Re: foam cutting current ?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Phil Mattison"
<mattison20@...> wrote:

>
> 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/

I am starting to think that is how it is done. just heat the wire and
watch the cut.

I don't suppose it is anything difficult as I am trying to make it.

I was envisioning using a feedback so the cutting would slow when the
wire cooled, and/or adjust the current automatically.

Dave

>
> ----- 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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