Re: foam cutting current ?

I haven't done any rigorous experiments, but observation suggests that the
temperature of the wire is lower inside the cut than outside in the case
where the material is thinner than the length of the wire. I have seen the
wire glowing outside the cut but not inside. If you are depending on the
wire to act like a thermistor for current regulation, you will be regulating
based on the average temperature, so the actual temperature where it counts
will be lower than calibrated where it matters. The material density and
feed rate will also affect that temperature differential. I have used my
cutter to cut foam rubber, which absorbs much more power from the wire. If
you want really accurate regulation you will need to account for those
variables. Probably not simple. If you use adjustable taps you will need to
account for length. If you don't need really accurate regulation then "TLAR"
is a lot easier and cheaper. I guess it depends on whether the thing is an
end in itself (fun) or a means to some other end.
--
Phil Mattison
http://www.ohmikron.com/

----- Original Message -----
From: Graham Stabler <eexgs@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, September 06, 2006 1:23 AM
Subject: [CAD_CAM_EDM_DRO] Re: foam cutting current ?


> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dennis Schmitz"
> <denschmitz@...> wrote:
> >
> > I was thinking to put power on the clips and use a heavy enough
> gauge copper
> > to make the resistance much less than the resistance wire.
> >
> > The control circuit would pump current through the wire and monitor the
> > voltage drop. Divide to get the resistance, which tracks
> temperature. If the
> > temperature drops as you feed material, the controller would
> compensate with
> > more power.
> >
>
> That sounds feasable as long as you are cutting something of constant
> width so you can get your clips next to the material.
>
> I'd just go with the TLAR approach at least to begin with and start to
> think technical only if you find you need to. The cnc aspect removes
> most of the problems associated with manual (non gravity assist)
> cutting such as non constant feedrate and snagging formers. A CNC
> wire cutter has been on my list for as long as I have been interested
> in CNC, one day.
>
> Graham
>
>
>
>
>
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