A hot wire foam cutter
is a great tool for cutting polystyrene
as pink foam
). This is useful for craft-work
and for making prototypes
Craft stores sell low-cost foam cutters (consisting of two D-cell
batteries, a metal arm, and a piece of nichrome wire), or you can make
The principle behind a hot wire foam cutter is to run current
through resistive nichrome wire, rapidly heating the wire. The hot
wire will then cut through foam like a knife through butter.
To make your own, you'll need a power supply, some nichrome wire,
and frame to put the wire under tension. You want to build the
frame to stretch out the nichrome wire while leaving enough space on
all sides of the wire to give you plenty of room to maneuver the foam
You'll need to put the wire under tension (with a spring or through
some aspect of the frame's design) as the nichrome wire will stretch
some when it gets hot. You want the wire to remain taut so that it
cuts a smooth line and doesn't bow out when you pull the foam
To heat the wire, you'll want to connect a power source to it. For a
few inches of wire, two D-cell batteries make a good power source.
You'll need more voltage if you're using a longer wire You'll also
want a simple switch so that you can turn the heating element on and
off easily. The nichrome wire doesn't solder easily so you'll
probably need to tie it to the frame both ends.
Make sure to use reasonably high-gauge wire (such as 14 AWG)
or a metal part of the frame for connecting the nichrome
wire to the power source. You want the nichrome element
to heat up, not what you're connecting it with.
When you start running current through it, the nichrome wire will
heat up within a few seconds. The wire will get hotter (and sometimes
excessively hot) when not in-contact with the foam than when
in-contact (as the foam absorbs the heat faster than the air does), so
you'll want to turn it off when not in use. The heat of the wire will
determine how quickly you can move it through the foam.
If using batteries as a power source, they will
stop being effective after a few minutes. If you
turn the cutter off for a few hours, the batteries
may be useful again.
To determine the voltage you need to heat the wire,
you'll want to take into account the length
of nichrome wire, the resistance of the wire (in
Ohms per unit length), and the amount of power / heat you
want the wire to generate (also as a function of the length
of the heating element. The resistance of the wire
will depend on the gauge of the wire (for example 32 AWG
nichrome wire has a resistance of about 10 ohms per foot).
You'll want about 1 watt of power per inch of length.
Some things that are useful in calculating
- The total resistance of the nichrome wire is
the length of the wire multiplied by the
the resistance per unit length of the wire.
- The total power dissipated by the wire is
equal to the square of the voltage across
the wire divided by the resistance of the wire.
For example, if your wire is 1 ohm/inch and 3 inches long, the
total resistance will be 3 ohms and you'll want 3 watts to power it.
This will require voltage = sqrt(p*r)
= sqrt(3 ohms * 3 watts) = 3 volts
and current = power / voltage = 3 W / 3 V = 1 amp
Two D-cell batteries will give you the 3 volts and should be able
to provide 1 amp. Note that smaller batteries may not be able
to output enough current.
You may make a hand-held cutter fairly easily with a small frame,
or for larger projects you can have the frame
stretch the wire upwards from the surface of a small table.
The latter configuration can be used similar to a jigsaw where
the cutter remains stationary and you run the wire through it,
using the table surface to help make perpendicular cuts.
Important safety tips:
- The nichrome wire heating element gets HOT.
Be careful not to burn yourself on it!
The cut surface of the foam may also be hot after
passing through the wire.
- Unless you really know what you're doing, don't use
a power supply other than D-cell batteries.
Using a transformer in combination with AC power
from an outlet is possible, but is extremely dangerous,
especially if you don't know exactly what you're doing
and don't follow electrical safety precautions.
- Do not use wire other than nichrome wire. Standard copper wire
has much less resistance than nichrome
wire and will mean that you're effectively shorting out
your power supply. This may cause the battery to explode
or may otherwise start a fire.
- Make sure to have good ventilation as the hot foam will give off fumes that you almost certainly don't want to breathe. Inhalation of fumes could result in lung damage or other nasty injuries.
- Make sure to wear safety goggles when building and
using this apparatus. It's better to look dorky than to get blinded.
- If you're a kid, make sure to have adult supervision at all
times when constructing and using this apparatus.