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23rd June 2017, 10:22 AM #46
Vaughan, I've been doing a bit of searching to see if I can get some quantitative data on the silica content of the woods we've been talking about, but if it's there, it's hard to find. When mentioned at all, it's just in terms like "moderate" or "high", which is a bit imprecise. I thought it would be interesting to put together a table with actual figures for silica, other minerals, and Janka hardness, but soon realised it would take far more time & effort than I can spare atm. But maybe if we had something like that, we might be able to draw some solid conclusions about what contributes to difficulty in cutting a given wood (oth, it may simply add to our present level of confusion! ).
I think turning & planing are a bit of a different test for a wood, too - the cutting speeds bring in a new variable. I've found that some woods that are an absolute bear to plane will turn quite easily, & I'd put some Gidgee I've used in that category. However, the various 'batches' I've worked with over the last 10 years or so, have been really variable, so its workability very much depends on the particular piece you're dealing with. I imagine you select pretty straight-grained stuff for instruments? I go out of my way to find truly wild stuff for marking-gauge stocks, etc., but usually select straight-grained bits for the beams, not trusting the highly figured stuff to stay straight in a long, thinnish section. The straight-grained stuff is usually not bad at all to plane, rather like Ebony, whereas the wild stuff not only has the crazy grain to contend with, it actually feels harder to cut & seems to dull edges faster.
Jarrah is rated as highly siliceous, but of the relatively small number of Jarrah samples I've hand-planed (which does include two moderately-large sets of kitchen bench tops!), I wouldn't call it sissy stuff, but still put it well down my list of truly horrendous dullers of plane blades. I've only turned a few bits, but don't remember them as being at all tough to turn (I do use HSS turning tools, so maybe that helped), so once again, sample sizes may be influencing our views.
Cheers,IW
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23rd June 2017 10:22 AM # ADSGoogle Adsense Advertisement
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23rd June 2017, 11:01 AM #47
I recall when I turned legs for a chair in Jarrah, the HSS chisel dulled very quickly, and I needed to use a carbide-tipped chisel instead. Those who work Jarrah with handtools are familiar with its ability to dull edges quickly. Some examples more so than others, as some examples are harder or easier to work than others. The characteristics change within samples, so-much-so that I can understand a few who work a single piece not experiencing anything particularly difficult.
And that is what started this thread. The books state that Jarrah is typically low in silica - because it does not grow in silica-infusing conditions? I have had an invitation from a friend in the USA to send him some examples for analysis. I think I will take him up on this.
This has been a wonderful, rich thread, and I thank all the respondents to date.
Regards from Perth
DerekVisit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.
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23rd June 2017, 11:46 AM #48Deceased
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Jarrah is found only on lateritic soils in south-west Western Australia, in the 650 to 1250 mm rainfall zone. Under optimum conditions it is a tall tree attaining 30 to 40 m in height with diameter at breast heightup to 2 m. On poor sites the species is reduced to a mallee form.Jarrah | Forest Products Commission
Laterite is a soil and rock type rich in iron and aluminium, and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and long-lasting weathering of the underlying parent rock.
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23rd June 2017, 11:55 AM #49SENIOR MEMBER
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23rd June 2017, 12:02 PM #50Deceased
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23rd June 2017, 12:05 PM #51GOLD MEMBER
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23rd June 2017, 12:07 PM #52
Aluminum is frequently associated with beer.
Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.
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23rd June 2017, 12:10 PM #53
I realise now this is a handtool forum section! Silly me.
Anyway, as fgar as turning speeds go I haven't yet quite figured out the best results in terms of longevity of tool sharpness. I go far fast as I can except whilst boring.
Indeed, I do work with the straightest grained pieces of wood for my flutes. Saving the figured pieces for end caps, etc. I have turned ringed and straight grained Gidgee and found next to no difference really except that the ringed/figured pieces tend to crack during boring or soon afterwards. Tough, but less stable at thinner dimensions.
Gidgee is great stuff, just expensive and hard to find in good lengths/widths.
The shavings/chips smell like bitter chocolate :P
Good thread
Vaughan
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23rd June 2017, 12:22 PM #54
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23rd June 2017, 12:26 PM #55GOLD MEMBER
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23rd June 2017, 12:27 PM #56
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23rd June 2017, 12:33 PM #57Jarrah is found only on lateritic soils in south-west Western Australia, in the 650 to 1250 mm rainfall zone. Under optimum conditions it is a tall tree attaining 30 to 40 m in height with diameter at breast heightup to 2 m. On poor sites the species is reduced to a mallee form.Jarrah | Forest Products Commission
Regards from Perth
DerekVisit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.
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23rd June 2017, 01:21 PM #58GOLD MEMBER
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I would expect that abrasive aluminium oxides would have a larger effect than silica (silicon oxide) on the sharpness of cutting tools as they are what a lot of sandpaper is made with.
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23rd June 2017, 01:27 PM #59
Derek
If I can wear my serious hat for a moment (it's the one that appears brand new) Australian Wood Review has published a number of articles on timber a little more recently than those mentioned in Ian's post (#19), which were more concerned with workability.
Hardness: Issue 59, p84
Density: Issue 74, p76
Toughness: Issue 84, p76
The articles were written by Hugo Ilic, who is a retired scientist who worked at the CSIRO for thirty six years. He has contributed several more articles than those above but these selected would have the greatest bearing on edge degradation and ease of use.
It occurred to me that it may be interesting to contact him, either directly or through AWR to ask his thought on this thread. I have to say that the articles do not delve any further into possible adverse properties of timber other than the contributors to this thread have discussed and he does indeed allude to the silica factor.
The article in issue 59 is particularly pertinent to the discussion here and also includes a table of species identifying hardness and density. Interestingly out of the top ten hardest timbers quoted, seven were from Australia (two were C.America and one Europe) not that I put this forward as being anywhere near definitive.
Regards
PaulBushmiller;
"Power tends to corrupt. Absolute power corrupts, absolutely!"
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23rd June 2017, 02:35 PM #60SENIOR MEMBER
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