Homemade Izod/Charpy impact machine

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 difficult.

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 >

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....

?index=7149 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 same conditions.

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 analytical approach.

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.

Good luck

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 particle board.

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

search engine.

It wasn't all that easy to find.

Evidently, you have a number of orig> The part undergoing lateral movement in the animation is called the