On Jul 24, 12:30*am, Derek Copeland wrote:
I assume that Bill's comment is intended to be yet another thinly veiled
attack on Skylaunch, who make an excellent winch! There is no hard
evidence that rollers are any less Dyneema friendly, and in any case
Skylaunch can supply and fit swivelling pulleys if you think they are
better. Our new Skylaunch winches at Lasham are so fitted.

Again the rollers he is talking about are as fitted to antiquated US
Gerhlein winches, and his Ford Model T analogy is about right.

The guillotine issue is more relevant. For some reason hardened steel
blades that will chop steel cable many times are instantly blunted when
used on any type of UHMWPE synthetic cable. I believe the fix is to
replace the anvil with a bronze component. So much for modern materials
and technology!

Derek Copeland

At 23:39 23 July 2009, bildan wrote:

On Jul 23, 12:45=A0am, Derek Copeland *wrote:
Chris,

Nothing special required, except that the rollers or pulleys should be
smoothed out and polished if they have been used for steel cable. Some
types of drum may need to be reinforced as Dyneema can slip and
tighten
o=
n
the drum to the extent that it get crushed.

More spectacularly bad advice from Del C.

Smoothing and polishing rollers will NOT work since the rope slides in
a helical path on the roller if the wrap angle is not exactly at right
angles to the roller. *All roller designs used with 'plastic rope'
show rings of melted plastic when used with Plasma Rope. *The rope
itself shows severe damage from melting. *Using rollers with Plasma
Rope is an expensive mistake

Plasma Rope (Spectra/Dyneema) should have swiveling pulleys with
specific pulley groove geometry. *I have a tested design for fairlead
pulleys with a Plasma specific guillotine that I'll let anybody use to
make their own. *E-mail me and I'll send the drawings.

It wasn't meant to be 'thinly veiled'.

Actually Derek's inexperience is showing. There is a difference
between guillotines for steel and Spectra/Dyneema in that the shearing
cutters used with steel won't cut "plastic rope". It doesn't 'blunt'
the blade, it just pushes them apart and defeats the cutting attempt.
Spectra/Dyneema is a lot tougher than steel.

You need a more aggressive guillotine with a "chopping" action that
forces a sharp steel blade against an anvil instead of a shearing
action. A steel edge cutting against a brass block works well as does
a plastic block which saves the edge.