Posted: Tue Jan 02, 2018 2:04 pm
by DwainSchroeder
You have taken on a very challenging project. Years ago, I toyed with the idea of making a 30" borer to look at growth rings on a giant burr oak in Goll Woods Preserve (northwest Ohio), for a precipitation history study. The tree was already dead but still standing The Preserve has a strict "no disturbance" philosophy though I believe I could have gotten permission to bore the dead tree. Long story short - I gave up on the idea after considering the design difficulties including that the wood would be somewhat dry and very hard; and also my interests moved on. I was in Goll Woods this Spring, but my failing memory won't let me recall if that tree has fallen yet....

Unfortunately, I don't have any specific details on the design aspects of borers to offer, but I still would like to respond. I have a 14" long "Suunto" borer which has worked well for me. I believe it was made in Sweden. It has three screws which I have been told, but it is not necessarily obvious to me, allows for easier and more efficient engagement than a two screw design. I believe what you call spreader bars, are located between the threads, but the last thread is tapered to allow for easier extraction. I believe that 28"/30" bores are available commercially but are quite expensive, and the idea of a do it yourself project is always interesting and educational.

I'm sure you already know, but material selection would have to be critical for your project. Borers are subjected to very high stresses. A 30" long borer may also be somewhat vulnerable to a "torsional squirm buckling" action - perhaps not, but something to look at when calculating the required wall thickness.

Good Luck!