a motor with a handle through which the supply wires run and a switch on the handle; current saws carry a trigger switch with a lock-off button.
Shoe (base plate): The flat plate that rides on the work. Its position relative to the blade sets depth of cut and bevel angle.
Depth adjustment lever: Releases the shoe so that it can be moved up or down relative to the blade.
Bevel adjustment lever: Releases the shoe so that it can be tilted for angled cuts.
Fixed upper guard: Covers the upper part of the blade. OSHA requires an upper guard that covers the saw to the depth of the teeth on portable circular saws with a blade diameter over 2 inches.
Retracting lower guard: Spring-loaded; pushed back by the work and returned by its spring. A retracting handle lets the user lift it manually for special cuts.
Kerf indicator: A mark or notch at the front of the shoe that shows where the blade will cut.
Arbor, blade clamping screw and blade lock button: The blade is held on the spindle by a clamping screw; the lock button holds the spindle still while the screw is turned.
Auxiliary handle: A second grip, so that both hands are on the saw.

Variants

Direct-drive (sidewinder): Motor beside the blade with its shaft parallel to the blade arbor; the type that Porter-Cable introduced after the worm-drive saw, according to a 2002 trade-magazine history.
Worm-drive and hypoid (inline): Motor behind the blade, geared to the arbor through a worm or hypoid gear set; see the separate entry for the worm-drive saw.
Cordless: Battery-powered; DEWALT lists 4-1/2, 6-1/2 and 7-1/4 inch models in its current cordless range.
Metal-cutting: Fitted with blades for non-ferrous or ferrous metal; Skil’s 1959 catalog listed hollow-ground slitting and friction blades for its saws.

Specifications

Blade diameter · in: 7-1/4Nominal size of the common framing saw; DEWALT’s DCS570 is a 7-1/4 inch saw and the Skil Model 77 took a 7-1/4 inch blade. Smaller trim saws and larger worm-drive saws exist.
Depth setting · half tooth below material: 1/2 toothDEWALT’s manual gives one half tooth projecting below the work as the setting for the most efficient cut.
Weight · lb: A 2002 trade-magazine survey gives 9 to 10 lb for a typical sidewinder and 13 to almost 17 lb for inline saws; no standard figure has been sourced.

Made to

UL 62841-2-5
IEC 62841-2-5
OSHA 1910-243

Safety and care

Safety

DEWALT’s manual describes kickback as a sudden reaction to a pinched, bound or misaligned blade that lifts the saw up and out of the work toward the operator. It advises a firm grip with both hands, the body to either side of the blade and not in line with it, and releasing the trigger and holding the saw motionless in the material when the blade binds.
The same manual says to check before each use that the lower guard closes instantly, and never to clamp or tie the lower guard open.
Do not reach underneath the workpiece. The manual states that the guard cannot protect against the blade below the material.
OSHA 29 CFR 1910.243 requires guards above and below the shoe on portable power-driven circular saws with a blade larger than 2 inches in diameter.
Never hold the piece being cut in the hands or across the leg; secure it to a stable platform (DEWALT manual).

Care

DEWALT’s manual says the lower guard spring and guard must operate properly before use; a guard that is sluggish may have damaged parts, gummy deposits or a build-up of debris, and must be serviced.
Use blades with the correct diameter and arbor hole, and with a maximum rated speed that meets or exceeds the speed of the saw (DEWALT manual).

Tips

Guide the saw by the kerf indicator
The indicator at the front of the shoe lines up with the left (inner) side of the blade, so the kerf falls to the right of the indicator. The user therefore allows for the width of the kerf to the right of the penciled line the indicator follows.1
Set the depth to show half a tooth
For the most efficient cutting, DEWALT says to set the shoe so that one half tooth of the blade projects below the material, measured from the tip of the tooth to the bottom of the gullet in front of it. The shoe then supports the blade, which reduces twisting and pinching.1
Put the good face down
The saw cuts upward through the material, so splintering appears on the face that is up. DEWALT’s manual tells the user to place the face on which appearance matters most down.1
Rest the wide part of the shoe on the side that stays
DEWALT’s manual says to place the wider portion of the shoe on the part of the workpiece that is solidly supported, not on the section that will fall off when the cut is made, and illustrates the right way to cut the end off a board.1
Use a straightedge or rip fence for long straight cuts
DEWALT’s manual says that a rip fence or straight edge guide improves accuracy and reduces the chance of blade binding when ripping.1
Calibrate the 90 degree stop against a square, then confirm with a scrap cut
To adjust the shoe for 90 degree cuts the manual says to set zero bevel, retract the lower guard, place the saw on its blade side, hold a square against the blade and the shoe, and turn the calibration screw until the shoe stops at the right angle. It then says to confirm the setting by checking the squareness of an actual cut on scrap material.1
Feed at a rate the blade can carry
The manual says to push the saw forward at a speed that allows the blade to cut without laboring, and to push more slowly but hard enough to keep working when knotty or damp sections load the saw. Forcing the saw can cause rough cuts.1

History

Earliest documented

5 August 1777 (blade); 1 June 1920 (portable electric rotary cutter)

England (blade); Louisiana (portable electric cutter)

Disston’s 1916 history says the earliest patent on circular saws is No. 1152, granted to Samuel Miller in England on 5 August 1777, and adds that similar saws are claimed to have been used in Holland nearly a century earlier. The earliest hand-held electric rotary cutter found here is Ernest Madere’s US patent 1,342,294 of 1 June 1920, for cutting sugar cane, which Michel’s 1924 patent cites as the device he was improving.1 2 3

The circular blade is older than the circular saw as a hand tool. Disston’s 1916 history dates the earliest circular-saw patent to 1777 and says that practical wood-cutting use in England began about 1790. By 1869 an American hardware catalog sold circular blades by diameter and gauge with mandrels to carry them. The catalog sold the mandrel, the shaft on which a saw runs, as a separate item, which marks these as blades for machines and not for the hand.

Moving the blade to the work required a small electric motor and a way to control depth and angle. The first hand-held electric rotary cutter found in the record is Madere’s of 1920, built to cut sugar cane. Michel’s 1922 application, which cites Madere’s patent as the device it improves, states its objects as guiding the cutter and limiting the depth of the cut, and as simplifying and making the whole implement more compact. Its claims are built around the front guide that rests on the work and the rear guide that runs in the kerf. The shoe-and-depth arrangement that defines the tool today was the point of the patent.

The companies that followed supplied the rest of the form. Wodack and Haas’s patent, filed in 1926, shows a motor in an aluminum casing, a guide rest adjustable in angle and depth relative to the motor frame, and a lower guard that dropped into place by gravity when the saw was lifted from the work. According to Skil staff, contractors were enthralled with “taking the tool to the work instead of the work to the tool,” and the company was at first competing with hand saws. A 2002 history in the Journal of Light Construction says six of the first saws were built, three taken to Atlantic City and three to Los Angeles, and that housing construction on the Pacific coast and Depression-era public works projects spread the Skilsaw in the West.

Gearing divided the market. The same 2002 history reports that, because Skilsaw owned the patent on the worm drive, Porter-Cable’s Arthur Emmons built a saw with the motor beside the blade and the blade driven straight off the armature, and that this direct-drive form was sold in Porter-Cable’s eastern markets. AskToolTalk’s account differs in date: it places Emmons’s invention in 1928, where the journal places Porter-Cable’s entry in 1929. Both sources are secondary and neither gives a patent number.

This archive does not rank the saws that followed; no independent test data on circular saws has been located. The guard rules have been settled by regulation instead: OSHA’s portable-tool standard requires upper and lower guards on every portable circular saw with a blade larger than 2 inches.

Timeline

1777 (5 August)
Samuel Miller is granted English patent No. 1152, the earliest patent on circular saws according to Disston’s history. Disston adds that circular saws had been used to cut the spaces between the teeth of clock wheels long before they were used on wood.1
c. 1814
Disston’s history says the first circular saw in the United States is “supposed” to have been made by Benjamin Cummins at Bentonsville, New York.1
1869
Sargent & Co. of New Haven list circular saws by diameter and gauge, with separate mandrels, in their illustrated catalog.1
1920
Ernest Hubert Madere of Hahnville, Louisiana, is granted US Patent 1,342,294 for an electrically operated hand-controlled rotary cutter, intended for sugar cane, with a motor on the handle and a worm and worm wheel driving the cutter.1
1924
Edmond Michel of New Orleans is granted US Patent 1,512,296 (filed 23 October 1922) for a portable rotary cutting implement with a motor, gearing, a guard plate, an adjustable front guide that sets depth and angle, and a rear guide that follows the kerf.1
1924
According to Skil staff quoted in Woodworker’s Journal, the name Skil was trademarked on 26 November 1924. AskToolTalk says the Michel Electric Hand Saw Company was incorporated on 1 July 1924.1 2
1929
Oscar Wodack and Joseph Haas are granted US Patent 1,708,345 (filed 11 June 1926) for a portable circular saw with an aluminum motor casing, worm gearing to the arbor, an adjustable guide rest, and a lower guard that swings by gravity.1
1929
Porter-Cable enters the circular saw market, according to a 2002 trade-magazine history, with a direct-drive saw designed by Arthur Emmons.1
1937
Edward Sterba of the Skilsaw company builds the first Model 77 with a 7-1/4 inch blade, according to AskToolTalk and the Journal of Light Construction.1 2
1959
Skil’s catalog of this year lists its “Super-Duty (worm-drive)” saws and blades marked for use on the Model 77.1
2003
Skil staff say the company introduced an anti-snag lower guard on the Skilsaw in 2003.1

Where the sources disagree

Who invented the circular saw?

Samuel Miller of England, by the patent of 5 August 1777 (No. 1152), the earliest circular-saw patent; similar saws are claimed to have been used in Holland nearly a century before.1
Henry Disston & Sons, The Saw in History (1916)
Benjamin Cummins, about 1814 at Bentonsville, New York, is “supposed” to have made the first circular saw in the United States.1
Henry Disston & Sons, The Saw in History (1916)
Tabitha Babbitt, a Shaker of Harvard, Massachusetts, conceived the circular saw while watching men saw wood and watching her spinning wheel; the first saw made under her instructions is said to be exhibited at Albany, New York.1
Clara Endicott Sears, Gleanings from Old Shaker Journals (1916), quoting an earlier account
The Babbitt story is most likely apocryphal. Historian Christian Goodwillie found that the account first appeared in the Boston Sunday Globe of 30 October 1898, supplied by the Harvard Shakers after Babbitt’s death in 1853, and that the first documented patent for a mill with saws “which are a circular figure” was Miller’s of 1777. Dana Rasso of the Shaker Museum calls the story likely apocryphal. Goodwillie writes that the Shakers were certainly early proponents of the circular saw.1
Snopes, reporting Dana Rasso (Shaker Museum) and Christian Goodwillie

When and by what instrument was the portable electric circular saw patented?

Filed 23 October 1922 and issued 21 October 1924 as US 1,512,296, to Edmond Michel of New Orleans, assigned to Electric Hand Saw Company, Inc.1
The patent itself
Skil “holds the original patent issued in 1921,” and Michel developed a power machete in 1921.1
Skil staff, quoted in Woodworker’s Journal
A patent for the first worm-drive circular saw was received in 1924; the earlier sugar-cane saw dates to 1921.1
Journal of Light Construction, 2002
A patent was issued on 20 January 1924, after only six saws had been built.1
AskToolTalk

Gaps in the record (7)

Skil’s own company history could not be read; the manufacturer’s history pages returned errors or carried no history text.
No patent was located for the Model E or the Model 77, for Sterba, or for Emmons’s Porter-Cable saw.
The patent record read here does not identify the year the Model E was introduced; secondary sources disagree or are silent.
The Miller patent of 1777 is known here through Disston’s 1916 history and Snopes’s account of Goodwillie, not from the specification itself; Goodwillie’s chapter in Inspired Innovations (2010) has not been read.
The date of the first portable saw with a tilting shoe is not sourced.
No independent test data on circular saw performance has been located, so buying is null.
The current ANSI/UL and IEC standard texts were not read; the standard slugs are guesses.