Heat treating checking on wood.

[BowEd]

Question......At what moisture content does the wood need to be to avoid any heat treat checkng of the wood? 8%,10%,12%????I know even seasoned shelacked ready wood staves for bow making of over 2 years I don't trust to heat treat right away on account of that checking.I'm always acclimating my wood to 50% humidity at 75 to 80 degrees which I know never causes me any problems.Usually then it's around 8 to 9 per cent moisture then.I was just wondering if a few points more is still out of danger of this.Thickness of wood I realize can be a factor too.
All of this I know can be mute with just a little more patience of drying but was just throwing this out there from different experiences.

[DC]

It's going to vary with the wood. Mostly dry Ocean Spray and Plum will check if you change your mind but Yew is just about check proof. I think this is going to be be "an experience in your area thing".

[simson]

I use the seasoned wood (about10%), but I do heat treating always with paraffin oil.

[BowEd]

This is osage I'm dealing with.I do plan to oil it some before I turn the heat gun on.This has a kink of abrubt reflex right from the fade.It's 3/4" thick there with a nice 1/4" cleaned out peep through knot hole there too with the hole larger on the belly side opposed to the back side.Which is good.Rather do it with dry heat instead of localized tin foil steaming.
It's been my experience if any wood is dry enough heat adjusting and tempering is a non issue.Also visa versa any wood too wet will check.Knots and probably pins are a different animal too.Wood there is more dense like your ocean spray and should be taken into account for.Knots don't like to be force bent too far.
A pic of the prospect.

[BowEd]

By parafin oil simson you mean the lamp oil that has parfin oil in it?I have that.Good clean burning oil I might say.Otherwise I'll just use good old crisco.

[BowEd]

I just roughed it out to a 50#- 55# bow.I'll let it set a few days checking the weight to get a guage on it's moisture content to be sure.Lengthwise cracks are a cosmetic thing mostly of course if it does'nt run out to the side but if I can avoid it I will.

[simson]

By parafin oil simson you mean the lamp oil that has parfin oil in it?I have that.Good clean burning oil I might say.Otherwise I'll just use good old crisco.

Ed, I get my parfin oil from IKEA. They sell it for using on boards for cutting vegetables. The lamp oil here in Germany is called 'petroleum' - not what I use. That will make an inferno, hahaha.

[willie]

Thickness of wood I realize can be a factor too.

Especially if the wood is not at the same dryness through out. Maybe the absolute dryness is not as important as the differential dryness in the crossection. A piece of wood that is drying has internal stresses that show up when the wood finally breaks open, or a check pops open. This is also related to how strong the wood is in tension across the grain. As DC points out, some species have less strength that way than others.

As a generality, I would say that the closer the middle of the piece is to the dryness of the surface you are heat treating, the better off you are. especially if the wood is not as dry as you might hope

Does anyone pre-soak with water?

mineral oil usp is unscented, unlike baby oil,  and can be found in the laxative section at the drug store

[BowEd]

Yes I was not serious about using an inflammatory oil for heat bending wood.Just asking.Mineral oil I'm familiar with but crisco has served me well in the past.I'm pretty well positive this wood is 10% or less.
Wood checks because the outside shrinks faster then the inside or too fast so to speak.Pre soaking with water I've never done.The whole point to avoiding checking is that the inner wood is as dry as the outer.Even overly tension strong wood opposed to weak will check if not internally and outwardly the same % of moisture content.

[upstatenybowyer]

I usually feel comfortable heat treating when a roughed out bow has reached an equilibrium MC. That is to say when it stops loosing weight. However, I've found that certain types wood can hold water in strange ways. I was recently heat treating some sugar maple that had reached equilibrium and when I came to a spot where there was some irregularity in the grain, along with some discoloration, a check suddenly opened up.

[Selfbowman]

I like my Osage at 7% to start working on. Even then in the middle of the stave it may be wetter than I like. I think it depends somewhat on how dense the wood is. I could be wrong on this though. This is how we learn patience in the bow making process. I am trying to get to a three year stave supply so my staves dry for a minimum of two years.just about there. Arvin

[Stick Bender]

Not a lot of heat treating exsperience here but the last couple bows I heat treated I put in the hot box/electric blanket for a few days and had no isues one of the hedge bows was only of the stump 1 year !

[BowEd]

It's the handle area that's always in question for me and this one needed bending there I thought.Variables in there like comments stated.Density/thickness/time etc.Even a stave that's been drying in the shed for 3 years I don't trust.Until I take it inside for a while.Anyway guess I just wanted to show my next project while waiting on others to dry or cure.No problems this time.No oil either.Always amazed how osage can bend like rerod.Make a stick almost look like store bought from the side anyway....lol.I'll let it reacclimate a few days.I've got a 10 day rule I try to live by.I'd rather use as little heat as possible myself on all my bows.Not much above 10 % I think probably is the limit to moisture % allowed before cracking can appear.
Roughed out a very nice winged elm stave and it torqued and twisted as a roughed out bow for some reason.Was nice and flat and straight.Should of clamped it down like I did with red elm years ago.Thank god for heat guns I guess!!!From the first pic to this

then to this

It's got a bit of snake character top view.It's the sister to the wiggle handled osage bow I showed some time ago.Good wood.I gave this one a lenticular cross section limbs to see what happens tillering any different from the first one.First one was great with a flat belly.They were both from a 4" log or large sapling.First one the wiggle gave it close to center shot without any heat except for flipping the tips.This one I had to invert to probably achieve the same thing I hope.Very slight deflex coming out of the left or bottom fade I can easily live with.I'll tiller it out to 24".Check the set.Then possibly flip the tips yet some.

[Selfbowman]

I like that reflex! Arvin

[BowEd]

Thanks.3 to 4 inches.It oughta serve the purpose for me.This one is a bit narrower then it's sister so I carried the parallel width out farther.Around 1.25" wide.Aligning the tips where I want.Just one actually so not much handle removal will be needed for center shot.It's at a stage right now other things can be done I guess.A D/R yet possibly.I gave it a good 2" length fades.Even so a reflex like this usually ends up with a more rounded type slightly elliptical full draw profile for me.I think the outside third of the limbs will need trimming in width in the final look which is a good thing in my book.