Chainsaw

How it works

An engine or motor turns a sprocket, and the sprocket pulls a loop of saw chain around the guide bar. Each cutter on the chain removes a shaving as it passes through the wood. The U.S. Forest Service training guide describes the cutting corner and side plate severing the wood fibers across the grain, and the top plate chiseling them out and lifting them from the kerf.

A depth gauge on each tooth rides on the wood and sets the thickness of the shaving, so its height controls how deep the cutting corner bites. The guide says a clamp-on file guide maintains the three angles of a cutter as it is sharpened, and advises setting depth gauges with a depth-gauge tool.

A clutch couples the engine to the sprocket above idle speed, a chain brake stops the chain when the sawyer’s hand or the inertia of a kickback trips it, and bumper spikes (dogs) hold the saw against the wood and serve as a pivot.

Anatomy

Saw chain: A loop of linked cutters. The Forest Service guide names three cutter types: chipper (the most versatile and the easiest to file), semichisel, and chisel (the most aggressive, for experienced sawyers).
Guide bar: The flat bar the chain runs around. The guide shows solid-nose, sprocket-nose and bow bars. A solid-nose bar is generally found on small saws.
Depth gauge (raker): The part of each tooth that sets the thickness of the shaving.
Chain sprocket, clutch and bar studs: The sprocket drives the chain, the clutch couples the engine to the sprocket above idle, and the studs hold the bar and sprocket cover.
Chain tensioner: Moves the guide bar to maintain proper tension on the chain; the guide describes front and side tensioners.
Chain brake and hand guard: The brake stops the chain when the sawyer’s hand or inertia (during kickback) activates it; the hand guard activates the brake and keeps the hand from the chain.
Chain catcher: Helps reduce the risk of the chain contacting the sawyer if the chain breaks or is thrown from the bar.
Bumper spikes (dogs): Hold the saw steady against wood and act as a pivot point in felling and bucking.
Gunning marks: Marks on the housing used to plan the direction of fall of a tree from the undercut.

Variants

Surgical chain saw: A flexible saw of small jointed links drawn behind a bone, described by Jeffray in 1806; the Science Museum Group holds French and other European saw chains of 1831–1870 cataloged as excision saws.
Link or drag chain saw (early timber form): Charles Wolf’s Electric Drive Link Saw of 1920, produced at Portland, Oregon, in three sizes weighing 70 to 90 pounds, according to Lucia.
Two-person bucking and felling saw: Stihl’s first electric saw of 1926 weighed 140 pounds and needed two people; its 1929 gasoline saw weighed 101 pounds and also needed two, according to FundingUniverse.
One-person saw: FundingUniverse dates Stihl’s first one-person saw to 1950 and its 31-pound, 4.5-horsepower BLK to 1954.
Chain type: chipper, semichisel, chisel, low-kickback: Forest Service guide: low-kickback chain is the most desirable for training inexperienced sawyers and is available in all three cutter types.

Specifications

Weight, complete saw · lb: Historical points from FundingUniverse: 140 (1926 electric), 101 (1929 gasoline), 26.65 (Stihl Contra, 1959). Lucia, writing in 1981, says power units weighing slightly less than seven pounds will cut a five-inch log in six seconds. No current typical weight has been sourced.
Guide bar length · in: Not sourced.
Chain pitch and gauge · in: Not sourced; the Forest Service guide advises selecting a file of the proper diameter for the saw chain.

Made to

ANSI B175.1
ISO 11681-1
IEC 62841-4-1

Safety and care

Safety

OSHA 1910.266(d)(1)(iv)–(v): chain saw operators wear leg protection of cut-resistant material covering the full length of the thigh to the top of the boot, and foot protection constructed of cut-resistant material.
OSHA 1910.266(e)(2): saws placed in service after the section’s effective date must have a chain brake and meet ANSI B175.1-1991; gasoline saws must have a continuous-pressure throttle control that stops the chain when pressure on the throttle is released.
Start the saw on the ground or where otherwise firmly supported, with the chain brake engaged. Drop starting is prohibited (OSHA; the Forest Service guide).
Hold the saw with the thumbs and fingers of both hands encircling the handles, and never operate it with one hand (OSHA; the Forest Service guide).
Do not cut directly overhead (OSHA), and never cut with the power head higher than the shoulder (Forest Service guide).
Fuel at least 10 feet from any open flame or ignition source and start at least 10 feet from the fueling area (OSHA).
Kickback occurs when the upper quadrant of the bar nose contacts a solid object or is pinched. The Forest Service guide advises knowing where the nose is at all times, never letting it contact another object, standing to the side of the kickback arc, cutting one log at a time and using a low-kickback chain.
Shut the saw down or engage the chain brake when carrying it more than 50 feet, or a shorter distance if terrain, underbrush or slippery surfaces create a hazard (OSHA).
Cover the bar, chain and bumper spikes with a chain guard when carrying the saw in a vehicle or by hand (Forest Service guide).

Care

Check the spark plug weekly when the saw is in frequent use; it should be dry (Forest Service guide).
Inspect the power head for loose bolts and damage; check the handlebars and bumper spikes; check the antivibration mounts for cracks in the rubber and excessive movement (Forest Service guide).
Rotate the bar so that it wears evenly, and check its alignment with the studs, adjuster and oiler (Forest Service guide).
Keep the bar, chain and roller tip well lubricated; the guide says otherwise bar and chain wear and damage excessively.
After the chain has been hand filed a few times, have it ground on a chain grinder to restore the angles and bring all cutters to the same length (Forest Service guide).
Test the chain brake before use (Forest Service guide).

Tips

The depth gauge sets the bite
The Forest Service guide says the depth gauge controls the thickness of the shaving. Set it with a depth-gauge tool that has the correct built-in setting for the chain: if a gauge stands above the slot, file it level with the top of the tool, never lower, and round off its leading edge afterward.1
Chain tension causes more trouble than anything else
The guide says more bar and chain problems come from incorrect tension than from any other single problem. The chain should be adjusted so that it does not hang from the bar and still turns freely.1
Let a sharp chain do the work
The guide says a sharp chain does the work, while with a dull chain the sawyer does the work, which tires the sawyer and wears the bar and chain.1
File with a guide that matches the chain
Use a round file of the proper diameter in a clamp-on file guide, keep the filing angle parallel with the chain as marked on the guide, file one side and then the other, and keep all cutters the same length. Square-ground chisel chain needs a square file and has no guide available.1
Match the cutter type to the work
Chipper chain tolerates the most dirt and dust and is the easiest to file. Chisel chain is the most aggressive but dulls quickly in dirt and the guide does not recommend it for brushing or limbing. The semichisel cutter is more tolerant of dirt and dust and stays sharp longer than the other cutters.1
Use the bumper spikes as a pivot
The guide says learning to use the bumper spikes (dogs) as a pivot point when felling or bucking improves control of the saw and its efficiency, and reduces fatigue.1
Aim the undercut with the gunning marks
The marks on the saw housing are used to determine the planned direction of fall of the tree from the undercut.1

History

Earliest documented

by 1790 (surgical chain saw); 1905 (patented timber chain saw)

Glasgow, Scotland (surgical form); San Francisco, California (timber form)

James Jeffray, professor of anatomy at Glasgow, wrote in 1806 that he had conceived a saw “with joints like the chain of a watch,” to be drawn behind a bone by a curved needle and cut the bone from behind forward without injuring the soft parts. He says the saw was made in London by a Mr Richards, that a sketch of such a saw had been published by Dr John Aiken of Edinburgh, and that the one he illustrates had been used every year in his anatomy class since 1790. For cutting wood, the earliest patent read here is Samuel J. Bens’s US Patent 780,476 of 17 January 1905, which describes an endless chain of teeth running in a guide frame pivoted at one end and driven by an engine or motor.1 2

The chain saw began as a surgical instrument. Jeffray’s 1806 account describes a saw of small joints that could be drawn through a wound behind a bone, a job a rigid saw could not do without a very large incision, and says it had been in annual use at Glasgow since 1790. The Science Museum Group holds jointed saw chains of 1831–1870 from France and elsewhere in Europe, cataloged as excision saws, which shows the form was still being made for surgery in the nineteenth century.

The timber chain saw solved a different problem. Bens’s 1905 patent states his aim as a saw for general use and particularly for crosscutting, for which hand-operated saws were almost universally employed, and says a band saw cannot crosscut like his because the band necessarily runs in two planes. His chain therefore runs on a flat frame in a single plane, pivoted at one end so that the saw can swing through a tree or log. His 1908 patent was written to stiffen the long guide frame and to add dragging teeth that clear the kerf. Lucia reports that at least a dozen patents were issued in the United States in the second half of the nineteenth century, but no chain saw was manufactured.

The limit was power and weight. Lucia says the problem remained the size and weight of the power equipment: Wolf’s electric saw of 1920 weighed 70 to 90 pounds and needed a portable generator, and a gasoline saw built in about 1933 in Alameda weighed 490 pounds. Stihl’s electric saw of 1926 weighed 140 pounds according to FundingUniverse, and its first gasoline saw of 1929 weighed 101 pounds and still needed two people. Lucia says Stihl’s 46-pound saw of 1936 had an excellent lightweight engine and drew the attention of a Depression-ridden timber industry; FundingUniverse dates the first truly portable one-person saw, the 31-pound BLK, to 1954.

The chain itself was the second change. Lucia describes dissatisfaction with chains that dragged teeth through the kerf, tearing at the wood fibers on the principle of drawing a sharp nail over a surface. Cox’s patent describes the same fault in the prior art: chains with side-cutting teeth alternating with separate raker teeth cut jerkily because each cutter gouges and then tears free. His chain balanced the load on both sides of the tooth’s center plane, used one form of cutter in right and left versions, could be stamped from blank stock and could be sharpened with a single round file. Lucia, relying on Cox’s own recollection, says the idea came from watching the cutting action of a timber beetle larva, and that the first year’s sales were $300,000. The Forest Service guide of 2006 calls chipper chain the most versatile cutter type and the easiest to file.

Safety features followed the saw into general use. The Forest Service guide lists the chain brake, chain catcher, hand guard and low-kickback chain among the parts and chain types that limit injury, and OSHA’s logging rule requires a chain brake and conformity to ANSI B175.1-1991 for saws placed in service after the rule took effect. FundingUniverse dates Stihl’s antivibration system to 1965 and says an inertial chain brake, which stops the chain in kickback, was added in later design changes.

Timeline

by 1790
Jeffray’s chain saw, with jointed links like a watch chain, is in use in the Glasgow anatomy class; a sketch of a similar saw has been published by John Aiken of Edinburgh.1
1831–1870
Metal saw chains of French and other European make, cataloged as excision saws, are made; the Science Museum Group holds them.1 2
1858
The U.S. Patent Office issues what Lucia calls the first chain saw patent, to Harvey Brown of New York City, for an “endless sectional sawing mechanism”; George Kammerl of New York is granted a second patent five years later. Lucia says at least a dozen patents followed in the second half of the century, none addressing power, and no chain saw was manufactured.1
1905
Samuel J. Bens is granted US Patent 780,476, an endless chain of toothed links running in a guide frame, pivoted at one end, for crosscutting trees and logs and driven by a steam engine, gas engine or motor. In the same year, according to Lucia, an experimental gasoline-engine chain saw is tested in the redwoods near Eureka, California; the inventor’s name is lost.1 2
1908
Bens is granted US Patent 893,897 for a stiffened guide frame and alternating cutting and dragging teeth that keep the kerf clear. Also in 1908, according to Lucia, Charles Wolf improves on a crude log-deck chain saw developed at the Potlatch Lumber Company, for the Blackwell Lumber Company of Coeur d’Alene, Idaho.1 2
1918–1920
James Shand, a Manitoba millwright, patents an endless chain saw in 1918 and lets the rights lapse in 1930. In 1920 Wolf introduces his Wolf Electric Drive Link Saw at the Peninsula Iron Works in Portland, Oregon, which Lucia calls the first successful portable chain saw.1
1925–1929
Andreas Stihl of Stuttgart builds a two-person electric chain saw weighing 140 pounds (dated 1925 by Lucia and 1926 by FundingUniverse), sells 50 in 1927 and brings out a 101-pound, 6-horsepower gasoline saw in 1929.1 2
1936
The H. A. Stihl Company begins exporting a 46-pound chain saw with a lightweight engine to North America, according to Lucia.1
1941
By late 1941 a half-dozen companies in North America are making power saws patterned on the Stihl rigs and copying the Stihl chain, which no longer had patent protection, according to Lucia.1
1948
Joseph B. Cox files the application that is granted on 23 May 1950 as US Patent 2,508,784, Power Saw Chain, assigned to Oregon Saw Chain Mfg. Co. Lucia says Cox established his company in 1947.1 2
1959
Husqvarna starts chain saw production; in the same year FundingUniverse dates the Stihl Contra, a 26.65-pound saw rated at 6 horsepower.1 2
1965
Stihl introduces an antivibration system; FundingUniverse also lists an inertial chain brake among its later design changes.1

Where the sources disagree

What was the first successful portable chain saw?

Charlie Wolf’s Electric Drive Link Saw of 1920, built at the Peninsula Iron Works in Portland, “ranks as the first successful portable chain saw.”1
Ellis Lucia, Journal of Forest History, 1981
James Shand patented an endless chain saw in 1918 and took a gasoline-powered model to British Columbia, but failed to interest the lumber industry and let his rights lapse in 1930.1
Ellis Lucia, Journal of Forest History, 1981
Stihl’s gasoline saw, ready in 1929, was “the first ever.”1
FundingUniverse, reprinting International Directory of Company Histories (the claim is the company history’s)

When did Stihl build its first chain saw?

In 1925 Stihl developed a two-man chain power saw weighing 140 pounds; it sold quickly after a demonstration and two saws at the Leipzig fair of 1929 brought orders from neighboring countries.1
Ellis Lucia, Journal of Forest History, 1981
Stihl began designing a tree-felling machine in 1925, had a first prototype, a 140-pound electric saw, by 1926, sold 50 in 1927 and exhibited at the Leipzig fair in 1930; the gasoline saw followed in 1929.1
FundingUniverse (International Directory of Company Histories)

Gaps in the record (8)

No patent by Andreas Stihl, Emil Lerp, Charles Wolf, James Shand, Harvey Brown or George Kammerl was read; their dates and claims here rest on Lucia’s 1981 article and on FundingUniverse. The claim, found in popular accounts, that Emil Lerp built a gasoline saw before Stihl was not verified in any source read.
Aitken’s original illustration was not read; Jeffray’s 1806 text is the source for it. The orthopedic chain osteotome of Bernhard Heine (about 1830) is not sourced.
FundingUniverse is a secondary reprint of a company history, and Lucia’s account of Cox’s beetle-larva inspiration is Cox’s recollection as told in 1981; neither the patent nor any other source read confirms it.
The 1905 Eureka experiment is known only from Lucia, who says the inventor’s name is lost.
Which of today’s cutter types descend from Cox’s design was not traced.
The history of the electric, battery and pole-saw forms, of the inertial brake date and of the effective date of the OSHA logging rule is not sourced.
No independent saw test data has been located, so buying is null.
The standard slugs are guesses (ANSI B175.1 is cited by OSHA; the ISO and IEC numbers have not been read).