If we are talking about woodturning, isn't it "obvious" the strength
to which he refers would be that of the fibres to be cut by the tool?

No, strength is measured as deformation to failure under load.

Can you explain how tensile strength is tested now? It certainly was
a destructive test some time ago (not that this has anything to do
with turning).

The point of
_cutting_ is to sever with minimal deformation. Unless, of course you're
talking about beating the fibers into submission with a dull or poorly
presented tool.

I know it is, that is why the force must be sufficient to cleanly
sever the fibre. Not all fibres are of equal strength. it would seem
to follow that for a given sharp tool, the force must be sufficient
to cut before deformation. I have a question...would you say that a
firm fibre would be potentially easier to cut than a softed fibre that
may deform more easily?

It is unlikely to be the tensile or compressive forces the blank can
withstand or its hardness to a punch test is it?

Seems that's what you're proposing. Though the proponents of toothed
"gripping" keep trying to say that there's no damage done on their punch
test.

I'm not trying to bring that into it at all, I was more trying to
limit the discussion to factors appropriate to woodturning rather than
construction. I have no idea what the toothed "gripping" is to which
you refer.

moisture loss would be a surface phenomenon and I'd expect it to soon
move back to the EMC. If the temperature is elevated, would not
moisture movement be increased as well (more energy present)? Not
that I can see how this impacts upon the cutting speed used...which
was what initiated your reply.

Moisture evolved from the object will cool and lubricate the bevel following
the cut. It _is_ independent of speed, as I contend and you seem to
acknowledge.


The heat is generated
at the junction of the two materials and surface temp of the wood will
reach something of an equilibrium in "normal" conditions where turning
is regular/continuous; let us say planing cuts (unless you are
attempting to scorch the wood, but even here both surfaces in contact
woudl be at similar temps) The metal tool will conduct some heat away
from the contact point more efficiently than the wood, but the
temperature at the contact points of both materials would be pretty
close.

Two words - Heat Sink. If you look them up, you'll figure it out. The one
with greater conduction cools the less.

Why must you try to talk down to people? My point was that the
difference would be minimal. Please tell me what the difference in
temperature will be between the timber and the tool tip. Also, I'd
like to refer to the source of this information if you can provide it
please.

Increased speed will increase heat generation and I doubt anyone that
turns would agree that convective cooling would be significant whilst
friction generating the heat was present. As an example, would you
say heat build up when sanding is faster at high revs or slow? That
is why it is suggested to sand at a low speed; to minimise surface
heating that may result in surface checking.

You want to look up the basic friction equation. Once the piece is moving,
friction is the product of the coefficient of friction and the mass or
applied force keeping the surfaces in contact.

I'm sorry, if I want to apply a wax finish...heat builds up faster at
a higher speed when pressure is much the same for all speeds used.
This seems to be a commonly expressed opinion and I can't fault it in
"use".

Press too hard with
sandpaper and you risk _eventual_ drying and checking of the surface. Of
course, if it were being cut, it would already be gone. Perhaps that's why
you don't see checks behind a friction-heated tool whose hot nose your
fingers can't tolerate. Of course, some people fool themselves when
cutting as with sanding by producing a smooth-looking burnished, hardened
surface which becomes a mess once moisture is re-applied. Of note, it is
the continued pressure of the bevel _behind_ the cut which compresses and
heats the very surface of the wood.

..... and generates the subsurface damage that was disussed before the
guy that started this thread had used the chuck.


I'd agree, but only in a case with a grain orientation that permitted
the tool to cut for more than an instant in a growth ring; I would not
expect it with spindle turning (unless the speed is very slow), but
perhaps when facing a horizontal trunk section where the rings are
concentric to the lathe axis.

You need to learn more about your material. Consider the relative closeness
of the late wood rings as a harder face (quarter grain), the spreading area
where it transitions to a face of purely soft early wood as a softer face
(face grain). A tool which spans one and a half year's growth or less will
react accordingly as if it's cutting harder or softer material. Thus it
applies to spindle turning as well. Anchor the tool and let the material
cut itself, don't push and chase it, or you will loose circularity.

I know you tend to turn at slower speeds than most (from your
continued mention of flying bits of wood (or similar)), but in spindle
turning I find it imposible to accept that the tool could be moving in
and out as you turn to an extent that results in a visible (or of
interest) loss of circularity. I am sure I would not be turning items
out of round in spindle work. Just work out what the tool's
reciprocation rate would need to be for a spindle turning. I find it
hard enough to accept this as a significant issue with bowl turning.

An interesting debate, but more of academic (?) interest to a most I'd
suspect.


No debate, just an attempt to get you on board with the knowledge required
to generate one. So far you don't seem to have hit the books. Curiosity can
be contagious. I'm not the kind to see things happen without seeking to
discover how. That "be a student if you wish to be a teacher" belief.
Kids used to tease me about teaching Physics in the shop, but there were
days when a good part of the room was still debating/working on equations
long after the ending bell. Understanding the principles makes the specifics
a lot easier to master.

I don't want to burst any ballons, but you seem to be saying you know
everything...a dangerous position to adopt. You may have noted I
don't simply accept everything and this includes your frequent broad
brush strokes about how you've looked at the physics and the
equations..Similarly, attacking someone that challenges your lecture
does not impress me. You make many statements, and intimidate in
order to have them accepted. You commented on the heat sink effect of
the tool, again I ask, what the difference in temperature will be
between the timber and the tool tip. Also, I'd like to refer to the
source of this information if you can provide it please.

Oh, if I didn't want to explore the ideas further, do you think I'd
bother responding at all....Catch up again in a day I guess.