My bow is stress cracking - What to do?

[stinkbelly]

My bow that I have been working on for 2 months and I showed you guys yesterday started to stress crack on the belly of the bow.  

I did a final sanding on the bow and began to shoot my 200 arrows at 28" before I stained and sealed it.  After 5 arrows I thought I saw a stress crack.  After 10 arrows I definately saw several stress cracks.  

The cracks on the lower limb are between 7-11 inches from the center of the bow.  The cracks on the upper limb are 6-9 inches from center.  The bow is a red oak with hickory backing.  It is 62" and 39# at 28".

Why is it cracking?  Is there anything I can do?  Is it trashed?  

I can definately feel them by hand.

Upper Limb:
 

 

Lower Limb:
 

 

[Pat B]

Your bow is probably bending more in those spots causing the compression fractures(frets, cheysals). You can relieve that only by removing wood from either side of the frets so you get a more even bend in the limb. In most cases frets are eventually terminal.
 Will you post a pic of the bow at full draw?

[Nim-rod]

We never saw a picture of the full draw but looks like improper tillering and it's bending too much in the fretted areas as Pat said. Shooting a bunch of times before finishing shows flaws like this and keeps you form wasting your time on it. With that much cracking it's days are numbered sorry to say. Could be the hickory overpowering the red oak. I don't try board bows anymore because I could never get them to last long so I moved onto staves and will never look back.

[30coupe]

If you backed it with hickory, I'd agree with Nim-rod. It's overpowering the oak. I did the same thing with a maple board bow. It fretted before I was even done tillering. Hickory backing needs to be THIN! I would say 1/8" would be maximum. I got my backing from 3Rivers and didn't thin it, just glued it up and started to tiller...wrong!

The good news is you get to learn from your failures.    :rolleyes:   I learned a lot from the bows I built that didn't survive. I know lots of folks make red oak bows, but hickory is a lot tougher. I built an oak bow that I backed with drywall tape. It lasted a few shots then cracked all the way across the bottom limb. Probably more a bad tiller job than the wood though.

Don't let it bother you too much. You would have built another anyway...it's very addictive.

[PEARL DRUMS]

Even a good tiller with a 62" red oak board bow at 28" is pushing it bigtime. Make that same bow 68" long.

[stinkbelly]

The bow is 62" long.  I have a stiff 8" end on both limbs.  The handle is 10" long.  That only leaves 18" of each limb to bend.  

As for the hickory.  I did order the 1/8" piece from 3 Rivers and glue it directly on.  In the areas of the cracks, the hickory is 1/8" and the red oak is 1/4".  Besides the handle, this is the thickest area of the red oak.  There are no visible cracks in the thinner areas of the red oak.

It looked really good on the tillering tree this weekend.  I used a 6" block of wood and it was consistent throughout.  Now it looks pretty off.  It did loose 4 pounds of draw weight since I had it on the tree last.


 

[Pat B]

Only the inner 1/3 of each limb is working. I like stiff tips on all my bows but only about 4" to 6" .

[Nim-rod]

Yea definatly not enough of that limb working. You really have to spread the load out evenly. The bottom limb is bending more than the top in that picture. You can always leave it strung up and make a wall hanger out of it. Better that than having it break the rest of the way. Too pretty to let it snap.

[mwosborn]

If it where mine I would try tillering out towards the tips and get the rest of the limbs working a bit and see what happens.  Might take enough stress off of the area of frets and last quite a while.

I have an ash bow (my first) that developed a chrysal on the back of one limb.  Been shooting it for a few months now and it is holding tuff.  Most likely just a matter of time, but I want to see how long it will last.

Good looking bow - hope it lasts you awhile!

[30coupe]

Pretty short and pretty thin. You are in the same boat I was with the maple one. Once it starts to fret like that, your tiller goes with it. I'm with Pat on the 4" to 6" too, though you may have had more bending before the frets started. The inner third must be the fretted area, I'm guessing. As it collapsed the middle started to look stiffer.

Long bows are called that for a reason. For a 28" draw 68" would work a lot better. Give that a try on the next one.

[fujimo]

if you REALLY wanted to save that bow- and not write it down to experience, i would try this.
 tiller it to get more of the limbs working- and in the process you will lose some weight off it- possibly take a little off over the whole limb as you do this- and get it down to a nice flat surface, then glue on a compression strong slat onto each limb- osage or ipe( i am sure there will be lots of other suggestions!!) or maybe even some hickory if you have nothing else( another slat from 3R!).
make sure the slat goes right up the fade , and  up to the handle.
i personally would use urac glue- better gap filling properties if the fit is not absolutely perfect.
hopefully you come out a little over weight, then you can scrape or sand down to your final #.

 or humble accept the lesson- and move forward- but i certianally think its worth a shot.
wayne

[stinkbelly]

I was amazed when I saw my picture last night.  The lower limb was the stronger limb.  It is the one that has more cracks and now it is weaker.  The limbs were really uniform before I started to shoot it.    

I started off with this bow at 72", but I made a huge mistate about 3 hours into it and had to lop off the ends.

[Art B]

You learn and you move on........or learn to repair what you got. Dish out the areas that are fretted and replace with wood of better compression strength. Repairs are an essential part of bow making too.

Looks like some limb twist in your upper limb.

String loops are catching on the back shoulder of the string grooves not letting your bow fully open up.

Understand that a tillering tree will lie to you. It can't account for your bow hand and split draw.

Get your short string on early in the process and then only use the tree sparingly to check for bending.

Exercising on the tree is a no no in my book. Do that by hand. Check for any tiller change often using a ruler at the fades.

Good luck........Art

[stinkbelly]

Thanks Art.  Those are things I didn't look at or see.

As for a repair, would it be possible or a good idea to sand down most or all of the red oak from the limbs and then place another piece of hickory backing on the back of the bow? At that point it would pretty much be a hickory bow. Or would it be a better idea to sand it down and put a strip of wood on the belly of the bow over the red oak?  

I guess either way, it is almost a total rebuild.  

If I were to make another board bow, what wood and backing would you use?  I have two more pieces of hickory backing from 3 rivers.

[Eric Krewson]

Lower limbs have a tendency to go weak, happens to me pretty often. I make my lower limb stiffer on purpose, shoot the bow in well then do my final tillering.

You do need to make a tillering gizmo, much better than a 6" block of wood.

When I am shooting a bow in I shoot a few arrows (20-30), check the tiller, shoot some, check tiller, readjust and so on until I have about 500 arrows through the bow.

If you catch tiller changes when they first start you can correct them before part of a limb is over stressed.

[Black Mockingbird]

That wood be a proper tiller for a narrow stiff levered bow. But I don't think your front profile is such. And even if it was your width thru the working limbs are too narrow. The frets are telling you so,that your design is too narrow to handle the stress. Learn this lesson and move one.

[stinkbelly]

Originally posted by Eric Krewson:
Lower limbs have a tendency to go weak, happens to me pretty often. I make my lower limb stiffer on purpose, shoot the bow in well then do my final tillering.

You do need to make a tillering gizmo, much better than a 6" block of wood.

When I am shooting a bow in I shoot a few arrows (20-30), check the tiller, shoot some, check tiller, readjust and so on until I have about 500 arrows through the bow.

If you catch tiller changes when they first start you can correct them before part of a limb is over stressed.

What is a tillering gizmo?

[Art B]

I just went back and checked the front profile of your bow on your other thead and you would have to correct your tiller (needs more bending mid-limb) first to fit your limb design.

So once you correct your tiller, your poundage may be way to lite except for a kid's bow. But I won't just trash the bow. You can practice patch repair, do a belly lam as you suggested or perhaps cut the back off and salvage for another bow.

It's all about learning first and then moving on.

[stinkbelly]

Black Mockingbird and Art, I know you guys are giving me a ton of information, but I honestly don't understand what you are telling me.  I am not sure what my front profile is.  What is a stiff levered bow?  I don't know if I really have a limb design, I just heard some things here and there and tried to combine them.  

My boys want a homemade bow.  Would it be safe if I removed wood to relieve the stress and retiller it?  It seems like if I take any more red oak off, this will only be a hickory bow.  Wouldn't the hickory definately over power the red oak if I remove more?  What draw length and weight would I shoot for for a kids bow?

[Art B]

There's two basic limbs shapes, a rectangular and pyramid.

Front profile is one of these shapes as you look at the back of the bow. Each shape requires that you have a drawn profile to match each shape for best efficiency. Some refer to this as tiller logic or matching profiles.

For a pyramid front profile you would want a circular drawn profile. For a rectangular limb design you would want a more elliptical drawn profile.

But, with you using a retangular limb design, your bow shows a circular drawn profile. Contrary to tiller logic.