ELECTRIC BENDING IRON This is intended as a short pictorial essay on the construction of an electrical side bending iron. As the items used may vary from the ones shown here, only limited dimensions are used. This device is primarily used for bending the wood sides of musical instruments. Other uses may be appropriate, but are not specifically covered here. Warning This project uses components that generate freakishly large quantities of heat, and is powered by 120 volt AC current. If you are not comfortable c working with potentially dangerous circuits, this may not be the project for you. Due to the nature of the high heat that this project generates, it may not be possible to prevent access to dangerous areas where exposed wiring might be contacted. If you choose to build this bender, the responsibility for safe construction and usage is YOURS. Neither the author nor the site where you obtained this outline accept any liability for anything unfortunate that may occur. NEVER LEAVE THIS DEVICE UNATTENDED NDED WHILE PLUGGED IN AND ACTIVE.
A Rough List of items used: 1 - halogen lamp socket 1 - bulb to fit halogen lamp socket (300 Watt) A 500 watt bulb may be used, but must be used at a lower setting once the desired heat is reached to prevent overheating. 1-2 NPT pipe flange 1 10 12 length Rigid Aluminum Electrical Conduit (one end needs to be threaded to engage flange) 1 600 Watt dimmer switch 1 wiring box to house dimmer switch 1 3-conductor electrical cord, 6, min. 16 gauge wire, with a molded 3 prong standard plug A section of heavy gauge steel strap (10 gauge), ½ wide X approximately 15 long (for socket carrier) Plywood to bolt flange to Section of 2X4 lumber at least as wide as the plywood High-Temperature Electrical Wire NOT PLASTIC COATED! Due to the high heat generated by the halogen bulb, the insulation of the electrical wiring MUST be rated for temperatures in excess of 400 degrees Celsius. Un-insulated crimp terminals for the High-Temperature wire (no plastic used in the hot zone) Whatever fasteners are necessary to hold everything together Scrap steel sheet metal for heat shielding Twist-on electrical connectors suitable for 16-gauge wire
WIRING DIAGRAM Hot Wire (Blk) Dimmer Hot Wire (Blk) LINE LOAD < To plug Neut. Wire (Wht) LINE GND Ground (Grn) Toward front > Halogen Bulb Socket Steel Strap The wires shown in orange should be the high temperature wire. Any wiring that will be inside the heat chamber (the aluminum conduit) MUST BE THE HIGH-TEMP WIRE. The dimmer switches will typically have short pre-wired pigtails on them. Connect the high-temperature wire and the 3-conductor cable to these pigtails with twist-on wiring connectors (inside the mounting box, away from the heat chamber). The ground connection to the steel strap, and the connections made to the halogen socket, should be made with the un-insulated crimp-on lugs. Ring-type terminal lugs are preferred over fork-type lugs.
CONSTRUCTION Make a hole toward the center of the plywood piece as big as the hole in the center of the flange to pass the heating assembly through. Center the flange on this hole, and fasten it to the plywood with wood screws. Polish and clean the section of aluminum conduit, and thread it snugly into the flange. The 2X4 block is fastened SECURELY below the flange (on the back side) as a place to fasten or clamp the bending iron to a bench top. Heat shield removed to show Bracket construction. Do not Operate without heat shield. Mount steel heat shield here to protect wire from socket front. This is the basic layout of the heating element mounted to the heavy gauge steel strap. The wire bolted to the strap at the left side of the picture is a safety ground wire. DO NOT OMIT THIS WIRE! Make sure it is fastened tightly to the steel strap. If something goes wrong, this may be the only thing that keeps you from being electrocuted. Fabricate a steel heat shield 1-1/4 to 1-1/2 wide and as long as the halogen bulb, and mount at the location shown on the above picture (under the bulb). This will help shield the forward wire from the intense heat of the halogen bulb. DO NOT OPERATE THE BENDER WITHOUT THIS HEAT SHIELD!
Mount the halogen socket about 1 back from the front of the steel strap. Fasten securely with machine screws and nuts. Attach the high-temperature wire to the halogen socket (both ends) and the steel strap. The entire assembly is inserted from the back of the bending iron (through the hole bored through the plywood panel) into the aluminum conduit. A small tab bent down at the front of the strap engages a notch cut into the front of the conduit. The strap is bent down at the back end for a tight fit in the conduit, and is fastened to the plywood with a small wood screw. TAB DETAIL (FRONT OF CONDUIT) Complete the wiring to the dimmer switch inside the electrical mounting box. Use twist-on connectors to attach the high-temperature wire and the plug cable to the dimmer switch (see wiring diagram). The electrical mounting box should be grounded to the rest of the components.
TESTING When the socket is wired and mounted to the steel strap, and the sheet steel heat shield is mounted in place, the halogen bulb can be placed in the socket. Do not handle the bulb with your bare fingers oil from your skin will leave a spot on the bulb that will cause localized heating internal to the bulb, and will prematurely shorten its life. When the bulb is in place, mount the strap assembly in the conduit, making sure the forward wire is running underneath the heat shield. With the wiring completed and all the components securely mounted, the unit can now be tested. Turn down the dimmer switch to the OFF position, plug the cord into a 3-prong (grounded) outlet, and turn it on. Slowly increase the dimmer setting until you observe the bulb glowing inside the tube. Continue increasing the dimmer until the setting is at maximum. The aluminum conduit will rapidly heat up at the full setting, and will retain heat for some time, so use extreme caution around the tube area. NEVER LEAVE THE BENDER UNATTENDED WHILE IT IS PLUGGED IN AND ACTIVE! As the tube heats up, there may be some initial smoke from the residue on the conduit or the socket, but this should dissipate fairly quickly. If you notice a great deal of smoke, visible flame, electric arcing, smell melting plastic, or observe anything that seems wrong, unplug the unit immediately. Do not use it again until the problem can be identified and properly remedied. To keep the heat in the forward section of the tube, a small sheet metal guard can be mounted over the hole in the rear of the plywood. Take care that no sharp edges cut into or rub on the wiring. Once the bender has reached operating temperature (a water drop on the surface of the tube will sizzle and turn to steam instantly), reduce the setting to maintain just the heat needed to bend the samples you are using. This will take some experimentation to get the exact results desired. Make test bends on samples of the same thickness and species of wood before attempting bends on your intended finished parts. A temperature probe, such as that found on a barbeque grill, or a non-contact infrared thermometer, can be used to gauge when the bending iron is ready, or to adjust the heat for more repeatable results. As different species of wood respond differently when bending, it is best to consult with sources most familiar with a given wood for information regarding how best to proceed.
REALLY IMPORTANT NOTES ON SAFETY As has been stated before, this device employs dangerous levels of heat and electricity, and should be treated with extreme caution and respect. No tool is worth risking your life or health for, so if you are in any way uncomfortable about the procedures shown in this document, do not attempt construction of this device. The use of heavy leather welding-type gloves will further reduce the risk of accidental contact burns or electrocution. As a further safety precaution, it is STRONGLY recommended that a ground-fault safety circuit be used to power this device. This can take the form of a ground-fault receptacle mounted at the wall, or a ground-fault enabled extension cord. This safety circuit will protect you from electrocution in the event of a short-circuit wiring fault in the bending iron or any other electrical device, for that matter. Inspect the iron before use EVERY TIME for loose connections.