Bow Design Flaws?

[fsubobcat15]

Greetings y'all,

Been lurking on here for awhile trying to glean as much information as possible on bow building.  I just started out a few months ago because I saw a few videos on Youtube and decided to try my hand at bow building. The first bow I tried to build was a red oak longbow based on the design from GoGeronimo.  After shooting this for awhile I decided to make a white oak longbow of the same dimensions. Anyhow, after following the bow design from GoGeronimo's page I have been left with one broken and one almost completely broken bow (Not implying his designs are flawed, but just to give background on the methods I used).

Both bows have cracks running across the backs of the bow, perpendicular to the grain.  Seems to me that these are tensile cracks.  However, my question is this: what is the most probable cause?  I used red oak for one bow and white oak for the other.  Both have fairly straight, clean grains.  I figure that the cause of the damage comes down to: improper tillering, handle length being too long, limbs being too thick.

Improper tillering leading to breakage is obvious, however I believe took the correct steps in making the bow bend.  The reason I suspect one of the other two causes is at fault is because a long handle restricts what proportion of the rest of the bow can bend meaning that more of the work is done by less of the limbs.  This might explain the tensile cracks, and might go hand in hand with the limb thickness.  On the second bow I was really straining to string up the bow and I believe the thicker handles were less elastic meaning they couldn't bend as much meaning that force put into the limbs caused the limbs to fail at any draw past its brace.  Which brings me back to tillering...

In summary this is where I'm at with my bow building...trying to figure out how to build my first bow that doesn't break, but understand why the other two did.  If any of yall have experience with this I would love to get some feedback!

[Hrothgar]

If you can any pictures, broken or whole this might help.

[fsubobcat15]

I completely forgot those, anyways here is a pic of both bows.  The bow on the top is the red oak bow.  Obviously I got farther with that one and had added all the accessories. The one on the bottom is the white oak bow, which broke during final tillering before I cut the arrow rest.

If you look close enough the red oak bow's bottom limb (right limb) has a hinge right where the rawhide wrap is.  Leads me to believe I just didn't take enough time tillering it.

[PatM]

Tillering really isn't about time per se. I think sometimes people get the impression that just scraping and flexing for an extended period somehow helps a bow not break.
    Your handles are too long and poorly transitioned but your weak spots are not because of that.
 Start out with just a full working D bow and then move to handled bow when you can make a whole bow length work evenly. Lots of help on here.

[bubby]

http://traditionalarchery101
Check out jawges site he will be a great source of info to grt you started

[fsubobcat15]

Thanks for the insight. Looking back now the designs do seem inherently flawed.

[Del the cat]

Main design problems are too short (too long in the handle is less working limb), too long draw, too thick/high poundage.
The main tillering problem is rushing and thinking you've finished once it's braced.
It takes a while to get your eye* in to seeing the curve. By the time a problem is obvious it may be too late, you are looking for the slightest hint of a problem, trying to catch 'em before they occur.
Taking photos, videos, getting a second opinion helps, as does making sure you are working in a clean consistent manner with the tillering tree set up somewhere without visual distractions to the eye.
Loads of video and pics on my Bowyers Diary (google it) where you can follow a variety of builds warts and all.
Some people like to use a tillering gizmo (a search should give you details) it can help with board bows. backing with fabric or rawhide may be a wise precaution too, until you feel more confident.
An ounce of practice is worth a ton of reading, so keep at it.
Del
*As well as your eye, run the limbs along between finger and thumb or put calipers on the limb and run 'em along looking for dips and bumps.

[Badger]

  How wide are these bows?

[joachimM]

Same question as Badger. They seem to be pretty narrow, more like a longbow with a stiff handle. Those designs stress the wood very heavily. Red oak doesn't like to be coerced into a narrow bow with deep limbs. Looking at the pics, the limbs seem only 4 cm (1.5") wide and around 22 mm (7/8") deep out of the fades.
 
Oak is better suited for wide-limbed flatbow / pyramid designs. Make it about as long as you are tall, min 65" to 70" for a 28" draw.  2 to 2.5" wide out of the fades to 1/2" at the tips, and about 1/2" to 9/16" (12-14 mm) thick throughout the length of a pyramid limb. That will give you a durable and decent draw weight oak bow, some 45-55# I guess. It's better to have wider limbs that you thin down extensively during tillering than to have narrow limbs that need to stay deep (thick) in order to get to your target draw weight.

[Knoll]

It takes a while to get your eye* in to seeing the curve.

Taking photos ..........

Loads of video and pics on my Bowyers Diary (google it) where you can follow a variety of builds warts and all.

Some people like to use a tillering gizmo (a search should give you details) it can help with board bows.

An ounce of practice is worth a ton of reading, so keep at it.

*As well as your eye, run the limbs along between finger and thumb or put calipers on the limb and run 'em along looking for dips and bumps.

All good advice.

Del's last point has been helpful to me, though it took awhile to get the "feel". A fellow recommended using the very lightest of touch as ya run fingers up/down limbs. That light touch was key to my feeling the bumps/valleys.

Keep at it, and GOOD LUCK!

[George Tsoukalas]

Some questions.
Width of bow?
Length of bow?
Draw length?
Non bending handle length?

Made many a red oak board bow 1 3/8" to 1.5? but they bent in the handle.

Jawge

[bradsmith2010]

I like what PatM said,, start out with the most simple design,, full working D bow,, no handle,,
make the bow 1 1/2 wide,, you success rate will go way up,,
glued on handles are over rated,, not necessary to a great shooting efficient bow,,
lots of ways to skin a cat here,, but you can't go wrong with keeping it simple and using one of the most time proven designs,,

[Badger]

I like what PatM said,, start out with the most simple design,, full working D bow,, no handle,,
make the bow 1 1/2 wide,, you success rate will go way up,,
glued on handles are over rated,, not necessary to a great shooting efficient bow,,
lots of ways to skin a cat here,, but you can't go wrong with keeping it simple and using one of the most time proven designs,,

  Brad I have tested several of Tim Bakers 1 1/2" slight bendy handle red oak bows and they were right up there close to the 170 fps mark. No real difference form a well made stiff handled self bow.

[loon]

By D bow, do you mean D cross section or even tiller flat bow? Circular tiller? The safest cross section depends on the wood? I guess weaker at tension would be flat on belly, and weak at compression flat on back??? or the other way around..

I really am wanting to try to make a 61" or so nylon cable backed bamboo static recurve as my first real bow, might be almost 2" wide at the widest though with a near pyramid tiller. bets that it'll blow up? no idea how heavy i could make it :| if that fails i'll just try a simple bhutanese style cable back

[fsubobcat15]

Some questions.
Width of bow?
Length of bow?
Draw length?
Non bending handle length?

Made many a red oak board bow 1 3/8" to 1.5? but they bent in the handle.

Jawge

To answer your questions pertaining to bow specs:
Length: 72"
Width: 1.25" at middle down to 0.5" at tips
Draw Length: 28"
Non bending handle length: 12"

Like I said in my first post I followed the design off of Go Geronimo's Youtube page, definitely didn't work the handle down enough which as y'all have pointed out leads to high stress over low surface area.  I'm guessing he did work his handles down more and I just missed that part.