How much heat is enough for heat correction

[Fred Arnold]

I need some slight correction on a couple of bows before finishing. Since our weather is on the high side, (between 95-105 with heat index of 103-112 over the next few days) I decided to clamp up a couple of bows to the form and leave them in direct sunlight in order to test the elements. The thermometer sitting on the form next to the staves was reading 138 about an hour ago.

Do you think that penetrating temperature is high enough to make the slight corrections needed or do I need closer to 190-200 degrees?

Modified: the relative humidity is between 47 and 87 depending on the time of day.

[jeffp51]

my osage doesn't bend until it is too hot to touch.  Not sure the sun would be enough.

[BowEd]

I use a laser thermometer occasionally while bending and heat treating wood dry.Wood plasticizes at 350 degrees from a slow crept in type heat.At that temperature my bends always stay.Horn is different because it's denser.
I seriously doubt whether you will get a serious correction to stay at those temps.They will creep back IMHO,but give it a try see what happens.
Your right though we are in an heat wave for sure here too.

[Badger]

  Yeras ago I made a solar box for heating and correcting staves. I used steady pressure over a period of days to make the corrections. This was not intended for any sharp curves. I know it worked to some degree but I don't remember now how well it held.

[Fred Arnold]

I'm going to finish off my trade bow with a heat gun just to make sure but there are 2 others I'm going to leave out in the heat and humidity for the next 3 days. One of them is a sinew backed BW that I can't use direct heat on. I'll take some pics and let you know if it works for me.

[Fred Arnold]

Here's a sinew backed black walnut. Too late to save it for my give away in the bow trade. I think I can still salvage it although lighter than expected. A lot of kids out here need bows so it won't be fodder for the fireplace. After heat correcting and initial tillering when I applied the sines ir went back to it's original form. Go figure!!!

Anyway the red lines give an example of where it went from where I wanted it to go. Since it has a sinew back the option of heat correcting it again wasn't an option. I figure if I can get it to correct 1/4" my tips will align.

I'm going to leave it out through rain or shine, heat and humidity for the next 3 or 4 days and then I'll bring the Workmate indoors intact and set it in front of the window AC. Wish me luck.

[Fred Arnold]

  Forgot the damn pic.

[mwosborn]

Never tried heat correcting with the sun before Fred.  I have cut and then clamped them right away to induce some reflex, but no corrections after they are dried.  If I had to say, I would say it is unlikely hot enough.  When I use heat, you can touch the wood for about 1 second and then it is to hot to keep your finger on it.  Let us know how it works!

[Fred Arnold]

Actually after 2 days and 1 night outdoors the bw darn near corrected. I'm going to do the other limb tomorrow and try to pick another 1/8". Although the sinewed back is well sealed the belly facing the sun only had 1 coat of shellac. I believe the humidity had more to do with it than the heat.

[jeffp51]

the question now is if it will hold when it dries out, or if it will go back to its old shape.  Keep us posted.