Application
There are several ways to bend guitar sides, including the traditional method of using a hot pipe. However, a faster and more cost-efficient method, which has become common, involves using flexible silicone heaters with a thermocouple and controller to measure and monitor the temperature of the silicone heater blanket throughout the bending process.
A second option for this application is to use the silicone heater without a temperature controller. In this scenario, the heater is plugged in, heated to the required temperature, and then turned off. However, we do not recommend this method as there is a risk of the silicone heater overheating, causing it to fail and the wood to burn.
OMEGA products used in this application
Products
The figure above shows the schematic of the guitar side bending process. The application is comprised of three products:
SRFGA Series: Silicone rubber fiberglass insulated flexible heaters can improve heat transfer and speed the warm-up process required to bend wood. Two circuit designs are available: etched foil or wire wound. However, the temperature must be controlled with as the safe maximum operating temperature limit of 450°F (232°C) may be exceeded. Available in varying sizes; the correct size will depend on the guitar size.
CN7523: This temperature and process controller can handle the most demanding applications. Requires mounting in a box to protect electrical connections and to ensure safety, the controller has dual, 4-digit LED displays for local indication of process value and setpoint. Control methods include on/off, PID, autotune, and manual tune. The dual-loop output control allows simultaneous heating and cooling. Mounting
5TC: These very thin, beaded wire thermocouples allow for easy placement between the silicone mat and the wood. They are made from class 1 wire in standard 1m and 2m lengths.
How it Works
- Build a sandwich. Many guitar manufacturers build the sandwich in the following order: outer slat, silicone heater, foil, kraft paper, wood, kraft paper, foil, and another slat. The benefit of this order is that the foil is inexpensive and helps protect the slats from staining while the slats protect both the silicone heater and the wood, thus increasing the durability of the heater.
- Moisten or wet the kraft paper to help absorb the stains from the wood.
- Situate the sandwich along the side frame of the guitar and align with the exact center of the waist.
- Crank the bending caul down with the veneer press screw and bring the entire sandwich down in contact with the top of the bouts.
- Use spring clamps to secure the sandwich.
- Place a thermocouple between the paper and the foil and connect it to the controller.
- Turn the controller on and set the temperature between 250 and 300°F.
- Turn the heater on. The heater will heat up fairly rapidly and will begin to emit steam.
- Begin to bend the waist when the temperature controller indicates a temperature near 200°F.
- Bend each side of the sandwich as the temperature reaches the set point.
- Let each side “cook” for 5 to 10 minutes at 200°F to ensure it dries completely.
Results
The main advantage of silicone heaters is the low thermal mass, which allows for a quick and efficient thermal transfer. Thus, this precise heating solution makes it easier to bend the wood and consistently obtain the desired shape.
Pro Tip
When selecting a thermocouple, be aware that the smaller the probe diameter the faster the time response.