Osage and Dry heat? Revisited

[Hamish]

 I've heat bent with shellac on the back, and still got little ruptures.  Osage from a 1" thick board, not kiln dried, but seasoned in my shop for many years, so it didn't have a high moisture content.
I've also got mixed results from shellac on staves, even when they have been roughed out, floor tillered, not from a supposedly seasoned large split with potential moisture.

I switched to canola oil and haven't had any splits since.

I think shellac is good for protection when the stave is green and you are going to use wet heat to bend.
Once a stave is dry, I suspect the shellac(which is quite tough) stops the air in the woods cells from escaping, until the pressure builds up and the air is forced violently out of the cells, causing fissures.

It doesn't always happen with shellac, and dry heat. Many guys never seem to have issues. Like I said once changing to oil I've never had any problems, ever.

[bentstick54]

So I repeated the process on the 2nd limb today with the same success. This limb needed about 1/2 the correction as the 1st limb.

I wiped a thin coat of canola oil on the belly, and hit it with the heat gun. It didn’t take very long before the wood started becoming pliable enough to move. I waited a couple of hours for it to cool and took the clamps off, and it held the correction, with no drying checks showing up on the shellaced back.

From never using oil before, my first impression is that it seems to help carry the heat deeper into the wood at a faster rate. I felt like it took a shorter period of time for the wood to become pliable with the same amount of heat when I didn’t use oil. I’m wondering if a combination of shellac retarding moisture being forced out the back, and the oil transferring the heat quicker into the wood causing less time for any moisture to be forced out, is a possibility?

I don’t have any other staves ready to rough in yet, but I do have a corner full of future candidates to test on. I will definitely try the same combination of shellac and oil in the future and see if the results repeat themselves.
Definitely worth the little effort to experiment with again.

[superdav95]

I haven’t used shellack yet but I do and have used oil based and water based poly coat on the back of my stave for drying.  I find the water based stuff little better.  I also use canola oil with good results as mentioned and no splits.  I will occasionally get splits with boiled or steamed tips if I rush the drying out and heat tempering of the recurve.  As long as I wait couple days then I’m usually fine. 

[bentstick54]

Well I finally got this bow finished up. Not the best looking bow I’ve made, but it shoots pretty well, especially for as much correction as the stave took. I wanted something a little less weight than my normal 50# goal, so I brought this one in at 46# @ 28”, 66” ntn.

[bentstick54]

So I had another piece of Osage with a serious dogleg in it so I thought I would try the dry heat with the back shellaced and some canola oil on the belly again. I did not mark the harvest date on this stave from some reason, but it is at least 2 years old and probably older and has been stored in my basement all along.
I used the high heat setting on my heat gun, held 4” to 5” above the belly, heated about 4” at a time, pulled the limb over, clamped, moved to the next 4” and repeated, plus going slowly back over to the previous area to hold heat in longer. Then after the whole limb was done and clamped, I slowly went back over the whole limb and then let cool. I tried to do a slow heat for deeper penetration without scorching the belly.
After cooling and unclamping, I hit the last 4” of the limb again to align the tips a bit better. After finishing and letting cool, I was very pleased with the results. I see no drying checks on the back or belly, and it’s holding the corrections.
For reference I left limb thickness at approximately 5/8” thick and 1-3/4” wide at the fades tapering to 3/4” at the tips. I wanted to leave it wide enough and thick enough to have room to narrow and thin.

[bjrogg]

Osage is just so cool for heat correction. Well actually it’s hot but it sure can be transformed into the shape you want.

Bjrogg

[Selfbowman]

Well done!

[bentstick54]

Kansas has a ton of Osage, but it’s still hard to find a straight one. So I’m just trying to figure out how far I can go with it. Learning every time. But so far seems like shellac on the back, and vegetable oil on the belly seems to be working on keeping the drying checks down.

[superdav95]

Bentstick. What is you mix for shallack?  Did you mix your own shellack flakes with a thinner or store bought stuff. 

[bradsmith2010]

nice work,,,

[bentstick54]

Dave, I just used the store bought stuff. I bought a quart of Zinsser brand. I’ve sealed about 24 staves, and maybe 6 roughed out bows after I chased rings, and maybe used 1/2 of the quart. And it is easy, lol.

[superdav95]

Ok that’s good bentstick. I think I have some of that stuff.  Good to know it works. 

[bentstick54]

Like everything, there’s no guarantees, but that’s 2 for 2. I will definitely go this route again as I have plenty of staves that will need corrections when their turn comes around.