Resistograph readings

[Dilz]

Just looking at some IML resitance drilling results as part of a learning process. One thing about the results on an oak tree im looking at this evening is that the amplitude of the reading is below 25% for the nearly the entire drilling. Does this indicate low wood strength? i got give the results for a maple to look at and it was off the scale so thess ones look really low.... Any feedback much appreciated.

[MATTMOSS]

Sorry I cannot help as I have no experience using one, but I would like to gain some experience if anyone has one and is within reasonable distance to me, oldham, Manchester area.

[Dilz]

THe process itself is very simple. Its the interpretation of the data that is important and in my mind the most difficult part, as well as how it effects the recommendations of a tree report. Just because there is decay found doesnt mean the tree is any greater risk, like wise just because there isnt decay doesnt mean the tree hasn't the potential for failure.

[Gary Prentice]

When you say below 25%, 25% of what?

 

M/C and temperature can also make a difference to readings. I spoke to Sorbus about this for an assignment, who contacted IML. They said it should be normal practice to take a 'baseline' or 'comparison' test in a undecayed area first.

 

Remember that the results aren't absolute values of wood density, but rather relative measurements of drilling resistance along the path of travel.

[Dilz]

the 25% referes to the amplitude reading . i.e how high up on the vertical axis the graph is. The higher it is the higher the resistance. So what you are saying is that the actual level of resitance recorded does not correlate to the actual strength of the wood? But by taking the baseline (which has been done in this case) a comparison can be made regarding the differeing levels of amplitude from other readings taken from the same tree, thus for example, if the base line and 2 other readings average out at an amplitude of say 60% but then another reading produces an amplitude average of only 25% then this could be suggestive of an area of inherent weakness with in the stem. or at least cause for a bit of chin scratching....

[Pete Bannister]

Dilz, not sure what you are looking at but all such resistance data (as Btggaz pointed out) are relative.

So, yes you need to calibrate the 25% against other tests and then decide if the resistance is 'relatively' low or not.

 

BTW my own experience is in the the use resistance drilling to detect decay in timber structures rather than trees. Although the tree is far more complex than most timber structures, the principles of resistance testing are much the same

[Gary Prentice]

Yes, you've got it. There's a lot of information out there, but not always the exact thing you're looking for. From what I understand, you'd want to take a baseline in an area of similar growth, i.e, avoiding areas where the grain is normal and not denser than average due to alignment and suchlike.

 

I've no idea how high a reading an average oak would give tbh, but it doesn't sound that high. IML stressed though that it doesn't give an absolute measure of density. A level reading, with increase in amplitude after drilling through the sapwood sounds odd. David Humpheries is probably your man for this, he uses onno e.