Color change required for compression benefits?

[peacefullymadewarbows]

Hey all. So I've been getting more experienced with using dry heat to straighten limbs and untwist prop twist and add hints of reflex but my question is do you need color change to reap the benefits of increased compression strength? I have an ash bow in the works that had a very uniform 90 degrees prop twist from tip to tip so about 45 deg from the handle to each. I've untwisted one limb and just did the identical process to get this other one untwisted. Something of note is that the way I was heating was by holding my heat gun 1-2 inches above the belly wood and oscillate slowly over about 10 inches of limb until the back was too hot to touch. While doing this progressively clamping more until board flat. Then repeat one more time to "set" my shape. Doing this I did not get any color change that I could see maybe a half shade off of the original ash white color. The first limb I did held about 80% of clamped shape so I know it got hot enough to change something in the wood. Will this bow still show any significant improved compression strength over a non treated counterpart? Thank you for your time.

[DC]

I'm going to say yes you need a colour change. I've spent hours with a heat gun tweaking twisting and aligning and I don't think I've noticed a performance increase until the colour changed. You only have to get the wood to around 200°f to move it but I like 400°f to treat it. It's just starting to change around 400.
I reserve the right to be wrong or change my mind at a moments notice

[Pat B]

Marc St Louis wrote the chapter in TBB4 about heat treating. He charred the belly.  I don't go quite that far but go to a chocolate brown color.

[simson]

I've found there is a difference from species to species. one likes more heat the other not. Ash and elm like more.

[DC]

Simon have you watched the temperature at which they brown? I should but I haven't. I have noticed that some brown way quicker. I've been putting that off to high sugar content. But some, Hazel I think, just seem to soak up the heat and take forever to brown. High moisture content would do that but all my staves have been curing for two years at least so I don't think it's that.

[SLIMBOB]

Add Hackberry to Simon's list.  The darker the better so far as I am concerned with Hack.  Ditto Sugar Maple.

[peacefullymadewarbows]

Interesting. Thank you guys very much. I've always heard white woods in general like heat treatment. Just didn't know how intense. I just pulled her off the form and it held the straight shape impressively. I'm going to try to trap the back pretty well but if it takes any noticeable set at 20" while being on track for draw weight I'll go back out clamp her straight and make the belly brown as a biscuit.

[burchett.donald]

  I would/wood say your ok in what I have experienced over the years, I have bent a lot of Osage without color change...You don't need to see a certain color or burn indication such as charred...When I use steam it stays where I put it without color change other than maybe a water stain...It's all about temperature...The finish of a piece of wood, such as a glassy fine finish vs a rough 60 grit will change using a heat gun because of all the small fibers that have raised above the surface, they will char quickly...I want my bows to harden deep into the belly beyond a charred surface on the belly...My opinion is, the charred most outter surface is weak in compression similar to charcoal...Color change can and will happen but I don't use color to depict temper....
                                                                                                                                    Don

[Pat B]

Heating for bending or straightening and heating for belly tempering are two different things. I only heat to a chocolate brown when tempering a belly and am careful not to let the heat wrap around the limb to the back and try to keep it off the sides. When I heat to bend I heat it only enough to get the bend, clamp it in place then set the bend with a little more heat.

[peacefullymadewarbows]

Thank you Don. Thank you Pat. So in the case of tempering you're maybe looking for a light color change it seems but nothing too drastic. And one more question. So let's say you steam some recurves into a piece of yew. I've heard/read that yew might try to bounce back a little of the steamed in bend and that you can "set" them with dry heat to help hold more of the bend. Is color change required for that "set" effect to take place?

[Pat B]

I've not worked much with yew but with other woods I've used, especially hickory setting the bend with dry heat really helps hold the bend. If I steam wood I usually coat the back with shellac to prevent checking if moisture gets into the wood and I set it with dry heat. Shellac can take the moisture and heat from steaming unlike other sealers.
Again not being familiar with yew I'm not sure about how dark the color should be but when I'm tempering(heat treating) other woods I like to go to a dark, chocolate brown color. Some woods don't get too dark but I try to be sure to get good heat penetration.

[peacefullymadewarbows]

I guess my question is specifically when setting steamed bends with dry heat do you go as far with the heating as when you do for tempering a belly?

[Pat B]

Not necessarily. I think just adding considerable heat works to set the bend.

[peacefullymadewarbows]

Sweet. Thank you Pat. I do appreciate the knowledge.

[willie]

I've found there is a difference from species to species...........

.

Simon have you watched the temperature at which they brown? I should but I haven't. I have noticed that some brown way quicker............

I have found that birch does not like too much darkening, it is easy to overdo it loose the benefit.

color vs temprature.   hmmm    maybe we should  keep notes or depend on color/species or temp/species before we assume what works for one will work for another