Author Topic: Need help to correct a propeller twist...  (Read 1193 times)

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Offline diegofabbri

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Need help to correct a propeller twist...
« on: May 01, 2020, 10:08:24 pm »
Hello........
I want to thank all this sharing.......
this is my first post......making my fifth bow now......

it is a Mollegabet/Hjarno.......69 inches long, 1.5 wide made from a short board of a dense hardwood found in the street......
I bandsawed it in two halves and joined them with a W-splice.....

It thought the board had straight grain.....but I didnt read it well.......
seeing it from the front view shape.......the wooden fibers are not following the center of the limb....

everything went well unstrung........until I braced it....

braced it has a propeller twist......

I am thinking about removing wood from the strong side....

but I am still confused on which side is weak or strong!...... 

so, I took a (bad) picture showing the propeller twist.......with a red tape and blue tape showing the low side and high side of the twist....

which side should I remove some wood to correct the twist?

« Last Edit: May 02, 2020, 07:14:19 pm by diegofabbri »

Offline Ricardovanleeuwen

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Re: Need help to correct a propeller twist...
« Reply #1 on: May 01, 2020, 11:51:38 pm »
If you look at the belly, the side that is the closest to you is the strong side

Offline Corvus

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Re: Need help to correct a propeller twist...
« Reply #2 on: May 02, 2020, 01:34:04 am »

Edit: like stated above. I was just judging off thumbnail which showed the picture flipped 90 degrees

Don't know if it is the angle messing with my perception. Limb closer to you looks a fair bit stiffer than the other limb as well.
« Last Edit: May 02, 2020, 01:43:12 am by Corvus »
Don't worry, we got yew!
-PNW

Offline Del the cat

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    • Derek Hutchison Native Wood Self Bows
Re: Need help to correct a propeller twist...
« Reply #3 on: May 02, 2020, 02:08:40 am »
There is very little real "twist" there is maybe a sideways bend due to misalignment of the limbs/levers.
I often say "solving problems is easy... the hard thing is working out what the problem is".
I'd bend the levers at the root with some heat to get the string line running true along them.
bend the lever nearest the camera to the right and the other a little to the left if necessary.
Levers, being narrow and deep can bend sideways if they are not lined up properly.
There's a picture in this post from my blog, showing how I have a bow hanging from the centre of the string checking the lever alignment.
https://bowyersdiary.blogspot.com/2015/10/bits-and-bobs.html
Del
« Last Edit: May 02, 2020, 02:13:16 am by Del the cat »
Health warning, these posts may contain traces of nut.

bownarra

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Re: Need help to correct a propeller twist...
« Reply #4 on: May 02, 2020, 01:03:43 pm »
The blue side of the limbs is the stiffer/thicker/stronger side.
A limb always twist towards the weaker side because it doesn't have the resistance to bending that the stronger side has thus the limb is twisted over towards the weaker side. The weaker side being less able to support the load being placed on it.

Offline diegofabbri

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Re: Need help to correct a propeller twist...
« Reply #5 on: May 02, 2020, 02:23:19 pm »
yes the picture came out totally distorted.......will try posting another.....

thank you Bownarra.......I was thinking that too........

the blue side of the limbs is the strong side.......as it bends less than the red side (seeing it from the string)......

gracias!
« Last Edit: May 02, 2020, 07:16:16 pm by diegofabbri »