Originally posted by NebClimber
What's the most effective way to fall a spar yet keep the spar on the stump?
Steven,
Things fall. Causing them to fall is to fell them. I know it's confusing because "fell" is also the past tense of "fall", but <i>(to )fell</i> is the proper verb to use when discussing the activity.
Your question really is "what's the most effective way to ensure hinge wood doesn't fail (in a spar)?"
Since it's a spar, by definition there are no limbs to hold it off the ground at the upper end, so assuming the ground is level in the direction of fall, the hinge will have to bend 90° plus a tad. Depending on species and length of time it was a spar that might be a tall order or it might be simple.
As Daniel has suggested, the notch will have to be 90°+ meaning it will be an open-face notch (both upper and lower surfaces will slope away from the apex of the notch). All that remains is to ensure the hinge wood will remain flexible enough so as to not entirely shear as it bends the 90°(+).
Hinge wood can be made more flexible by lengthening the fibers which bend and this can be easiest accomplished in one of two ways:<ul><li>make the back cut above or below the apex of the notch</li><li>do not form a tight apex, but instead leave a vertical section between the upper and lower faces of the notch</li></ul>The first item is discouraged practice when using an open-face notch, but can work. The second item may require a bit more effort but would be the better choice. Either way, you want to terminate the cuts as cleanly and precisely as possible.
There really is a fair amount of freely available literature covering this topic. <a href="http://www.google.com/search?num=100&lr=lang_en&q=tree+felling" target="_blank">Here</a>'s a good starting point.
Glen
[edit: <a href="http://www.ca.uky.edu/agc/pubs/for/for60/for60.pdf" target="_blank">This</a> link from among the above results could almost be the article Daniel wrote, almost.]