DIY: Kanthal Acrylic Bending Table
Acrylic plastic comes in many sizes, thicknesses and colors. It's used to make aquariums, picture frames, motorcycle windshields, shelving, hard contact lenses, dentures, dental fillings and medical devices. Acrylic is very strong and virtually shatter-proof, making it an ideal choice for fabrication of items that need to be durable and resistant to mechanical shock.
Acrylic is technically known as polymethylmethacrylate. It can be formed easily into almost any shape. In this tutorial you'll learn how to make a bending table to "fold" acrylic at various angles. For example, if you wish to make a tabletop picture frame or a stand for your PC printer, the bending table is just the tool you'll need.
Of interest in this article is the use of Kanthal resistive wire to build a device for bending acrylic plastic, commonly known as a "bending table."
Kanthal A-1 and Kanthal D are both alloys of Chromium, Aluminum and Iron. They become very hot when electrical current is passed through them, making them ideal for applications where high temperature heating elements are needed. Both Kanthal varieties melt at 2732°F (1500°C). Kanthal A-1 has a maximum operating temperature of 2550°F (1400°C) while the Kanthal D's is 2370°F (1300°C). Kanthal is used to make resistive heating wire, piping for use in furnaces, heating elements and other high temperature form factors.
Do It Yourself – Make a Bending Table
Materials
• An aluminum channel with a "U" shape cross section. The channel should be an inch or two longer than the width of the acrylic piece you want to bend. The depth of the channel should be no greater than the plywood you use in the project. For example, if you use 3/4-inch plywood, the aluminum channel depth should be about 1/2-inch.
• Plywood or particle board to be cut as shown below
• Two hinges and wood screws to affix the hinges onto the plywood
• Two flat-bladed wood screws.
• Two alligator clips
• One small spring
• Kanthal resistive wire, 20AWG, about six inches longer than the aluminum channel. Note that Nichrome wire can also be used.
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Step-by-Step Instructions
1. Begin by cutting your plywood into three pieces as shown. Position the boards and aluminum channel as shown. Nail or screw the stationary board to the base board.
2. Mount hinges to connect the stationary and moveable sides of the bending table over the aluminum channel at the edge of the boards, as shown. These hinges will allow you to lift the moveable side of the table to the degree you want to bend the acrylic.
3. Install the alignment screw (shown below) with the slot in the screw head parallel with the length of the aluminum channel. This will serve as a guide for the resistive wire. DO NOT allow the alignment screw to make contact with the aluminum channel at either end of the channel, as this will create a short circuit and keep the heating wire from getting hot. A short circuit is also likely to damage your power supply unless it is properly fused.
4. Install the power connection screw an inch or two away from the alignment screw. Repeat the process at each end of the channel.
5. Attach the Kanthal (or Nichrome) wire and spring as shown. The wire will stretch as it heats; the spring takes up the "slack" and keeps the wire from drooping down to the channel. Trial and error will show you how much tension to use once you begin heating the wire. If you need more tension, remove and re-install the power connection screw farther away from the alignment screw. For less tension, re-install it closer.
6. Attach one power lead to the power connection screw at the end without the spring. Attach the second power lead directly to the heating wire, not to the power connection screw or the spring. Alligator clips are the best way to make these connections. You can use AC or DC power, but a variable power supply (rather than a battery, for example) is the best choice because you can continuously adjust the voltage being supplied to heat the wire to just the right temperature. A Variac (variable transformer) is an ideal power source.
What is the right temperature to bend acrylic?
When the wire begins to glow orange it's at the correct temperature to melt acrylic. Acrylic melts altogether at about 212°F (100°C) so you'll want to keep the effective heat applied to the acrylic to about 190°F (88°C). That orange glow gives you just the right result.
You may wish to mount a piece of guide wood to the stationary side of the bending table at right angles to the channel, allowing you to place your acrylic accurately on the table, as shown below. With the work piece placed with the area to be bent over the heating wire, turn your power supply ON and adjust it until the wire glows orange. Hold the plastic in place for about 30 seconds, then slowly lift the moveable side of the bending table to the angle needed for the bend. If the acrylic has heated sufficiently, it will bend easily.
Once you've reached the degree of bend you want, turn the power supply OFF. Hold the moveable side of the table in position for about 30 seconds, allowing the plastic to cool and harden. Remove you piece from the bending table and your creation is ready to use for whatever application you might have in mind.
Other Considerations
This home made bending table can be used as described here for acrylic up to about 3/16 inch thick. If you want to bend a thicker stock, you can simply heat both sides of the plastic equally before you make the bend.
Be aware that the Kanthal or Nichrome heating wire is not insulated, nor are the connection points to your power line. Disconnect your power supply when the bending table is not in use and avoid touching electrical connections. Likewise, the heating wire becomes very hot, so use caution as you work with your new bending table.
For the video edition of this DIY project, view our YouTube video above.