Bendywood® Technical Guide
Please read these guidelines before working with Bendywood®. Our web-site is
regularly updated with technical information:
www.candidus-prugger.com
Introduction:
Bendywood® can be bent in the cold dry state to a radius of about 10
times its thickness i.e. a 10mm thick board can be bent to a radius of 100mm.
However it should be noted that Bendywood® is natural wood and therefore each
piece is different in nature. Some pieces will break before this 1:10 ratio, and
some will be able to be bent further. It can be stored indefinitely in dry
conditions (e.g. in a workshop) but should not be stored in damp conditions.
The Patented production technique involves steaming and then compressing
hardwood along its length. The maximum size that can be produced is 100mm X
120mm X 2200mm. Longer lengths are supplied jointed. This jointing increases the
minimum bending radius to 20 times the material thickness. (i.e. a 10mm thick
board can be bent to a radius of about 200mm).
Most sections are supplied with a machined or sawn finish. The exception being
the largest blanks. These sections of 100mm x 120mm are supplied in their raw
state straight out of the compressing machine. The surface on these blanks may
have some discoloration & small ripples on the surface. This is a trade off for
offering the maximum size possible without us machining any material away. The
usable section is at least 80mm x 100mm.
Different sections bend in different ways. It is always easier to bend in the
thin direction. As with any material, any given section has a natural direction
in which it tends to bend. A rectangular section will try to buckle if bent in
the thick direction. A circular section however, can be bent in any direction.
DO NOT USE BENDYWOOD® OUTDOORS!
Working:
Bendywood® can be machined using the same tools and machine processes as
normal wood. However since it has been compressed, it can have an increased
tendency to tear. Therefore the following guidelines should be observed:
1. Saw and sand as with normal wood.
2. When using rotary cutters on machines or hand planes, pay particular
attention to grain direction as planing or cutting against the grain can cause
severe tear-out.
3. When spindle shaping, routing or planing to thickness, increase cutter speeds
by 20% and hold tightly against the fence to avoid any chatter. It is best to
make a series of small cuts to remove material prior to a final finishing cut.
Sharp cutters should always be used. Power sanding works particularly well. It
is best to use a slower feed rate than normal. Always test your cut on a spare
piece of Bendywood® prior to machining the work in progress. HSS tooling is the
best.
4. If the material has been moistened to aid in making a difficult bend, make
sure that the machining is done after the bendywood® has dried to at least 8-10%
moisture content. If you try to machine the material when it is above about 12%
moisture content, there is a greater tendency for tear out. Further drying to
6-10% will improve the machining quality considerably. Please avoid cutting
fixed lengths and then stocking them.
5. Since the length of Bendywood® increases with moisture content it is very
important to check that if it has been dampened, it is fully dry (6-10%) before
gluing or fixing in any way. The force of shrinking wood is enormous. If it is
fixed while it is still too wet, it will break joints & fixings as it shrinks to
its fully dried size. When it is dry, it can be glued or fixed as if it were
normal wood.
6. Moisture content through the largest sections will be higher in the middle
than on the surface. When a blank is being cut into smaller strips, initially
the center pieces will be damper and more flexible. If these smaller sections
are left out in the workshop for a few days, they will soon dry. Please note
that it is impossible to evenly dry thick sections throughout their thickness
prior to cutting into smaller sections. Bendywood® can be dried relatively quick
when cut into thinner sections. Actually it is more forgiving in this respect
than normal wood.
Bending
Bendywood® can be rebent.
Bendywood® should not be bent back and forth repeatedly, as this will cause it
to weaken & break.
• Thin mouldings and sections can be bent by hand. Thicker sections need more
force to bend them, and therefore they are stiffer once bent. There are a number
of ways of applying force. These ways include using pulleys, clamps or weights
all the way to using mechanical rolling machines which are commonly used for
metalwork (see picture below).
• When using a ring rolling bending machine, the following guidelines should be
observed:
1. Rollers must be exactly the correct diameter, for example a 40 mm handrail
can’t be bent with 42mm rollers.
2. Always work slowly. A difficult bend should be worked very gradually so that
the wood can adjust to the new shape without breaking (please let the pieces go
back and forth through the rollers at least twice). A 19 feet long 1 7/8“
diameter handrail should take about 1 hour to gradually bend. On the other hand
lippings, mouldings & skirtings, etc. can be bent around gentle curves at a
normal working speed.
3. We suggest wiping the surface of the bendywood® with a damp cloth just prior
to bending with the bending machine. This makes it adhere better to the rollers
of the machine.
4. When bending to a particular tight radius, bend up to 80% of the radius to be
achieved. The remaining 20% should be bent by hand. It is also better to over
bend 10% more than the required radius if you have to achieve a particular shape.
This slight over bending is required, because bendywood® has a tendency to open
up a bit after bending.
5. If you bend square pieces, make sure you slightly round the corners before
rolling. If you do not, the bendywood® may break.
• If a bend is difficult or when bending handrails, it is important to raise the
moisture content to about 16% prior to bending. This can be achieved by putting
the Bendywood® between two layers of moist cardboard for a day or two & wrapping
in a plastic sheet to keep the moisture in. Spacers should be positioned between
the bendywood® and the wet cardboard to avoid actual contact with the cardboard.
SANDWICH METHOD
This technique (“Sandwich method”) allows the Bendywood® to absorb moisture from
the air without getting wet. Bendywood® MUST NOT BE IMMERSED IN WATER OR BE IN
DIRECT CONTACT WITH THE WET CARDBOARD. Direct contact will not increase the
moisture content uniformly. Also if the pieces are jointed this could cause the
joints to come apart rendering the piece useless.
• When bending un-jointed material the minimum radius is about 1 to 10, and when
bending jointed material it is about 1 to 20(i.e. 3/4" thick material = 15”
smallest achievable radius).
• After bending, Bendywood® should be bent and then temporarily held to a shape
while it shrinks along its length (about 1%). For example after about one week a
19 feet long handrail temporarily held to the banister should have shrunk &
stiffened to the point it is ready for final fixing. Please note that if you
permanently fix the handrail to the banister before it is sufficiently dry, it
may break while shrinking.
• Pay attention to the fact that during the final assembly, bendywood® shrinks
along its length as the moisture content reduces. For this reason it is better
to start fixing the components in the middle working toward the ends using
slotted fixings that can compensate for any further shrinkage.
Gluing & Staining
1. Bendywood® can be finished like normal wood, except that water based
stains and glues should be avoided if the subsequent expansion caused by wetting
will cause a problem.
2. If bendywood® has been moistened to achieve a tight radius, check that it is
completely dry (to 8-10%) before gluing or staining.
3. If 2 pieces of Bendywood® need to be jointed (glued) in the length, it is
better to joint them on a sawn, angled cut. The length of the slanting cut
should be 3-4 times the size of the section to be glued:
Finally, we can not cover all applications & situations in this brief
introduction. Therefore if you are in any doubt, please contact us & check
www.candidus-prugger.com for updated technical information. We have a photo
gallery on the website to show examples of Bendywood® being used. If you have
questions about a particular custom project or application, please contact us
with your specific company details.
Conclusion:
A: Bendywood® thin sections
1. Work them.
2. Bend them by hand.
3. Stain them.
4. Fix them.
B: Bendywood® thicker sections
1. Work them.
2. Raise the moisture content up to 14%-16% (sandwich method).
3. Bend them with application of sufficient force (bending machine).
4. Hold them temporarily to a shape until they are again dry.
5. Work them again if you need to.
6. Stain them.
7. Fix them permanently.
A video showing the bending process is available for here.
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