SamirCanada - 7-8-2013 at 06:30 AM
Hi fellow builders,
I am having a really tough time bending this african mahogany (also known as Khaya) I am working with.
Even If I get it hot to the point of scorching it bends very slowly.
however, the main issue is I am getting fibers spliting towards the sharp bend. I ruined my first 2 ribs that way so I am seeking your help !
Any tricks for bending difficult woods?
jdowning - 7-8-2013 at 12:18 PM
I have no experience with this wood but suggest that you might try boiling the ribs in water for 10 minutes or so before hot bending (use what is left
of the ruined ribs as a test).
Good luck Samir
jdowning - 7-8-2013 at 12:48 PM
A further thought.
What is the diameter of your bending iron? If too small (less than 4 inches (10 cm) in diameter - and you try to push the bending process too quickly
- you might induce localised, point loading, high stresses in the rib blank that could lead to separation of the wood fibres during hot bending?
bulerias1981 - 7-8-2013 at 02:21 PM
Samir,
What is your method of bending, and what are you using for a bending iron?
SamirCanada - 7-9-2013 at 04:42 AM
Thanks for your thoughts gents,
I did some more reasearch yesterday on the Internets and I figured out a way that works. I have to heat bending aparatus quite a bit more and spritz
the rib a little more than usual.
I use a large aluminum 1/8" thick sheet bent into the shape of the ribs. I can heat with a torch or a heat gun or eventually I will get a silicone
heating blanket for it.
Dr. Oud - 8-23-2013 at 08:03 AM
http://youtu.be/iT3DvVoGZ-Y
works well for ribs or purfling. Ribs take a little more heating, harder woods should be soaked in warm water a few minutes and moisture applied as
they dry out while bending. The heat gun applies heat more evenly, so the rib is less likely to break. A bending iron only heats a small spot.
Dr. Oud - 8-23-2013 at 08:07 AM
http://youtu.be/iT3DvVoGZ-Y
works well for ribs or purfling. Ribs take a little more heating, harder woods should be soaked in warm water a few minutes and moisture applied as
they dry out while bending. The heat gun applies heat more evenly, so the rib is less likely to break. A bending iron only heats a small spot.
SamirCanada - 8-24-2013 at 11:53 AM
Thanks Doc that's what I ended up using for bending.
Fritz - 10-24-2013 at 11:00 AM
I use a normal bending iron for guitars or violins... Depending on the curve of the rib (near back or near the neck-end) I use the different curvature
of the iron (aluminium) to give heat to the area of the rib with the most curve needed... the nearer the neck-end the shorter the heat is used. I
"wipe" the rib a few times to give heat on a larger area, than with a flower-sprayer a bit wetness... and go on. Never let the rib dry out, and
allways swing the rib on the iron... so there isn´t only a point touching the iron...
With the curve as near as possible to the mould let them dry complete, and than (next day) heat the iron up and bend dry... to correct the curve, try
to bend a bit more as needed and bend them back in the right curve while pressing the very slightly "overbended" area against the flat uper surface
of the iron. So the ribs are fitting well and the hold the curve a long time !
Some woods are to bend dry, some wet... but never boil the wood ! (my opionion)... the fibres loose their features for instrument making ! ( their
cellular structure and rigidity !)
Good luck
Fritz
jdowning - 10-25-2013 at 11:37 AM
Some guitar makers prefer to bend guitar sides by immersing them in boiling water for 15 minutes or so until soft and flexible, then clamping them to
a mold (while still hot and flexible) and allowing the wood to dry. They claim that it is safer than bending with a hot iron. As far as I know this
procedure does not adversely affect the cell structure of the wood - although it is not a lutherie method that I have tried.
Indeed softening wood with steam or boiling water prior to bending for non instrument structural applications is standard woodworking practice and
does not appear to weaken the wood in my experience. Of course, any excessive or prolonged heat application - including bending at scorching
temperatures on a hot iron - can result in irreversible cell damage.
Other luthiers will pre-soak and so soften/moisturise guitar sides in scalding hot water for about 10 to 15 minutes as a preparation for bending over
a hot iron - particularly for the more difficult to bend woods.
Note that wood that has been kiln dried may be impossible to bend without problems as the lignin (i.e. the 'glue' surrounding the wood cells) has lost
its ability to be re-softened with heat and moisture.
The hardwoods that I use for instrument work (including ebony, boxwood and rosewood) are all air dried. I do not use tropical hardwoods for ribs and
rib thicknesses are usually within the 1 mm to 2 mm range. These are formed on a propane heated bending iron (plenty of heat, provided quickly, as
required) the wood surfaces moistened with a damp cloth prior to bending. Never a problem.
SamirCanada - 10-25-2013 at 12:17 PM
Hi everyone, thank you for generously contributing to help me. Its apreciated.
With regards to this particular model, I am making some good progress. only 3 ribs to go. I have been using a light spritzing before bending which has
helped. I researched Khaya and foudn that is has many similarities with mahogany with the exception that it is one of the harder woods to bend given
its cell structure does not hold up to bending as much as genuine mahogany. In retrospect I shouldnt have used it but I was able to bend make it work
in the end. My problem was also compounded by not having uniform rib thicknesses between 2 - 3mm range and the thicker ones where a lot more
chalenging to bend and stay bent