How to Use The GLS Heating Bender Controller

GLS Side Bender Controller PanelThe digital temperature controller, if purchased separately, should be installed in your guitar or ukulele side bender. All elements of the controller are mounted on a plywood panel which is the width of your bending machine and replaces the rear panel of the bender (if you have that installed).

The temperature controller is pre-set for at maximum temperature of 140 degrees celcius, which is adequate to steam the wood thoroughly and permits you to bend viturally any wood of any figure with ease.

Once installed in the bender, all you have to do is plug the unit into a wall outlet and the controller does the rest. Please do not change any of the settings on the temperature controller as it may be difficult to return it to the default setting when shipped.


If you wish to change the set temperature please do the following.

  1. Plug in the unit without a heating blanket and let the temperature controller boot up.
  2. Press the “Raise Temperature button once and the decimal point will begin to flash. Move the Set Point Decimal to the desired position using the <<  or >> key on the unit.
  3. Raise or lower the temperature set point by repeatedly pressing the “Raise” or “Lower” Buttons shown on the illustration above.
  4. If you make a mistake, simply continue to move the decimal using the << button and change with the raise and lower buttons. You will see the Set Temperature (In Green) change as you make these changes.
  5. Once satisfied with the changes in temperature press the “Set” button and disconnect the unit. Upon restarting the set temperature should remain at your settings until you change them once again.

So, that is about the only items you need to be concerned with for this unit. Everything is set for you so you shouldn’t disturb any of the settings.

Preparation For Side Bending:

  1. Prepare your wood sides and sand them smooth to the desired thickness. Remember that thinner wood will bend more easily that thicker wood and the heat time will me much less.
  2. Be sure to use (2) stainless steel slats when bending wood with this system as the stainless steel keeps the wood encased and will give you much better and smoother bending results.
  3. Mark the center of the guitar waist on the stainless steel with a permanent dry marker or a scratch awl.
  4. Place a bit of masking tape on the edge of each side so you can mark the center of the waist on the tape an veiw it when registering the sandwich through the guide slot in the bender. Do this on either side of each piece of side wood.
  5. Thoroughly wet both sides of the wood side, let set a few moments to let the water soak into the wood. Just before assembling the side sandwich, wet the wood again with a spray bottle.
  6. Anchor your bender down to the work bench or table so it will not move during bending operations.
  7. Assemble the following:
    1. The wood side that is to be bent. Be sure to check the book-matching of each side before you place the side in the bender
    2. (2) stainless steel slats
    3. (2) spring clamps (if they have vinyl, rubber or plastic jaws they need to be protected from heat by using thin strips of wood.
    4. Suitable timer – I use the timer on my iPhone with the alarm function.

Step by Step Side Bending Use the GLS Side Bending System:

  1. Lay the stainless steel slat out (this will be the bottom of the sandwich.
  2. Place the Heating Blanket on the stainless steel. Keep the cord end of the blanket out from the end of the stainless steel just a bit.
  3. Place the wet wood side on top of the blanket, being sure to exactly line up the waist centerline with the slat
  4. Place the top stainless steel slat on top of the wood, completing the bending sandwich.
  5. Place a spring clamp on each end of the sandwich to keep everything in place. Use wood strips to protect the clamp jaws from melting from the heat of the sandwich if required.
  6. Open the Bender Waist Retainer all the way open (to the top).
  7. Place the side retainers each on the springs closest to you as it is easier to reach around the bender to hook up the other side.
  8. Slide the sandwich into the bender and crank down the waist retainer to hold the sandwich in place.  Now take your time to both align the sandwich with one side of the form insert, so the sandwich is straight – at lease one edge of it that is.
  9. Place the aluminum guide bar through the guide bar slot and hook each side up to the springs. Your sandwich will now be squeezed between the waist retainer and the aluminum guide bar.
  10. Take your time and line up the mark you make on the masking tape on the wood side with the center of the guitar bar slot on the bending machine. At the same time make sure the guitar form insert is also lined up properly.
  11. Crank in more tension on the waist to allow the guitar bar to just be “seated” in the guitar form insert about 1/8 to 1/4” or so. There is no risk of cracking the sides by doing this as long as you don’t apply too much stress to the side wood.
  12. Go ahead and swing each end retainer over the form insert and hook up each spring on the other side of the machine. These retainers should now be seated snuggly next to the vertical column of the bending machine, which is the least amount of tension.
  13. Visually check everything to make sure nothing has gone out of registration.
  14. If everything checks out, plug in the temperature controller and the heating blanket, and start your timer.
  15. Now put on some heavy leather gloves to protect your hands from being burnt. Also use long sleeved shirts when bending to prevent arm burns. Make sure your work space if perfectly dry as well.
  16. Place the thermocouple between the heating blanket and the wood. I usually select a spot right next to the waist retainer. To aid it placing the probe deep in the sandwich, I use a very small screwdriver to carefully create a gap for the probe end.
  17. You should now see the top number quickly raise.
  18. For guitar wood, let the sandwich “cook” about 8 minutes. For ukulele wood 6 minutes should be sufficient. You will see steam raising from the sandwich, which means the wood is ready to bend.
  19. At the end of the 6 or 8 minutes, remove the spring clamps from each end of the sandwich and carefully slide the lower bout retainer about 2/3 to 3/4 around the form insert. Make sure it will stay but and not spring back as this can cause injury.
  20. Repeat for the front bout retainer.
  21. Crank in the waist retainer so the guide bar is about 1/4” from fully seated. Sight through the guide bar slot to reaffirm this.
  22. Let the wood “cook” for another couple minutes.
  23. Finish bending the lower bout and make sure the retainer is at the very bottom of the form insert and that the wood is tightly conformed to the from insert shape. Do the same with the upper bout retainer.
  24. Finally, crank in the full tension on the waist retainer. Be careful not the force the press screw as this can crush the fragile wood fibers of the wood side. Visually inspect the side to make sure it is conforming exactly to the form insert.
  25. Leave the heating blanket on until the timer reaches 14 to 15 minutes for guitar sides and 12 to 13 minutes for ukulele sides. More time is not better as the wood scorches very easily at these temperatures.
  26. When your alarm sounds, carefully unplug the temperature controller and let the side set over night.

If you wish you can keep the side in the bender and re-heat it about 10 to 12 minutes the next morning. This will enhance the bend and minimize spring-back, but is not absolutely necessary.

Once the sides are removed from the bender, immediately place them in an inside form and keep them clamped tightly to the form with a spreader jack at the upper and lower bout. To minimize additional spring-back, consider placing blocks at the head and tail block areas between the sides and the inside form to give an over-bent condition. These block could be from 3/8” to 1/2” thick and support the full width of the side and clamped into place.


Be sure to unplug the bender immediately after bending is complete to prevent fire and shock hazzards. The bender should not be operated longer than 20 to 30 minutes at a time. 

to prevent damage to wood and the heating blanket, do not use bending temperatures above 140 degrees C. That is all that is necessary for any wood.

Operate this bender only in a completely dry condition.

Only plug the unit into a 120v wall outlet x 15 amp rating.

Be sure to use heavy leather gloves and long-sleeve shirts during bending. Do not have any exposed skin anywhere near the bending operation or severe burns can occur.

The temperature controller is rated up to 240v input. In order to do this you will need to replace the receptical in the plywood control panel and wire an appropriately configured wall plug. 

The temperature controller feeds 120v power to the blanket. Do not direct wire the blanket to a wall outlet. You will burn out the blanket and create a fire risk.

Keep tension off the extension springs when the bender is not in use.

Only remove the extension springs with the sliding retainers in their most relaxed position. Hold the retainer firmly with one hand while removing the spring with the other hand.

Do not touch the stainless steel slats while the blanket is heating up or within about an hour after the bender has been disconnected. If you do so, be sure to wear your heavy leather gloves.


Leave a Reply

Copyright © 2015 Georgia Luthier Supply