Tillering help - Full compass longbow

[dobson]

Hey guys, not sure exactly what is going on here bow is drawn 30" but the right (top limb) seems to be very off not sure where exactly I should be taking wood off

https://drive.google.com/file/d/0BzK_zsquTPH_d05lX0R0VWZKVUU/view?usp=sharing

Any ideas?

[BenBen]

I would suggest you to ease off the outer half of the top limb, and maybe just a bit at the handle If the top limb seems really too weak compare to the bottom limb (which will probably be the case), remove some wood all along the bottom limb as well.

Ben

[PEARL DRUMS]

Your drawn line as compared to the actual bend tells you all you need to know. Where that gap lessens is where it needs to bend. The wider the gap the more its bending, and vice-versa.

[DC]

I'm a little unsure of this but if you use a clock face for directions I see a flat section at 12:30. Like the handle is too wide on one side. Is it possible that a little scraping at 12:30 would bring that side down to match the circle? The right side would still be bending more than the left though.

[Del the cat]

Middle 1/3 of right limb (and to a much lesser extent the left limb) is weak.
It depends how much weight you can afford to lose.
The centre doesn't seem to be working much, I get the middle of a bow just moving a hint at full draw weight and work outwards. If you ease off the centre now it will drop some weight.
I would ease the centre a tad, then ease off the left limb a whisker on the inner and outer thirds. The right limb should then be looking slightly stiff by comparison. That will allow you to ease off the right limb outer third to get it coming round.

Basically take a tad off everywhere except mid limbs, but it's important to do it in the right order. Also only remove half of what you think you should 'cos each small change will effect the rest of the bow , and the next change will effect the previous change!
Del
BTW What's the draw weight and whatdraw  weight/legth are you aiming for?

[Hamish]

 The amount of set in the unbraced stave will also help you work out if the bow is bending too much in a certain area or a limb is too weak compared the other. 

[mikekeswick]

For a start a longbow shouldn't be an arc of a circle tiller...... Also don't pull it so far when the tiller is off, that weak spot has just been heavily strained by pulling it that far. The weak area will lose elasticity when strained so much (set) and you may well end up playing 'catch up' now with this bow.

[dobson]

Lots of really good replies and advice! so ill try and answer them all


Took timber off as recommended by Ben Ben and followed Pearl Drums simple adage (really helped me get my head around how to use those lines on MS paint, thanks!)

Unfortunately, I had already started work before I saw Dels sage comments, but the changes I made are not far off - I am hesitant about having too much bend near the handle because of hand shock but I'm willing to try it

Mikekeswick - what should it be? I heard for a "medieval style" bow it should be "full compass" and you are quite right it has been carelessly tillered, - what you get for rushing I suppose.

To give the context to this bow it was one that I had written off for lack of a better term because it was way under the weight I was wanting (60#) so it's been sat in the corner for a while, I decided to work on for some experience and because something is better than nothing (hence some of the rushing,I had nothing to lose), currently it is pulling just under 30# at 30" and has taken a fair bit of set  I might donate it to a friend provided it doesn't blow up before then.

Heres where I have got to - slight improvement, but every change to the tiller is sapping the draw weight

https://drive.google.com/file/d/0BzK_zsquTPH_amZhWGt3TENiVHM/view?usp=sharing

[WillS]

The tiller is still a long way off - as said above, you definitely shouldn't be pulling it that far until it's absolutely perfect.  It's gonna be taking lots of set and losing performance the whole time you're heaving it back beyond the necessary drawlength.  The issues with that tiller should be visible at around 18" or so, which is where you should be stopping until it's pretty much flawless.

Your red lines show exactly where it's bending too much, and not enough.  Take wood off both mid-limbs until the red lines you're drawing sit smack in the middle of the bow.

Mike's point about full compass longbows is true in some cases, but not always.  Depending on how you want the bow to perform, how long you want it to last, what poundage you're after, what woods you're using and what the front profile looks like dictates the final tiller shape, in an ideal world.  There's nothing wrong with having a perfect arc of circle tiller shape, provided it meets the particular bow's design brief.