Digital manufacturing techniques in woodwork

Two ways to start a design

Designing from scratch: The piece, its parts and its joints are drawn on the computer to exact dimensions.

3D scanning: An existing piece, such as an old carved door, a damaged panel or a traditional chest, is scanned with a 3D scanner or photographed from several angles and turned into a digital model. The model is then cleaned up and edited on the computer, so it can be used to restore damaged parts, reproduce the piece on a CNC machine, or resize it while keeping the detail of its carving.

The software

Engineering design software such as SolidWorks and Autodesk Fusion (formerly Fusion 360) is used to design furniture and parts to precise dimensions, draw the joints between parts, and check that everything fits together before production.

Freeform modelling software such as Rhino and Blender suits sculptures, organic shapes and relief ornament.

Parametric design tools such as Grasshopper build a pattern from rules and variables instead of drawing it line by line, so changing a single value alters the number of repeats, the size of the openings or the density of the pattern across the whole design. This suits geometric patterns, mashrabiya and pierced screens.

Toolpath (CAM) software such as VCarve Pro and the manufacturing workspace in Autodesk Fusion turns the design into motion paths for the CNC machine: profile cutting, pocketing, V-carving and 3D carving, as well as nesting parts on the board to reduce waste.

Vector drawing software such as CorelDRAW, Adobe Illustrator and LightBurn is used to prepare cutting and engraving files for laser machines.

Design considerations

Grain direction and wood movement: Solid wood expands and contracts across the grain as humidity changes, while its movement along the grain is almost nil. Wide surfaces are therefore given room to move, and joints are designed so that they do not restrict this movement.

Internal corners: The cutting tool is round, so internal corners come out rounded to the tool's radius. A 6 mm tool leaves a corner with a radius of about 3 mm, so small relief cuts (dogbones) are added in the corners to let a square part fit snugly.

Actual board thickness: A board's real thickness often differs from its nominal thickness, so it is measured before designing, and the sizes of joints and slots are set to it with a small fitting tolerance.

Laser kerf: The laser beam removes a thin strip of material, known as the kerf, and the design compensates for it when parts need a tight interlocking fit.

From file to machine

3D models are exported in formats such as STEP and STL, and flat drawings in vector formats such as DXF and SVG. Toolpaths are then prepared in CAM software and converted into a G-code file that the CNC machine reads. Cutting and engraving files go to the laser directly from the drawing software, and models for 3D printing are sliced into layers in slicing software such as Cura.

How does it work?

A V-shaped bit with a fixed angle is used, and the cutting depth changes with the width of the line, so letters and patterns come out with crisp edges and graduated depth that resemble hand carving. Wide areas are first cleared with a flat-end bit, then the V-bit completes the detail.

Traditional patterns, such as Omani door carvings, can be drawn digitally and then cut into wood with the same precision every time.

How is it done?

A V-bit cuts a recess in the shape of the design in the base wood, then the same bit cuts a mirrored insert from a wood of a different colour, so the two parts match exactly. A small gap is left beneath the insert for glue, and a clearance is left between the back of the insert and the surface of the base wood so that it does not bottom out, letting the angled sides seat tightly.

After gluing, clamping and letting the glue dry, the excess is sawn off and the surface is levelled with a flat-end bit on the machine or by sanding, leaving the inlay flush with the wood. The piece is then sanded and finished.

How is it done?

The picture or pattern is divided into pieces on the computer, and each piece is assigned a wood species and colour. The laser then cuts the pieces from thin sheets of veneer, giving precise edges that fit one another. The pieces are assembled like a jigsaw on paper masking tape, then glued to a base board, pressed, sanded and finished.

The kerf is compensated for in the design so that the pieces fit together without gaps, and the laser-cut edges show a fine dark line that can be used to emphasise the outlines of the pattern.

How is it done?

3D carving is done in two stages: roughing with a flat-end bit that removes most of the wood quickly and leaves the shape as a series of steps, then finishing with a ball-nose bit that follows the curves of the surface and leaves it smooth to the touch.

The stepover between passes determines both surface quality and machining time: a smaller stepover gives a smoother surface and finer detail, but multiplies the machine's running time.

How does it work?

Flatbed UV printers print ink directly onto the wood surface, and each section cures under UV light as soon as it is printed. A primer layer can be printed to improve ink adhesion, white ink beneath the colours to make them stand out on dark wood, and then a gloss varnish layer to protect and enhance the print.

For example, the Roland VersaOBJECT MO-240 prints on an area of 610 × 458 mm and on objects up to 204 mm tall.

Assembly

A CNC router cuts joints precisely, such as finger joints for box corners, cross-halving joints for dividers and frames, and holes for dowels and screws in exactly the right places, so parts go together easily without measuring by hand.

3D printers such as the UltiMaker S7 print jigs, drilling guides and assembly squares made for each piece, which speed up assembly and keep it consistent.

Finishing

Pieces are sanded progressively from coarse to fine paper, then finished with oils, varnish or paint depending on their use. Both faces are best finished equally to limit warping.