Heat treating cracks

[osage outlaw]

I've been heat treating most of my bows lately and I keep getting cracks in them.  They don't really hurt anything from what I've seen so far.  I soak them in superglue and keep on building the bow like they aren't there.  I thought maybe I was overdoing it with the heat so I just lightly toasted a bow this evening and it still cracked.  When I take the bows off my form I usually find a few cracks that opened up on the back.  I know moisture will cause it sometimes.  The bow I did yesterday was from a stave that was cut sometime in the early 90's.  It's been in my shop for the last year and a half.  I roughed the bow out and left it alone for a week or two in 50% humidity.  I didn't think it would have that much excess moisture left in it.  Is there something I could be doing different to avoid these cracks? 


The lightly toasted bow




The old stave that I put a darker temper on.




The same bow on the back.  This crack was barely visible before the tempering.  It opened up quite a bit.

[JonW]

I used to use oil. When I quit I started getting cracks. Went back to oil and no cracks. No science just experience.

[osage outlaw]

Thanks Jon.  I'll try oil on the next one.  I used it on my first couple bows but haven't since.  Do you just oil the belly or do you put it on the back also?

[PEARL DRUMS]

Moisture is my bet. 50% is still a bit high, unless you had constant air moving past it.

[crooketarrow]

  Even seasoned staves have mosture. You've taken out what moisture was in the stave by heating the limb to hot to quick causeing the cracks.

[Marc St Louis]

Moisture is always the culprit in this case and it seems that the denser the wood the more of a problem it becomes

[Aaron H]

When I use dry heat, I always grease it up good all the way around where I'm aiming that heat gun.  If I am steaming, I put on 2 coats of shellac.  Seems to work well, haven't had one crack in a long time

[Del the cat]

Doesn't matter how long wood has been seasoned it can still shift move warp and crack when the ambient conditions change (e.g when you heat it).
Del

[MWirwicki]

It's just one of those things, Clintster.  Can't do much about it.  Oil does seem to work however, it is hard to glue on a snakeskin over top the oil.  Or sinew...

[osage outlaw]

That's why I quit using oil Matt.  I had an entire sinew backing peal off in one big strip.  I didn't get all the oil out of the wood. 

[PEARL DRUMS]

I have had oil lathered sticks do that, that's why I don't use oil anymore. When moisture expands and needs to escape, its going to go right through a film of veggy oil.

Just chalk it up to being a rookie......

[JacksonCash]

Cracks like that were the death of my Marshal bow from last year. Well, that or me being a bit over zealous trying to get that lower lim to work its way around. I filled them with super glue, but must have missed something, drew it back and heard a crack, one of them(the largest) had grown. Haven't drawn it since.

Does make me feel better that someone with as much experience as Clint still runs into the problems I have.

[Pat B]

Was the back sealed, Clint? I seal newly exposed backs wit shellac and make sure they are sealed before correcting with heat.
 Filling with super glue is what I've always done.

[Springbuck]

Moisture is always the culprit in this case and it seems that the denser the wood the more of a problem it becomes

I second this.  I live in a very dry climate, and get sall kinds of drying checks, but almost never have checks during heat treating........except on black locust and red mulberry heartwood.  I don't get a lot of osage, but the one time I tried heating some jatoba and ipe, I got some checks.

Definitely try oil.  I started using coconut oil recently and it's the bomb.  Also, in lieu of a hotbox, maybe try running over the wood with the heat gun, warming it all over the belly, but not toasting it, and letting it settle a day or two before the actual tempering?

[osage outlaw]

Thanks guys. 

Pat, the back was sealed with a thick layer of polyurethane.

Jackson, there are a lot more experienced guys on here than me.  That's why I'm asking them for advice.