How to cut straight with a circular saw or handsaw, and why your cuts aren't square

A cut that wanders is one of the complaints I found most often searching woodworking forums. Sometimes it’s the hand and sometimes the tool. I have not tried these methods or calibrated a saw. This is what I read, split into circular saw, handsaw, and how to tell whether the saw is what’s crooked.

The short answer

High confidence on circular saw safety: the two manuals agree almost word for word. Medium on the rest, which comes from magazines that don't always say the same thing.

• With a circular saw, use a guide. Bosch says to always use a rip fence or straight edge guide when ripping, because it improves accuracy and reduces the chance of binding.¹ Fine Homebuilding only cuts freehand what will be covered up.²
• Don’t trust the factory edge. Family Handyman says straight factory edges are far from universal.³
• Keep the blade just below the work. Bosch and Makita want less than a full tooth showing.⁴⁵
• With a handsaw, arm and saw in line, no pushing down. Schwarz says excess downward pressure almost always drives you off the line.⁶
• Before blaming your hand, check for square: the blade, the miter saw and the square itself.⁷⁸⁹

Part lengths, before you cut, are what the cut list calculator sorts out.

Circular saw

The guide. Bosch suggests fastening a board or rail to the workpiece as an auxiliary guide for straight cuts.¹⁰

Tom O’Brien, in Fine Homebuilding, builds one from 3/4 in. plywood about 1 ft. wide: he rips a 2 to 3 in. strip that includes the factory edge and screws it onto the base. The base width equals the distance from the edge of the saw’s baseplate to the blade, so the guide’s edge lands right on the line.¹¹

Guides that ride the panel’s edge have a catch. Woodcraft warns that Kreg’s Rip-Cut follows the edge: if the edge isn’t straight, neither is the cut.¹²

Depth. Bosch and Makita say less than a full tooth should be visible below the work.¹³

¹⁴ Makita adds that the right depth reduces kickback.¹⁵

Support. Bosch and Makita say to support large panels on both sides, near the cut line and near the edge, because they sag under their own weight and pinch the blade.¹⁶

¹⁷ Makita says the saw should rest on the larger piece.¹⁸ Family Handyman says never to cut between supported ends, like the middle of two sawhorses, because the cut falls into the blade.¹⁹ Kreg supports the whole panel on a sheet of 2 in. rigid foam.²⁰ Bosch is plain about the basics: never hold the work in your hands or across your leg.²¹

If you drift off the line. Makita and Fine Homebuilding agree: don’t twist the saw back. Release the trigger, wait for the blade to stop, back up to where the cut was true and restart with the blade centered in the kerf.²²

²³ Bosch adds never to pull the saw out or backward while the blade is moving.²⁴

The blade. Bosch says dull or badly set blades cut a narrow kerf, which causes friction, binding and kickback.²⁵

Family Handyman lists the signs: rounded or chipped teeth, burn marks, and having to muscle the cut.²⁶

Tearout. Kreg and Fine Homebuilding cut with the good face down, and score the line with a utility knife first.²⁷

²⁸

Handsaw

Christopher Schwarz has ten rules. The ones other sources repeat:

• Relaxed grip, index finger extended along the handle. Clenching pushes you off the line.²⁹ Norm Abram also points his index finger.³⁰
• Arm and saw in one straight line. If you feel your elbow touching your torso, you’re doing it wrong.³¹ For a right-hander, left foot forward and right foot back.³²
• Don’t let the blade hide the line. If you can’t see it, you can’t follow it.³³
• Almost no downward pressure, using 80 to 90 percent of the teeth on each stroke.³⁴ Norm lets the teeth do the work, with a little pressure on the push and none on the pull.³⁵
• Follow two lines at once, on the face and the edge.³⁶
• Hold the work firmly. Norm says if the wood jiggles, the line comes out wavy.³⁷

The reflection. If the blade is shiny, the board’s reflection in it should line up with the real board. Schwarz uses it to check he’s square,³⁸

and Eric Richter, in Fine Woodworking, to cut square without a line.³⁹ Norm notes it doesn’t work on rusty or coated blades.⁴⁰

Which saw to start with is in how to choose a first hand saw, and how to lay out the line in measuring and marking.

Why it isn’t square

The circular saw blade. Family Handyman says that if the blade isn’t at 90° to the shoe, any bevel you set will be off. You check it with a square and adjust a set screw, with the saw unplugged or the battery out.⁴¹

This Old House warns not to rest the square on a tooth, which gives a false reading, and that a quarter turn of the screw makes a big difference.⁴²

The miter saw. Popular Woodworking cuts a board with straight, parallel edges in half, flips one half over and butts it against the other along the fence. The gap is twice the saw’s error.⁴³

For a table saw sled, the five-cut method multiplies the error by four.⁴⁴

The square. Draw a line off a straight edge, flip the square and draw another. Andy Rae, in Woodworker’s Journal, says the difference between them is twice the square’s error.⁴⁵

What users say

On Foromadera, a Spanish-language forum, someone has a circular saw that cuts at an angle, on a rail and off it. Members suggest checking for a warped base, play in the arbor, loose bevel screws and the blade: for another member a worn blade pulled to one side, and changing it fixed things. One member doesn’t trust a square because the blade is thicker at the teeth; they cut the thickest piece they have and adjust the 90° stop, which they say is normal to have to touch. The saw went back to the store, and the thread doesn’t say how it ended.⁴⁶

In another thread, about Japanese saws that wander, the advice is an extended index finger, moving only the shoulder, a 35 to 40° angle and very light pressure.⁴⁷

Where they disagree

How far the blade goes below. Bosch and Makita: less than a tooth.⁴⁸

⁴⁹ Kreg: material thickness plus about 1/8 in.⁵⁰ Family Handyman: about 1/4 in.⁵¹ Fine Homebuilding: no more than 1/4 in.⁵² The manufacturers’ rule is the shallowest.

How to support. Family Handyman lets the cutoff drop free and clamps one side only.⁵³

The manuals want support on both sides near the cut for large panels.⁵⁴⁵⁵ On the forum, one member clamps both pieces and another says a sound saw doesn’t push the offcut.⁵⁶

Which side of the line. Kreg, Family Handyman and Norm cut on the waste side.⁵⁷

⁵⁸⁵⁹ Schwarz, with a handsaw, says to work right against the line and avoid sawing a set distance away from it.⁶⁰ With a knife line, he says he usually splits it.⁶¹ Nobody gives a number for how much to leave.

Freehand or guided. Bosch wants a guide for rips.⁶²

Family Handyman says that without a guide, watching the blade on the line is enough.⁶³ Fine Homebuilding cuts sheathing freehand and finish panels with a guide.⁶⁴

My take

For a first piece of furniture, the circular saw gets a homemade guide like Fine Homebuilding’s, good face down, at whatever depth my saw’s manual asks for. Before cutting anything that matters, I check the square by flipping it, and the blade with the saw unplugged. With the handsaw, I practice on scraps before touching good wood. Schwarz says it takes a couple of days to learn to follow a line.⁶⁵

Angles for a frame or a many-sided box come from the miter angle calculator.

The photo is a circular saw cut from Wikimedia Commons. It isn’t my shop and doesn’t show a guide.