Help Bending the Sides

[PabloCem]

Hi everybody. I'm in the process of building my first guitar. I'm sorry if I go straight to the point, but I hit a wall and I need some help. The problem is with bending the sides.
The technique I chose for doing it, is the one with a semi-body mold with clamps, using 150W lamps inside it to heat the wood.

The problem is that when I heat the side and bend it, everything is fine. But when I release the clamps, the side tends to return quite a lot to its previously straight shape.
When I take it to the body gluing jig, the side obviously doesn't match the contour. I have to make a lot of force if I want it to match it. I'm afraid that if I glue them together and then to the top this way, they will break the top due to the force.
My questions are:
- Should I expect the side to return a little when I take the clamps out? Or should it stay tight to the mold? Is the force I have to make something normal?
- What am I doing wrong? To little heat? To little time? How much time should I let it set it in the mold? I tried 24 hr, without to much success.
- Should I disregard the hole thing and just glue them together and to the top?
Thanks for your attention. And sorry for my English.

Pablo

[Aubade Acoustics]

Pablo, could be a few things. Wood type, thickness of sides, temperature not hot enough when bending or not leaving it under the heat long enough. I would post what type wood, thickness, what temperature you are bending at if possible and for how long. Most sides I bend require 300-350 for about 20-30 minutes and cool down of 8-12 hours or longer.

[charles Tauber]

1. when making the mold inserts for the half-pattern of the guitar, make the curve in the waist a little tighter than the shape of your finished guitar. Do the same for the curve from the largest part of the lower bout to the end block. Over-bending will counter some of the "spring-back" that occurs when you remove the bent side.

2. You will get less spring-back if you let the side cool in the mold. Pre-heat the mold, put the side in the press and let it heat for 20 minutes. Then turn of the light bulbs and let the whole thing cool to near room temperature before removing the side.

[Ned Milburn]

Or you could bend the traditional way and just bend to the correct shape and then you are done. Takes me 20 to 30 minutes per side.

Charles and Armadillo make good points that should be heeded, but 12 hours to cool...?? It won't take that long for cooling.

[printer2]

Originally Posted by Ned Milburn

Or you could bend the traditional way and just bend to the correct shape and then you are done. Takes me 20 to 30 minutes per side.

Charles and Armadillo make good points that should be heeded, but 12 hours to cool...?? It won't take that long for cooling.

Ned is referring to bending on a hot pipe. I had some sides I bent last year and they sprung back a little and I touched them up on a pipe. I also did some unbent sides rather than get out my form, the heating blanket, variac, all the little things that I needed to bend with a blanket. It takes a little getting used to at first, knowing how much to bend and where. But now I sort of enjoy doing it this way.

Oh, and there is nothing wrong with your English.

[WaddyT]

Just one more suggestion. After bending, leave the side in the form to cool - maybe a couple of hours should be enough. Doesn't have to return to room temp. Then re-heat to 250 degrees or so and let it cook for an additional 15 minutes. Then let it cool again until not too hot to handle before taking out of the form. Depends on the wood, but I also recommend bending fairly dry. Just a spritz when you start is enough. When I do it, I use Kraft paper on each side of the side. I just wet the paper. If you are having problems knowing temperature of the side, get yourself a digital meat thermometer. The sharp end can be inserted next to the wood just enough to get the temp. They are accurate enough to know if you are really hot enough. I suspect you are bending cooler than you think you are, with 150 watt bulbs. Most benders with bulbs use 200 - 300 watt bulbs. Big difference in heat output.

[arie]

-fwiw, i'm not a fan of the lightbulb bending scheme, imo too clumsy and unpredictable. some people love the rustic fokelore, others set stuff on fire.

-.080 to .093 is the range i like for side thickness.

-hard tooling like bending forms need springback built into the contours. this will vary with species of wood and its dimensions, mc, and processing conditions. it takes experience to judge how much and where -probably not the best choice for a first timer imo unless you go through a pile of sides and work your form contours just right. agreeing that a "bit" tighter on the waist and upper and lower bouts at the block areas is what works, defining that "bit" takes practice.

-consider making a setting board. a simple plank with dowel rod inserted like fence posts to a desired final contour. bend your wood, and put it onto the setting board. now your tooling is freed up and you can keep working. your sides can settle in or store until needed while you stay productive. it's so amazingly basic, but i've not see anybody use one. this idea is for sale for $5

-try an electric bending iron. i can bend my sides to within a 1/4" with one of those things. small, controllable, no hard tooling to store, and unlike the hot pipe, there's no gas to mess with. imo, just perfect for small artisan level output. handy for binding and purfling too.

[printer2]

Originally Posted by arie

)

-try an electric bending iron. i can bend my sides to within a 1/4" with one of those things. small, controllable, no hard tooling to store, and unlike the hot pipe, there's no gas to mess with. imo, just perfect for small artisan level output. handy for binding and purfling too.

My 'hot pipe' is a piece of muffler pipe and I heated it with my heat gun aimed up the inside. I am going to make a dedicated electric bending pipe yet. Just much too useful if only for bending bindings.

[WaddyT]

I bent my first 13 guitars using a piece of Truck Tail Pipe with a charcoal lighter bent and stuck inside. Easy to bend exactly to your form, however, once I started bending with a form and heat blanket, I'll probably never go back. Since I changed the only thing I use the pipe for is rosettes and a tiny occasional touch up of the bent sides. I never tried light bulbs, but plenty of folks have been doing that for years.

[PabloCem]

First of all, thank you a lot for your answers!

Armadillo:
Thanks for your reply.
Wood type: Mahogany
Thickness: Scraped to around 0.078
Temperature: Hard to say. I will try to measure it in a couple of hours.
Time: Around 30 minutes with light bulbs on. Then I tried leaving it stay for several hours.

Charles Tauber:
1- Good idea, I will consider it for future molds!
2- Already tried :/

Ned Milburn:
Yes, I could. But I guessed that it would take a little experience to know how to bend it the manual way. As it is my first one, I chose the mold technique thinking it would minimize the error (mistake?).

WaddyT
Thank you! You might be right regarding to the temperature. I've got a non-digital termometer I'll try to use in a couple of hours to have a rough idea. What you say about the 200-300 W light bulbs is a sign that I'm bending too cool.

Arie:
Thanks for your advice. I will consider the setting board once my production rate increases. In this moment, my struggle is to build just one! Haha.
The thickness of the sides is about 0.78, with is pretty thin. Thickness shouldn't be the problem.

[printer2]

How many bulbs do you have, what is the total wattage? My heat blanket was running about 600-700 watts. I did turn turn the power down a little once it got up to temperature.

[LouieAtienza]

I've been pretty lucky as far as bending is concerned. I found mahogany in particular more prone to spring back.

My preference is a torch fired pipe. I can bend quite a few sides with one small propane tank. I typically keep my sides thicker than most. over .090" and up to .105". The key for me is heat; the hotter I can bend without scorching the better.

That said, at .070" I don't see the force of spring back to be overly excessive. Just the right amount can keep your sides tight to your mold. But if I had to guess I'd say you're not using enough heat.

[PabloCem]

Yes!!
I could finally bend the sides to an almost perfect shape. The tip seems to be temperature. I kept the bulbs working longer than usual, until it reached 155°C (311°F). When I took the clamps out after 2 hours of setting, the side sprung back just a little (which is more that acceptable, compared to the other attempts). Before, I was reluctant to push the temperature, fearful of scorching the wood. Apparently, I was being too conservative (first-timer mistake).
Thank you all for your advice. They were of great help.

I take this occasion to make another cuestion:
What kind of wood do you use to make the neck and bottom blocks? I've already made them in a very hard wood called Lapacho (I googled it as Tabebuia in English). But I think it will be too hard to carve the dovetail joint. Plus, as it has very little pores, it might not be easy to glue. So... what wood do you usually use for this pieces?

Thanks,
Pablo.