Osage "driftwood" short bow, part 4 - tillering

Now the long but critical part: Tillering.

For those who don't know, tillering is the art of removing wood carefully from the belly (and sometimes sides) of the bow to reduce thickness and/or mass in order to get the wood to bend in the way needed for the particular bow profile. (This bend might be circular and bend through the handle for bows with a straightline taper or it might be elliptical for longer bows, bows with limbs that have a more parallel taper in the midlimb, or bows with a stiff handle. It is also possible to create stiff or "whip-tillered" tips for different reasons.)

Rather than bore one with all of the details, here are some photos of the bow in progress, from start to close-to-finished tiller. Because this particular stave had some dips and whoop-de-doos that fooled the eye into thinking that they were hinges (weak spots), I found it helpful to take a series of photos and then to draw an ellipse or circle over them using the computer in order to see the weak and stiff spots better.

First, the bow braced with only a rough tiller followed by drawn to 40# @ 22". Note the stiff tips and slightly stiff lower limb (left in image):

The next photo is after quite some time tillering. It shows 25 inch draw and the drawing of the ellipse I mentioned. Because the limbs want to pull off center, I had to lighten the tips and narrow the handle a bit, lowering the max draw weight. At this point, I theorized it would probably come in more like 45 @ 28 after all of the sanding, rounding over edges, break in, etc. as it is close to 43 @ 26.

The overdrawing of the ellipse shows well that although it is pretty close to final tiller, the bottom limb (left in the image) is still stiff out near the tip and the upper limb has a slight weak spot (though it looks worse than it is because of the front to back whoop-de-doo in the limb):

At this point I was slightly disappointed that the mass was still as high as it was for the draw weight it appears to be coming in at. I think it has a lot to do with the fact that the rings are not particularly thick/wide and that there is more porous early wood, i.e. it is not the best osage. However, heat-treating the belly might squeeze a few more pounds out of it yet.

A couple of pictures close to final tiller:

Tips are still slightly stiff, but I didn't want to free them up too much, because at full draw (28") it would increase the angle between the string and arrow and cause finger pinch. Tillering shorter bend-through-the-handle bows is a little different than tillering longer bows.  Tim Baker's general tillering mantra from TBB (Traditional Bowyer's Bible) vol 4 is

Make inner limbs wide or long enough for virtually no set. Make midlimbs wide enough for little set. Make outer-limbs and tips narrow enough for lowest possible mass.

BUT, as Baker notes regarding short bows:

Unless designed for short draw, short bows must bend more in the inner limb, far more so than long bows. Whip-tillered shorter bows become shorter in tip-to-grip length during the draw, increasing string angle at full draw, increasing stack and reducing energy storage even further than typical for shorter bows. So mid and outer limbs should bend a little less, inner limbs a little more. (p.127)

Of course, too much bend in the middle or through the handle would shock the hand and, I imagine, cause accuracy to suffer. Bow building is certainly a matter of compromises.