Woodturning (rec.crafts.woodturning) To discuss tools, techniques, styles, materials, shows and competitions, education and educational materials related to woodturning. All skill levels are welcome, from art turners to production turners, beginners to masters.

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  #41   Report Post  
Alan
 
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Kevin,
Do you know what you are restarting? You may have missed the earlier
corrections from George to anyone that posed the suggestion that
higher speeds can produce better finishes. I agree with you, but then
I have never turned with tools sharpened to the edge of a carver's
chisel, like George.
Mike Darlow's books provide a good alternative to those that lack any
serous attempt to delve into details of what is going on as you cut.
Remember, look both ways before turning...or is that only with
crossing?
Alan



On 28 Sep 2005 12:38:30 -0700, wrote:


As the lathe speed goes up, the temperature at the cutting edge goes
up. At temperatures as low as 150 degrees Farenheit some woods lose up
to half their strength, making them easier to cut. So at higher speeds
you will get better finishes. This information comes right out of one
of Mike Darlow's books.
regards
Kevin


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George
 
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"Alan" wrote in message
...
Kevin,
Do you know what you are restarting? You may have missed the earlier
corrections from George to anyone that posed the suggestion that
higher speeds can produce better finishes. I agree with you, but then
I have never turned with tools sharpened to the edge of a carver's
chisel, like George.


Don't agree. It's pure baloney. Note that "strength" on its own is a
meaningless term, because it does not specify in which aspect the wood is
loaded. What is fairly obvious is that wood is "softer" in all loaded
directions wet than dry, which is why friction heating would result in a
tradeoff in increased strength in any load direction as the wood began to
dry from EMC as it warmed. This would continue to the boiling point of
water, where evaporative cooling would cease, and the wood approach zero MC.
See FPL pubs.

Not to mention the obvious - that metal in the tool draws and transmits heat
far better than wood - check the K - and the way to increase friction
heating is to increase friction, which, if you look at your equations, is a
result of the coefficient of friction times the pressure exerted (mass, in
static applications). Speed is not mentioned, but it would certainly begin
to trade off in convective cooling from the increased airflow over the
rotating surface even as you attempted to heat the wood by pressing down.
Of course, the wood will have already been cut by the time the bevel
generates any heat to dry it.

Pressing on the wood messes up the cutting, too. Causes the tool to follow
the differences in hardness in the wood, instead of making things circular.



  #43   Report Post  
Alan
 
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On Thu, 29 Sep 2005 10:35:56 -0400, "George" George@least wrote:

Don't agree. It's pure baloney. Note that "strength" on its own is a
meaningless term, because it does not specify in which aspect the wood is
loaded.


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

What is fairly obvious is that wood is "softer" in all loaded
directions wet than dry, which is why friction heating would result in a
tradeoff in increased strength in any load direction as the wood began to
dry from EMC as it warmed. This would continue to the boiling point of
water, where evaporative cooling would cease, and the wood approach zero MC.
See FPL pubs.

If the temperature continues to increase, any evaporative cooling
would seem to be insufficient to prevent the temperature
rise...wouldn't it? So what is the point of mentioning it? The
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.

Not to mention the obvious - that metal in the tool draws and transmits heat
far better than wood


A statement of fact, but why do you mention it? 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. If anything was hotter I'd suspect it to be the wood, but the
metal should absorb any excess heat so the cycle continues about an
equilibrium point...doesn't it?

- check the K - and the way to increase friction
heating is to increase friction, which, if you look at your equations, is a
result of the coefficient of friction times the pressure exerted (mass, in
static applications). Speed is not mentioned, but it would certainly begin
to trade off in convective cooling from the increased airflow over the


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.

rotating surface even as you attempted to heat the wood by pressing down.
Of course, the wood will have already been cut by the time the bevel
generates any heat to dry it.


Only if you start from 0 revs or mean the cut during one revolution.
Once you start cutting the bevel is in contact with the wood
immediately adjacent to the cut and if any significant heat is
generated it would surely spread away from the cutting point.

Pressing on the wood messes up the cutting, too. Causes the tool to follow
the differences in hardness in the wood, instead of making things circular.


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.

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

Alan



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George
 
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"Alan" wrote in message
...
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. 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.

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.

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.

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. 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.


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.

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.


  #45   Report Post  
Arch
 
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Hope the bell for recess rings before we are assigned homework or a term
paper.

Charlie may be too busy taking notes to fear for his bearings.

Likely, anyone who understands this thread has progressed beyond
'learning to turn' and is now 'turning to learn'. IOW, they can find
out for themselves by practicing, whether 'speed kills' or 'sloth is
sinful' or like most of us, find both to be useful speeds without much
deep thinking.

'The devil is in the proprioception'. The bell hasn't rung, so as an
assignment add that to your palimpsest and discuss. 'G'


Turn to Safety, Arch
Fortiter



http://community.webtv.net/almcc/MacsMusings



  #46   Report Post  
Alan
 
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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.
  #48   Report Post  
George
 
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"Alan" wrote in message
...
Can you explain how tensile strength is tested now?


The methods of test are described in the wood handbook (FPL) in the
appropriately-named chapter. It's the one I keep referencing in hope that
we can agree on it's being common ground.

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?


Basic turning principle that the fiber to be cut should be supported by its
fellows. Thus "turning down hill" and turning down grain. Means the softer
cuts easier.


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.


A heat sink in the form of the tool, resistance to heat flow in the wood
means the tool is heated well, the wood, hardly. That plus the undeniable,
that the tool remains in contact with wood, while any section of wood is
only briefly - and less briefly if you follow the faster is hotter theorem -
in contact with the metal, should be enough to understand that the wood
doesn't heat in normal cutting.


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".


You're mistaking lack of cooling for friction heating. Look at the
information in reply to heat sinking, and consider how much less time the
_same_ wood has to cool when you're friction polishing.


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.


Get yourself some calipers and try it. Simple enough experiment, really.
Press to just the first point of squirm (caused by differential cutting
resistance!) on one section, hold tool distance on another, then see what
results you get. If you skew along the cut with an edge held like this (/
or \), you'll get a better "average" of grain differences, and so a more
rounded piece. Oddly, that's the planing conformation of a skew chisel.
Almost as if they knew how to get the best average, and thus the best round.
Of course, other factors make it more significant in bowl turning across the
grain. Greater centrifugal force distorts the bowl, greater resistance when
grain is picked up rather than peeled, difference in the coefficient of
friction on end versus long grain, jumping the hard latewood ridge between
two areas of earlywood as you come across the bottom and so forth. That's
what makes for chatter - the wood flexing / tool moving. It's a relative
thing. The less tool force applied in the direction of the natural flex,
or the less flex permitted, such as with a steady, the better. Pressing
with the gouge is one reason why folks resort to scrapers to even surface
and circularity. Some increase speed, of course, but unless they back off
the radial force, that just makes smaller chatter patterns.

I don't want to burst any ballons, but you seem to be saying you know
everything...a dangerous position to adopt.


Now who's talking down? You have demonstrated a lack of understanding which
is not conducive to good turning, and I am attempting to ease your way by
getting you to think. Things won't be as much of a mystery to you if you
understand the principles which limit what can or cannot happen.

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.


I'll get the lab right on it. Let me know how near to the edge and how
insulated from the tool I'll have to get to satisfy you. Of course, if you
can demonstrate that wood conducts or acquires heat anywhere near the rate
of HSS, I won't have to. You'll find information on the thermal properties
of wood in the same source I keep referencing.

Thanks for the ad hominem. As they are generally just a fig leaf for the
ego, designed to avoid concession, perhaps you've gained some understanding,
as uncomfortable as the source may have made you. I will continue to answer
the questions you pose to the best of my ability and knowledge, even when
they're not questions at all, but foundationless assertions.


  #49   Report Post  
william_b_noble
 
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here's an easy experiment to prove that cutting heats the wood - I won't
waste time arguing about the mechanism

put a 24 inch wet bowl blank on your lathe, take a 3/4 inch bowl gouge, and
hollow agressively, so that the shavings are about 1/4 inch thick by 1/2
inch wide - make a nice long cut so you have a good pile of fresh shavings -
Oh, Look!! they are steaming - Gee, they must be getting hot!! Amazing
isn't it. Oh, feel the tool - not very hot.

now, back to the arguement already in progress



"George" George@least wrote in message
...

----snip------------

A heat sink in the form of the tool, resistance to heat flow in the wood
means the tool is heated well, the wood, hardly. That plus the
undeniable, that the tool remains in contact with wood, while any section
of wood is only briefly - and less briefly if you follow the faster is
hotter theorem - in contact with the metal, should be enough to understand
that the wood doesn't heat in normal cutting.


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".


You're mistaking lack of cooling for friction heating. Look at the
information in reply to heat sinking, and consider how much less time the
_same_ wood has to cool when you're friction polishing.



  #50   Report Post  
George
 
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"william_b_noble" wrote in message
news:1128191922.53dd79d62054bf1d3fae7b8a069ab2f1@t eranews...
here's an easy experiment to prove that cutting heats the wood - I won't
waste time arguing about the mechanism

put a 24 inch wet bowl blank on your lathe, take a 3/4 inch bowl gouge,
and hollow agressively, so that the shavings are about 1/4 inch thick by
1/2 inch wide - make a nice long cut so you have a good pile of fresh
shavings - Oh, Look!! they are steaming - Gee, they must be getting hot!!
Amazing isn't it. Oh, feel the tool - not very hot.

now, back to the arguement already in progress


Congratulations, you've just demonstrated that water absorbs heat faster
than steel. I'm sure it's not news to most of us, since we use water to cool
steel beginning with blooming in the mill, to grinding at the wheel. Now,
would you care to tell us what it has to the question at hand, which is
whether hotter wood is softer than cooler?

Of course, I'd prefer to save my elbow and hollow cleverly, rather than
aggressively so I don't build up all kinds of heat.




  #51   Report Post  
Alan
 
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Can you explain how tensile strength is tested now?


The methods of test are described in the wood handbook (FPL) in the
appropriately-named chapter. It's the one I keep referencing in hope that
we can agree on it's being common ground.


Sorry George, The FPL meant nothing to me in your earlier post, though
perhaps in the USA it is a well known abbreviation to describe the
USDA publication (I'm in Australia). I have located it online and am
downloading the current edition. I'll take a look later.

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?


Basic turning principle that the fiber to be cut should be supported by its
fellows. Thus "turning down hill" and turning down grain. Means the softer
cuts easier.


I understand the "down hill" fully, but can't see how this practice
means softer cuts easier.
I wondered whether you found firmer fibres, which would likely have
firmer support cut easier (giving good finish) than softer. I expect
you can follow my thought here, being that a fibre that is better
supported will cut more cleanly and the resulting surface be better.


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.


A heat sink in the form of the tool, resistance to heat flow in the wood
means the tool is heated well, the wood, hardly. That plus the undeniable,
that the tool remains in contact with wood, while any section of wood is
only briefly - and less briefly if you follow the faster is hotter theorem -
in contact with the metal, should be enough to understand that the wood
doesn't heat in normal cutting.

I agree that the tool is in constant contact and hence should increase
in temp faster (and this would occur in a steady cut until an
equilibrium temp was reached where the friction generated heat
"balanced" the conductive heat up the tool. I cannot accept that the
wood doesn't heat up. If it does, and each small area of the surface
is only in contact with the tool for a brief time, cooling would be
slowed due to the poor thermal conductivity of the air. Cut shavings
would remove a quantity of the heated wood mass, however.


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".


You're mistaking lack of cooling for friction heating. Look at the
information in reply to heat sinking, and consider how much less time the
_same_ wood has to cool when you're friction polishing.


Are you suggesting that a speed change, when other factors remain
constant, will not affect the rate of heat generation (no matter how
the friction is created, tool , paper, cloth,). Heat either is, or
isn't, generated more quickly as a result of incresing speed (extra
cooling would only be appropriate if additional heat was present to be
cooled. Or do you believe that incresed speed increases cooling and
therefore lowers the surface temperature?).

I think you are saying that the wood does heat up, but it cools faster
when heated during the cutting, rather than polishing. This seems to
follow. As heat is created by friction and you agree it is the product
of a coefficient of friction (surface) and the pressure applied, the
more surface passes the area under pressure, the greated the
generation of heat must be...so heat temperature will increase faster
at faster speeds.


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.


Get yourself some calipers and try it. Simple enough experiment, really.
Press to just the first point of squirm (caused by differential cutting
resistance!) on one section, hold tool distance on another, then see what
results you get. If you skew along the cut with an edge held like this (/
or \), you'll get a better "average" of grain differences, and so a more
rounded piece. Oddly, that's the planing conformation of a skew chisel.
Almost as if they knew how to get the best average, and thus the best round.
Of course, other factors make it more significant in bowl turning across the
grain. Greater centrifugal force distorts the bowl, greater resistance when
grain is picked up rather than peeled, difference in the coefficient of
friction on end versus long grain, jumping the hard latewood ridge between
two areas of earlywood as you come across the bottom and so forth. That's
what makes for chatter - the wood flexing / tool moving. It's a relative
thing. The less tool force applied in the direction of the natural flex,
or the less flex permitted, such as with a steady, the better. Pressing
with the gouge is one reason why folks resort to scrapers to even surface
and circularity. Some increase speed, of course, but unless they back off
the radial force, that just makes smaller chatter patterns.

I don't want to burst any ballons, but you seem to be saying you know
everything...a dangerous position to adopt.


Now who's talking down? You have demonstrated a lack of understanding which
is not conducive to good turning, and I am attempting to ease your way by
getting you to think. Things won't be as much of a mystery to you if you
understand the principles which limit what can or cannot happen.

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.


I'll get the lab right on it. Let me know how near to the edge and how
insulated from the tool I'll have to get to satisfy you.


You made the statement, I simply asked for you to justify it. Thermal
conductivity is not a measure of whether a material CAN get hot, it is
a measure of how well it conducts heat. Once hot, do not poor
conductors cool slower? If the friction generates heat, you contend
that only the tool gets hot and that heat is conducted along the tool.
I cannot see where you demonstrate that the wood will not be very
close to the temperature of the tool tip. Examining a table in a
reference won't tell anyone the answer.

If the tool tip is at 50 temp units it can't be conducting heat from a
surface at 30 temp units can it?
I am actually attempting to follow your explanations, but as I said, I
don't simply accept them.

Of course, if you
can demonstrate that wood conducts or acquires heat anywhere near the rate
of HSS, I won't have to. You'll find information on the thermal properties
of wood in the same source I keep referencing.

Thanks for the ad hominem.


Perhaps you can check the meaning of that yourself as there seem to be
several references to "my understanding" when I question or present an
alternate case. I haven't put myself forward as having all the
knowledge, just one of the few readers interested enough to pursue the
discussion.

As they are generally just a fig leaf for the
ego, designed to avoid concession, perhaps you've gained some understanding,
as uncomfortable as the source may have made you. I will continue to answer
the questions you pose to the best of my ability and knowledge, even when
they're not questions at all, but foundationless assertions.

You make it clear you are the one with the knowledge and you want to
impart it. Great, I hope more join you, but please take a look at the
way you do it. If challenged, you rely on references to a table of
properties which have questionnable relevance to turning a fruit bowl
or finial rather than taking teh time to simply explain it aand
provide the proof. Rather than stating easily followed procedures to
turn safely and enjoyably, you delve to levels most here have no
interest in following.
Woodturning can be performed safely and to good result without
overburdening oneself with a physics or materials science degree.
YES, it is interesting to discuss now and again, but don't feel most
here care to delve to such depths. If they do, and there are few of
them, little is gained by dismissing their opinions. Hell, one day
you may find that someone else was actually be right ...

Turn safely and don't stand under a large flock of geese...well I
suppose you could in some cases... if they are travelling at 1500
feet, say 15 miles per hour, no wind...does goose faeces falll with
minimal air resistance? (safest to work it out with, and without, I
suppose)...standing outside just got tougher.
Maybe just carry and open umbrella.

Above all have fun..
  #52   Report Post  
Bruce Barnett
 
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"George" George@least writes:

Congratulations, you've just demonstrated that water absorbs heat
faster than steel. I'm sure it's not news to most of us, since we
use water to cool steel beginning with blooming in the mill, to
grinding at the wheel.


I don't really see this. Metal conducts heat faster than water, so how
can water "absorb" heat faster than metal?

As I see it, absorbing heat is transfering temperature from a hot
medium to a cooler medium.

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  #53   Report Post  
George
 
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"Bruce Barnett" wrote in message
...
"George" George@least writes:

Congratulations, you've just demonstrated that water absorbs heat
faster than steel. I'm sure it's not news to most of us, since we
use water to cool steel beginning with blooming in the mill, to
grinding at the wheel.


I don't really see this. Metal conducts heat faster than water, so how
can water "absorb" heat faster than metal?


As I see it, absorbing heat is transfering temperature from a hot
medium to a cooler medium.


Back to the sink concept. Water takes a lot of heat to raise one degree, as
you know. Means it stays relatively cooler than what it contacts for a
longer heating period. Difference in heat translates to faster heat flow.

Of course, it takes a lot longer to air cool ten grams of water than ten
grams of steel, too. Now, if there is sufficient evaporative cooling ....


  #54   Report Post  
George
 
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"Alan" wrote in message
...
I understand the "down hill" fully, but can't see how this practice
means softer cuts easier.
I wondered whether you found firmer fibres, which would likely have
firmer support cut easier (giving good finish) than softer. I expect
you can follow my thought here, being that a fibre that is better
supported will cut more cleanly and the resulting surface be better.


Exactly, thought I said that was a basic turning principle, support. Hard
may snap, but soft cuts great. Soak one piece of pasta, leave the other
firm and see how it works supported on a cutting board.


I cannot accept that the
wood doesn't heat up. If it does, and each small area of the surface
is only in contact with the tool for a brief time, cooling would be
slowed due to the poor thermal conductivity of the air. Cut shavings
would remove a quantity of the heated wood mass, however.


Can you accept that the wood which heats by the bevel is behind the cut?
Unless you've got a dull tool with a high coefficient of friction and are
pressing (perhaps speeding up the lathe!) to attempt to remove wood like
Bill, that is. That's the definition of sharp, isn't it? Low friction.


Are you suggesting that a speed change, when other factors remain
constant, will not affect the rate of heat generation (no matter how
the friction is created, tool , paper, cloth,).


I believe the oft-referenced equations for friction, where the only velocity
is the acceleration of gravity. Use your favorite search engine. I can't
make Greek characters with this ASCII set, but Friction = Coefficient of
friction * Normal Force (weight). If you use the search, you can find
enough illustration and explanation to internalize it to your own
satisfaction.

You're supplying heat at a faster rate than it can sink into wood or cloth,
therefore the wax melts. Interestingly, at that point, the temperature
remains constant unless you heat the wax to ignition.


I think you are saying that the wood does heat up, but it cools faster
when heated during the cutting, rather than polishing. This seems to
follow. As heat is created by friction and you agree it is the product
of a coefficient of friction (surface) and the pressure applied, the
more surface passes the area under pressure, the greated the
generation of heat must be...so heat temperature will increase faster
at faster speeds.


Can't say it often enough. See the Physics. Faster is _not_ a player in
generation, but merely shortens the cooling interval where there is constant
contact.


You made the statement, I simply asked for you to justify it. Thermal
conductivity is not a measure of whether a material CAN get hot, it is
a measure of how well it conducts heat. Once hot, do not poor
conductors cool slower? If the friction generates heat, you contend
that only the tool gets hot and that heat is conducted along the tool.
I cannot see where you demonstrate that the wood will not be very
close to the temperature of the tool tip. Examining a table in a
reference won't tell anyone the answer.


The best cut is defined by the minimum friction it generates, and any area
of wood is so briefly in contact with the generator or reservior (tool) of
that heat that it can't heat much. Wood has 4 times the specific heat of
iron, so it gains slowly. Then there's the cooling provided by the moisture
in the wood, the effects of which are shown in the table of heating data
versus strength.

I am actually attempting to follow your explanations, but as I said, I
don't simply accept them.


There's the rub. Your personal firewall. Look at the information given.
Make the effort to understand. This means suspending yourself, accepting
and evaluating the information, not whether you like George. Once you
integrate the physics, wood technology, and your experience, you'll find
yourself nodding your head in agreement. As you continue to follow the
group, you'll also find yourself shaking it in disbelief as such things as
"greater mass is good, but only if it's heaped on the stand. Don't make your
lathe part of the earth itself by bolting it to the floor," or "serrations
provide greater grip without altering the surface of the wood," to name but
two, keep coming up again and again.


  #55   Report Post  
Martin H. Eastburn
 
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Water does it in complex transform rate to boiling. The boiling point
of water is the key - it releases energy cools itself and grabs some more.

Martin
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder



Bruce Barnett wrote:
"George" George@least writes:


Congratulations, you've just demonstrated that water absorbs heat
faster than steel. I'm sure it's not news to most of us, since we
use water to cool steel beginning with blooming in the mill, to
grinding at the wheel.



I don't really see this. Metal conducts heat faster than water, so how
can water "absorb" heat faster than metal?

As I see it, absorbing heat is transfering temperature from a hot
medium to a cooler medium.


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