The Koentopp Cutaway Bender

I have been hand bending sides for over fifteen years now. I am pretty efficient at it and the methods that I use work well for me. It is one of the tasks in guitar making that is fun, intuitive, and always a puzzle that takes concentration. In the past I would hand bend the cutaway side as the upper, non-cutaway, side was cooking and cooling in a Fox-Style bender.

With the joy of hand bending comes a lot of down time as well. After being bent on a pipe, the side has to setup and dry in a mold for about a day in order to help eliminate spring back. So here I am thinking to myself, there must be a way to do this that is cleaner, more controlled, and still fun;) As a guitar maker I am always solving puzzles and here was a situation that I could find a new ‘clever’ solution. I am not claiming this to be the best solution, it is just another way of doing the same task.

I’ve tried other jig setups including the well known Fox-Style bender with a cutaway attachment. The Fox-Style bender has become very popular because if its simplicity and success, however I have always run into issues on this style of bender when dealing with a cutaway. I manipulated my Fox-bender many times for the cutaway until I reached a setup that kinda worked, but it was clumsy. I built an attachment that put the supporting steel slats under more tension and I still was not happy with the annoying and somewhat blind procedure. The biggest problem with this setup was there were two bends happening simultaneously at the cutaway location, which puts a lot of unwanted stress on the wood.

This method is actually very similar to the procedure of pipe bending. On a pipe, the wood is supported as it’s fed and pulled around a hot pipe. With this bender the rotation pulls the wood around a form as the steel slats support the bend. Unlike the Fox-Bender, the side is always supported and you are safely making one bend at a time. It is also very easy to keep the side parallel, without twist, as you are always bending perpendicular to the base of the bender and can use this as a table guide.

The jig in this video is my third prototype and I already see room for adjustments and tweaks but it works wonderfully. I custom ordered a few heating blankets from MEI, and opted to not get a thermocouple installed in case I wanted some window for adjustment in the future. I would now get one permanently installed somewhere at the middle edge and use the blanket solely for this bender. I start with the cutaway first and clamp the wood/steel sandwich at the neck block. There is some latency at the end of the blanket with the thermocouple and LMI temperature controller at this location. The blanket and controller work much better if placed in the middle. I also am using stainless steel shim stock here because it allows me to bend without getting mineral staining in my wood, which saves me from wrapping in foil.

I still have to make sure the slats are tight as the sandwich wraps around the forms. I had one test buckle on me because I wasn’t paying attention and there was too much slack in my sandwich. Once around the forms, the procedure is similar to the other benders, letting it cook for about five minutes and letting it cool. After that the side is set and ready for the mold and blocks!

Please let me know what questions of comments you have. This is still a developing idea and so far I am excited about how its working!

Thanks for checking this out!

Danny

Posted on Friday, May 6th, 2016 at in Guitar Construction, Tools.