Miter saw

How it works

The work lies on the table against the fence. The blade, driven by a motor mounted with it on an arm, swings down through the work. The first power miter saw, designed for Rockwell in 1964, mounted the saw on a pivoting arm that brought it down into the wood in an arc, with a spring that returned the arm to the top and a clear plastic guard that slid out of the way as the blade plunged into the work.

The table turns to set the miter angle. On the DEWALT DWS779 the miter lock handle and latch button allow the table to be set to 60 degrees right and 50 degrees left, with stops at common angles that a latch override releases. The head tilts to set the bevel, 49 degrees left or right on the same saw, and in a compound cut the two angles are combined.

On a sliding saw the head rides on rails and can be pulled forward through the work, which widens the cut. A rail lock knob fixes the head so that the saw can make a straight chop cut or be carried. A depth stop limits how far the blade descends.

Anatomy

Base and turntable: Hold the work and turn to set the miter angle against a scale and pointer.
Fence: The vertical surface against which the work is held; the DWS779 has a fence adjustment knob on each side.
Kerf plate: The insert in the table around the blade slot; the manual says to replace it when damaged.
Miter latch, latch override and lock handle: Stop the table at common angles, release it for others, and lock it.
Head and arm: Motor, blade and handle on a pivoting arm; tilts for bevels.
Rails and rail lock knob: Present on sliding saws.
Blade and lower guard: The lower guard covers the blade and retracts as the head descends. OSHA requires a swing cutoff saw’s hood to cover the lower portion of the blade automatically.
Depth stop: Limits the descent of the blade for grooving.
Dust port and electric brake: The 1964 original already had a dust port and a blade brake; the DWS779 has an automatic electric brake.

Variants

Hand mitre box: The precursor. Stanley’s 1932 catalog lists mitre boxes with a swivel, saw guides and a quadrant indexed for 3, 4, 5, 6, 8, 12 and 24 sides; Disston sold saws made for use in a mitre box.
Single-bevel and dual-bevel compound saw: The head tilts one way or both ways; the DWS779 is a double-bevel saw.
Sliding compound saw: Head on rails; the radial arm saw is its stationary ancestor.
Radial arm saw: Raymond DeWalt’s machine of the 1920s, in which the saw moves along an overhead arm over fixed work; Fine Homebuilding reports that table saws and compound miter saws have taken its place.

Specifications

Blade diameter · in: 12The DEWALT DWS779. The Rockwell Model 34-010 of the 1960s took a 9 inch blade.
Miter range · degrees: 50 left, 60 rightDWS779; other saws differ.
Bevel range · degrees: 49 left and rightDWS779.
Blade speed · rpm: 3800No-load speed of the DWS779; blades must be rated for at least 4800 rpm.

Made to

UL 62841-3-9
IEC 62841-3-9
OSHA 1910-213

Safety and care

Safety

DEWALT’s manual says to use clamps or a vise to hold the workpiece against the table and fence whenever the hand would be within 6 inches of the blade.
Never reach around or behind the blade, never perform freehand operations, and never lock the switch in the on position.
Allow the blade to stop completely before raising the arm or clearing debris from the blade path; the electric brake is not a substitute for the guards.
Use only crosscut blades of the correct diameter and arbor, rated for at least the saw’s speed; the manual forbids rip blades, combination blades and blades with a hook angle above 7 degrees.
Do not use lubricants or cleaners, especially sprays, near the plastic guard, which certain chemicals attack.

Care

Replace a damaged kerf plate; chips that accumulate under the saw can interfere with the blade or make the workpiece unstable (DEWALT manual).
Clean the blade and blade clamps before use so that cracks or damage can be seen (DEWALT manual).
Clear chips and sawdust from the motor air slots; clogged slots can overheat the machine (DEWALT manual).
DEWALT says that if the brake delays or skips, the saw should be switched on and off four or five times, and serviced if the condition persists.

Tips

Use the stops, and override them for odd angles
The DWS779’s table stops at the common angles. The latch override flips to a vertical position to pass them, and the manual suggests checking the miter lock at an angle without a detent, 34 degrees for example, to confirm the table will not rotate.1
Crown molding: use the bevel pawls and the published angles
The saw carries bevel pawls for 22.5 degrees and for crown molding. The factory setting suits typical North American crown (52/38), and the pawl can be reversed for 45/45 crown. For crown laid flat on the table the manual gives 33.9 degrees bevel with the table at 31.62 degrees.1
Test every compound setting on scrap
The manual says the angles given for crown molding are very precise and hard to set exactly, that they shift easily, and that very few rooms have exactly square corners; it states that pretesting with scrap is extremely important.1
Lock the rails for a chop cut and use the depth stop for grooves
The rail lock knob holds the sliding head so that it cannot move, which the manual says is necessary for certain cuts and for transport. The depth stop limits the descent of the blade for work such as grooving and tall vertical cuts.1
Cut aluminum with a stick wax lubricant and the thinnest cross-section against the blade
DEWALT says to position extrusions so that the saw cuts the thinnest cross-section, to apply stick wax cutting lubricant directly to the blade before cutting (never to a moving blade), and to use a triple-chip-grind blade for non-ferrous metals.1
Read the polygon marks on an old hand mitre box
Stanley’s 1932 mitre box has a quadrant graduated in degrees and indexed for 3, 4, 5, 6, 8, 12 and 24 sides, so frames and boxes of those numbers of sides can be cut at the marked stops.1

History

Earliest documented

1964 (design begun); introduced after about three years of development

Pittsburgh, Pennsylvania (Rockwell Manufacturing Co.)

According to the Journal of Light Construction, Ed Niehaus, a tool design engineer at Rockwell’s Pittsburgh facility, was asked early in 1964 to design a tool that would do the jobs of a handsaw miter box using a motor-driven saw. After three years of product development and production tooling, Rockwell introduced the model 34-010 power miter saw with a 9 inch blade. The hand mitre box that it replaced is older; the earliest hand-box source found here is Disston’s catalog of 1926.1 2

The miter saw took its first form from a task and a tool. Rockwell asked its designer in 1964 for a power tool that would do the same jobs as a standard handsaw miter box. The task was cutting angles in trim and framing, with two requirements recorded by the Journal of Light Construction: the tool had to crosscut and miter a 2 by 4 and to miter standard crown molding. The hand mitre box, as Stanley’s 1932 catalog shows, already had a swivel carrying the saw guides and a degree quadrant indexed for polygons.

Niehaus rejected a design that moved the saw up and down on tracks because he thought it would be hard to keep stable, and mounted the saw on a pivoting arm that brought it down in an arc. The remaining features recorded in the article are the return spring, a housing that kept the spring in place if it broke, a clear plastic guard that slid away as the blade plunged, a wood table that could be replaced when chewed up, a dust port and a blade brake. Most of the features of a current saw are in that account.

The design spread because it was not protected. The article says Rockwell did not patent the idea, that the model became the company’s best seller, and that rival companies brought out their own versions. The date at which the sliding compound saw, whose head rides on rails, first appeared is not established from the sources read. Fine Homebuilding reports that the radial arm saw has been displaced in many shops by table saws and compound miter saws.

OSHA’s woodworking rule for swing cutoff saws requires a hood that completely encloses the upper half of the blade, the arbor end and the point of operation, and that automatically covers the lower portion of the blade when the saw returns to the back of the table. DEWALT’s present manual adds a rule that no hand come within 6 inches of the blade without clamping the work.

Timeline

1872
Gear’s catalog illustrates a saw bench with two swiveling squaring rests for sawing miters.1
1925
Raymond E. DeWalt is granted US Patent 1,528,536 (filed 27 January 1923) for a woodworking machine in which a motor on a yoke slides along an arm and can be set at different angles to the work: the radial arm saw.1
1926
Disston’s Saw, Tool and File Book describes a mitre box saw made thin and tested in a mitre box, for picture frames, moulding, cabinet work and pattern making.1
1932
Stanley’s catalog offers mitre boxes with a malleable iron swivel and uprights, saw guides with automatic catches, and a quadrant indexed for 3 to 24 sides.1
1964
Rockwell asks Ed Niehaus to design a power tool to do the work of a handsaw miter box; he mounts the saw on a pivoting arm and adds a return spring, a sliding clear plastic guard, a dust port and a blade brake.1
c. 1967
After three years of development and tooling, Rockwell introduces the model 34-010 power miter saw with a 9 inch blade. The article states the interval but not the year; the date is arithmetic from 1964.1
1981
Rockwell’s portable power tool division is sold to Pentair and becomes Porter-Cable Power Tools, according to the same article.1
2019
Fine Homebuilding reports that the radial-arm saw’s influence has shrunk as table saws and compound miter saws take over.1

Where the sources disagree

When was the power miter saw invented?

Ed Niehaus designed the first power miter saw for Rockwell in 1964.1
Journal of Light Construction, Hall of Fame 2002 (headline)
Niehaus started the design early in 1964 and Rockwell introduced the 34-010 only after three years of development and tooling.1
Journal of Light Construction, Hall of Fame 2002 (text)

Gaps in the record (6)

No patent for the Rockwell 34-010 was found; the Journal of Light Construction says none was taken out.
The year in which the sliding compound miter saw first appeared, and the maker, are not sourced.
The earliest hand mitre box is not dated; the oldest sources found are the Stanley catalog of 1932 and the Disston book of 1926.
Rockwell’s own catalog of the 1960s was not located, so the year of introduction rests on arithmetic.
No independent test data on miter saw accuracy has been located, so buying is null.
The standards were not read, and the slugs are guesses; DEWALT’s manual is cited for one current saw.