Warren asked me a question here recently essentially about the silica content of Jarrah, since I had mentioned that Australian timbers can have a high silica content. The context of this is the high wear properties that Oz timbers have on tool steel.
As it happens, Jarrah has low silica content, and therefore its high wear properties are due to something else. My thoughts ran to its hardness (Janka ratings are high) and resin content (it is common to find pitch holes and veins in Jarrah). Jarrah is a eucalyptus, and these are common through Australia (although Jarrah is only found in my neck of the woods, in the south western section of Australia). The other common species are the acacias. These are more common to the Eastern states (other side of the island).
I decided to post the question on the Australian forum. Commonly, we Ozzies tend to bang on about the impact our timbers have on tool steel, whether this is in plane blades, chisels (both lathe and bench), and machine blades. Over the years we have seen the introduction of HSS (M2), A2, recently PM-V11, and even M4 replacing the O1 and high carbon steels commonly used by Stanley and many other manufacturers.
Our timbers do tend to be harder than those in other countries and we assume that this is a central cause for steel wear. The question I ask is "is this really so"?
The Janka rating for many of our timbers is much higher than most other countries. But is this enough to create the extra wear we experience? Other than silica, what else causes extra wear? Jarrah (among other eucalypts) is often quite interlocked. Is this enough to cause wear?
On a Google search I came up with a gem of an article, AUSTRALIAN EUCALYPTUS TIMBERS, which has a chapter on "The Chemical Products of Australian Eucalypts". Editing this to the salient factors, the introduction starts,
1. General. - The important Australian genus, Eucalyptus, is remarkable for the number and diversity of its chemical constituents. It might perhaps appear from a cursory glance that these were distributed throughout the several groups in an irregular manner, but research has shown that this is not so, for a most orderly arrangement is traceable through the various members and groups of the genus, a peculiarity which suggests a predominating influence of evolutionary conditions.
The article then goes on to discussing a number of influences:
Inorganic factors: Understandably, different regions in Oz will influence differently, however "A striking peculiarity in the eucalypts is the relative constancy of the element manganese in the ash of related species." ...."In some eucalypts the calcium oxalate is present in such abundance that at times as much as one-sixth of the entire air-dried bark consists of crystallised calcium oxalate." ...
Another relevant influence is tannin. "All the exudations of the earlier members of the genus, as well as those of the closely related genus Angophora, contain the crystallisable body aromadendrin ... Economically this is of importance because the tannins in those species which contain eudesmin and aromadendrin in their kinos can be utilised for tanning purposes". One of the thoughts I had - lacking any knowledge of chemistry and how these chemicals develop over time in their natural state - is whether this is the same as the resins in the wood, and then whether these hardened resin veins we so frequently see in gums, create an abrasive compound?
A friend of mine, Bob, mills trees as a hobby (he is a retired physics professor). He wrote about his experiences (anecdotal evidence but still ..): "Silica content seems to be dependent on climate stress. This is quite noticeable when milling a yard tree versus a tree that has been in an area of bush where it has not seen much water especially in the last few decades around Perth. Tuart seems to be the most common trees that have this problem. Some deposit enough silica so that occasional sparks can be seen when cutting a clean dry wood on a long dead tree i.e. tree has probably died from lack of water. This is also supposed to happen but to a lesser extent in Jarrah and Marri.
In general timber hardness still dominates chainsawing because it's as much a puncture and tearing action akin to chiselling as it is cutting. The first time I milled an ironbark I could not believe how much extra it demanded of the chainsaw. If ironbark had been the first species I had milled I would have given up and gone home. About the 3rd log I milled was some sort of rock hard desert gum and it was bone dry and I managed to blow up the 50cc 40 year old well used chainsaw I was using at the time. I was not that fussed because that saw owed me nothing and I treated it as a learning exercise.
Another species that has given me grief is Rock Oak, a type of hard sheoak that grows in the WA (West Australia) wheatbelt. This also pulls up a lot of silica and I won't mill these unless they promise to yield a decent bit of timber."
While I have mainly posted about Jarrah, it is simply an example of trying to understand what properties are responsible for wear in tool steel. That different timbers wear steel differently is clear. What can we learn from American woods?
Regards from Perth
Derek
