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newSchoolWorks.com › VoTechWorks › Building & Construction › Carpentry › Stair Construction: Layout, Framing & Finishing › Lesson 5
BLD-CARP03-05 · Lesson 5 · 15 clock hours · lab

Cutting Stringers: Circular Saw Technique and Safe Practices

Objective. Students will cut a full open stringer using a circular saw and jigsaw, completing all notches cleanly with saw cuts stopping at layout-line intersections and finishing cuts within 1/8 inch of the line.

Why Stringer Cutting Technique Matters

A stair stringer is the structural backbone of a staircase. Each notch you cut removes material from a 2×12, and every cut corner that goes even a fraction of an inch past the layout line weakens the remaining cross-section. Code and standard practice both require that the minimum net depth — the narrowest remaining section of the stringer board at any notch — be maintained. Over-cutting at the corner intersection is the single most common stringer defect, and it cannot be fixed by filling with wood glue or a scrap block. Getting clean, stopped cuts every time is therefore a foundational skill.

Circular Saw Safety Before the First Cut

Before powering any saw, every student must complete the following checks. These are not optional; they match OSHA Outreach and NCCER safety standards.

Your instructor must sign off on your safety demonstration before you energize a saw.

The Over-Cut Problem

A circular saw blade is round. When you push the saw forward, the blade begins cutting before the front of the shoe reaches the layout mark, and — crucially — the blade continues in an arc past the corner if you do not stop early. Stopping the circular saw cut precisely at the intersection of the tread line and the riser line requires practice and focus. The rule is simple: stop the blade before it reaches the corner. It is always safer to stop a little short and finish with a handsaw or jigsaw than to run the circular saw through the corner.

Sequence for Cutting Each Notch

1. Orient the board. Lay the laid-out 2×12 flat on the sawhorses, crown edge up, with the layout lines facing you.

2. Make the tread cut first. Align the saw's blade with the tread layout line. Start the saw to full speed before contacting the wood. Feed steadily; watch the blade and the layout mark simultaneously. Stop the blade when the kerf reaches 1/4 to 1/8 inch from the corner intersection. Release the trigger, wait for the blade to stop completely, and back the saw out.

3. Make the riser cut. Rotate the board or reposition yourself. Repeat the same approach: full speed, steady feed, stop short of the corner.

4. Complete the corner. Use a handsaw or jigsaw to connect the two stopped cuts at the corner. Cut exactly on the layout line. The waste piece should drop free cleanly. This prevents the circular saw blade from arcing past the intersection and creating an over-cut notch.

5. Inspect. Look at the corner: the saw kerf from the tread cut and the kerf from the riser cut should meet cleanly at a right angle, with no blade travel beyond the intersection on either face.

Using the First Stringer as a Template

Once your first stringer is cut and inspected, it becomes the pattern for every additional stringer. Lay the finished stringer flat on top of the new 2×12. Align the ends and the top and bottom edges. Clamp both boards together at several points so they cannot shift. Trace all notch profiles with a pencil. Remove the template, re-clamp the blank to the sawhorses, and cut using the same stopped-cut technique. When done, stack both stringers, clamp them face-to-face, and check that all tread seats and riser faces align within 1/8 inch along the full length. Misalignment causes treads to rock or lean after installation.

Jigsaw Use at Corners

The jigsaw is well suited for corner completion because its blade is narrow and its cut is controllable at low feed rates. Set the orbital action to zero or the lowest setting for the cleanest cut in dimension lumber. Start the saw before entering the kerf; feed slowly toward the corner. Keep the shoe pressed flat on the wood surface to prevent blade deflection. If the jigsaw blade begins to wander, back out and re-enter from the other stopped kerf.

Checking Your Work

Use a square to check each tread seat: it should be flat and level relative to the stringer's run. Tread seats that are not flat will cause squeaks and uneven wear. Check riser faces for straightness with a straightedge. Finally, measure the net depth of the stringer at each notch: from the tread seat down to the bottom edge of the board, measured perpendicular to the stringer's length. If net depth has been reduced below the acceptable minimum due to an over-cut, that stringer must be flagged for instructor review and a corrective strategy discussed — which often means cutting a new board.

Summary

Clean stringer cuts depend on three habits: proper circular saw setup, disciplined stop-short technique at every corner, and careful corner completion with a handsaw or jigsaw. Template tracing ensures paired stringers match. Inspection before installation catches problems when they are still correctable.

Key terms9

Open stringerA stringer in which the tread and riser profile notches are cut all the way through, so the tread nosings and risers are visible from the side of the staircase.
Net stringer depthThe remaining depth of the stringer board measured from the tread seat to the bottom edge of the board, perpendicular to the stringer's length, after all notches are cut.
Over-cutA saw kerf that travels past the corner intersection of the tread and riser layout lines, reducing the net stringer depth and weakening the board structurally.
Blade depth settingThe adjustment that controls how far the saw blade projects below the shoe; set to no more than 1/4 inch below the stock thickness to limit kickback hazard and blade exposure.
Template stringerThe first fully cut and approved stringer, used as a pattern to trace and cut all remaining stringers so they match identically.
Lower blade guardThe spring-loaded retractable guard on a circular saw that covers the blade below the shoe; must spring back freely after each cut and must never be disabled.
KerfThe slot or channel removed by a saw blade as it cuts through material; its width equals the blade's set (the offset of the teeth).
Tread seatThe horizontal flat surface cut into the stringer notch on which the stair tread rests; must be flat and level for the installed tread to sit without rocking.
KickbackA sudden, violent rearward movement of a circular saw caused by the blade binding or pinching in the kerf; controlled by proper blade depth, secure stock, and two-hand grip.

Worked examples4

1. Your stair has a unit rise of 7 1/4 inches and a unit run of 10 inches. You are cutting a 2×12 stringer (actual thickness 1.5 inches). After completing all notches, what is the net stringer depth at each notch, and is it larger than 3 1/2 inches? (A common practical minimum; always verify against the applicable building code.)
  1. Step 1 – Identify the dimension being measured. Net stringer depth is measured from the tread seat perpendicular to the bottom edge of the board — it is NOT simply the board width minus the unit rise.
  2. Step 2 – Use the Pythagorean relationship to find the perpendicular depth. The notch removes a right-triangle corner with legs equal to the unit rise (7.25 in) and unit run (10 in). The hypotenuse (the stringer's length direction per step) = √(7.25² + 10²) = √(52.5625 + 100) = √152.5625 ≈ 12.35 in.
  3. Step 3 – The actual width of the 2×12 is 11.25 inches. Net depth = 11.25 − (unit rise × unit run / hypotenuse) ... Use the standard formula: net depth = board width − (rise² / hypotenuse) = 11.25 − (7.25² / 12.35) = 11.25 − (52.5625 / 12.35) = 11.25 − 4.256 ≈ 7.0 inches.
  4. Step 4 – Compare to the practical minimum. 7.0 inches is well above 3.5 inches, so the stringer retains adequate structural depth at each notch.
Answer: Net stringer depth ≈ 7.0 inches, which exceeds a common 3.5-inch practical minimum. The stringer is structurally acceptable at this rise/run combination.
2. You stop your circular saw 3/16 inch short of the corner intersection on both the tread and riser cuts. How much material remains for the jigsaw or handsaw to remove at the corner, and is this within acceptable practice?
  1. Step 1 – Visualize the corner. Both saw kerfs stop 3/16 inch from the intersection. The uncut material at the corner forms a small square of roughly 3/16 × 3/16 inch.
  2. Step 2 – A handsaw or jigsaw easily removes a square of material that small in one or two careful strokes. There is no structural concern about leaving this small amount for a finish tool.
  3. Step 3 – Compare to the alternative: if the circular saw had continued to the corner, blade geometry would likely have carried the kerf 1/4 inch or more past the intersection on the opposite leg, creating an over-cut.
  4. Step 4 – Conclusion: stopping 3/16 inch short is within good practice. The remaining material is trivial for a jigsaw or handsaw to remove cleanly.
Answer: Approximately 3/16 × 3/16 inch of material remains at the corner — a negligible amount that a jigsaw or handsaw removes precisely. Stopping short is correct technique.
3. When you stack your two finished stringers face-to-face and clamp them, you measure the offset between matching tread seats at three locations: 1/16 inch, 3/32 inch, and 1/8 inch. Do both stringers pass the tolerance check?
  1. Step 1 – State the tolerance. The lesson and lab check require all notches to align within 1/8 inch (0.125 inch) along the full length.
  2. Step 2 – Convert measurements to decimals for easy comparison. 1/16 = 0.0625 in; 3/32 = 0.09375 in; 1/8 = 0.125 in.
  3. Step 3 – Compare each to 0.125 in. All three values (0.0625, 0.09375, 0.125) are less than or equal to 0.125 in.
  4. Step 4 – All three measurement points are at or within the maximum allowed offset.
Answer: All three offsets are within the 1/8-inch tolerance. Both stringers pass the alignment check.
4. You are setting blade depth on a circular saw before cutting a 2×12 (actual thickness 1.5 inches). The depth-adjustment scale shows depth in inches. What is the correct blade-projection setting, and what total blade-depth number do you set on the scale?
  1. Step 1 – Recall the rule: blade projects no more than 1/4 inch below the bottom face of the stock.
  2. Step 2 – Total blade depth = stock thickness + projection = 1.5 in + 0.25 in = 1.75 inches.
  3. Step 3 – Set the depth-adjustment scale to 1.75 inches (or just under, since staying at the maximum of 1/4 inch projection is the upper limit, not a target). A setting between 1.625 and 1.75 inches is acceptable.
  4. Step 4 – Verify by holding the saw against the edge of the stock before cutting: only about 1/4 inch of blade should be visible below the board.
Answer: Set the blade depth to approximately 1.75 inches total (1.5 in stock + 0.25 in maximum projection). Confirm visually that the blade barely clears the bottom of the board.

The math in this lesson1

Learners compute remaining throat on a notched 2×12 stringer, leftover cut material, and blade depth for 1.5 in stock.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Tool safety review and blade-guard inspection: before any cutting, each student demonstrates proper circular-saw guard operation, blade-depth setting (blade projects no more than 1/4 inch below stock), and two-hand grip; instructor signs off each student before they power a saw. · Full stringer cut: using their laid-out 2×12 from Lesson 4, students make tread and riser cuts with the circular saw, stopping each cut at the corner intersection, then completing corners with a handsaw or jigsaw to prevent over-cut weakening. · First stringer used as template: students trace the cut stringer onto a second 2×12 and cut a matching stringer, then clamp both together and check that all notches align within 1/8 inch along the full length.
Materials: Circular saws, jigsaws, handsaws, sawhorses, 2×12 lumber (two pieces per student), clamps, measuring tapes, safety glasses, hearing protection, push sticks, NCCER Carpentry Level 3 stair module
Check: Instructor checks both stringers: all tread-riser corners must be clean (no over-cut past the intersection), paired stringers must align within 1/8 inch when stacked and clamped. Any over-cut that reduces net stringer depth below minimum must be identified and corrective cutting strategy discussed. Pass = both stringers within tolerance.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Tools, Equipment, and Work Methods
1. Why must a circular saw cut be stopped before the blade reaches the corner intersection when cutting stringer notches?
Safety and Health
2. What is the maximum blade projection below the workpiece when setting blade depth for stringer cutting?
Safety and Health
3. A student notices the lower blade guard on the circular saw does not spring back when released by hand. What is the correct action?
Quality Control and Inspection
4. After cutting two stringers and stacking them face-to-face, you find one tread seat is offset 3/16 inch from the matching seat on the second stringer. What does this mean for the lab check?
Tools, Equipment, and Work Methods
5. What is the correct sequence for completing a stringer notch cut?
Safety and Health
6. Which personal protective equipment is required at all times during the stringer cutting lab?
Stair Layout and Framing
7. The net stringer depth is measured:
Stair Layout and Framing
8. When using the first cut stringer as a template for the second stringer, which step is most important before tracing the notch profile?
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