Re: foam cutting current ?

I use nichrome wire from the hobby store with spring tension, a 12v
transformer and a light dimmer. I've found that when cutting, the foam draws
heat from the wire so the temperature (and therefore current) is highly
dependent on foam density, thickness and cutting speed. The wire expands
quite a bit when hot so the spring is needed to maintain tension. Unless
you're setting up a production system where repeatable conditions and
results are needed, it may make more sense just to play it by ear. I just
turn up the power until the wire starts to glow, back it off a little, and
start cutting. How much to back it off depends on the thickness and density
of the foam.
--
Phil Mattison
http://www.ohmikron.com/

----- Original Message -----
From: turbulatordude <dave_mucha@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, September 05, 2006 7:36 AM
Subject: [CAD_CAM_EDM_DRO] Re: foam cutting current ?


> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dennis Schmitz"
> <denschmitz@...> wrote:
> >
> > The coefficient of resistance wire isn't as linear as platinum but it's
> > stable. You can design the current regulator to maintain a set
> temperature
> > once you've calibrated it.
> >
> > Come to think of it, this will be an average over the length of the
> wire, so
> > if it's not all being used in cutting the foam, the temp wouldn't be
> > inaccurate. So if you string the wire on a tension mount with
> insulators,
> > then bring the current in with copper wire and clips. Then you put the
> > length of the resistance wire doing the cut in the controller, or the
> > controller could measure it if it was cold. Should get an even
> temperature
> > across the wire that way.
> >
> > Just thinking out loud...
> >
>
>
> If I follow, one could put some sensing leads with alagator clips, and
> 'store' them on the ends of the wire. for many cuts, measuring that
> would be good enough, then on the heavy cuts, one can move them to
> the edges of the part....
>
> or, would one put the power on the clips ?
>
> or, does it really matter ?
>
>
>
>
>
>
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>
>
>
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