wirewound resistors - how are they made? (and rheostats, same deal?)

[dave]

I guess nichrome wire wound around a ceramic core, then coated with
(maybe?) epoxy. my biggest question: I assumed the resistance wire was
originally UNcoated, bare wire, wrapped with each turn touching the next.

BUT

if it IS bare wire, then the makers either must keep each turn from
touching the next turn over (with a very small clearance), *OR* the wire
is coated -prior- to the winding process. otherwise, the 'resistance per
turn' wouldn't be controllable - right? I mean like if one turn, near
the middle of a wirewound resistor, was 'shorted' to the next winding
mid-turn...

like in these things:

http://machines.scienceontheweb.net/shocker/photos/photo23.html
wirewound03.jpg

thanks for info, guys

bubba here is kind of contemplating making a rheostat...this recipe
calls for a 6 ohm, 11.1 amp type (see bottom right of page 2)

http://www.countryplans.com/vintage_farm//metalshop/AutoArcWelder.pdf
AutoArcWelder.pdf (application/pdf Object)

of course, i have this ol' powerstat, but it's a 5 amp model

http://machines.scienceontheweb.net/shocker/photos/photo16.html
powerstat07.jpg

 

[James Sweet]

I guess nichrome wire wound around a ceramic core, then coated with
(maybe?) epoxy. my biggest question: I assumed the resistance wire was
originally UNcoated, bare wire, wrapped with each turn touching the next.

I've had several damaged wirewound resistors in which I could see the
wire. There's a gap between each turn, and the lower resistance,
generally the wider the gap because the wire is shorter.