Thoughts on tillering

[Badger]

  One aspect of tillering that a lot of us may do unconsciously is the monitoring of the condition of the wood by picking up on small amounts of set early on. The most common form of tillering is to evenly distribute the load. This is probably the overall best way. While we may not have monitored the process closely in the initial bow we were building it will help us to determine design changes we may want to make in our next bow. Now if we are looking to squeeze out a few extra ft per second by reducing working limb area then monitoring becomes more important. If we can detect small amounts of set early on we can make adjustments early on by employing more working limb area. Very often have set out to build a 120# bow for instance but careful monitoring of te wood forced me to back off all the way down to maybe 80#. But if you are dead set on the building say a 50# bow, then all you can do is try and distribute the strain better.

[Selfbowman]

Yes I agree on the design side of it . Steve You build a 80# bow 1” wide and you will have more set! But I think we are trying to address a normal bow design for example 67” Osage bow 1-1/4 to 1-1/2” at the fades 1-1/4” at mid limb.  With less than 1” of set.

[Kidder]

The question I have about your premise Kidder is, to what degree does it make a difference? I think as people gain experience making bows, the tiller starts out even earlier in the process. I have seen or at least heard of bows failing later in the process where, even though final tiller looked good, there was a hinge that later broke the bow or failed in compression. A though experiment might be, how much would a bow that was tillered very carefully through normal means differ in performance/set from a bow that was cut perfectly to shape from the beginning? The only example I can think of would be bows by David Dewey where he used his spreadsheet to create dimensions and cut out the bow. I know Steve (Badger) tested one such bow and it was fast for the time.

I’m not sure we will ever know to what degree. I think we can say it’s noticeable though. Where the  importance of the “process” over the end result became apparent to me was when I started using one of Eric’s tillering gizmos. I don’t believe that the final tiller is any better than I would have achieved before, after all the last few inches is done without it anyways, but you definitely get there quicker, and somewhat surprisingly given that it’s used on a tree rather than a pulley rack, you get there with less strain. The bows I’ve built since adding a gizmo to my process show substantially less strain when unstrung and maintain more even set and a higher degree of induced reflex.

[SLIMBOB]

Tillering for me is more than just shaping the bow. It starts early in the process. How do I want to lay this bow out on the stave. What style and in what dimensions are best with the material I have. Then for me, it’s a slowed to a crawl process as I start taking wood from the belly. I want the shape I’m going for at the end, to be present from the beginning. If it takes hours or days, I won’t go farther than low brace, until it’s close to perfect. Then the end result will typically, if all goes well, settle into place. I’m patient to a fault early in the bending phase.

[Gordon]

One of the big insights I had over the years is that it is not necessary or helpful to over exercise a bow during the tillering process. I recognize that you may have to exercise the wood somewhat to register changes to tiller, but it is less than is commonly believed. For me, the keys to a good tiller with minimum set is to establish a tiller that evenly distributes strain along the limbs (with the exception of tips which I leave a little stiff until the end) as soon as possible with as little bending and exercising as possible. It helps if you are skilled at monitoring limb thickness taper using your fingers - I can usually feel where I need to remove wood without having to bend the wood enough to visually reveal an emerging concern and that helps preserve the belly. When I'm satisfied with the general tiller, I begin removing wood more or less evenly to hit my target draw length and weight while carefully monitoring for changes that may lead to problems. When I'm within 5# of target weight and 1 inch of draw length I adjust the thickness of the tips and remove all tool marks and that usually gets me to target. Then the gloves come off and I exercise the crap out of the bow to make sure that the tiller is stable, and the bow is durable.