Hot Cutting

In article <1992Jul15.141441.14757@rchland.ibm.com> ericj@rchland.vnet.ibm.com writes:
>As I was looking through the Into the Wind catalog I noticed that the hot-
>cutting tool that they offer for cutting rip-stop looks a lot like a soldering
>gun that I have out in my garage.  My wife and I are dabbling in kite 
>making and are considering picking up something to use for hot-cutting.

Here's something that I wrote a while ago and posted to this group.
I've edited it a bit since I've thought of a few new things. Remember
these are my opinions...
I've done a lot of experimenting with hot knifes and can relate the

Soldering gun: The standard soldering guns don't produce enough heat
        for lots of fabric cutting and is heavy and bulky too. My
        soldering gun is now used only for heat sealing plastic and
        similar tasks.

        Actually, they work pretty well, but don't cut quickly enough
        for me. I guess I should be more patient.

        The sailmakers equivalent does work well and is convenient to
        put down, but is still heavy and bulky.

Soldering irons: I take a standard soldering iron and then file the
        tip into a rough knife shape. The heat does the
        cutting/melting, so you don't need a sharp edge. I use a
        standard soldering iron stand to hold the iron.

        Soldering irons work pretty well and you can get high wattage
        and high temperature units. The price isn't too bad either.

        The cheap irons burn out pretty quickly though, so if you are
        going to do a lot of cutting, it is worth it to buy a more
        expensive unit.

        Wattage doesn't directly correlate to temperature, so check
        the iron's specs before buying.

        I use a 40 watt Weller iron for tacking, cutting curves and
        making small holes.

Wood burners: There are two types of wood burners, one looks like a
        soldering iron (sometimes with temperature adjustment) and the
        other has a separate hand piece which is connected to a box
        with a transformer and some sort of heat control on it.

        The soldering iron variety works fairly well, but has the same
        problem that soldering irons do, eventually it will burn out.

        The other sort is expensive, but is by far the best hot knife
        that I've used. Mine was made by a friend in return for some
        kites. I've seen them for sale in woodworking stores starting
        at around $100 and going up to $250.

        The dial controls the temperature of the knife. On full power
        the actual blade will heat up to cherry red in a few seconds.
        At this temperature, the nylon will actually begin to burn, so
        I don't use this setting except to impress people :-)

        The blades on the hand pieces are a little thin for use with
        cutting nylon, so when I originally got mine, I bought two
        handles. When one blade broke, I sent it in for a new tip, and
        asked for the "unflattened" tip, which has more material on it
        and is perfect for cutting nylon.

A bit on hot cutting:

Hot cutting is using the heat from the knife to melt through the
fabric. The temperature of the knife should be high enough to easily
cut through the fabric, but low enough not to set the fabric on fire
or to heavily char the templates or cutting surface.

If you use metal templates or straightedges, then you will need a
slightly higher temperature since the metal will tend to conduct the
heat away from the cutting edge of the knife.

The adjustable temperature makes getting the cut right very easy.

The best surface to cut on is probably glass. Glass isn't charred like
wood or cardboard, isn't as easily cut as many other materials, and is
easily to clean (the act of cutting leaves a bit of melted fabric on
the cutting surface). A metal surface would also work, except that it
tends to conduct the heat away from the tip.

My cutting glass is a glass tabletop that I bought when it went on

Hot cutting nylon and dacron does produce fumes. Some of these can be
very bad for you, especially in enclosed areas. It depends what the
fabric is coated with. So, do any hot cutting with adequate ventilation.

Keep the cutting edge clean, a few swipes on a wet sponge will usually
do the trick. Make sure that the sponge is wet, I set a sponge on fire
once, and it took days for the smell to disapate.

For more burned on things, carefully use a piece of sandpaper or steel

Having said all of this, I have to admit that I usually cold cut
fabric these days. I double fold all seams so there is no fabric edge
to fray. I use a razor knife, which is quicker than a hot knife.

I still hot cut exposed edges of nylon and dacron.
Marty Sasaki                            sasaki@tle.enet.dec.com

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