My First glass bow broke :(

[hightop_hunter]

Hi guys I was hopping that I would be uploading with happier news but I could really use some pointer from the pros. I spent the last month or 2 building a jig an putting together my first fibber glass long bow. I thought she came out beautifully but when i went to shoot it for the first time the laminations started showing lifting. at first is was a VERY small dot of smoky looking fibber glass. but the more i pulled the bow the bigger the cloudy spot grew until it reached the edge.  i lifted the glass slightly and injected the area with epoxy. I pulled it a few times and took it to the range. To try firing some arrows through it. About 20 mins after i strung it the limbs came apart completely right at the spot that i had tried to fix before. SO here I sit a little sad but happy to learn from my mistake. Is it my jig ? is it the fact that instead of using a heat box I decided to let it cure for 24 hours? was the poundage to high and the glue couldn't keep it together ? any advice or thoughts could help me plan a strategy on my next bow.


 
     

[mikkekeswick]

It's hard to say without knowing more on your processes.
Smooth-on does get a stronger bond if cured with heat so I would certainly recommend that for your next one. However i've read about people letting it cure with no heat-box and their bows being fine. I suspect this was part of the issue though.
Smooth-on is amply strong to hold a bow together so that isn't the problem.
How did you prepare your laminations?
What temperature was the bow cured at?

[hightop_hunter]

im not sure what you mean by preparing the laminations. I didn't do much other than cleaning them with a little alcohol . the bow was cured at a little above room temperature. 23degrees or so.

[KenH]

It sounds to me as if you had a dry spot -- an area with no glue, and as you drew, the laminations came apart there and the void worked its way to the edge.  The rest of the glue up may have been 'starved' as well -- not enough glue.

It wasn't the draw weight.  People make wood-glass composites in the 100# ranged all the time.

It probably wasn't the form, although I don't know which type you used -- air-pressure or open top with rubber bands, or whatever...  

I've built a lot of bows using ambient heat with Smooth-on -- you DO NOT NEED AN OVEN to cure a bow.  There is no verifiable evidence that I know of, which shows that an oven gives you a stronger bond.  People built wood-glass composites for decades before those who were too impatient to wait 24 hours invented the bow oven.  

You DO need a constant temperature above 70F, and your "23C or so..." temperature is what I would call border-line for adequate; especially if it dropped below that during the curing process.

If the wood and fiberglass were not clean -- even the slightest bit oily or dusty -- you might not get a good bond between the laminations.  Many of us wipe each lam down with acetone or another solvent to get rid of oil and dust, just minutes before gluing the stack together.

[Robertfishes]

That was a nice looking bow you made. What kind of alcohol did you use to clean the laminations? How long between cleaning and glue up?

[fujimo]

what pressure system did you use on the form, clamps? air hose? rubber bands?
i think air hose is the most fool proof- good for folks like me!!
clamps work, and people use them all the time- but can be prone to pressure spots and in turn glue starved areas- but people make them work all the time- so who am i to say!   :D  
rubber bands are a good system too.- used that a fair amount too.

if clamps, are you using pads under the clamps. to spread the load.

what grit were the lams ground with- did you buy them or grind them yourself- i grind mine with 120gr- and thats the finest a person should go i think!

[mikkekeswick]

KenH - Have a look at the data sheet for EA40 I think Smooth-On have plenty of 'evidence' on the subject!! That's not to say that EA40 isn't strong enough without heat curing but if the manufacturer says that heat curing is better and gives a stronger more heat resistant bond I'm going to go with what they tell me.
I always, always get the data sheet for any product that is new to me as they are a real wealth of information that is scientific and not subjective.
Also wiping wood surfaces with acetone actually pulls more oil to the surface. A good brushing with a stiff nylon brush will work to clean wood sufficiently. Fiberglass however is well worth rubbing down with acetone.
Are you certain you coated all surfaces with glue? No dry spots? You have to really cinch down on a clamp to squeeze too much glue out. What I meant by 'preparing the surfaces' was did you grind them yourself? How did you make the riser and prepare its final gluing surface?

[Krasus]

Sounds like glue starve. Don't be liberal with your glue. Also if your using plastic wrap to control your glue over flow make sure is not in between the lams.  Like Wayne was saying hose clamping is easiest but if your using clamps use pressure blocks. I clamp my bows and I use a strip of aluminum 1/8" to distribute my clamping pressure evenly.

Don't get discouraged. My first bow failed to.oh and my second too lol.  

[hightop_hunter]

Holly smokes!! Im so glad for all the comments. Glue Starved is a new one for me. I have never herd that until now. I will Definitely double up the amount That I made. especially because I ran out half way through and had to make a second batch. I also ran in to a problem were the seams in the glue looked like they were getting slightly larger after i strung it the first time. I think after all the comments It might have been a case of a little of column A a little of Column . I think i probably didn't use enough glue and It may not have cured quite as well as it could have. I wonder if Adding a rubber strip all the way down the length of the Jig might help with more even pressure and less shifting around. For reference I used the inflated hose type of jig. Thanks for all the help. Next year maybe I will enter the Bow Swap.

[jsweka]

Yep, don't be afraid to use lots of glue.  Makes a mess, but that all gets cut away.

Glue is cheap compared to the cost of other materials.

It did look like a real fine bow until it broke, so you certainly seem to know what you're doing otherwise.

[fujimo]

adrian, when you use more glue- and it squishes out everywhere- and like cody says youre using the saran wrap to contain the glue and stop it from getting on the form, REMEMBER to put masking tape on the backs of all the glass- after you have ground to profile- the tape will peal off nicely leaving a nice clean surface.
maybe you did that already- but i have seen the results of fellas not using tape on the glass.
good luck- keep on keepin on!!  

[bamboo]

alcohol contains a lot of water--the lams were probably not as dry as you thought--its also pretty easy to rush -and forget to wet one surface with glue--maybe??
 don't give up--it looks like a good design

[Krasus]

It's ok if you have to batch up more glue part way thru glue up. With smooth on you have a hour open working time.  Just make sure you are doing equal parts a and b. I never batch up enough during my glue ups and sometimes even end up batching more up to 3 times.  :D

FYI it was a beautiful bow. Don't get discouraged. I'm signing up for the swap next year too. Pm me if you want to chat.I'm more then happy to help you in any way I can.  

[JamesV]

Originally posted by hightop_hunter:
im not sure what you mean by preparing the laminations. I didn't do much other than cleaning them with a little alcohol . the bow was cured at a little above room temperature. 23degrees or so.

If 23 degrees is correct, that could be the problem. The bow design looks good, so your form is not the problem. Did you check the moisture content in your lams before glue up?? Bamboo and Hickory are really bad about holding moisture. My shop is not heated and I have to be really careful about moisture in the lams.

James

[Robertfishes]

I think he means cure temp of 23 degrees Celsius.. Which would be around 74 degrees Fahrenheit..still not to warm for a good cure. I have several stiff nylon bristle brushes for cleaning tapers and glass, I have never applied alcohol or acetone to the lams..
As far as ammount of smooth on to mix, I would mix a minimum of 10 oz for the next one..8oz should be plenty but better to have too much.  I like to mix mine on a new 8" plastic dinner plate using a 4 inch autobody bondo squeegee cut in half, I buy them in a 12 pack.. Then I put the mixed glue onto another new plastic plate, clean the squeegee and continue to stir and mix..my goal is to have a complete mix of epoxy.. then I use the other 1/2 of the squeegee to apply the smooth on.

[mikkekeswick]

Smooth-on should be mixed at 83:100 not equal parts.

[fujimo]

Mike, I think it is equal parts by volume, but the different ratios come in when it is by weight. I believe you can mix it 2:1 for better heat resistance, so I guess that means there is a whole range of mix ratios that will still work, without compromising the glue. But I have never done that , I always mix equal parts , volumetric ally

[Tim Finley]

Mix the smooth on just a little more of part A than B it gives the bow more heat resistance . You do need to heat the bow, don't get it over 200 degrees 150 to 180 is perfect you get a stronger bond and is more heat resistant. Always use acetone I have been making bows for over 30 years and have cleaned everyone with acetone, as far as bringing the oils up this was something that OL Adcock came up with, not true, brush your glass and lams off, blow them off, then take a clean cotton cloth soaked in acetone and see what you have on the rag after wiping its the difference between a clean glue up and one mixed with dust. Make sure you put glue on both surfaces. Any bow can break any time, a lot of advice on these threads may help for next time its just too bad you have all that time, labor, and money into it and then failure !

[mikkekeswick]

Tim - there is quite a lot of evidence about the acetone thing. I've spent reasonable amount of time reading about it. It's unlikely to make a real difference - if all your other processes are good it probably won't tip the scales. I use a stiff nylon brush to remove wood dust from grinding. Fortunately for us bow makers Smooth-On EA40 is a very strong glue!
Here is the datsheet.
  http://www.smooth-on.com/tb/files/EA40.pdf

[mikkekeswick]

https://books.google.co.uk/books?id=GGGkJdbnt4UC&q=98#v=snippet&q=98&f=false

Read on until pg 101