Compression cracks?

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Ok...I have been trying my hand at some bow making recently. I have made about seven bows (3 red oak board bows, 3 tri lam hickory backed cherry and maple, and 1 tri lam hickory backed red oak) only 4 survived. It's been a bunch of trial and error and research (thanks tradgang!). But pretty much every bow I make has these compression cracks. They usually show up near the bottom of the limb where it meets the handle. Am I doing something wrong or are these normal?

Also, I know tillering is a patience game and I'm a pretty patient guy but with all of the bows I've made, by the time I get confident enough to pull the bow to full draw, I'm only at 25-35lbs. My goal for most of them is about 45-55@26 inches but my bows that didn't survive... broke because I tried to pull too much too early. In the research I've been doing it seems like this isn't a problem. I'm hoping for my sanity, it is.

Any thoughts?  

 

[Black Mockingbird]

That's called operator error...that bow is really hinged there....I don't need to see it strung to know that..and I can see its thinner there at that spot....that's the worst place to hinge a bow...lots of stress there,and any major set taken there will amplify string follow big time and rob a lot of cast,and also the bow can be shocky if not bending correctly and not enough in the outer limbs...looks to me like your experiencing tiller error more than improper design(which is another cause of frets)

[Eric Krewson]

It appears you have a very abrupt angle as your fades transition to the handle. Feather your handle into your limbs over a couple of inches and the area that cracked won't be over stressed.

Just curious, did you use a belt sander to shape this area? I notice the darker lam cut straight across, no taper, and the sides of your limb trapped toward the belly(wrong way for trapping) at the cracked area. If you did use a belt sander for your fades, bad, bad, bad, easiest way to screw up a bow in a heart beat that I know of.

After typing the above paragraph I walked out to my shop and took a picture of a BBO I am working on. I had to build the handle section up and added two 1/8" strips of osage first to allow the fade area to flex without popping off.

As you can see I feathered these 1/8" strips into the limb gracefully. On this bow the fade transition to the limb is is 2 3/4" long.

   

[Bowjunkie]

Yes, you need to be especially careful with tool use as you use them coming down off the handle. It's easy to dig a hole there if you're not careful, and well... you know the result. It's pretty obvious in that picture that that's what's going on.

I prefer to work most of my tools in this area up into the handle, instead of down into the limbs. It helps, but you still need to be conscious of the effects of every stroke.

You can also wrap the area in masking tape or write a big NO there in pencil until you get the hang of it.

[John Scifres]

Cherry and red oak are not strong in compression and are easily chrysalled in a composite bow.  Use good wood, good design and good tillering.  Do a search of this forum for "frets" and "chrysals" and you will find a bunch of good info.

[LittleBen]

x2 what john said. x2 what eric said.

You can taper the fades in steep like you did, but then you really need to leave the first few inches after the fade pretty stiff to prevent overstrainign the belly there. Basically just follow eric's advice.

[John Scifres]

You are correct when you say tillering is a patience game.  However, it is also a process and it seems that maybe you are skipping some parts of the process.  You should start out with a stave bending just a little, but evenly, when you floor tiller.  From there, you should work it a few inches at a time on a tillering tree, making sure there are no stiff or hinged areas.  You should know approximately how much it is pulling at every stage and never pull it past your intended draw weight or draw length.

Here is how I tiller:   http://hedgerowselfbows.webs.com/fromblanktobow.htm

[George Tsoukalas]

If you are using power tools, then stop until you have 6-12 bows under you belt. Jawge

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Thanks everyone...input already being implemented on the next one.