Cracks in glass

[Aeronut]

I was the lucky winner of Kennym's first giveaway and this is the Curly Hickory bow that I made last year.  I have probably not shot it more than 5-600 times, if that much.

Last week my nephew stopped by to get some arrows and we did some shooting.  I noticed a short crack in the belly glass of the upper limb.  I unstrung the bow with the intentions of getting some pictures and posting a question about it here.  Today I take the bow out of the sock and this is what I found.    

There is now a crack in the upper limb that lacks just about 1" from being completely through the full length.  Two cracks have appeared in the lower limb belly glass that run about 3/4 of the limb.  There is absolutely no limb twist and it looks like the cracks started just about mid limb and traveled from there.

This bow is my baby and has never been dropped or hit in any way and hasn't been subjected to any extreme heat variations.  What could have caused this?  My only thought at this point is some bad glass.

Any and all thoughts on this are welcome.

Bow specs:     62"  54#@28"

Dennis

Crack in upper limb   Belly side
 

Lower limb   Belly side
 

[kennym]

Dang Dennis!!

That is a new one on me,my .02 is:

I'm sure you shoot heavy arras.

If it is bad glass,wouldn't it crack in the same manner on both limbs? The white lines I've had were along the whole piece of glass in a strait line.

What kind of finish on limb edges? Any chance the lams took on moisture and swelled a bit while the glass remained the same?I've had bows where the overlays shrank or swelled with good finish and made the glass/wood  surface feel out of whack.

No critique here,just thinkin out loud!

[Wind D Ranch]

I sure hate to see that.  It'll be interesting to see what the cause is.

[recurvericky]

I had a set of limb for a take down recurve that did the same thing and it was due to moisture. I had the limbs ruffed out and was not able to get back to them for several months. During that time period we had alot of rain. When I went back to finish the limbs the glass had cracked lengthwise. I contacted Binghams, since I bought the glass and lams from them, Elmont said that it was due to moisture getting into the lams.

[Pennsyltuckey pete]

I do have a question about the cracks.  I had the same thing happen on two sets of take down limbs that I made.  Enough to really irritate!  Is the crack on the inside of the glass or will it catch your thumbnail?  I spoke to Elmont at Binghams when this happened and he told me to check and see if my limb form was perfectly flat.  He said that if there is any dish in the limbs it can cause the crack to develop especially where the limb bolts to the bow.  Elmont told me to make sure that the limbs are sanded perfectly flat. He also said if you dont use a stout enough pressure strip the hose can cause the limb to be dished.

Hope this helps.  I am interested if any one else has had this type of a problem.

pete

[Aeronut]

The bow is finished with five coats of True Oil with the first three just wiped with 4/0 steel wool, not sanded, between coats.

The cracks are on top.  You can feel them the full length.  There is another one starting along side the single crack on the top limb.

I took my time making the form for this and everything was square and flat.  I used the same form for my Hickory and Hedge bow I just made about a month ago and I checked it before using it.  Everything was still square.  I don't think it was the form.  I used the pressure strip I got from Binghams.

The only thing I can think of concerning moisture is I had the glass for a couple of months before using it.  I warmed it in the hotbox for about two hours before I started the layup.  When I cut the glass in two for the belly I put the cut end out past the tips.

I got the glass from Binghams and plan on emailing the pictures to them to see what they say.

Got me completely befuddled.  Gonna start sanding some new laminations tomorrow.  Looks like another build-along coming up.

Dennis

[muskiedaze]

I got short white cracks in glass limbs on my very first bow, The limb core was actionwood. I have to assume the edges were inadaquitly  finished as a dozen other bows were fine. There were high humidity conditions.   John

[Dano]

I think it was moisture in your lams before glue up, I was talking to a glass bowyer when I was at Compton's, he had a bow start that on a TD right at an alignment pin, the bow had been in the rain and the pin filled with water, the moisture caused the lam to expand causing the crack in the glass. Don't most bowyer's keep lams and all in the bot box for days before glue up?

[Randy Morin]

Doubt it was your form either....the Adcock bows are dished on purpose and he used to use glass.  Moisture would be my bet....in your core lams.
I dont heat my lams much before glue up but I live in a very dry climate.

[kennym]

It would have to be moisture after glue up.

 A shrinking lam wouldn't crack the glass  without pulling it loose from the core woods somewhere.  

JHMO

[Dano]

That makes a lot of sense Kenny.

[Aeronut]

Moisture does seem to be a culprit but I don't know how it could have drawn moisture with the finish I put on it.  Oh well, at least I got one deer with it.  One shot, one kill.

Now you guys will have to put up with another build-along.  I was thinking of starting another bow sometime after the new year but I guess I'll do it now.  I've got an idea for the riser strips that I'm going to try.

Here are the ingredients.

Shagbark Hickory core
Black Walnut lams
Osage riser.
 

Kenny, I'm going to send an order for some .050 glass your way.

I think these lams will reside in the hotbox for a couple of weeks before I start layup.  I'm trying to figure out some way to hook up my basement dehumidifier to it.

Dennis

[Pennsyltuckey pete]

Good luck on your build.  I am looking forward to it!

pete

[Aeronut]

Here's a peek at a dry run on the riser.
There will be another Walnut strip in it.

 

One of my nephews wants to help build this one.  I think I may have created another bow junkie.

Dennis

[Robertfishes]

I live in a high humidity area. I bought a used $35 dehumidifier for my 8 x 11 glue up and spray finish room, I also have to run an 8000btu  air conditioner in my 11 x 24 shop, I pull air conditioned air thru filters from the shop and into the glue room using two 50 cf/m bathroom exaust fans. After seeing this thread I will be paying more attention to humidity in the shop. I run the dehumidifier during glue up and during spray finish drying.

[longbow from LW]

You can use a moisture meeter for checking your lams at glue up.  I think you should be shooting for 10% moisture in the lams at least that is what I have heard.  An acquaintance from long ago used to make longbows and he would put his lams in the hot box on low for several hours.  Never seemed to have a problem with cracking.  I would also think that if it is moisture the glass would have a cloud under it from not drying correctly, kind of like brown sugar looking that is caramelized for lack of a better definition.  Also if it was moisture I would think that the crack wouldn't be uniform in appearance as a straight line.  Just cause the way glass is made.  Hey beats me, interesting though.  keepem sharp

[Bob Morrison]

I would bet everything was fine at glue up as far as moisture and at finish time. There has had to be a expanding of the lams that the fiberglass could not keep up with and split. All woods even after they have finish on them will still take on moisture in hot humid areas, even in a basement. I have never seen a limb split that far,so it could be lams were to dry at buildup and really sucked up some humidity. That my story and I'm sticking to it