So I decided to give electric guitars a break for awhile and try my hand at another acousitc guitar. In 1999 I finished my first acoustic guitar and still play it to this day. I also started a pair of acoustic guitars in early 2000's, but they never saw the light of day. I still have the 1/4 finished projects, but time has not been friendly to them and they will likely never receive any more attention.
Bending wood is pretty strait forward, you need some thin wood, a hot iron and steam. The steam can be generated from soaking the wood then applying the wood to the hot iron. There's many ways to make a hot iron and due to the curvy nature of guirat sides, it usually involves a propane torch and a piece of 2" steel pipe. While this does work (I used this method for my previous acoustic guitars) there many drawbacks to this setup. Heat regulation and safety are the largest issues. Putting a torch flame inside a pipe heats it very quickly, but also makes the pipe way too hot for bending. The minute you start to bend the wood, the pipe drops in temp and makes it difficult to get a feeling for what's happening. Having an open flame shooting through a pipe in a dusty garage for hours at a time is not the safest thing you can do in your shop. I vowed that if I ever built another acoustic guitar I would acquire the proper tool for this job.
I researched buying this unit from Stew Mac and LMII, but for the price they wanted, I figured I might as well have the fun of building my own. I figure I already had a PID temp controller from a previous project, all I had to do was some machining to build the iron itself.
As with any project the first thing to do was to model the item in Solidworks. I always find that most of the kinks are ironed out at this stage. It allows me to go through multiple design scenarios before setting on the way it will be made. I have to admit that my design was not complete before starting and did quite a bit of off the cuff work when finishing the iron. Oh well, sometimes you just have to wing it and use what you have available.
First off, I would need to buy the guts of the machine; a heater and a thermocouple. I was able to source both items from McMaster-Carr for a reasonable price.
Cartridge Heater: http://www.mcmaster.com/#3618k472/=139mylk
Thermocouple: http://www.mcmaster.com/#9251t93/=139mz25
I picked a fairly high power heater to avoid the long heat up times that some users of the Stew /Mac unit complained about. Because I'm controlling this with a digital controller, safety was not considered an issue.
Picking the material for the main body was pretty simple: whats the thickest aluminum I have laying around? 1 1/4" plate from my Massload days would fit the bill. After squaring a couple blocks, I bolted them together and drilled the 1/2" hole for the heater cartridge.
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| Squared up blocks with heater cavity done |
Not shown here, I milled a 1/8" x 1/16" slot in one block to house the thermocouple. With this done, I was able to start the major process of shaping the outline of the halves. I cutout a template from my drawing and scribed the profile on the ends of each block. I used a 1/2" rougher end mill to hog out the majority of material.
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| Roughing end mills rule! |
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| Rough machining process |
After some creative clamping, I was able to get the shape roughly to my scribed line. If I had to do it again, I would have spent more time getting it much closer to the line. To finish the shape, I clamped my belt sander in my bench vise upside down and worked the pieces to the line while the halves were bolted together. I basically mounted the pieces on a chunk of 1/2" brass rod just to be able to hold it. It took probably an hour on this lousy setup to achieve the desired shape.
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| After quite some time on teh belt sander. Blahh |
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| Profile sanding done! |
So there's a bit of a gap in my pictures with regards to making the end plate and the junction box plate, but here's a pic of what the junction box plate looked like during final assembly.
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| Power and thermocouple connections |
Like most things that I make out of aluminum, I like to take the extra time to annozide and color the parts. My color scheme is a bit pukey but hey, it;s just a wood bender.
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| Finished parts ready for final assembly |
To isolate the hot side from the base, all I had laying around were some small plates of teflon that I've been saving for years. I got them from PetroTAG when an order was screwed up. The spacers are about 1/4" thick and I capped the wiring hole in the base with a piece of high temp gasket material. The 1/4" gap between the iron and base does a great job of keeping the base cool. It still gets warm, but not too hot to hold onto. I also used conductive paste on both the heater cartridge and thermocouple during final assembly.
With the unit together, I reconfigured my temp controller to use a type K thermocouple and plugged it in. I didn't really have to tweak anything else in the controller and the unit heated up to the setpoint and stayed there happily.
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| First heating! Dang, it overshot by .74% |
All in all it really worked out well. Having the ability to dial in an exact temp will certainly help in the future, that is after I figure out what the optimum temps for various wood is...I can tell you that 350 is WAY too hot for East Indian Rosewood, unless you like the toasty variety. 250 seems to be a good temp. Creates good steam and does not flash off all the moisture instantly, giving you some time to feel the wood turn to plastic and bend in a uniform way.
Now it's time to build some guitars!
