Beginner question about tillering (too thin)

[selectfluor]

Hi All,

I've recently decided to make my first flatbow (25", 30-40 lbs), but now I may of made a rookie mistake, by tillering the bow to thin. Starting from a 63" red oak board (18 mm x 42 mm x 1.8 m), I managed to get the limbs to taper from 15 mm to 10 mm. However, when I tried to bend the limb, there wasn't too much bend, so I decided to tiller it more. Unfortunately, it is now 10mm and tapers to about 5mm, which i suspect is too thin.
My questions are, how thin is too thin and can this be fixed by adding a backing (jarrah, red oak or bamboo). I also apologise for using metric measurements, i have no idea how to convert those into those inches with fractions.

Thanks

[Josh B]

Don't worry about a set measurement for thickness.  Every piece of wood will be different in how thick it needs to be to achieve your desired draw weight.  Even within the same species of wood.  Once you get the profile shaped and a good floor tiller, you only remove wood to make the limbs bend evenly and equally until you get it to your desired draw weight at the desired draw length.   You check that by bending the wood and seeing where it needs to bend more not by measuring the thickness.  This iincludes tillering from the long string to brace to full draw.  Wood is too varied to tiller by blueprint or recipe.  That being said, if you're in the process of tillering and believe the limbs are getting too thin and you still have draw weight to lose, you can tiller from the sides of the limbs.  If you haven't already removed so much wood that your underweight, you should be fine.  Josh

[Pat B]

Exactly what Gun Doc said!
 If your bow does come in under weight, continue tillering. That is the hard part of bow building and it usually takes someone a few bows just to get that part right. Once you are there achieving weight is easier.

[George Tsoukalas]

There is a red oak board bow buildalong on my site. You can modify the width to 1 3/8" for a lighter bow.
Jawge


http://georgeandjoni.home.comcast.net/~georgeandjoni/index.html

[Pat B]

Read George's site. It will answer most of your questions and we can help translate what you still don't understand.

[paco664]

Read George's site. It will answer most of your questions and we can help translate what you still don't understand.

+100.. gold mine of info there

[okie64]

Im not real savvy on metric conversion but to answer your question it does sound like you have it too thin already to reach your desired weight. You said you have it tapered from 10mm down to 5mm which would be a little under 3/8" to a little under 1/4" thick. Unless it is completely tillered at this point you're probabaly gonna end up with about a 20lb bow.

[arachnid]

Not sure about red oak, but with white oak of that length, 5mm of thickness all along the limb with a pyramid taper, is well enough for a 40# bow. At that length I whould suggest making it bend in the handle.

[RyanY]

Not sure about red oak, but with white oak of that length, 5mm of thickness all along the limb with a pyramid taper, is well enough for a 40# bow. At that length I whould suggest making it bend in the handle.

Even my thinnest and lightest bows are no where close to 5mm thickness. For the width necessary to get that poundage it would be a nightmare to tiller.

[arachnid]

Not sure about red oak, but with white oak of that length, 5mm of thickness all along the limb with a pyramid taper, is well enough for a 40# bow. At that length I whould suggest making it bend in the handle.

Even my thinnest and lightest bows are no where close to 5mm thickness. For the width necessary to get that poundage it would be a nightmare to tiller.

I'm just finished tillering a white oak board pyramid, 2" wide fades tapering to 1/2" tips, 64" TTT, about 5mm thickness and it came out 40#@26".
Not my first white oak pyramid coming out like this...

[selectfluor]

Thanks for the info and I've bookmarked George's site, and will be referring back to it. I'll see how much weight the bow can pull over the weekend, before considering restarting.

[mikekeswick]

That's the densest white oak in the world then!! Keep hold of it!
There is no way a 5mm thick slat will give you a 40# bow - even out of ipe!
5mm = 0.196850394 inches   that's less than a fifth of an inch....I suspect there has been crossed wires in conversion somewhere

[arachnid]

Damn it... I'm soooooo dumb!
I got comfused with inches and milimeters.... my bow is 1/2" thick and I got it mixed up as 1/2cm (5mm)...

Oops..... sorry about that...

[Pappy]

Yep 1/2 inch sound more like it.
  Pappy

[crooketarrow]

  You can shortin it a couple inchs and start over shaping the limbs.
 Or you can sinew it. My advive is to set it in a corner to make a kids bow out of it later.
  And start over on another bow. Remmber when you get to tillering. Go slow the only rush is what you put on it.  Go slowwwwwwwwwwwwwww
  You can't build a bow from measerments. General idea is all. All  staves or boaders are different even from the same tree.