scorched side in bender

[peter havriluk]

Being self-taught only goes so far, and then ignorance does its mischief. Like today. I scorched the daylights out of a side of curly cherry, using the same temperature and hardware I successfully employed on boire sides on my prior two projects. So I must have missed something important. I think I need to know some basic parameters , like temperature, duration, and dampening, at least.

I realize side bending shares some characteristics with voodoo, but I could sure use some safe practices described to me.

Thanks very much!

[John Parchem]

When you say scorched do you neab burned from one side to the other. There are metals that will blacken so wood. I do all my wood the same, I slowly start bending around 220 F and usually am finished as the blanket hits 300, I then let it sit around 300 F for another 10 minutes. I do it all within 15 minutes. I had a blanket get a hot spot and I scorched some side, I questioned my technique until I realized its the blanket.

How are you controlling the temperature? If the blanket temperature is not controlled it could literally burn the wood,

[peter havriluk]

John, thanks for answering. You described just what I did: Put the wood in the bender, got the blanket up to 300 degrees from room temperature, let it sit at 300 for ten minutes, turned off the power and let the temperature settle down to room temperature, and removed my toasted wood from the bender. Really, really, toasted. Wood was 'curly cherry'. I used a digital controller to hold blanket temperature stably (plus two, minus one, degree). I am tempted to make up a third slat, to go between the outer slat and the wood surface, sandwiching the heating blanket between the two outer slats. Maybe I can achieve more even heat distribution by using the third slat. I now have a good idea of how the heating blanket resistance wire is arranged inside the blanket. Maybe getting the wood drenched with Windex before putting it in the sandwich?

[Dave Bagwill]

Never heard of Windex for this!! Tell me more!!

[peter havriluk]

Windex is (I think) water, ammonia, dye, and I'm not sure what else. Somewhere along in my forum wanderings I picked up a suggestion to use it to promote side bending, as the ammonia was claimed to be a chemical that would relax the natural adhesive (lignin?) in the wood, and water was water. Look up 'ammonia' on the 'official luthier forum' for a discussion about ammonia.

[John Parchem]

The wood should not have charred at 300, wood burns much hotter. But if the thermocouple was not positioned to accurately measure the blanket temperature, your 300 may have been much hotter at the blanket.

[Dave Bagwill]

I've seen a couple of very good vids about using household ammonia to bend some very tight curves, and I may try it.
I did not know that Windex might work also - just found it interesting.