Replies to This Discussion

Permalink Reply by Habanera Hal on February 28, 2012 at 1:15am

Good luck, Rand!  This interests me a lot, too, so I'll be watching your progress.

Permalink Reply by Michael Fred Johnson on February 29, 2012 at 1:28am

Permalink Reply by Mark Lillo on February 29, 2012 at 1:36am

Hi Rand, I don't believe the water has to be heated at all. I have bent 5 pairs of sides using room temp. water and they maintain their shape really well when released from the jig. But I would make sure they are dry before removing them. I also used thinner pieces. They were 3 3/4 " wide and .09 (3/32") thick. The pair of parlor guitars I am doing now have some fairly tight curves to them and they held their shape really well. Good luck on your dulcimer, I look forward to seeing how it turns out.

Permalink Reply by Rand Moore on March 1, 2012 at 12:15am

Hi Mark.

Thanks for the tip that heating the water is not an essential requirement for bending wood as it greatly simplifies the build process. I first came into this thinking that I would need to build a special steaming chamber for bending wood. I was thinking of using my PVC pipe and probably 1 or 2 water kettles (the type with built-in heating elements) and pipe in the steam. But then I read some builders had success using hot (but not boiling hot) water and soaking the wood in that for about one hour. So, rather than building the steaming chamber, I decided to try the soaking method. Then, much to my satisfaction, I found that soaking the wood for an hour in "hot" (42 degrees Celsius) tap water worked as well. I'm happy to hear lukewarm water works, too. So far, it's turning out to be a lot easier to bend wood than I thought it would be. So, for all you reluctant builders sitting on the sidelines, I encourage you to give it a try. 

Now a question for you, Mark. How long do you let your wood dry before taking it out of the form/jig? I was thinking a couple of days, but I will likely keep the wood in the rack a lot longer because the weather here is really humid now. It's rainy season here in southern China now. I sure hope the instruments I build can hold up to this tropical weather long term.

One thing I have noticed about your forms/jigs, and those of some other builder's is that you bend your wood in smaller pieces and then assemble those pieces to form the frame of your sound box. I, on the other hand, am trying to do much the same with one long piece of wood with one big bend. I hope this won't be a mistake. I think the teardrop body shape will be simple enough to let me get away with it, but I'm wondering if I'm just building a big spring. I certainly will play it safe and treat it as if it is a spring by attaching the neck/head assembly while the wooden side piece is still in the mold. But, if the wood really is holding much of its new shape, then maybe the extra concern and build precautions aren't necessary. Well, I guess I could find out by potentially sacrificing this first wood bending experiment. Let me think about that.

-Rand.

Permalink Reply by Mark Lillo on May 19, 2012 at 12:03pm

Permalink Reply by Michael Fred Johnson on February 29, 2012 at 1:40am

Hi Rand

The two photos I've sent you show  1. the tubes I use to bend wood. The wood is brushed with water the bent over the heated tube. 2. The guitar ribs bent using this method inside a mould. I like doing it this way as you can add the end blocks, then the linings then glue on the strutted sound board while the mould holds the ribs to shape.

Also used this bending method for the lute ribs then glued together over a male mould

Permalink Reply by Rand Moore on February 29, 2012 at 11:14pm

Hi, Michael Fred Johnson...

Those are interesting photos. So, when you bend wood, you select a pipe (tube) of the right size and preheat it using something like a propane torch. Then you brush water onto the piece of wood you want to bend and work it around the hot pipe until you get the curve you want. So, the hot pipe causes the water on the wood board to turn into steam and this steam speeds up the transfer of heat to the wood, making it pliable. Do you then stick it into a forming-rack (jig) so it will retain the desired shape? Or, will the wood hold the shape immediately after it cools off from being worked on the hot pipe? 

It seems that some builders are happy to let the wood soak, some without even applying heated water, while others like to use a steaming chamber, and some people use hot tools to apply heat directly to the wood as you do with your hot pipes. I wonder what the strengths and weaknesses are with each of these approaches? It seems to me that the less you soak the wood either in water or steam, the quicker it will dry. So is speed the main advantage with your hot pipes wood bending technique? I guess you also need to keep brushing on water to avoid scorching the wood. Is that much of a problem?

Your guitar body shaping form, as you say, looks ideal for the task. But, I'm thinking it might be to difficult for me to build given that the only power tool I use (other than my computer) is an electric hand dill. This is another topic I'd like to discuss -- How to build useful wood shaping jigs (for those who haven't invested in expensive power-tools). I'll likely be refining my jig to build a second teardrop sound box, this time with a long neck. But first give me time to design and build a headstock for my current lap dulcimer teardrop. I've got some plans which I'll add to this discussion thread later, but I wanted to respond to all the comments first.

That Oud (I believe that's what it is) in your third photo is a real beauty! If you can build these then you must really be a skilled luthier! Stave construction techniques is another advanced topic that I'd like to learn about. It is used for building Ouds, Balalaikas, and other Oud-like lutes, but I'll have to put off tat topic until I have put more time into the basics of wood bending and shaping - with and without using heat or steam. At least I'll know who to ask when I feel I'm ready to tackle such an advanced build. That really "Wows!" me!

-Rand.

Permalink Reply by Michael Fred Johnson on March 1, 2012 at 3:54am

Hi Rand

I use the pipe thats nearest to the radius of the bend I want.

You can see the gas blow torches that I use for heating in the background of the photo.

You do need to brush on extra water during bending and scorching is not a problem if you are careful not to overheat the pipe ( as you heat the pipe flick some water onto it from your brush. If the pipe isn't hot enough the water will bubble up where it lands, when the water forms a ball and dances off the pipe start your bending)

The wood will hold its shape as it cools but as the radius of the pipe isn't always exactly what you want I put the bent wood in the mould and clamp/wedge it into shape.

I used a jig saw to cut the mould for the classical guitar.You can see from the photo tht it was built up to the required thickness  by laminating various bit of sheet materials that were lying about in the garage.

Hope this is of help.

Michael

Permalink Reply by Rand Moore on March 1, 2012 at 11:41pm

Hi Michael,

Yes, the details help a lot to clarify the "picture" in my mind. The heated pipe approach sounds interesting, and I may give it a try sometime. But, I'll need to find a workshop to do it in, as my wife would run me off if brought a gas blow torch into our home. One reason I'm so limited tool-wise is that we live in a flat with no garage or side buildings that I can turn into a proper workshop.

I had thought you probably used a band saw to cut the guitar body shaping jig. But, yeah, a jig saw could be used to cut the identical shape into a series of boards that could then be stacked, aligned and fastened together. Then a rasp and sand paper (sanding block) could be used to finish the interior forming shape across the several boards. Maybe a jig saw will be my next power tool acquisition as it looks pretty useful for building more sophisticated forming jigs.

-Rand

Permalink Reply by Michael Fred Johnson on March 2, 2012 at 4:24am

Hello Rand

Thats exactly how the mould was built and finished.

Notice also that once complete the mould is cut into halves on the centreline and the bottom end fitted with a hinge to make it easy to remove the guitar when needed.The top end can either have a hook and eye, a strap screwed across the joint or a sash cramp to hold it closed.

On moulds for ukes I only cut through at the top end and push a wedge into this joint to release the instrument

Michael 

Permalink Reply by Rand Moore on March 9, 2012 at 10:32pm

Okay!  Back after a 7-day hiatus to entertain some "in-laws" visiting us from the States...

I was able to find time to construct a redesigned headstock. Instead of the wider "9-slat" headstock shown in the drawings above, I chose to narrow it down to a "6-slat" headstock, where each "slat" is a 8.5" long length of trim wood, 5cm wide and 0.5cm thick. So, with 6 slats the headstock is just about 3cm wide (about 1 + 3/16" wide). The main reason for making this decision came when I was thinking how the machine tuners would fit the headstock. The little hole on the shafts of the tuners need to be near the center-line of the headstock, and a 6 slat headstock looked like the best fit. Hopefully, I'll still have enough room on the fretboard for 4 strings. If not, I may do just 3 strings. Here's a photo showing my new headstock design:

And here is a photo collage of how this design turned out in wood...

As I said earlier, it's composed of 6 layers of trim wood ("slats") laminated together with white carpenter's glue. Two of the slats are of an unknown dark wood to give it more visual appeal. Rather than cutting out the center slot, I glued the wood up with a 4.5" gap in the middle 2 slats. I have done this trick before and it makes slotted headstock construction a lot easier, and it seems to workout well, too. The curved cut-away that reduces the thickness of the headstock was done by a series of perpendicular cuts about 1/4" apart with a handsaw and then a chisel was used to pry and coax out the small rectangular pieces of waste wood. Then a wood rasp, a wood file and sand paper to finish shaping the headstock.

In the next photo we can see how the headstock will fit the teardrop shaped frame or "hoop" as I have begun to call it.

I still have a clamp on the teardrop hoop near the ends of the hoop where they feed into the headstock to minimize the spring-back pressure on the headstock. This spring-back pressure has actually damaged my headstock as you can see in this next photo:

Talking about spring-back, I was wondering how well my teardrop hoop would hold its shape after being released from my forming-rack and any other clamps. The next photo shows this...

Yes, when closed and inserted into the headstock the hoop like one big loaded spring. This problem coupled with a warping problem have caused me to decide to re-soak and re-form my teardrop hoop. But, before talking about the re-soaking and re-forming, let me describe these two problems in a bit more detail.

First the spring-back pressure problem on the headstock... It seems to be at least theoretically possible to cure this problem by reshaping the "middle reaches" of the teardrop hoop with two reverse curves. These reverse curves need to be located between where the sides come off the 8" drum hoop in my forming-rack and the last 10" of the teardrop hoop, which I need to have shaped in parallel to feed into my headstock with minimal spring-back pressure. To make these two reverse curves, I've sacrificed a 6" tambourine by removing its skin drum-head and all the side jangles. I then cut the hoop into halves (semi-circles) and plan to use clamp to force this shape into each side to form the reverse curves. More on this later.

The warping problem is also in the "middle reaches" of the sides of the teardrop hoop. It was most likely caused by the lack of shaping support structures in my primitive forming rack. As you may recall, a 8" drum hoop was used to form the bottom rounded part of the teardrop, and the two "loose ends" of the teardrop were clamped down between a block of wood with some more wood forced in to fill the empty space between 2 supporting posts. Crude. The problem is that with no support between the "loose ends" and where the teardrop comes off the drum hoop, the wood was free to twist and warp as it pleased. So, to correct for this, my form will need more clamps and structure to support these "middle reaches" of the teardrop shape.

Above is the teardrop hoop released from its forming rack, but with a block of wood and a pair of clamps to close the teardrop and to maintain the shape. This is how I "store" and handle the hoop when its not in its forming-rack. If you look closely you will see signs of warping. If you take a carpenter's square to it, you can see just how warped it really is. Without reshaping the hoop again, the warped hoop will lead to a warped and ugly sound box and instrument, so I've got to try reshaping it again with a lot of attention to these "middle reaches" of the teardrop.

So, it's to the bathtub I go to soak my teardrop hoop in water for 3 more hours (more time = more flexibility?). So, here's the 10:00 am photo...

And here's the 1:00 pm photo...

And yes, that is a little yellow rubber ducky. I also heat-dried the file over an open flame, so hopefully it won't rust.

After the soak, the teardrop hoop went back on my forming-rack like so...

Oops... In the photo above, it should say 6" tambourine, not 9" tamborine.

The two reverse curves can be better seen in this next photo:

And now to wait 2 or 3 days for the wood to dry out to see if the problems with excessive spring-back tension and warped sides have been fixed.

As always, any constructive comments and advice you have are welcome!

-Rand

Permalink Reply by robert jones on March 10, 2012 at 10:02am

Crap! Now you've got me wondering if the tennis rackets buried in the nether depths of my storage shed would work as clamping forms. LOL

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