Slow Learner recuring limb twist.

[DD9000]

Ok, I have asked this question before but I will ask again as I cannot seem to get this to work reliably yet.

I am still really new at this, but I have made a couple successful board bows for myself and my kids.
However every one has suffered from a propeller twist on the limbs to one degree or another.
I figure I must be doing the same wrong thing each time so since this occurs each time.I am curious what would lead to this on each an every one.

It is always the same thing one limb will twist one way and then the other limb will twist the opposite way.
The string will mostly track down the center when first braced  and since they twist the opposite directions it still mostly passes the handle in the middle even when drawn and the twist is at it's worst.
But what could I be doing so reliably to get this opposing twist all the time?   :confused:  

I would like to avoid all the trying to fix a twist and just plain not introduce it in the first place since I don't seem to be able to do that well either.

David

[Art B]

Is this a bias/quarter/flat sawn cut board?  Art

[razorback]

My guess is that you are being strong to one side with your scrapping. I tend to scrape the right side of the limb too much and have to concentrate to avoid it. You are probably doing the same thing. Scrape the limb strong on one side and flip it around and do it again on the other limb and Pow you have propeller twist.
measure the thickness of your limbs and see if the strong side of each limb is thicker that the other side. This will tell you if this is the problem. Good luck and let s know how it goes.

[macbow]

That's my guess also.
Was using drum sanders and my guy always held it to one side.

[DD9000]

The latest piece is a nice quarter sawn board.One of the nicer ones I have found in a while.

I do tend to do all my scraping from one side of my Table\\Bench so perhaps that is it that I simply am more enthusiastic about one side and then flip it...

I guess I am just looking for an easier answer when there is likely not one.   :p

Thanks for the ideas. Maybe I need to just switch to the other side of the table and try to keep them even that way.

David

[macbow]

Have you been able to use a caliper or something to verify that is the reason it's happening?

[Pat B]

Put the bow limb between your thumb and fingers and feel the thickness along and across the limb. You will probably feel the thickness difference. This is quite common problem especially if you are working from a work bench.

[DD9000]

I bought a pair of small calipers and tried to measure every 5 inches down the sides on this one and still have the problem.

I try to run my thumb and forefinger down the sides as well. I find I can feel the differences although I am not good at evening them out yet.

I wonder if perhaps my bench is not quite level I may look at that....


David

[macbow]

David, like was stated above there is a natural tendency to be off kilter
. Just have to be aware of it and check often.

[Art B]

You can eliminate any strong/weak sides by using a slight crown back/belly or both..........Art

[critman]

DD9000-I've had the same problem on my last bow. Blamed it on grain not being perfectly straight. Took the time to put the calipers on the limbs and guess what? WAAAYYY off on trying to keep limb thickness the same on each side. I clamp my bow on a work table and see where the "too much scraping on one side" deal really comes into play. Makes perfect sense. Will fix that bow tomorrow.

[DD9000]

Thanks everyone. I hear you, I'll get the calipers back out and measure every inch and see if I can sus out the uneven sides.

David

[Pat B]

Your fingers will be more sensitive and quicker than dealing with calipers.
 The problem when working from a work bench is that one side is easier to get to. Flip the bow to get the other limb and the opposite side is easier to work on giving you a stave that will propeller twist as you draw it.
I get my staves to floor tiller stage from a vice on my work bench but then move to my Stave Master(or bow horse) for the rest of the tillering so I'm assured of even wood removal.