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Bending Woes (Read 4076 times)
lawofaverage
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Bending Woes
Apr 7th, 2009 at 12:07pm
 
Hi all,

We're having a lot of trouble bending the bubinga sides that come with the kit. Our bending form is like the one in the instruction manual except it's solid wood. When bending we place a piece of aluminum flashing on top of the mold then the heat blanket then a strip of stainless steel and finally the wood. This last bending session all went well for the first side; clamp down the center slowly then one of us worked on the top bout while the other the bottom. After about 25 minutes the bend was finished with only a slight split on the edge of the top bout. The second side fought us the whole way. After the waist was seated we worked much the same way as the first side. The top developed a small split after a few minutes and the bottom seemed like it didn't want to bend at all. We placed the front bar across the top where the split was starting to try and keep pressure on it. Because the wood wasn't giving as easily as the first side we clipped the blanket to stay in contact with the whole rest of the top and bottom as we applied pressure. A split on the bottom developed too & I put the back bar across it as well. after about 20 minutes the lower bout cracked to pieces - splitting in a diagonal the whole way across the board.

Where did we go wrong?

My thoughts are:

-working both the top and the bottom at the same time - not good.
-clipping the blanket to the whole length of the board = too hot - not good.
-spraying more water on the wood because it's too hot may be making it too brittle - not good.
-using the top and bottom cross-bars in the middle of a bend - not so good.
-sometimes it's just a difficult piece of wood - neither bad nor good.

Please give us your feedback!

Thanks.

Bill & Rebecca
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Quine
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Re: Bending Woes
Reply #1 - Apr 8th, 2009 at 10:15am
 
Sounds to me like you were bending much too cold. 
I use a solid bending form with a heating blanket on top and then the wood.....no metal slats or anything.  (sometimes I use tin foil to prevent resin stains)
The wood needs to be around 240F for good bending (hotter than boiling water at 212F)  When you mist it with a spray bottle, the water will turn to steam very quickly.  Over wetting will cool the wood and not help you.
Maybe your temp controller was set too low??
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mblue
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Re: Bending Woes
Reply #2 - Apr 8th, 2009 at 3:23pm
 
I just finished bending my first sides, after a number of trials and errors with test wood. I have a way to go before I am good at it, but I have some thoughts...
How thin were the side pieces? You should thickness sand them down to about .070 inch before bending. If you go to .060 it will be even easer to bend.
I believe that you should hear the water sizzle, or it is not hot enough.
I made a bending jig and used a heat blanket. That worked not too badly. However, I ended up ordering a luther's bending iron, and I liked it better than the shaped jig/heat blanket method. With the bending iron, I felt like I could take my time more, and it felt like I had more control. After bending with the iron, I put the sides in a mold for 2 days. I was very happy with how they turned out.
Anyway, I think that side bending is something that you have to try different methods (using cheap test wood) and see what feels good for you. It is definitely one of parts of uke construction that can't be totally learned from a book. Good luck.
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lefty
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Re: Bending Woes
Reply #3 - Apr 9th, 2009 at 11:16am
 
Bill & Rebecca,
†Sorry to hear about your problems. †Hang in there. †It will get better.
†Just thought I would share how I bend.

This is a photo of my solid wood bending form. †It is sprayed with high temperature engine part to help protest the wood. †

...

†I spritz both sides of the side with distilled water and †let it sit about 10 minutes. †Then I wrap it in a single layer of paper towel and spritz the paper towel. †This gets wrapped in aluminum foil with both ends folded over to contain the steam that will be generated. †
†Set this package on a piece of stainless steel shim stock. †Put heating blanket on top and then another piece of shim stock. †I hold everything together with a bunch of wooden clothes pins.
†I set the package on top of the bending form and turn on the blanket. †325 degrees with the timer set at 350. †After 7 minutes I bring the waist down very slow until it is in contact with the form. †Then bend the lower bout and then the upper bout. †After just a few more minutes the 15 minutes is up and the timer shuts off the blanket.
†I let the whole thing cool down for about 2 hours and then cycle the blanket for another 15 minutes at 325 deg. †and let it sit in the form over night. †When I remove the sides I place them in a holding form.

†The last set of sides I bent I did a bit different. †I sprayed the sides with Super Soft Veneer Softener the night before and let them soak it in them proceeded the next day as described above. †I had read about this on another forum and decided it might be a little insurance.

†I hope this helps. †If you have any questions just ask.

Lefty
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konacat
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Re: Bending Woes
Reply #4 - Apr 10th, 2009 at 8:55am
 
Bill and Rebecca,

One of the members at the OLF, Todd Stock, has put together a video on bending that is now on youtube. I have not seen it yet because I have no access to that site from work. However I did read some positive comments regarding the video. Take a look and see if it helps.

http://www.youtube.com/watch?v=Q7vd9wGG4LM

Iím not sure if your wood was reaching the temperature that was needed to bend effectively. Without a thermometer included in your sandwich you donít know what temperature you attempted to bend at. The wood itself was on the outside of your bending package so some of the heat is being blocked from reaching the wood. The metal slats are used for supporting the wood, holding in moisture, and it helps minimize splitting and cracking. The heating blanket get pretty hot fast so the whole procedure shouldnít take too long one the correct temperature is reached and 25 minutes seems very long. As you pull the wood down over the form you should feel the wood releasing as you bend. This is an indicator that the wood is ready to bend. Cracking noises indicates the wood is not ready to bend. LOL  Grin

Good Luck

Philip


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Louman
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Re: Bending Woes
Reply #5 - Apr 10th, 2009 at 2:43pm
 
That's a nice video session on how to bend.....a picture is worth a 1000 words!  He really has a nice set up and was able to describe what he was doing rather well.  Helps a lot.
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Matt Blacka
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Re: Bending Woes
Reply #6 - Apr 12th, 2009 at 1:00am
 
Hi Bill and Rebecca,

Ahh bending can be frustrating.

I would guess one of two problems....

Side timber was too thick. For the 5 ukes I've made, all have had the sides bent at about 1.8 mm thick, or

Not enough steam/heat. I have steamed all of my sides directly in the bending form (boiled water in a seperate base chamber with the steam ducted up into the bending jig). I didn't ever break/split a side using this technique, but the wood was getting too wet and always cupped a little and stained.

I have since bought an electric bending iron, and just love the small size of the unit, and the flexabillity to bend different sizes and shapes. I have only used it to bend timber bindings so far, but I love how much you can feel the wood give when it is ready. There is much more control with this technique.

What I have learnt by using the bending iron, is that any water sprayed on, should vapourise immediately and sizzle, otherwise you don't have enough heat. If the water doesn't turn to steam, the wood doesn't bend. Simple as that.

I would recommend getting some practice strips, and testing different thicknesses and blanket temperatures until you have success.

Good luck,

Matt
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MAKAIO Ukuleles, Australia www.makaioukuleles.blogspot.com
 
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lawofaverage
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Re: Bending Woes
Reply #7 - Apr 15th, 2009 at 3:09am
 
I'm happy to say that the last bending session was a great success! In fact it was much easier than I had previously imagined. The sides were sanded a bit with 150 grit until they "felt" right. Then after wiping the dust off they got a spritz of water then wrapped in aluminum foil then the blanket & steel sandwich like in the videos.  The thermometer was the key - bending started at 240F and the blanket was switched to variable at around 380F. This time the whole process took about 7 minutes from when I turned the blanket on until all the clamps were snug and the blanket was coasting at about 350F or so.

In addition to the video mentioned above we looked at this one from Pete Howlett:

http://www.youtube.com/watch?v=s0TU-OfLKkw

Plus the "Tech Fridays" ones from Taylor Guitar.

Thanks again everyone -

Bill & Rebecca
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