Tillering question.....

[Stingray45]

I have a quick question to put out there. I've seen guys mention when tillering right after floor tillering and bringing to brace height to put the bow on the stick and pull to the desired draw weight. So say you want a 55#@28" bow you should put it on the stick and pull it to 55# which could possibly be @15" to start. Then you just work from there to get it pulling to 28". My question is what if I want say a 60# bow and when I put it on the stick it's getting to say 58# at 14" but I feel like it's going to break if I pull it any farther. How do I proceed? All feedback is welcomed and appreciated. Thanks.

[George Tsoukalas]

With that method  you have to make sure the limbs are bending well and evenly before you pull to target weight. If you feel they are not ready then don't. See the thread "Tiller Check Please". Also take a look at my site.
http://georgeandjoni.home.comcast.net/~georgeandjoni/
Jawge

[adb]

As you're tillering, to avoid unwanted set and other nasties, you shouldn't pull the stave past your final intended draw weight. However, that doesn't mean on the first pull. You need to teach the stave to bend, and that takes time & patience. I've been making some heavy weight bows lately (100+#), and I certainly wouldn't pull the stave to 100# until fairly late in the tillering process, otherwise I'll end up with very expensive firewood. Dean Torges calls it "chasing tiller"... work your way slowly and patiently to your final intended draw weight and length. Put the stave on your tiller tree, and each time you remove wood from the belly, exercise the limbs slowly up through your weight range... 10 pulls at 30#, 10 pulls at 35#, 10 pulls at 40#, etc., up to whatever your final weight will be. If you fell stacking, stop. Listen to the wood... it'll tell you what it wants to do, or not do. Sometimes i may not get to my final weight, if the wood isn't up to it. If the stave is starting to take >1" of set, you're pushing too hard.

[snag]

What does "set" mean? Is that when the limbs stay bent a little (in this case 1") after you let down on the tillering string?

[adb]

There are two different terms to describe a bending of the limbs (at rest) towards the belly. Set and string follow. They describe the same thing, but in different ways. Set is the permanent deformation caused by tillering. String follow is usually temporary.

I'll try to explain the difference. After bracing and shooting a bow, and then unbracing it, the limbs may follow the string 2", but after resting for a period, the limbs may only follow the string 1". This permanent deformation of 1" is set, where as the temporary deformation of 2" is string follow.

Set will rob cast, but makes the bow much sweeter in the hand, and more forgiving to shoot. I shoot for about 1" or less of set. Excessive set can be caused by: high moisture content, rushed tillering, uneven tillering, or poor bow maintenance. To avoid or minimize set: patient and careful tillering, never pulling past intended draw weight or length, being kind to your wooden bows, heat treating, and proper maintenance.

Minimal set is good. Don't sweat some set!

[Del the cat]

I'll just add that you do need to be pulling a force somewhere related to the final target weight.
I've just been tillering a Yew longbow and trying to take it easy, I got the string shortened to about 4" BH, and pulling it back to 40 pounds, however I'm aiming for 60. By the time I'd corrected the tiller at 40 It was back to 28 at 55# whoops!
Mind I'll fix it by taking the deflex out of one of the limbs (it was one of those S shaped stave one limb deflexed, one reflexed).
But I'm going to be struggling to get her pulling the full 60.
So to sumarise, it's no good getting to BH at 20 pounds if you want a 60 pound bow.
You gotta pull the full weight eventually, but obviously it needs to be when the tiller is at least passable.
BTW, I'll be tillering longbow right back to 32" 
Del

[adb]

If you tiller your stave by keeping the limbs bending evenly throughout the entire process, and exercise the limb changes carefully and slowly, you will make a bow with minimal set. You need to teach the stave to bend slowly, and this requires patience. If you're getting frustrated, take a break. Remember, the draw weight usually changes somewhere around 2-5# per inch of draw. So, tiller your bow to short string as soon asap, but don't move past your end weight. Make sure before first low brace, that your limbs are as evenly tillered as possible. However, don't go to brace too soon. If you go to brace, and your bow is already pulling past your final weight in only a couple of inches of movement, you've gone to brace too soon. Going to first low brace is often one of the trickiest parts of good tillering.
So, if you want 40#@27", and your bow is pulling 40#@22", you have 5" to move, or about 20-25# of weight to lose. Keep removing wood, exercising the limbs, pulling to 40#, and wait for the limbs to move. Be patient, keep your limbs tillered evenly, and you'll get to your final draw and weight with minimal set. Check for set as you go, and if it starts to become excessive, stop, you're making a mistake somewhere, or the wood (or design) isn't up to the task. Exercise the limbs with slow, even, increasing pressure... don't yank or jerk the limbs quickly.

[adb]

One other thing, I don't use a tiller stick. I use a tiller tree only, with a pully and scale inline, so I can stand back and watch what's going on. I never leave the stave at full draw for more than a few seconds while tillering. Leaving a stave on a tiller stick at full draw for even a few minutes will cause set.