Tutorial 9: Laser-Cut Box with Finger Joints

Goal#

Create a lidless storage box (open on top, or with a sliding lid as a variation) cut from 3 mm sheet material on a laser cutter. Outer size: 120 mm long x 80 mm wide x 50 mm high. All four walls join to the floor and to each other with finger joints at a 10 mm nominal pitch. You will compensate for the laser kerf, keep everything in a few parameters, and end with a single DXF file whose parts are laid out flat and do not overlap.

Laser-cut joinery is the best case study for parametric thinking. One small change (material thickness changes from 3.0 to 3.2 mm, for example) should ripple through every tab and slot. You will build the model so that this actually happens.

What you'll learn#

• Defining material thickness, finger width and kerf as parameters.
• Modeling panels as separate bodies so they can be exported individually.
• Generating fingers with a sketch and Rectangular Pattern, driven by a computed count.
• Using Combine > Cut to notch the mating panels, rather than drawing both sides twice.
• Compensating for kerf correctly: tabs wider, slots narrower.
• Laying parts flat on a plane and exporting DXF with clean geometry.
• Test-fitting with a small coupon before cutting the whole job.

Prerequisites#

• Tutorials 1 and 2.
• A laser cutter, or a service that accepts DXF or SVG. Know the kerf (typically 0.1 to 0.2 mm for CO2 lasers on 3 mm plywood) and the real thickness of your material (measure with calipers; "3 mm" plywood is often 2.8 to 3.2 mm).

Parameters#

An odd number of fingers means both ends of an edge have the same type (tab at each end), which gives symmetric panels and avoids a slot at a corner. The actual finger width follows: edge length / count. The bottom (floor) joint runs along the inside of the walls, so its edge length is L - 2*mt = 114 mm and fL = 114 / 11 = 10.36 mm; for the width, fW = 74 / 7 = 10.57 mm; for the height, fH = 50 / 5 = 10 mm. Check that every finger width stays between 6 and 14 mm (general guidance, not Autodesk data).

Note: these steps assume Fusion's default Z-up orientation (Preferences > General > Default modeling orientation); with Y up, swap the Y and Z wording.

Panel plan#

The box uses a common, easy-to-cut layout. The outer size is L x W x H.

The floor sits inside the four walls with its bottom flush with the bottom edge of the walls. Its tabs fill rectangular notches cut into the bottom edge of each wall.

Kerf rule used throughout: the laser removes a strip kerf wide centered on the cut line, so every cut part ends up smaller than the drawn outline by kerf/2 per edge. To compensate, draw each tab (material) kerf wider than nominal and each gap (void) kerf narrower than nominal. With kerf = 0.15 mm and a nominal finger of 10 mm, draw tabs 10.15 mm and gaps 9.85 mm.

Steps#

Part A: Panels as plain slabs#

1. New design Finger Box. Add all parameters in Modify > Change Parameters. Also add fH = H / n_H (10 mm), fL = (L - 2*mt) / n_L, and fW = (W - 2*mt) / n_W; these are the nominal finger widths on each edge.
2. Front component. Right-click the root > New Component, name Front. Sketch on the XZ plane, Center Rectangle dimensioned L x H, with the bottom edge on Z = 0 and the rectangle centered on X = 0. Open Extrude, set Start to Offset with the offset W/2, and extrude a distance of mt toward the box centre (the Y range W/2 - mt to W/2; use the Direction arrow or a negative distance if the preview lands outside). Operation New Body.
3. Left component. New Component Left. Sketch on the YZ plane, rectangle W x H, bottom on Z = 0, centered on Y = 0. Extrude mt with Start set to Offset -L/2, direction +X (X range -L/2 to -L/2 + mt). Its ends overlap the front and back panels in the corner zones, which is intended: the finger cuts in Part B remove the overlap.
4. Back and Right. Leave these for later. After the Front and Left panels are completely finished (Parts B and C), use Create > Mirror with Pattern Type Components, mirror plane XZ for Back and YZ for Right.
5. Floor component. New Component Floor. Sketch on XY, Center Rectangle L - 2*mt x W - 2*mt. Extrude mt upward (Z 0 to mt) as a New Body.

Part B: Corner fingers#

6. Sketch on the Front end face. Select the end face of the Front panel at X = -L/2 (a thin mt by H strip) and start a sketch. Draw one gap rectangle: mt wide, height fH - kerf (9.85 mm), with its lower edge at Z = fH + kerf/2. This is position 2 of 5. The Front panel carries tabs at positions 1, 3 and 5 and gaps at 2 and 4.
7. Cut. Press E, select the rectangle, Operation Cut, Extent Distance mt (through the panel thickness).
8. Pattern the gap. Create > Pattern > Rectangular Pattern. Set Pattern Type to Features, select the cut from the timeline, Direction to the Z axis, Quantity 2, Distance Type Spacing, Distance 2*fH (20 mm). The second gap lands at position 4.
9. Mirror to the other end. Mirror the cut and its pattern across the YZ plane (Create > Mirror, Pattern Type Features) so the opposite end of the Front panel has the same gaps. Because n_H is odd the pattern is symmetric.
10. Left panel complement. On the end face of Left at Y = -W/2 sketch the complementary gaps: gaps at positions 1, 3 and 5 (the Front's tabs go there). Each gap is a rectangle mt x (fH - kerf) (narrower than nominal), centered on each odd finger center (centers at fH/2, 5*fH/2, 9*fH/2). Cut it through mt, pattern with Quantity 3 and spacing 2*fH, then mirror to the far end.
11. Tab widening. Tabs are what remains between gaps, so they are automatically wider than nominal by kerf when gaps are narrower by kerf. End tabs (positions 1 and 5 of the Front) are the leftover at the panel edges, which stays correct.

Part C: Floor joint#

12. Floor tabs. Select the top face of the Floor and sketch. Along the two long edges (length L - 2*mt), draw rectangles that protrude outward mt from the edge, each fL + kerf wide (10.51 mm). For n_L = 11 fingers, place tabs at odd positions 1, 3, 5, 7, 9, 11 (six tabs). Draw the first one, constrain its center at fL/2 from the corner, then Rectangular Pattern in the sketch with Quantity 6 and spacing 2*fL. Do the same for the two short edges with fW and n_W = 7 (four tabs). Extrude all tab rectangles mt downward from the top face (Z mt to 0), Operation Join.
13. Wall notches. On the bottom edge of the Front panel, cut rectangles that mirror the tabs: each mt tall, fL - kerf wide. Because the Front panel stands on the XZ side, the notch positions along X must line up with the floor tabs; project the floor tab edges into the sketch (P) and offset by kerf/2 inward to narrow the notches. Cut through mt of the panel thickness. Repeat on the Left panel using the fW spacing.
14. Corner clash check. The bottom corner finger (position 1) of each wall is a tab; make sure no floor notch overlaps it. Floor tabs begin mt in from the floor corner, and the notches are mt away from the panel ends, so there is no overlap with these dimensions.

Part D: Interference and fit check#

15. Interference. Inspect > Interference with all bodies; overlaps indicate a tab sized larger than its slot. Because kerf compensation is applied to the cut parts, the digital model will show a tiny interference of kerf on each tab; this is intended. To avoid false alarms, set kerf to 0 temporarily, check, then restore.
16. Section analysis. Cut through a joint and confirm the tab reaches the full thickness of the mating panel, no more.

Part E: Lay flat and export#

17. Create a Layout component. New Component Layout. The easiest approach is to copy each panel and lay it flat on the XY plane. Use Move/Copy with Create Copy checked to produce copies in the Layout component, and rotate them with the Rotate move type so the large face is parallel to XY. Spread them with 5 mm spacing between parts.
18. Project outlines. In the Layout, create one sketch on XY and use Project on each panel's top face (select the face, project; the projection outlines include slots). Projection of faces yields all the loops, including interior slots and holes.
19. Add engraving or scores. Use Text to add FRONT, BACK etc. as sketch text and set the text to a separate layer if your laser software distinguishes layers by color.
20. Check geometry. There must be no duplicated lines and no tiny segments. Zoom on corners.
21. Export. Right-click the sketch in the browser > Export DXF. See Export PDF, DWG, DXF for scale and layer options; check the units in your laser software. Open the DXF in your laser software (or a free viewer) and verify the overall size 120 mm for the front.
22. Optional SVG. Sketch export is DXF; to get SVG, convert the DXF in a vector editor or your laser software.

Part F: Test coupon#

23. Make a coupon. Before cutting the whole box, cut a 40 x 20 mm coupon with three fingers at fw = 10 mm using the same parameters. Fit two together. If the fit is loose, increase kerf by 0.05 mm and regenerate; if tight, decrease it.
24. Record. Add the final kerf and thickness in the parameter comments so you have the numbers next time.

Checkpoints#

• Front panel width 120 mm, height 50 mm, tab count 3 on each side.
• Panels do not overlap in the layout.
• DXF opens at the correct scale.
• Changing mt to 3.2 regenerates all slots without errors.
• The timeline contains sketches, cuts and patterns only (no hand-dimensioned numbers).

Variations#

1. Sliding lid. Add a 3.1 mm groove along the inner top of three walls and cut a lid panel.
2. Dividers. Add T-slot dividers with half-lap joints.
3. Living hinge lid. Lines cut at 1 mm pitch in a 20 mm region create a flexible area (verify with your material).
4. Nut traps. Add T-slots with captive M3 nuts for screwed corners.
5. Engraved logo. Import an SVG into the layout sketch (Insert > Insert SVG, which places it on a sketch plane).

Troubleshooting#

Related#

• Flat Pattern and DXF Export (sheet metal).
• Export PDF, DWG, DXF in Drawings.
• Text and Imports for SVG.