I've seen and used "homemade" impact testers. You can do a very good job
if you think it through and are reasonably good at design.
Do you want anybody to believe your numbers? Or are they numbers you
will generate for your own personal interests?
You can do something "on the cheap" that generates a number of energy
loss during impact. Getting anybody else to believe it can be more
Have you researched the use of impact testing in the timber industry,
yet? Or, are you "gung ho" about doing rather than thinking?
It's not exactly for the timber industry. It's actually for evaluating
timber species for a component of a full-circle bell called a "stay".
An animation of how the full-circle bell works can be found at
The purpose of the stay is to be weak enough to break in preference to
the bolts, axles, etc. if the bell is swung to hard. It also must be
strong enough to prevent nuisance breaking when the bell is only
slightly over swung.
The manufacturers and about 98% of bell installations reside in the UK,
where European Ash is used for the stay. However I reside in Australia
where a number of bell installations have used substitute timbers
(mainly Eucalyptus species), without really knowing whether it is too
strong, too weak, or equivalent to European Ash. At my bell tower in
particular we had used wood too strong for the purpose and have broken
some of the metal fittings.
Hopefully an impact testing machine can compare the strengths of a
variety of Australian timbers to a reference European Ash sample.
This is about as much thought I've put into it. Are there any other
tests which might be more suitable? I've seen a video of an Izod
impact test and it looks very similar to how a stay on a bell breaks.
The only other question that probably matters is whether a sample of
wood will behave the same as the real thing
It looks like your "stay" is a wooden beam with some kind of lateral
movement that slows and stops the circular motion of the bell. And, as a
safety valve, of sorts, you would like this woodem beam to fracture if
the bell ringing force is too high.
Some sources of information on wood....
Actually, your problem may be restated as the construction of a "stop"
which duplicates the fracture characteristics of an existing "stop" but
in a different and cheaper or more available local material.
One route is analysis.... use simple beam theory to make preliminary
calculations of how to make a substitute, assuming that you have a
source of decent material properties of the different woods (including
the effects, perhaps, of density and dryness... which might be important).
The second route is to make a beam breaker machine and using a standard
"original wood" geometry, try to make substitutes which break under the
Of course, you could also use this to verify your analysis approach.
Some of the information on the mechanical properties of wood is freely
downloadable. It would be good for you to look at some of this
information, or have it handy if you find an engineer locally to help
with this effort.
Other members of the list may decide to work with you on doing the
My father built his own jigsaw using an electric motor, a cylinder
assembly out of a small gasoline engine and a welder with a lot of
springs and junk parts - immediately after WWII.
I didn't inherit the desire and ability to assemble things from
improbable cast-off materials.
The part undergoing lateral movement in the animation is called the
"slider" (it slides left and right, hence "slider"). The vertical bit
which rotates on the opposite side of the bell is the "stay", and this
is the wooden beam that acts as a safety valve.
I found a better labelled diagram to clarify the parts
I will look at the timber resources you've provided. Hopefully they'll
have property specifications which are applicable (I don't care about
what the texture or colour of the wood is like), and comparable (I can
convert and compare psi to kPa but can't compare kg/m^3 to J/m^3)
I'd like to construct a beam breaker machine and have a rough plan in
mind. But I was wondering whether someone had constructed something
similar, or knows a source for plans for a machine, before I go ahead
and reinvent the wheel.
Yes, someone who has built an impact tester would be a great help to
you. This old report from 1922 has a poorly reproduced picture of Charpy
and Izod impact testing of wood (for aircraft). Note the mechanical dial
indicator for measuring the swing parameters.
You might find some help at the Wood Science group at Oregon State Univ.
Washington State Univ also has a Wood Science group.
The Stay impact more closely resembles the Izod impact conditions than
the Charpy test. However, the resemblance between the Stay and the
actual Izod test isn't good because the impact occurs pretty far away
from the clamping point of the Stay. That allows the Stay to act as an
energy absorbing spring, prior to fracture.
It might be possible to control the fracture load of the Stay by 1) wood
selection 2) Thickness and width of the Stay or 3) notching the stay to
control the fracture load. Notching of wood might work less well than
notching of metal because the wood might delaminate easily at the notch
tip, rather than initiating through beam bending fracture.
There is some Australian forestry product group which has been
researching ways to use native wood species in construction, including
My guess is that group would have the best chance of having the native
wood data on hand. I apologize for not having made notes of the
location.... I ran across them while searching for "Modulus of Rupture
Eucalyptus" or similar term (MOR ?)in
It wasn't all that easy to find.
Evidently, you have a number of original geometry and material bells in
addition to some which have been overloaded. I would tabulate the
geometries for later reference, and I would save the scraps of original
wood for any future comparative material replacements. Nothing like
having a successful design to reverse engineer.