The Importance of Tiller

[upstatenybowyer]

We all know that a good tiller is a good thing. In fact, we all know that a good tiller is arguably the most important thing. However, and correct me if I'm wrong, we don't often talk about why it's so important.

My understanding is that when the tiller is perfect (if there is such a thing) every bit of wood is exactly where it should be. When the string is released, all of the potential energy goes directly into the arrow. No energy is wasted. Thus, no hand shock, no stacking, straight arrow flight, ect.

I'd love to hear your thoughts on this, if you care to share... 

[willie]

When the string is released, all of the potential energy goes directly into the arrow. No energy is wasted

I am still looking for that tiller 

If you want max performance and efficiency,  you need to getting all you can out of every part of the working limb. a poorly tillered spot in such a design breaks down faster than if the whole bow was overbuilt

hmm, that response begs the question a bit, does it address your question?

[DC]

I've always looked at it as a longevity thing, spread the load out evenly like the "Parsons Carriage". I'm not sure but I think any inefficiency is kind of inbred into the wood, the hysteresis of the stuff and I don't know if the tiller would worsen/improve that.

[upstatenybowyer]

These replies are great fellas. Not looking for any answer in particular, just wanted to hear what ya'll had to say. Thanks!

[Del the cat]

Simple:- bad tiller means one bit of the bow is stressed more than the rest... that's where it will break, maybe now, maybe in a month...
Probably just when you've been presented with the only clean shot of the day...
A chain is only as strong as the weakest link... all the other links are just adding unnecessary weight!
If it doesn't actually break, it will take a load of set and shoot with the crispness of a Christmas pudding...
Del

[joachimM]

When the string is released, all of the potential energy goes directly into the arrow. No energy is wasted. Thus, no hand shock, no stacking, straight arrow flight, ect.

The very best primitive bows, with a tiller as perfect as can be, have an efficiency of c. 80%. Energy waste is inevitable, due to hysteresis for example (internal friction in the wood), and because part of the energy is required to return the limbs as well (they aren't mass-less...).

Stacking is not a matter of poor tiller, it's just a mechanical leverage thing. As the bow is drawn further, the effective lever length (giving mechanical advantage) decreases. This is more pronounced in short bows, as the draw length relative to the bow length is higher. A very short bow (50") drawn to 28" will have a 30% leverage length decrease. A longer bow (70") will only have a c. 10% lever length decrease.

Hand shock is not necessarily a matter of poor tiller, but also (and mostly) of bow design. A Meare Heath design, even though tillered perfectly as per its front view, will always have plenty of hand shock with light arrows because so much mass is present in the extremities.


just my thoughts.

[Stick Bender]

Wow for a simple stated thread ,there is a lot in there I would argue the wood is as important or even more so then the tiller , you can have a perfectly tillered bow but it will be temporary if done on crap wood we have all been there ! Theoretically if you have the correct dead flat taper for the type from fade to tips the bow should be tillered correctly but sense wood varys in strenths it doesent always work but I have noticed the bows that come off floor tiller with little adjustment perform the best and hold the most reflex , so to answer part of your question in my humble exsperience the bows that are 95 % tillered before long string put the least stress on the wood via tiller and get better performance !

[upstatenybowyer]

That makes sense joachimM. I've always had trouble understanding hysteresis and this helps a bunch. I appreciate your thoughts. 

Stick, very good points indeed. It's easy for me to start thinking of everything as if we're working with man made materials, but we're not! The individual piece of wood and it's subtitles are what make this hobby so cool. 

[leonwood]

Good tiller is really important, as Del said, strain the bow evenly so every part of it works equally hard.
But the most important thing to me about tillering is matching the tiller shape to the limb profile AND matching the profile of the limbs to the capabilities of the wood you are working with.

Just finished a mulberry flatbow (finish is drying now). First bow I really tried to combine all this and used Badgers mass theory on and it as well.  Amazing how well it holds its shape and how light it is for it's draw weight. Will post pics and story soon.

[FilipT]

Most interesting thing to me regarding tiller question is its theory and its reality. In theory perfect circular tiller of longbow has even taper from center to the tips with width having less effect. But in reality wood is denser at some places and less dense in other. Not to mention possible deflex or reflex in limbs or combination of both! That really complicates stuff.

I will use my hazel longbow as recent experience. Before I even begun to tiller it, I spent a lot of time getting taper correct. So think of marking equal decrements in thickness over intervals of 10 cm to the tips and checking them with calipers. I wanted to simply minimize tillering procedure.
So what happened is when I put my "perfectly shaped" bow on tiller there were a lot of unevenness. Bow was reflexed with upper limb having also a deflex because of kink. That really messed it up. After much correction I managed to get final shape.
Now when I took calipers to the bow to measure thickness, the result is thickness being different between upper and lower limb. Also you can see that rings have different look on one limb compared to other.

So bottom line for me, in theory you can shape bow perfectly, but if the wood is in any configuration apart from straight, knotless stave, you will have to work on tiller to get it to bend evenly.

[Badger]

  You could probably write a book about tiller and you could not separate it from design. The energy used to propel the limbs forward is not all lost energy. The mass in the limbs sucks out some energy but can also be sucked back out by the arrow as it gains leverage over the limbs if string angles are low enough. The more momentum the forward moving limbs have the harder it is for the arrow to regain control over them. This is why keeping out limb mass low is so important. Another thing is limb distortion, If a limb has to much working area all working at the same time it gives the limb an opportunity to distort at the end of the power stoke. If it cannot distort the arrow can suck more energy out of it. Shorter working areas in the limb address this and I suspect that a limb unwinding kind of like a fly rod can do similar on some of the deep cored bow styles. Hysteresis is one of our major power losses, it can be over 10%! It can also be reduced by up to 90% using good tillering techniques and proper design. This is why we have been experiencing some very high performing light bow recently. The limbs were not overstressed and hysteresis was very low. 

[George Tsoukalas]

I agree with Flip. What is important is having a perfect tiller for the stave as the perfect picture tiller is not always what the stave needs. For example, if knots are present that area should not bend as much as the rest if the limb. Jawge

[Badger]

     Checking your set in a bow is not as simple as simply measuring the difference between your starting profile and your finished profile. The part that used to puzzle me was how do you tell the difference between a bow taking true set and a bow that just didn't hold the profile you gave it. The easiest test of this is to simply see how much of the profile returns after the bow rests. A bow that keeps the same shape after resting as it did when first unbraced will suffer less negative affects from set than a bow that keeps regaining its profile after resting.

[Dances with squirrels]

'Good tiller' to me means not only that each part of the limb is contributing equally to the cause as I see fit, but also, and equally as important, is that the limbs are balanced with each other as it's drawn relative to the archer's holds on bow and string.

Even if each limb flexes evenly along its length, and on the tree both travel the same distance with everything held and pulled on center, one could be considerably stronger in the archer's hands at full draw. If unbalanced as its drawn, that bow could be tillered better... for him, at least. And tillered better/better balanced in strength means the bow is more predictable, tiller won't shift, the bow is more efficient, less hand shock, less noise, arrows fly better, the bow is easier to tune, etc. You know, the good stuff about bows

[BowEd]

Well put and good subject.It's been said before but true bows that take less than 1" of set while tillering and after shot in are longer living bows/more resilient with no adjustments put on them later from any tiller shift etc.It'll show ya if it likes the design and weight.To me realizing where along a limbs length that it does the most work is crucial for this to happen with a given design.Putting enough wood there to handle the stress and less where it's not needed.