Handheld cutter

A project log for Hot wire foam cutter

A power supply, bow and table for cutting foam with a hot wire

QuinnQuinn 04/04/2021 at 18:560 Comments

I also wanted to test out using a handheld cutter.  As a first test, I wanted to cut a slot into the back of the wings to insert a carbon fiber strip.

As a general tool, I used a strip of scrap bamboo wood.  I pre-drilled and attached several screws to use as attachment points.  The wire can be sandwiched between the screw and the wood, and alligator clips on the other side.

For this first one, I needed a cutter that would cut down 1/4", and 1mm wide.  The wire I'm using is 0.7mm, so pretty well sized already.  I created a loop that would hang off the wood to slide down a channel.  Because the wire is so short, I added an extra loop above just to bleed off a bit more voltage.  Even with this, it only takes 2.3V to get to 4.5A.  In the second picture you can see the extra loop, and how the cutting part shows a very thin profile when lined up right.

In trials, I found that the wider loop would create too much heat concentration at the bottom, resulting in a wider slot than desired.  I reshaped the loop to be more pointy.

To make the cut perfectly straight and narrow, I created a guide.  I found 2 very straight 1x2's, and clamped them together with some scrap of the carbon fiber as spacers.  This set the space between them at precisely the 1mm I needed. 

To make the cut, I measured out where I wanted it on the bottom of the wing, and placed the guide over it.  I used a couple dead SLA batteries as weights to hold it in place.  To support the wing so it didn't get crushed, I set it in the top of the foam block it was cut out of.  Saving these pieces is great support for when working on the wings.

The test cuts showed the issue with the wider cutting at the bottom, followed by a better one when I made it more pointed. 

The setup for cutting the slot in the wing:

The result:

With the CF strip inserted:

With the guide, this worked way better and easier than expected, which was fantastic.