Everything was going so well until . . .

[Stray Feathers]

IMG_8123_resize.jpg

[tippie53]

what was your bending process?
often this happens
too thick
waited to long
didn't wait long enough

one way to help is use a little weight, about 3 lb
set it near the end of the slat and when it falls your ready to bend

[MaineGeezer]

Ouch. Been there. Done that. Doesn't make it hurt any less.

[Stray Feathers]

John, I've been using the methods in your bending videos, lower bout at 240, then the upper at 275 or so, then the waist. Prior to this incident, I had just bent Australian Blackwood and Black Locust guitar sides, and two sets of Sweet Cherry ukulele sides (one in the background in the photo) successfully (the Blackwood came out with some flat spots which I have to deal with). The Ovangkol uke sides were at .075", same as the cherry sets. There were no warning sounds, steam was coming out, all looked good. I have been flexing the sides over the bouts to sense when they were ready to bend, but not with a weight. LMII says in one of their blog posts that if you move too slowly, the wood can overdry so that may have happened. But they also say some of their people are having better success bending more slowly at lower temperatures. So maybe it's just a message that we aren't REALLY in control . . .

[tippie53]

yes too slow isn't good
from the time you turn on the machine you should be done in 4 minutes

[nkwak]

I’m guessing too thick. What species of wood is it?

FWIW I have this page bookmarked. It got me through the same problem you’re having.

viewtopic.php?f=29&t=2108&p=12346&hilit ... ure#p12346

PS: RC Tonewoods sells orphaned “practice” sides for really cheap.

[Stray Feathers]

Yes, I have the excellent piece by John Mayes printed and I use it when bending, in conjunction with John Hall's information. The wood is Ovangkol (Shedua) and the sides were the same thickness as two sets of cherry that bent beautifully just before this set, and thinner than two sets of guitar sides I also did recently. I think I was just slow enough that the wood dried out too much in the process. But it may have been partly the wood; although the two sides were a good match, they were not bookmatched, and the back pieces had some fractures (marked by the seller) so I wondered if the wood was suspect in the beginning; who knows how vulnerable to cracking they were already. These two blog posts by LMII on bending I also found sobering but useful:

https://www.lmii.com/blog/2019/10/02/si ... ing-guide/

https://www.lmii.com/blog/2019/09/25/be ... t-to-bend/

[tippie53]

Glenn and I are putting up a bending library we will continue to add different wood
https://www.youtube.com/results?search_ ... ng+library

[nkwak]

Glenn and I are putting up a bending library we will continue to add different wood
https://www.youtube.com/results?search_ ... ng+library

I saw your short on Youtube and commented the numbers for my last succcessful set of bends there but will include them here as well:

Wood species: black walnut

Slat thickness: 085"

Softening agent: Windex with Ammonia D

Paper used: white kitchen parchment paper (don't tell my wife!)

Amount used: I just spritzed enough to soak the paper; I didn't soak the wood overnight or anything like that

Initial Bending temperature: 250 degrees F

Bending "sandwich" arrangement (top to bottom): silicone heating blanket, metal slat, paper, wood, paper, metal slat.

Bending sequence: lower bout, top bout, waist

Final bending temperature: 305 degrees F (basically I never unplugged the blanket and just let it continue to increase while I'm in the process of moving the cauls)

Total duration of bending process: 5 minutes (4 minutes for the blanket to heat up from plug in to 250 degrees, 1 minute to do the actual clamping; on the upper bout I proceeded slower and "walked" the caul down because I'm using a tauter set of springs.)

PS: on my failed bending attempts (when I would just use water) I was watching for steam and that's not quite hot enough to start the bend. 212 is the boiling point of water but apparently the cells haven't had time to fully soften yet.

After this, I begin the "plug and play" process (because I don't have a thermostat to vary the voltage) and try not to let the heat go above 310. I do this for 15 minutes before unplugging the blanket for good. Then I let it sit overnight to set the bend. The next day I pull it out and haven't had any spring back.

PS: I did this process successfully with zebrawood. The key thing I appeared to be doing wrong was not sanding the thickness down enough, starting when there wasn't enough heat and cranking down on the upper bout too quickly.

I've also filmed each attempt (3) and put them on youtube. What's apparent to me is that I'm less nervous with each attempt. The last one was really smooth and I"m actually looking forward to starting another build as soon as I can.

https://youtu.be/IM1UBkEgPvI (I'm hoarse and talky in the beginning but the actual bending takes place from 1:22 to 2:16 and there's a cut of just a couple of seconds between.)

[tippie53]

where did you get the blanket? I use a 5 watt per sq inch the 2 1/2 watts just need more help