Close to full draw - tweaking the tiller?

[Tommy D]

Ok ... so another bamboo backed ipe. This one has static tips for 5 inches using kerfs. I slightly whip tillered it and then glued it up in a form with the bamboo backing. Unbraced it has about 4.5 inches of backset/ reflex at the moment. I have got it bending close enough to put a string on but can see one limb still a bit stiffer than the other. I can also see that stringing it induces quite a bit of twist to the point where I am worried the string will pop off and the bow will flip inside itself. It is still about 45 pounds at brave height and I am going for 65 - at 31 inches - so have a bit of wood to remove ... but I can feel I have hit that point where a little wood removal is having a big effect.

I don’t want to take wood off the wrong place to correct the twist. Can you all help me get it right?! I have read the tutorial that says the tip bends to the weaker side so take wood off the opposite side? Or file the string groove deeper on the weaker side?












Any advice greatly appreciated. Thanks

[Hamish]

When you have twist, it means the side that bends away from straight is weak. Therefore you need to remove wood from the opposite side to straighten it. Weaken the strong side and the tip will start to bend towards that direction.

In the pic with the view on the belly along the length, you would remove wood on the right side of the belly at the tip.

You have to exercise the bow regularly when you remove wood otherwise the change can be too dramatic and you overcompensate to the opposite direction.

Also you have to pay attention to what's happening along the entire limb at the same time as you make corrections to the twisted spot.
You can unintentionally create a hinge.
Think of it as removing more wood at the tips, if the bow had no twist. The tip will start to bend more than the rest of the limb along its length. Therefore you will likely need to remove wood along the whole length. You want to do this evenly along the belly and then bias removal on the tips strong side.

Stay aware of how the good limb is bending whilst all this is happening, you might need to slightly weaken it if the other troublesome limb needs a lot of work.

Will you get it perfect? Maybe,  maybe not. It depends on how much sideways set has already taken place. You will definitely get an improvement, that you can live with.
Good luck Tommy, I really like the shape of your bow. Very graceful. Hope it turns out well.

[Tommy D]

Thanks Hamish. This is one of those I get it but I have to see it ones. I  sure I fall in the “I find this counterintuitive” group.

Anyone know why I can’t see images on the “Mechanics of Limb Twist” post?

[artcher1]

I've corrected many tips like yours using a heat gun. Placing the tip in a leather padded vise, I'd heat the curve and gently over-twist. Making sure to not move the bow up or down to preserve the recurve as it cools down. Surprisingly quick and easy to do...Art

[Eric Krewson]

It depends on what kind of glue you used, I think TB3 and Unibond can stand some heat, You don't want your lamination to turn loose. You will never get that kind of twist out of a limb by removing material, get out your heat gun.

I do like Archer 1, I call it the heat and tweak method, heat the limb portion you want to twist, put it in a padded vise and give it a quick twist in the opposite direction from the offending twist. Take it out of the vise and see where you are, repeat as necessary. Once you get the limb where you want it, let it cool, it doesn't need to be clamped to anything while it cools, it will hold its shape.

When I am tweaking a limb I don't tighten my vise on the limb, I keep the jaws loose so I can put the limb in and out of the vise quickly to check my progress a tweak at a time.

I use these pads on my vise, they hold a lot of area.

[Tommy D]

Eric and Artcher1 thanks - will heat work on epoxy? I’ve used the GFlex and it was post cured to about 140 F. I know that to some degree epoxies can be reheated and when cool they return to somewhere near their original strength.

I took some time to get my head around limb twist and I made a few disposable slats to practice on. Based on this and some good advice on this forum (thanks Hamish) I seem to have brought my tips back in line by reducing weight. Bow is still heavy - so now I have to try and keep everything in line as we go. This is the most backset I’ve ever tried to tiller so am taking it slow. Still amazed how much scraping I did for no change and then suddenly the slightest scrape makes a big difference with this Ipe.

Some images ... not at full brace. It’s about 50lbs at 20” now. The tips have come across. I have found it helpful to twist the limb with my fingers in different places with the bow braced - I figure this simulates weaking and stiffening a limb -similar to what  I do the same to try and get the top and bottom limbs even. This has helped a little to know where to try and even the twist. I definitely think that it’s not necessarily right where the twist is that is causing the issue. I am also going to start double wrapping when I do the glue ups - I feel like I have induced this “torque” in a few bows with the rubber inner tubes





Eric - Off topic - I see you are into muzzle loaders? We still come across subsistence hunters/ poachers (depending on which side of the fence you are on) who are using muzzle loaders that are copies of some of the ones from the old Arab slave traders. They are still made (illegally) by village blacksmiths using a Land Rover steering rod as a barrel. I will PM you a few images if you are interested. They also cook their own powder from soil collected in caves where rock hyraxes live and then they make their percussion caps from match heads.

[Eric Krewson]

I don't know about your epoxy, someone else may chime in.

[Tommy D]

55lbs at 26” .... thoughts? I was thinking of taking a bit more off towards the handle and smooth out the right limb slightly
 

[Hamish]

How does the side profile look when unstrung? That should help tell you where its taking set, and where it can bend more.

[Tommy D]

First image is before tillering, second is now after tillering and resting over night





I think it has taken about 2 inches of set overall - and most of that is about a third in from the tips. This seems to be consistent with what has happens on the other couple of bamboo backed R/D bows I have tillered. Not sure if that’s a good thing or not!

[Tommy D]

 Few more pics - I reckon that’s about 29 inches now at about 55#. Hoping to get to 32”. Thinking it’s a little whip tillered and a bit more needs to come off inner limb.









Was also wondering what the consensus is on nodes? Does one leave them untouched or can one take the ride off them?

[Hamish]

Looking good, but you are right if you want to increase the draw you need to get the inner limbs bending a bit more.


As for the bamboo nodes its safer to leave them untouched. Anything more than a light sanding with fine sandpaper invites trouble on most types of boo. Tonkin cane seems to be the exception.

[DC]

Lots of people sand the nodes off, I'm with Hamish, I never touch them.

[spyder1958]

Looks like the bottom limb is bending more.

[Tommy D]

Been tweaking the tiller a little with sandpaper now.  This is 29 inches at 55#. Aiming for 31. Any suggestions much appreciated. I struggle to pull more than 29 - but here are some pics of me and also on the tree.