About: Former electronics technician, former MIS tech support, former corporate call center help desk tech support

In 2019 I plan to expand my gardening activities, and for this I am going to build several small greenhouses with styrofoam as part of the building materials. For this I need a way to cut styrofoam quickly and cleanly, that is where the hot knives come in. One is a stationary one with an adjustable guide that can cut pieces 11" wide and one is a handheld one. These are not my original designs, others have published this before, I am just adding to the pile of designs and builds.

Step 1:

PART 1 - The stationary knife

Picture one shows the original stationary knife built from PVC tubing. The PVC made it FLIMSY and the second picture shows the schematic. The third picture is the final design made from ALUMINUM . As can be seen from the second picture the parts used were as follows:

Electrical Parts

1 - 12V 3AMP center tapped transformer

1 - on/off switch

some nichrome wire

electrical wire, a a couple of marettes(electrical connectors)

1 power cord


aluminum tubing

1 aluminum elbow

wood, a couple of brass bolts, spring, washers and nuts


Drill and drill bits

soldering iron

various tools as needed

I originally built the stationary knife from PVC tubing but changed the build to aluminum as the PVC even though 3/4" was not stiff enough and the cuts were not smooth

PART 2 - The handheld knife

Picture four shows the schematic diagram, five and six show the hand held knife. Picture five is of the knife being powered by a 7.5V DC 1A adapter, picture six is the final knife.

Electrical Parts

1- 24V AC 2A center tapped transformer

1 - dimmer switch

1- electrical cord

some nichrome strip

electrical wire


PVC tubing

3/4" wooden dowel

piece of 3/4" copper pipe


Same as above

Step 2: Using the Knives

As I mentioned before I intend to build several small green houses using styrofoam. Picture one shows a styrofoam thing from some type of appliance. It is approximately 24"x24" square. 24" wide is OK but 24" deep is too much. The space available to me is 15" deep from the wall, it needs to be cut.

PART 1 - The stationary knife

Pictures 1-4 show the results of cutting with the stationary knife. Results acceptable for first time use, the spring on the knife needs to be stiffer.

PART 2 - The handheld knife

The hand held knife was made to remove the material as shown in pictures 5-8. As I was finishing item in picture 8 the power supply failed. As I was working in the garage with no heat my feet were freezing, so I cleaned up the garage and went inside to warm up and to figure out what to do next. Picture 9-10 is the final design.

The link goes to my google drive INSTRUCTABLES folder

Step 3: Next Project in This Journey

I guess I will have to build a heater for the garage. It's getting too damn cold.