Workshop

Designing an intarsia and transferring the pattern

Transferring the pattern is the bridge between the design and the knife. What looks precise as a digital pattern or a drawn design has to be transferred physically onto the veneer before the first cut can be made. Errors in this step cannot be repaired: they are locked into the cut, visible in the assembly and permanent in the pressed object.

Design with the woods assigned, grain arrows and registration marks — The design before cutting: every field with its species, its grain direction and its position relative to the registration marks.

Why the transfer decides the quality of the cut

The design exists first as an idea, then as a digital file or a drawn pattern. Both are abstract. Only the transfer onto the veneer makes the design physically binding. In this step the cutting lines are defined, grain directions fixed, materials assigned to the individual fields and registration points set that coordinate every step that follows.

Whatever is unclear at cutting cannot be made up for by precision at the cutting tool. A shifted line cuts a shifted piece. Too thick a line leaves room for interpretation about exactly where to cut. A missing grain arrow forces a decision at the material itself, under time pressure and with a greater risk of choosing the wrong end of the sheet.

The link to the following assembly is direct. A piece cut out with a slightly turned template does not fit precisely in its intended position. The joint is not down to bad cutting but to a faulty transfer. If you can rule out transfer errors, you know for sure that a gap arose in cutting, and you can rework it there.

Preparing the pattern digitally

Before a pattern is printed or plotted, it has to be prepared for physical transfer. That means every cutting line is exactly defined, has a consistent line weight and no unintended gaps or overlaps at crossing points. Open paths at crossing points that are invisible on screen turn into breaks in print, which lead to errors of interpretation in cutting.

The scale must be verified before printing. Printers can scale if no exact scale is enforced. A test print with a known reference size, for example a 50-millimetre calibration square at the edge of the file, allows an immediate check of scale before the template goes onto the veneer. On small objects such as a pen holder, a deviation of one per cent is already half a millimetre over a width of fifty millimetres, which is critical for the precision of scale these formats demand.

The assignment of materials and the grain direction are marked in the file before printing. Every field gets a short code for its species and an arrow showing the intended grain direction. This information is visible on the printout and goes with the template all the way to the cutting table. A file with only cutting lines and no marking of materials forces decisions at the veneer that are better made beforehand.

Paper templates and printing

Printed paper templates are the most common way to transfer a pattern to veneer. The paper is applied to the back of the veneer so that the show face stays untouched. The cutting lines are cut through the paper into the veneer. The paper is then removed; no ink or pencil line is left on the show face.

The quality of the paper affects the quality of the cut. Paper that is too thick increases the depth of cut and can hide the edge from view. Paper that is too thin tears under the cutting tool and shifts the line. 80 gsm printer paper is a workable compromise for most cutting methods. If you cut with a scalpel, you will prefer thinner transfer paper; if you work with a cutting machine, you can use thicker paper as long as the depth setting is right.

Fixing the template on the veneer calls for low-tack tape that leaves no residue. Ordinary tape or strong double-sided tape can tear fibres out of the back of the veneer when peeled off, which is invisible but affects flatness. On very thin veneers of ash or oak that are sensitive to pull, the template is fixed with tape only at two opposite edges, not over the whole area.

Scale and line weight

The cutting line on the template has a physical width. A line 0.5 millimetres wide is not an abstract boundary; somewhere within that width lies the cut. In geometric patterns with tight fits, that means either the cutting line is treated as the centre of the joint, or the pieces are drawn smaller in the design by half the joint. If you do not decide this beforehand, you get either pieces that are too tight and do not fit, or pieces that are too loose and leave a gap.

For geometric intarsia at a small scale, the line weight on the template should be 0.2 millimetres or less. Thicker lines give too much room for where within the line's width the tool is guided. In very small fields, less than ten millimetres along a side, a 0.5-millimetre line can be more than five per cent of the field's width.

True scale is checked with calipers after printing. If the printed scale differs from the target, print again before sticking it on, rather than measuring and correcting. Calculating corrections on the physical template multiplies errors and is more error-prone than a clean reprint.

Registration marks and shared reference points

Registration marks are crosses or crosshairs defined on the template that get a matching physical reference on the sheet of veneer. They ensure the template lies exactly in its intended position. Fixing the template half a millimetre off shifts every cutting line by the same amount, systematically and in the same direction.

Registration marks have to lie outside the cutting area so that they can still be read after cutting. Inside the cutting area they are destroyed by the cut. A good position is the four corners of the template, each at least five millimetres outside the outermost cutting line. The marks are made on the sheet of veneer as a pinprick or a fine pencil dot; the show face of the veneer is not marked.

In compositions of several parts made from several sheets of different species, registration marks are coordinated between the sheets. If wenge pieces and walnut pieces come from separate sheets, the cuts have to be registered so that the pieces from both sheets fit together in the assembly without rework.

Registration mark: template and veneer mark aligned against offset — Registration marks have to lie exactly on top of each other. Even half a millimetre of offset carries on into every joint.

Marking the grain direction before cutting

The grain direction decides how a piece of veneer looks in the finished pattern. If you decide it only after cutting, you no longer have control: the piece can be turned or flipped, but its cut shape decides which orientation is possible at all. So the grain direction has to be marked on the template as an arrow and matched with the actual grain of the sheet before the template is fixed.

The arrow on the template shows the desired grain direction in the finished pattern. On the sheet of veneer, this arrow is lined up with the visible fibre. With quarter-cut veneers, which have a straight fibre, this alignment is unambiguous. With crown-cut veneers with a pronounced cathedral figure, the fibre direction can deviate locally; there the alignment has to be set by the main fibre direction running through the sheet, not by a local figure.

Errors in grain direction show in the assembly: a piece fitted against the intended grain direction reflects light differently from its neighbours and stands out of the pattern. This error cannot be corrected in the pressed object.

Assigning materials and planning contrast before cutting

Assigning materials is the decision which geometric area gets which species. This decision is made in planning the contrast and has to be physically visible on the template during transfer. If a template has only cutting lines and no marking of materials, the maker decides at the cutting table which veneer goes into which field. That decision is made worse there than in the design, where the whole pattern and the effect of the contrast can be judged.

The material map on the template shows the species of each field as a code (W for wenge, N for walnut, O for oak, A for ash) and optionally a colour or hatching. If several fields have the same species, they can be marked with the same code but different numbers or letters, so that the next step shows whether they should come from the same section of the sheet or not.

Checking the contrast before cutting means testing the planned assignment on real veneer. The chosen sheets are laid side by side and judged for the actual difference in lightness, the difference in colour temperature and the figure. This step can change assignments that looked plausible on screen but do not produce the planned contrast on the real material.

Numbering pieces and sorting

Once the pieces are cut out, they have to be kept sorted and identifiable until assembly. In geometric patterns there are often several pieces of the same species with a similar shape. A rectangular wenge strip that appears six times in the pattern looks like six identical pieces in a loose pile of cut pieces. Which one belongs where is no longer clear without a mark.

Pieces are numbered on the back of the veneer with a soft pencil. The number matches the field number on the template. The grain arrow is added next to the number. If you keep both on the back, you can identify every piece clearly after cutting and set it in the right position in assembly, even if time passes between cutting and assembly.

Pieces that are very similar in shape also get a note of direction on the back: "top left", "right edge" or similar. Small triangles in a repeating pattern can differ by mirroring or by tiny differences in size. A clear mark on the back prevents a slightly turned or mirrored piece from being fitted in the wrong position.

Mirrored layouts and planning symmetry

For patterns with mirror symmetry it has to be decided beforehand whether both halves consist of mirrored pieces or of identical pieces (symmetry and mirroring). For mirrored pieces two templates are needed: an original version and a version mirrored horizontally or vertically. If you use only one template and turn the pieces, you change the grain direction with them.

Mirrored templates are made by mirroring the file horizontally or vertically before printing, not by turning the printout over. A printout turned over shows the cutting lines from the wrong side and can lead to cutting errors at asymmetric angles. Mirroring digitally before printing ensures the lines stay readable and clear.

For patterns where the mirroring shows in the grain, the planned grain direction of both halves is checked on screen before printing. In a symmetric stripe pattern of quarter-cut veneer, both halves are identical in grain. In a pattern of crown-cut veneer with an asymmetric cathedral figure, mirrored halves differ visibly and have to be planned as such.

Dry planning before the first cut

Just before cutting, all the templates are placed on their sheets of veneer without being fixed. This last overall look checks whether the assignment of materials, the grain direction and the scale look right on the actual pieces of veneer. Unexpected irregularities in the grain, knots or differences in colour in the sheet can mean a template is moved to another part of the sheet before cutting begins.

Dry planning also tells you about yield. Whether all the pieces of one species can come from the same sheet, whether grain direction and sheet size are compatible, and whether spare material is planned for rework only becomes visible when the material is physically laid out. If you skip this check, you risk finding out in the middle of a cutting session that the sheet is too small or the planned grain direction cannot be reached.

Dry planning is also the last moment to fix the order of the cuts. Pieces from the same sheet are cut out together. Pieces of different species are sorted into groups so that changes of tool and material can be bundled. This planning saves time and reduces the number of moments at which a wrong piece can be cut from the wrong material. How the dry fit and inspection of material fit into the whole quality process is described in checking quality in geometric intarsia.

How transfer errors show in the object

Transfer errors are treacherous because they hardly show in the step itself. A template fixed 0.5 millimetres off looks unremarkable on the sheet of veneer. The cut piece looks right. Only in assembly, when the piece meets its neighbours, does it show that a line does not run through or an angle is wrong.

Especially critical are systematic transfer errors that affect all the pieces from one sheet equally. If a template was fixed turned on a sheet and all its pieces were then cut out, all those pieces are wrong in the same way. In assembly that creates a consistent error of angle or position across a whole area of the pattern, which looks like a planning error even though the design was correct.

Errors in marking the grain direction only show fully after pressing. A piece with the wrong grain direction reflects light differently from its neighbours. With wenge, which is meant to be aligned in a particular direction, a 90-degree misorientation can change the impression of lightness of the whole area. These errors cannot be undone after pressing.

Correct against offset transfer, visible at a single joint — An offset transfer shows at the joint: instead of a tight line there is a dark gap.

How Reihax transfers patterns

At Reihax every pattern starts as a file. The laser cuts most pieces straight from this file; no printout is needed for that. Pieces cut with the knife, such as straight edges or pieces that need trimming, get a printed paper template that is stuck onto the veneer (working with templates).

The same checks apply to both. The file has to be at the right scale, have closed lines and assign a species and a grain direction to every field. A printout is measured against a known reference size before it is stuck on, because printers scale slightly. On small objects, one per cent of deviation already makes half a millimetre over five centimetres.

The assignment of materials is checked on real veneer. The sheets are laid side by side and judged under workshop light, because the veneer shows colours and reflections that no screen shows. This check can change decisions that already looked final on screen.

Frequently asked questions

Why does a pattern sometimes have to be mirrored before it is transferred to the veneer?

Whether it has to be mirrored depends on which side of the veneer you work from. If the template lies on the later show face, it is printed the right way round. If you work from the back, the later glue side, the template has to be mirrored, or an asymmetric pattern comes out reversed after pressing. Symmetric patterns are not affected.

How thick may a transfer line be?

The transfer line defines the cutting line. Because the cut itself has a physical width, the line has to be thin enough to show an unambiguous centre for the cut. Lines over 0.3 millimetres wide leave room for interpretation about which side of the line to cut. On small objects with tight angles, that room turns directly into a gap or an overlap at the joint.

Why do you need registration marks when transferring?

Registration marks are shared reference points between the template and the veneer. They make sure the template is in the right position before the cutting line is taken over. Without them a template can easily lie shifted or turned, which creates an even transfer error that only shows in the assembled pattern as a systematic fault.

How do you transfer a pattern to veneer without damaging the surface?

Common methods are: printing on transfer paper and fixing it with low-tack tape; tracing with a soft pencil over a sheet of tracing paper laid in between; or sticking a printed template directly onto the back of the veneer. The show face of the veneer should not be written on directly, because pencil or ink marks can stay visible after sanding.

Why does the grain direction have to be marked during transfer?

The grain direction affects how a piece of veneer looks in the finished pattern and how it responds to cutting. If you decide the grain direction only after cutting, you no longer control how the piece sits in the whole pattern. An arrow on the template, lined up with the grain on the sheet of veneer, ensures that every piece gets its intended visual effect.