[Artemisia] Re: Cord Question

[Catherine Helm-Clark]

It is simply a matter of picking the right material for the job.
You need a thin line with high tensile strength that's
capable of not losing strength with increasing temperature.
If I remember that lathe set-up correctly, it looks to me that
while size was scaled, the tensile stress of the spring/pole
mechanism did not.  I don't find this very surprising since
the force of the pole may scale linearly but the stress in the
line scales by 1/r^2 where r is the diameter of the line/string.
So if you apply a force of 100 lb to a rope of 1/4" diameter,
the tensile stress is 1600 psi.  But if you scale by 1/4 and
apply a 25 lb force to a rope/string with 1/16" diameter, the
tensile stress will be 6400 psi - tensile strength that most
natural-fiber rope or cord can not withstand.  In the real
world, you would have to go to fatter line or change
materials to steel.  This is probably not an option for a 1/4
scale lathe.

I would not recommend industrial-grade hemp as a line
material for you high tensile stress application (Holy Moo!
I'm sounding like a marketroid!  HELP!).  Hemp is inferior
to the synthetic fibers or even jute as a material for line.
It can catch on fire from friction in hawsers (I've seen this
happen), it has mediocre tensile strength compared to
other rope fibers and it rots in a second.  On old boats, it
was common to coat it with tar to keep it from rotting when
used as stays.  Flax has better tensile strength and it does
not have the rotting problems of hemp, but it's expensive
and it is hard to find as a rope fiber in the US.  It's also is
easy to catch on fire in high friction applications, just like
hemp.

Personally, I would not use a waxed natural fiber like
linen for a lathe.  What's the wax going to do here?  It
does not improve the tensile strength of the fiber at all.
It might increase the coefficient of static friction (gripping
power) at room temperature, but with the first few turns
of the lathe, the wax will heat up and act as a lubricant
instead.  Get it hot enough and you've just lit it up like
candle wick.  Come to think of it, that is what period
candle wicking was...  In the world of fire forensics, wax
is considered an accelerant.  Ever see those barbeque
fire starter sticks that don't use some form of volatile
liquid petroleum derivative?  They're woodpulp sticks
impregneated with wax.

I suspect that good latigo lacing would do a good job.  As
a high quality leather, latigo has good tensile strength. The
problem would be maintenance here.  Leather is actually a
felt.  You need to keep the organic molecules that bind the
felted organic stringy bits hydrated - and in leather, you do
this adding fats or by sealing the leather insides from the
outside world or both.  But this is kinda silly for a lace which
is not intended to last forever in the first place - not to mention
that it would be a chore.  I suppose you could go down to
CalRanch or the Leather Factory shop and buy a bundle
of latigo lacing and just replace the laces that broke on the
lathe as you used it.  Considering the application, your rate
of breaking down the fiber bits and dehydrating the interior
structure of the leather would be much faster than usual.
Leather is a good material for rotating machinery applications.
Most drive belts in the 18th and 19th centuries used to be made
out of leather - just make sure you use leather with the correct
tanning or tawing, which in this case would be latigo or veg
tanned with an oil retanning.  It will be pricey though since the
last tannery in the US that made latigo went out of business
in the 90s - so all the oil tanned leather these days is an
import.  I suspect that a high tensile strength fiber would be a
better choice here in terms of tensile strength and wear and
overall cost.

Some of the newer synthetics don't look bad but they
usually don't look natural.  Most of the nylon and dacron
lines are shiney.  Kevlar is always that disgusting puke
yellow color and it won't dye.  Rayon is often black, shiny
white or this weird split-end waxy yellow. On top of this,
most of the synthetic fibers made specifically for strength
(i.e. not for clothing) don't dye worth a damn.  They're all
polymers with no room in their structures for the extra
cations that usually impart color to idiochromatic materials.

I'm not too sure if you can get artificial sinew in any colors
other than brown or black, but it would probably work great
if the color and look were compatible with your going for a
material that wasn't blatantly modern-looking.  It has
superior tensile strength compared to natural fibers, though
there are a lot of other synthertic fibers with better tensile
strength.

After having given this problem some thought, personally
I would try Gorilla Tough brand braided fishing line.
Extremely high tensile strength.  By design to be used for
reeling out on really big high velocity fish like halibut and
swordfish so it can take the heat of friction on the rod hoops
and reel of a large ocean-grade fishing set up.  And it's a
braided line, not mono-filiment like a lot of fly-fishing lines,
so it looks natural.  It comes in only one color: grey.  It's not
the light straw brown of flax or the darker brown of hemp or
jute but it's not the usual artificial green of a lot of other fishing
lines, braided or otherwise,  and it's not the obnoxious shiny
white of nylon boat line.  It's a relatively unobtrusive grey and
it doesn't look like a shiney synthetic.  Hop down to the local
fishing-addict hang-out, eyeball a spool of the stuff and see if
you like the look.

Consider trying horse hair if you have any cooperative
horsey firends.  In period, fishing line was made out of
white tail hairs from a female horse.  I suspect color is not
important, since white was specified because fish had a
hard time seeing it, but the gender is possibly essential.

That's just my two schillings worth.

ttfn
Therasia