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A 3D CUTTING METHOD FOR INTEGRAL 1DOF MULTIPLE-TAB-AND-
SLOT JOINTS FOR TIMBER PLATES, USING 5-AXIS CNC CUTTING
TECHNOLOGY
Christopher Robeller1, Yves Weinand2
ABSTRACT: Integral Mechanical Attachment (IMA) uses features in the form of components for their connection. In
addition to the transfer of forces, locator features are used as integral assembly guides. Prismatic, single-degree-of-
freedom (1DOF) joints only allow for a single assembly motion and therefore a simple, rapid and precise assembly. In
modern timber construction, such CNC-fabricated 1DOF joints are commonly used in frame structures. Recent research
is investigating the application of similar techniques for the joining of timber plate components, inspired by traditional
handcrafted joints from cabinetmaking. The method presented in this paper builds upon previous research, allowing for
new geometric variations such as non-orthogonal 1DOF plate joints and a simplified cutting process using a 5-axis
simultaneous cutting technique. In addition to the use of milling tools, the method is compatible with 5-axis laser
cutting and 5-axis waterjet cutting. Advantages and disadvantages of the different methods are being discussed.
KEYWORDS: Timber plate joints, 5-axis CNC fabrication, Dovetail joints, 5-axis laser cutting, 5-axis waterjet cutting
1 INTRODUCTION AND STATE-OF-
THE-ART 123
Integral Mechanical Attachment (IMA) is known as the
oldest method of joining. It uses features in the form of
parts for the connection, instead of additional fasteners
or adhesives. Connector Features are used to transfer
forces, and Locator Features are used for a rapid and
precise assembly. [1]
IMA used to be common in traditional timber
construction, but was widely replaced by mass produced
mechanical connectors during the industrialization. A
Renaissance of IMA has begun with the introduction of
numerical controlled machine technology. With the
proliferation of automatic joinery machines, IMA was
repatriated to timber frame structures, bringing back
joints such as mortise and tenons. These joints are so-
called prismatic, or 1DOF-joints, where the form of the
joint constrains relative movements between the parts to
a single remaining motion path. In addition to the
mechanical features, such 1DOF joints are used as
guides for a simple, rapid and precise assembly. Other
joints with multiple DOF, such as 3DOF finger joints are
the subject of related research. [5]
For plate-shaped wood components, 1DOF integral
connectors such as dovetails have been used in
traditional cabinetmaking rather than carpentry. Instead
of single tabs and slots, plate joints are using multiple
1 Christopher Robeller, EPFL, christopher.robeller@epfl.ch
2 Yves Weinand, EPFL, yves.weinand@epfl.ch
tabs and slots (MTSJ). These joints were used for the
joining of solid wood boards, for furniture such as
cabinets or drawers and their use was limited to plate
edges which are oriented perpendicular to the wood
fibers (Figure 1, bottom right). Analog to the use of
CNC-fabricated 1DOF joints in timber frame structures,
recent research is investigating the application of 1DOF-
MTSJ for the assembly of cross-laminated timber plates.
Due to the quasi-orthotropic behavior of cross-laminated
panels, joints can be applied to both sides of the plates.
Figure 2 shows how this allows for various new
applications, such as box girders or hollow wall or roof
elements.
Figure 1: 1DOF-MTSJ, top left: CNC fabricated on cross-
laminated wood veneer plate, bottom right: Handcrafted on
solid wood
In 2010, the application of 3-axis CNC cut dovetail
joints on plywood, for the production of furniture has
been examined by Simek and Sebera [2]. A first
application of dovetail-jointed CLT panels in an
experimental building structure was demonstrated in the
Curved Folded Wood Pavilion in CH-Mendrisio in 2013,
where the joints were combined with adhesive bonding.
[3]. A self-interlocking folded-plate structure, made of
1DOF-MTSJ jointed laminated veneer lumber (LVL)
plates, without adhesive bonding, has been examined by
Robeller et al. in 2014 [4], followed by a study of the
semi-rigid behavior of 1DOF-MTSJ on LVL composite
box girders (Fig. 2) by Roche et al. in 2015 [6], and the
examination of the rotational stiffness of 1DOF-MTSJ
on LVL by Roche et al. in 2015 [7].
Figure 2: Application of 1DOF-MTSJ connectors for the
construction of LVL composite beams.[6]
1.1 PREVIOUS 2D CUTTING METHOD USING 3-
AXIS SIDE-CUTTING AND SPOT-FACING
State-of-the-art methods for the CNC fabrication of
dovetail joints [2] use CNC routers with three
translational axes. Figure 3 illustrates this method, where
the tail part of the joint is using side-cutting, with the
milling tool positioned normal to the plate surface, while
the pin part is cut using spot-facing, with the tool
positioned normal to the side face of the plate.
Figure 3: Fabrication of dovetail joints with 3-axis CNC
technology, limited to orthogonal joints between plates.
This method allows for the cutting of the typically 10-
20° inclined faces on the pin part with a 3-axis machine,
but it also results in several constraints, such as the
vertical clamping of the pin-part, which is difficult with
flatbed routers. Furthermore the method requires the re-
clamping of parts where multiple edges are to be jointed
and it allows only for the joining of plates at a dihedral
angle of 90°:
• Vertical clamping: The vertical clamping
(YZ-plane in figure 3) of parts is time
consuming and it is more difficult to properly
clamp the cantilevering work pieces, avoiding
vibrations which reduce the cut quality and feed
rates. The vertical space (z-axis height) of CNC
flatbed routers is limited for plate cutting; larger
parts cannot be fixed vertically.
• Re-clamping: When applying joints to multiple
edges on one plate, the part must be released,
rotated and fixed again. This requires a new
referencing of the work piece and causes
imprecision. This problem may be solved with
an additional rotational table, synchronized with
the machine [2], however it only works well
with circular or quadratic shaped plates, and a
sufficient clamping is difficult to achieve.
• Dihedral Angle φ: Traditional dovetail joints
were used for the joining of plates where the
dihedral angle is =90°, such as the drawer in
figure 1. Recent research projects have
demonstrated the use of 1DOF MTSJ with non-
orthogonal dihedral angles [3][4][7][8]. This is
not possible with the previous method.
2 3D SIDE-CUTTING METHOD USING
5-AXIS MILLING TECHNOLOGY
The cutting method presented in this paper takes
advantage of 5-axis flatbed CNC routers (Figure 4),
which are already used by many larger wood processing
companies. Figure 5 shows that in addition to the usual
three translational axes X, Y and Z, 5-axis enabled
machines are equipped with two additional, cardan
rotational axes (here A and B), which allow to orient the
tool along directions which are not perpendicular to
the machining table (XY-plane). With such rotations of
the tool, we can fabricate integral 1DOF MTSJ joints,
while the work piece is simply clamped on the
machining table.
Figure 4: 5-axis CNC router with automatic tool changer
Figure 5: 5-axis CNC router schematic with axis notations
The maximal tool inclination that can be achieve
with our method depends on the plate thickness ,
the geometry of the cutting tool (cutting length,
protrusion) and the geometry of the tool holder and
spindle, as shown in figure 6. Larger inclinations can be
achieved with longer cutters and tool extensions, but the
feed velocity
needs to be reduced accordingly. In our
experiments, we have cut with cutter inclinations of up
to =60°.
The right side of figure 6 shows how the minimum and
maximum possible dihedral angle and result
from the maximum tool inclination . With an
inclination of =50° , we can fabricate dovetail
joints for folds with dihedral angles ranging from
=40° to =140°.
Figure 6: relationship between maximum tool inclination and
minimum / maximum producible, variable joint angles.
Polytonally shaped plates with multiple 1DOF MTSJ
joined edges can have both positively and negatively
inclined joints on the same work piece. We want to
fabricate these parts without re-clamping or reversing of
work pieces in order to achieve precisely fitting joints.
Figure 7 shows a cross-section schematic drawing of the
tool position on a positive (regular) and negative
(undercut) inclination. The tool center point lies
above the flatbed router XY-plane for regular cuts, and
below it for undercuts. This is taken into account for the
maximum possible inclination, which we adjust
accordingly.
Figure 7: vertical shift of the tool center point during inclined
cutting, positive for regular cuts and negative for undercuts.
The manual programing of 5-axis CNC cutting with
standard computer aided manufacturing software (CAM)
is not adequate for the fabrication of MTSJ. The manual
programing of hundreds or thousands of tabs and slots
with various 3D rotations and custom details would be
too time consuming. We have therefore developed a
custom algorithm for the generation of the G-Code
(ISO6983) machining instructions, which are sent to the
CNC router.
2.1 CUTTING OF CONCAVE CORNERS
The fabrication of MTSJ requires the cutting of
polygonal shapes, for which we use tungsten steel shank-
type cutters with a diameter of 10-20mm. The
polygons include various concave corners or slots (cut-
outs within parts). In contrast to convex corners, such
sharp, concave corners cannot be cut with a shank-type
cutter, as its radius will remain as a fillet. We solve this
problem through additional notches (sometimes referred
to “Mickey Mouse Ears”), as illustr ated in figure 8.
Figure 8: FSS made from LVL using open-slot MTSJ [2]
The figure shows a schematic tool path offset around a
polygon , at a distance equal to the milling tool
Diameter . Notches must be added at the concave
corners and . Such notches are required for the
assembly of the MTSJ; also they reduce the notch
stresses compared to sharp corners. However, the
notches also reduce the important contact surfaces of the
joints. We therefore minimize the size of the notches
through the use of tangential circles, see figure 9, option
c. Also our algorithm will cut the notches in a final pass,
using a smaller diameter tool than for the nesting and
cutting of the joints.
Figure 9: Different types of notches possible with the side-
cutting method with cylindrical milling tools. Depending on the
type of notch, different contacts of the joint are reduced in size.
Our 3D method uses tangential bisector notches (c.), similar to
[2], adapted to the aligned 3D cutting process.
Figure 9 illustrates how different types of notches reduce
the contact surfaces (a) of the joints in size. We have
chosen the tangential bisector notch (9c) to minimize this
problem. Generally, the ratio between notch size and
plate thickness decreases with thicker plates. Let the
ratio between cutter diameter and cutter length
(protrusion) be 1:7.5, and we require a protrusion of
90mm to achieve a 3D tool inclination of =50°, the
cutter diameter must be =12. In consequence the
notch radii, and therefore the loss of contact surfaces is
critical for thin plates (such as in the fabrication of scale
models with plate thicknesses of 8-15mm) but greatly
reduced for thicker plates (21-39mm) in building
construction applications.
2.2 AUTOMATIC TOOL PATH GENEARTION
For the 3D cutting, we define the shape of plates through
pairs of polygons, as shown in figure 10a. There is a
lower polyline and a top polyline
in every pair,
each consisting of a list of points. The 3D geometry of
the part is described through a loft surface between these
pairs of polylines. A plate with cut-outs (e.g. slots)
within the outer contour is described through additional
pairs of polylines for each cut-out, where the orientation
is clockwise, while outside contours are oriented counter
clockwise. Figure 10a shows a pair of polylines,
describing the pin part of a dovetail-type MTSJ, with a
single slot. As explained in figure 7, the tool center point
must be offset three-dimensionally, in contrast to a 2D
offset, as shown in the schematic figure 8. We therefore
process the pair of polygons in segments, where each
segment (representing a joint face) is described by 2
points on the lower polygon , and 2 points on the
top polygon , . The line, on which the tool center
point of a cylindrical tool with the radius
will
translate, is defined through a point , which is
offset from along the vector , which is the cross
product of =
and =
, multiplied by the tool radius
=/2.
= + (×)
The tool center point must pass through this point, in the
direction . The start and end points of the tool
path, which both lie on this line, are found through the
intersection of the line with two bisecting planes. The
planes are bisecting between the plane of the current
joint face, and the neighboring ones before and after.
The figure 10b shows how the tool center point transits
on these planes, between the tool path lines of joint faces
with different, three-dimensional inclinations.
Figure 10: new 5-axis milling algorithm using 3D offset
On concave corners, which can be identified through a
negative cross product × , we add a tangential
notch, as described in section 5.1. In 3D, we find the
center axis of this cylinder (shown as a blue line in
figure 10b) defined through the point =+
((×)/2)
and the vector at this point.
Figure 10c shows the simultaneous translation and
rotation of the tool, in segments where the tool
orientation at the start point of the segment is
different from the one at the end point of the segment.
A pseudo-code algorithm for the generation of such a 3D
tool path is given in Figure 11:
Figure 11: Pseudo-Code Algorithm for 3D cutting
2.3 IMPLEMENTATION IN 3D CAD
We have implemented the previously described
automatic G-Code generator algorithm as a plug-in for a
visual programing environment in a commonly used 3D
CAD system. Figure 12 shows that the plug-in consists
of individual components for functions such as 3d
cutting or drilling, which we have used for fixation holes
for the clamping of parts. Input parameters include a
hatch-selected and automatically sorted and processed
list of closed polyline pairs defining the polygonal plate
contours, as described in section 3.2., as well as
adjustable values for the tool radius, security and retreat
planes, the number of vertical passes and separate tool
feed rates for horizontal and vertical movements. The
automatic cutting of tangential notches in the final pass
can be activated and de-activated. On the right, output
values side, the figure shows that we instantly obtain the
G-Code file, including various automatically generated
comments, which are skipped by the CNC control
system, but allow for simplified reading and checking of
CNC files. Changes in the input parameters will appear
directly in the G-Code display.
A third algorithm, visible on the output parameter side in
figure 12, is used for the real-time visualization of the
tool paths in the CAD software. Figures 14 and 15 show
the display the tool paths, and how the motions of the
machine can be simulated to check for collisions with
the tool, tool holder or spindle.
Figure 12: Automatic G-Code Generator CAD Plugin. Left:
input / cutting parameters, middle: separate components
(functions) for predrilling (clamping) and 1DOF MTSJ side-
cutting, right: live G-Code display with comments.
Figure 13: Detailed view of 1DOF MTSJ side- cutting function
inputs top to bottom, 1. Curves: hatch-selected list of closed
polyline plate contours, which will be automatically sorted into
pairs. 2. Zret: retreat plane, 3. Zsec: security plane, 4. Header:
Editable G-Code header, 4. Tool radius, 5. Number of infeeds,
6. Horizontal feed rate, 7. Vertical feed rate, 8. Notches on last
infeed on/off, 9. Rotational axis letters
Figure 14: Display of tool paths and tool orientation for 3D
cutting of 1DOF MTSJ in the CAD software [5]
Figure 15: Integrated Machine Simulation to check for
collision points (Tool path display in this figure is without tool
length offset G-Code function G49). [4]
2.4 FABRICATION OF FREEFORM SPACE
STRUCTURE PROTOTYPES
While the LVL composite box girder in Figure 2 shows
the application of the 1DOF-MTSJ for a simple
orthogonal plate assembly, the methods allows
producing non-orthogonal joints for the fabrication of
freeform space structures such as single-layered Folded
Surface Structures [4] (Figure 14), curved-folded surface
structures [3], double-layered Folded Surface Structures
[8] (Figure 15) or segmented Curved Shell Structures [9]
(Figure 16). The figures show both photos of the final
prototype structures and schematic drawings of the
plates, which are defined through polygon pairs, as
explained in section 3.2.
Figure 14: Single-layer Antiprismatic Folded Surface
Structure made from LVL using open-slot MTSJ, 2014 [4]
These experimental structure prototypes combine the
generally advantageous properties of wood, such as its
sustainability and favorable weight-to-strength-ratio,
with the particular easy machining of the material with
the dimensional stability and quasi-orthotropic behavior
of cross-laminated veneer lumber, and the widely
available 5-axis enabled CNC technology in the wood
processing industry, which allows for the efficient
production of large series of individually shaped parts.
This enables the efficient design and fabrication of self-
supporting thin shell structures, where the structurally
beneficial global shape of the structures is achieved
through incremental changes in the shape of the
individual plates. In addition to the load-bearing
performance of the 1DOF MTSJ joints through integral
connector features, the integral assembly guides in the
form of locator features are essential for the rapid and
precise assembly of freeform structures.
Figure 15: Double-layer Miura-Ori Folded Surface Structure
made from LVL using closed-slot MTSJ, 2015 [8]
Figure 16: Double-layer segmented curved shell structure
made from LVL using closed-slot MTSJ, 2016 [9]
2.5 DRAWBACKS OF CNC MILLING
The fabrication of integral 1DOF MTSJ requires the
cutting of polygonal contours with concave corners and
slots. Such cuts are not possible with saw blades.
Instead, cylindrical shank-type cutters must be used,
which results in multiple drawbacks, such as the need for
notches and increased waste and emissions such as dust.
The dust contains particles from both wood and the
adhesives used for the lamination of the veneer layers.
On 3D cutting systems, such as the 5-axis machine for
our tests, the extraction of the dust is particularly
problematic due to the large motion space of the cutting
spindle. The motion space is extended even more
through long cutting tools, which are required for the
cutting with a large tool inclination , in order to avoid
collisions between parts of the machine and the
workpiece.
Another challenge is presented by the clamping of work
pieces on the table of the flatbed CNC routers. The
milling with shank type cutters creates vibrations, which
are influenced by the machine feed rate, tool geometry
and the clamping of the work piece, requiring
compromises. Standard cutting tools are typically
designed for perpendicular, not inclined cutting, and
nesting cutters also create traction forces normal to the
plate for the dust extraction, requiring rigid clamping of
the work piece. Rigid clamping is particularly
challenging in large batches of individually shaped
plates such as in the prototype structure examples
[3][4][8][9].
=
60 1000
=
1000
=
1000 /
From the above equations, we see that a high tool
rotational speed is required to achieve a sufficient
cutting speed
. It results from this that also a high
machine feed rate
is required, but these required feed
rates cannot be realised with standard cutting equipment
and tools, due to the polygonal shape of the plates with
MTSJ. In consequence, cutting too slowly, cut quality is
reduced while tool wear and emissions are increased. We
have cut our parts with a feed rate = 6 m/min and
multiple vertical passes (infeeds). The cutting parameters
are provided in table 1:
(mm)
21
27
39
12
12
20/10
2
3
4
, (m/min)
3
2
1.5
Table 1: Effective cutting speed using 3D milling
3 ALTERNATIVE 3D CUTTING
TECHNOLOGY 1: 5-AXIS LASER
CUTTING
The 3D side cutting method that we have used with the
5-axis enabled CNC milling machine is compatible with
our 5-axis enabled flatbed cutting systems, which we
have investigated as alternative cutting technologies. The
first alternative cutting technology which can be used
with the method and algorithm are 5-axis laser cutting
systems, such as the one illustrated in Figure 4, which is
commonly used in the automotive industry.
In state of the art literature, the laser beam for
woodworking purposes such as separating parts is
considered as a possibility, but infeasible due to a lack of
efficiency, caused by its excessive energy use [10].
However for our application, the cutting of polygonal 3D
contours with concave corners, the laser system provides
advantages. The cut width of the laser system is only 0.6
mm, which allows for the cutting of LVL plates with a
thickness of up to 39 mm. In contrast to the milling
system, this low cut width is greatly reducing waste and
cut offs, and the previously introduced notches on
concave corners are not required (see Figure 19).
Figure 17: 5-axis Laser Cutting System
The system peak power consumption of the 5-axis
milling system used for our tests was 19.5 kW; the one
of the 5-axis laser system used for our tests was 96 kW.
The high power consumption on the laser system is
largely due to its external cooling system. However, the
cutting of up to 39mm LVL with the laser system was
performed at
, = 11 m/min in one pass. With the
milling system, we have cut 21mm LVL with
=
5 m/min in two passes, resulting in an effective feed
rate of , = 1.5 m/min. The comparison shows that
the laser system allowed for precise 3D cuts at a feed
rate which was more than four times faster than the one
on the 5-axis CNC milling system.
Figure 18: 5-axis 6kW CO2 laser system setup for LVL cutting
Table 1 shows that on a milling system, the number of
vertical passes increases with an increasing
thickness of the LVL plates. Therefore the
effective feed rate
, is reduced. Table 2 shows our
tests using a 3D laser cutting system, where cutting is
always performed in one infeed. We have cut spruce
LVL plates of up to 39mm with a feed rate of =
11 m/min.
(mm)
21
27
39
0.6
0.6
0.6
1
1
1
, (m/min)
11
11
11
Table 2: Effective cutting speed using 5-axis laser cutting
While the effective feed rate is greatly improved with the
laser system, the system peak power consumption for
our two testing systems is 19.5kW for the milling and
96kW for the laser system. The 4.9 times higher energy
consumption of the laser system is balanced by the 3.6-
7.5 times faster effective machine feed velocity we
observed in our test cuts with 21-39mm cross-laminated
spruce LVL plates. On the 5-axis laser-system, cut
quality was independent from the cut inclination ,
which was tested up to =45°.
Figure 19: 5-axis 30° inclined laser cut of a convex (left) and
concave (right) corner on 13-layer 39mm spruce LVL plates.
With its cut width of 0.6mm, a major advantage of the
laser system is presented by its ability to cut sharp
concave corners (or with very small radii), allowing for
cutting MTSJ without notches or “Mickey Mouse ears”.
(Figure 19). As previously discussed this is particularly
relevant for the cutting of thin plate thicknesses, where
the notches would be relatively large and reduce the
contact surfaces considerably.
3.1 Drawbacks of 5-axis Laser Cutting
Two major drawbacks of the laser cutting system are the
burning or charring of the cut edges (Figure 19) due to
the high temperature cutting process, which is mainly a
visual, aesthetic problem, as well as the burnt odor of the
final work pieces. Hazardous emissions are presented by
the fumes generated during the laser cutting, as well as
the laser light. Provided a class 4 visible-light,
continuous-wave laser system, which was used for our
tests, even scattered light can cause eye or skin damage.
Therefore, a complete enclosure of the machine is
required. For the hazardous fumes, extraction and
filtering systems are used. For the cutting of LVL, the
fume emissions are higher than for the laser cutting of
metals. Particularly powerful extraction systems and
measures for fire protection are required for such
applications.
4 ALTERNATIVE 3D-CUTTING
TECHNOLOGY 2: 5-AXIS ABRASIVE
WATERJET CUTTING
The second alternative cutting technology compatible
with the previously presented side-cutting method are
abrasive waterjet cutting machines that are equipped
with an additional tilt axis (see figure 20). We have
performed our tests with a system where the tilt axis can
be rotated up to a maximum of =59°, which
allows for the fabrication of non-orthogonal 1DOF
MTSJ with a dihedral angle ranging from =41°
to =139°.
Figure 20: Abrasive waterjet cutting system equipped with an
additional tilt-axis
The cut width of our water jet cutting test setup was
0.6mm, for spruce and beech LVL plates with a
thickness of up to 39mm, which is identical to the 5-axis
laser cutting system (Table 3). The same applies for the
number of vertical passes, only a single cut is needed to
separate the pieces. With the values provided in table 3,
high edge quality was achieved, as shown in figure 21.
Similar to the laser system, the cutting speed is not
greatly affected by the thickness of the plates.
(mm)
21
39
0.6
0.6
1
1
, (m/min)
2
1.5
Table 3: Effective feed rates using 5-axis waterjet cutting
Identical to the laser cutting system, the low cut width of
0.6mm allows for the cutting of concave corners without
or with very small additional notches. As explained in
section 3.5, this is particularly important for thin plate
thicknesses. Similar to the laser cutting system, the
clamping of workpieces is simple. Only small clamps
(figure 18) or even only weights (figure 20) provide for
sufficient clamping. There are no hazardous emissions
such as dust and fumes, only noise protection is required.
Figure 21: 15mm thick plates for a CSS [7] scale prototype,
cut with a 5-axis equipped abrasive waterjet cutting system.
Due to the cut width of only 0.6mm, no notches are needed.
Milling(1)
Laser(2)
Waterjet (3)
19.5
96
22
,
1.5
11
1.5
Table 4: Peak power consumption and effective feed rates for
the cutting of 1DOF MTSJ with our side-cutting method and
our systems used for testing: 1. Maka mm7s, 2. Trumpf
TruLaserCell 7040/TruFlow6000, and 3. OMAX 5555/30HP.
4.1 Drawbacks of 5-axis Abrasive Waterjet Cutting
Waterjet cutting is performed with the work pieces over
water basin. The work pieces are either completely
submerged (10mm under the water surface), or just
above the water surface, for splash and noise protection.
For the second case of cutting just above the water level,
we have still observed the work pieces getting wet due to
water splashing.
5 CONCLUSION
The 3D side cutting method introduced in this paper
allows for the rapid and precise fabrication of single-
degree-of-freedom (1DOF) integral timber plate joints,
such as dovetail joints or through-tenon-joints. In
contrast to time consuming manual programing with
CAM software, the automatic geometry processing
allows for a rapid generation of machine code for CNC
milling, laser or waterjet cutting. Unlike in previous
methods, it is not necessary to position the cutting tool
normal to the side face of the plate. The method
therefore allows for the use of standard flatbed routers
without any technical modifications, and it allows for the
processing of parts of any size that fits on the flatbed
table of the CNC machine. Instead of positioning the tool
normal to the side face of the plate, inclined faces are cut
with the tool inclined at an angle , which is possible
with modern 5-axis enabled CNC routers. For the
milling with shank type cutters, the maximum tool
inclination is determined through possible
collision points with the tool, tool holder or spindle and
the work piece. With standard CNC cutting tools, we
have found this limit at 60°. The 5-axis abrasive waterjet
system used for our tests is constrained to a maximum
rotation =59°. With the laser system, we have
successfully cut inclinations of up to =45°.
Unlike previous methods, the variable inclination of the
tool allows for the fabrication of 1DOF MTSJ (such as
dovetails), where the dihedral angle between two
joined plates is not constrained to =90°. Instead we
can fabricate joints with a large range of dihedral angles.
While a fixed rotation of =15° would be
sufficient for the fabrication of orthogonal assemblies
with inclined dovetails, such as the box girder presented
in section 1, a large variable range of angles is required
for the fabrication of freeform shell and spatial structures
built from timber plates, where the global curved shape
is achieved through incremental modifications in the
shape of a series of individually shaped plate elements.
In the last two sections of the paper we have discussed
the drawbacks of 5-axis CNC milling, and presented two
alternative side cutting technologies, which are
compatible with the method and algorithm presented.
While the mechanical behavior of 1DOF MTSJ
produced with 5-axis milling machines has already been
studied [5][6], further research is required to investigate
the behavior of 5-axis laser and 5-axis waterjet cut joints.
6 Acknowledgements
This research was supported by the Swiss National
Centre of Competence (NCCR) in Digital Fabrication.
The Authors would like to thank TRUMPF Laser
Technology, OMAX Waterjet Cutting Systems, Eric
Vassalli and Francois Perrin.
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