Bass string winding Tension

[Newton Hunt]

You are getting into some of the arcane aspects of string making.

First, some string winders "straighten" the wire as it comes off the coils. 
Some do not, thinking that curve is important to the quality of their strings.
The copper, which is not all the springy, will not impart much of a twist to the
string when hanging loose.

60% of what?  Your question, as stated, is not clear.  You do not want to exceed
65% of the breaking point of that size of wire.  This does not happen often but
it can on big pianos and on the tiny ones with real heavy wraps. 

The amount of tension placed on the core while being wound varies from string
maker to string maker.  Some use air pressure and some just know how much to
tension by hand.  This involves "technique", one of many arts to master to
become a great string maker.

What we need to know about is the actual tension, breaking %, loudness factor
and inharmonicity, not necessarily in that order, in order to evaluate what is
there, and what you get back from the string maker.  

First you have to have an idea of what is "normal" and what the consequence is
of varying one or more of those factors.

Loudness factor controls the transition from mono to bichords.
Inharmonicity controls tone and tunabilty.
Breaking % effects tuning stability and durability.
Tension has a range and is used to control the above factors.

All these factors are interdependent but tension must fit into a range of
"normalcy" and inharmonicity must transition from one section to another
smoothly but also fit within a range of "normal".

The formulas are available, you can set up your own spreadsheet or database or
get a one of two programs that I know of, PScale from the US or Mensarat (sp?)
from Europe and play with them for a while then order a set of strings make to
your specification sheet.  Really listen to a bunch of pianos and measure
speaking length, core and wrap diameters and look at the graphs.  Listening and
looking.  Listening and looking and more of the same.  Eventually you will come
to some of your own conclusions about what you like to hear, what the
manufactures had in mind and see the errors of their ways as well.

Oh, this is SO much fun. :)

		Newton