Andrew,
Thank you for your excellent scientifically supported explanation.
I found the comment on the short fibers allowing the slanted blade to
cut through (verses 90 deg cut that hits each short fiber) to be
especially illuminating.
Also the comment about the "glue" made me think of the difference
between cutting green wood verses dry wood. Dry "glue" lack
lubricating function and becomes a hardened obstacle to cut. BUT dry
"glue" allows for pieces to be snapped / broken cleanly whereas the
green wood bend and is hard to get a full break. (This might be all
wrong, but it just seems logical. Can anyone confirm or refute the
comments?)
And I thank Tom Miles and Tom Reed who many years ago explained to me
the "beaver angle" that the beavers use when cutting down trees. I
think it has been measured at 27 degrees (but do not quote me on that.).
Paul
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: psand...@ilstu.edu
Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 1/4/2014 5:45 AM, ajheg...@gmail.com wrote:
[Default] On Thu, 2 Jan 2014 20:31:27 -0500,"Crispin Pemberton-Pigott"
<crispinpig...@gmail.com> wrote:
There is some merit in the slicer when looking to cut woody things. The
guillotine is much more difficult to operate, in my experience. If it bends
the material away before slicing, things get even better. You can try it
with a pen knife: cutting directly at 90 degrees or slicing into wood at 45.
Sorry for the delay in replying Crispin
This comment is pertinent: if you have cleft material for things like
wattle fencing you will have learnt to steer the split by putting
tension on the side of the piece you want the split to go toward. This
must be because wood is short fibres glued together with widely
differing properties in shear, bending and tension. So in cleaving we
are mostly shearing the glue between fibres and this does not require
much force.
We need to separate the force to comminute the wood from the energy
necessary. With efficient gearing force is not a problem, though the
device becomes more costly. For a man powered device we need to
minimise the energy required to produce a particle of the desired
size.
Rolf has commented on a hacker that minimises the number of cuts and
cuts at an angle, Richard mentions the need for the cutter to maintain
an optimum angle. Has anyone measured the forces in these differing
scenarios. Energy is force moved through distance and even though the
force may be lesser on the angled cut as it is cutting a larger face
the distance is increased.
One of the principles of the teardrop chunker was that the cut pieces
dropped under gravity and the cutting did not impart any kinetic
energy to the particles, this differs considerably from commercial
chippers which blow particle a long way (principally to load a truck),
this pneumatic delivery is energy costly.
Another thing about commercial chippers to be avoided is making
unnecessary cuts or producing small particles because each of these
particles has needed energy to produce. I noticed early on that the
chippers that cut at an angle would not feed at all well if slightly
blunt, all out modern chippers cut at right angles and will continue
loading the truck even if the blades are dull, albeit the chips then
become stringy with a lot of fines ( i.e. a lot more energy has been
expended making them).
AJH
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