Chapter 10: Longstring Tillering
Up to now we’ve just roughly floor tillered. I also like to do a lot of this early stage tillering in a vise. Or you can simply pull your bow manually, ideally in front of a mirror or a camera.
The profiles of the bow influence the ideal tiller shape. In other words, there’s not a universal perfect tiller shape that applies to all bows.
For this design, and straight stave bows in general, a perfectly tillered bow will have limbs that bend in an elliptical shape. Sometimes that’s a circle, sometimes a more eccentric, stretched out ellipse. Which ellipse is exactly right for each of your bow’s limbs is a bit of a judgement call.
Common Tiller Issues
Here are some common tillering problems you’re likely to encounter, and how to work through them.
1. Stiff outers. Characterized by too much bending from the inner limbs and occurs if you don’t taper your limbs enough. Correct this issue by scraping wood from the mid and outer limbs. In bad cases, you’ll have to go back to the rough out stage to correct the thickness taper.
2. Whip tiller. This is the opposite of stiff outers: a whip tillered bow has outer limbs that bend too much. Correct this issue by working the inner and mid limbs. A whip tillered bow can be very sweet shooting in a mild case, and isn’t as harmful if you shoot light arrows, but in general this tiller shape will cost you some efficiency.
3. Hinges. If you remove too much wood from any particular spot, it will bend too much and might start to hinge. If you let a hinge develop too far your bow will break, or at least take a lot of set in that spot. If you catch a hinge early, save the bow by removing wood everywhere else. If you encounter this issue it may be a good idea to drop the target draw wight
4. Set. A permanent deformation in the wood due to bending. This is a sign that you’ve overstressed the wood because it’s too moist, or there’s a design or tiller issue. For more about set, string follow, and heat treating see Chapter 12.
- Try to always pull with roughly the force of your target draw weight—unless you see one of the tillering issues above.
- Always remove wood from the stiff parts of the limb, and leave the bending areas alone.
- Every time you remove some wood, the bow will pull a little further. When you hit your target draw length at the target draw weight, then you’re all done.
Before we go back to tillering, I’ll just touch up the fades a little bit. This will slightly lengthen the fades, and ensure that all the bending stays away from the glue line in the handle.
Don’t take off so much wood that the inner limbs get thinner than the rest of the limb. The inner limb should be the thickest part, and the thickness should decrease smoothly all the way from the fades to the tips.
Make sure you have a good thickness taper before you tiller. If any spots get thicker as you go from the handle to the tip, address those now, before you move on.
Since the bow isn’t ready to brace, we have to tiller it with a longer string. Personally I like to longstring tiller very late into the process, but some bowyers brace the bow as soon as they have the chance.
Every bow is a little different to tiller. Here’s the play by play for this one. To simplify I’ll be keeping the top limb always on the right side. For the best explanation watch the video.
Starting off, Im seeing too much bend on the right limb in the inner third. If I keep removing wood from that spot, I could potentially see a hinge develop. Otherwise, both limbs are stiff in the mids and outers.
Next, I scrape or shave some wood everywhere I thought was stiff, leaving alone the areas I noticed bending. Roughly 20 scrapes a side will do, or a few grams of wood. A little more during early tillering and a little less in the final stages. Better to scrape less and check the tiler more often, rather than make a hasty mistake.
Looking better, but there’s still a little too much bend in in the inner limbs. Next I’ll focus on the top limb mid and outer limb.
5 Ways to Assess the Tiller
How do you decide which areas are stiff, so you know where to remove wood? There are a 5 methods I use, each giving their own second opinion on the tiller.
The first is obvious, it’s the shape of the tiller, and how the bow moves on the tiller tree. This is the most widely used input on where to remove wood next, but its also fallible. The ideal tiller shape depends on the front profile and the side profile of the bow, so you can’t just look at a tiller shape and know if its good or not, you need more information to make a comprehensive evaluation.
The second method to get an opinion on the tiller: check the thickness taper. You can sight down the limb to get a visual sense of the taper but there’s nothing like using your fingers as calipers. Very gently pinch the limb—very gently, you barely want to touch it. Then slide your fingers along the limb like a scanner. You’ll be able to feel things that you can’t see.
When both methods agree on where to remove wood you can be much more confident about where to scrape, without fearing that you’ll create a weak spot. The vast majority of the time, if you have an area where the thickness taper is not aggressive enough (in other words the limb is too thick) then usually that will correspond to an area that looks stiff on the tiller tree. If you only use one method, its easy to misinterpret what it’s telling you. But if two or three methods agree, then you can confidently remove that wood.
Number three: Set. Once again I’ll gloss over this quickly, because set is so important that it’s getting its own chapter. For now—keep track of the original shape of the bow. Any areas that permanently retain the bend are overstressed, and are extra likely to correspond to areas that bend too much on the tiller tree, or seem to get thin too fast in terms of the thickness taper.
Number 4: look at the wobble on the tiller tree. If your bow has a stiff limb it may rock to that side while you pull it on the tree. Some bowyers like to clamp the bow to the tree, or use a wide flat bow mount— both interfere with this method. Putting a grid behind your tree also interferes with this method.
Use these four methods to crosscheck where you should remove wood, and you can tiller much more confidently. Finally there is one more option you shouldn’t overlook, and that’s to ask the community for input. If you need to borrow more experienced eyes, the bowyer community is incredibly friendly and willing to help. Just make sure to post at least 3 pictures. You need the front profile, the side profile, and the drawn picture. I’ll go into more details about that later. If you want my help in particular post on the reddit forum r/bowyer and I’ll drop in when I can. Or post some links to pictures down in the comments section.
Shorten your longstring as much as you can to get the most accurate reading on your tiller and draw weight.