Hairline cracks when heat/steam bending?

[Marin]

So I've been working with a juniper stave and usually I don't have trouble with heat straightening and bending. I am able to shape the wood but for whatever reason I sometimes see these small hairline longitudinal cracks appear in one area of the same limb, usually on the belly but someimes also on the back. Luckily they are very shallow and can be scraped away. They however keep reappearing, and seem to have reappeared especially now that I've been using steam to shape the bow. I would not be concerned for the ones on the belly but the one on the back keeeps reappearing and I have to scrape it away, and if I keep doing this, it will create an uneven back. I am going to back this bow with 2 - 3 layers of sinew fyi, so I could put extra sinew there, but I am not sure......
Anyone else seen this issue with small shallow hairline cracks appearing after heat/steam? The wood was cut back in october but has been shaped for more than a month so I definitely don't think it is still green and that these somehow are checks.
Is this something to be worried about?

[bradsmith2010]

it think your ok with the sinew

[superdav95]

Ya it’s happened to me as well.  My hairline or Small cracks happened when I rushed the drying of the corrections and recurves or if wood has had rapid air drying(faster then normal) dry time.   I would just fill with very thin hide glue when you size the surface of the bow in prep for sinew. Size (applying initial layers of thin glue) the bow well before with very thin glue and use a hacksaw blade to put shallow fine groove your bows back.  Good luck. 

[Marin]

Do you guys know what causes the cracks tho? I’ve been trying to figure it out and have my own theories but nothing that makes full sense

[George Tsoukalas]

It is hard to find a reason but these 2 come to mind. Could be the stave was not dry enough. Could be the wood was forced before was ready.

[Marin]

Is it bad to try and scrape them off on the back of the bow ? There was only one I noticed and I didn’t know if it would just get deeper if I didn’t scrape it off

[Pat B]

This is why I use shellac on the back of most bows that are going to be heated for tempering or corrections. Since I've started doing this I don't get checks in the back.
 Generally speaking, these checks are mostly cosmetic unless they run off the bow.

[bradsmith2010]

Pat,, how do you get the shellac off before sinewing

[Pat B]

Brad, a good wipe down with denatured alcohol will remove the shellac. Shellac has an alcohol carrier and the shellac will dissolve when wiped with alcohol.  Also, shellac is impervious to steam so you can still steam a stave with the shellac on the back. Dean Torges talks about using shellac when he would shape unseasoned osage staves in his "Hunting the Osage Bow".  If necessary a very light sanding works too but usually the alcohol rubdown is enough.

[Marin]

As to the cracks on the back, the small one has reappeared. I had tried to scrap it off before (it was shallow and I am backing this bow) so I know it doesn't go that deep but I don't reallt want to shave the back in one spot. I am however cautious that when I back this the crack will only grow as it would be under similar stresses to what caused the crack in the first place, and with this crack being not in the center, I am a little worried. Would just filling it in with hide glue and putting an extra strip of sinew be enough caution, on top of the 3 or so layers of sinew I'll be covering it with?
PS Don't be too alarmed at the violated grain in the photo. This was very very tight grained juniper to begin with s9 wyat seems like a major divot is actually barely noticeble when feeling the bow back. 

[superdav95]

As to the cracks on the back, the small one has reappeared. I had tried to scrap it off before (it was shallow and I am backing this bow) so I know it doesn't go that deep but I don't reallt want to shave the back in one spot. I am however cautious that when I back this the crack will only grow as it would be under similar stresses to what caused the crack in the first place, and with this crack being not in the center, I am a little worried. Would just filling it in with hide glue and putting an extra strip of sinew be enough caution, on top of the 3 or so layers of sinew I'll be covering it with?
PS Don't be too alarmed at the violated grain in the photo. This was very very tight grained juniper to begin with s9 wyat seems like a major divot is actually barely noticeble when feeling the bow back.

That’s what I would do.  If it’s a good piece otherwise I’d say go ahead.  In such cases as these minor hairline cracks if filled in with lots of layers of thin hide glue to prep for sinew is a very good preventive measure as the glue wicks down into the pours of the woods and strengthens it along with the added sinew.  If done right it essentially becomes one piece.  Proper sizing of surface would be your friend here for really good adhesion.  Best of luck with it

[Pappy]

Is the checks you are talking about the 2 lines i see in between the 2 pencil marks ? if so yes i would be worried about them. Heat or steaming checks usually run with the limb not across it. Maybe I am looking at the wrong checks 
 Pappy

[Marin]

Yeah sorry those aren't checks but due to the bad photo they do look like it. Those are tool marks from my scraper, they just look like cracks in this bad line. The tiny hairline crack is the sort of black line that runs through these two scraper marks. That's why the scraper marks are there actually

[Pat B]

Checks or drying cracks occur when wood with moisture in it dries a bit too quickly. They generally are only a cosmetic problem. You can fill the checks with thin super glue which will usually seal them and keep them from getting larger.
 Checks run with the grain, cracks run otherwise, across, diagonally, etc. Correct terminology generally helps with the diagnosis and remedy.

[Marin]

But that's the thing. These aren't drying checks, at least not in the way I usually see checks. I initially said in the first post of this thread that they only appeared very very recently and specifcally when I was using heat to straigten this area. They have not appearend anywhere else, and this wood was cut back in october and has spent quite a bit of time at this thickness and dimension before these cracks appear. I don't think they have to do with drying, as the wood is completly dry by now.
And I have heard the term "cracks" applied to lengthwise cracks before, like with cracks that form in the belly of sinew backed bows. I don't think people call those "belly checks" because those weren't formed from the drying of the wood but from different types of stresses the wood is undergoing as the sinew dries.
Unless this juniper somehow has been retaining a lot of moisture after over two months of drying close to finished dimensions, I'm not really sure how moisture of the wood caused it. Unless juniper retains moisture really really well, but I haven't heard anything about that.