Cowiche Archery

Tillering a bow is a method by which you remove wood from the stiff places in a bow limb to make each limb bend evenly.  It is also the way you reduce the pull weight of the bow to within your target weight.  Say the bow came off the mold weighing 70# and you wanted a 60# bow.  You then have to shave off 10# of "weight" or approximately .030 thousandths per inch of bow limb.  You can see the tolerances for error are small . . . . You can figure .001 to .003 per inch per pound of draw weight.

If you can see it, this guage shows .030 thousandths.  This equates to approximately 10# in bow weight.  As you can see you don't have to remove a lot of wood to get where you want to go.

Just remember, once it is gone you can't put it back on!!

Tillering in Bowmaking is where the rubber meets the road so to speak.  It requires patience, workmanship, and repitition.

With the bow securely fastened in a vice and using your scraping tools, (I use mainly a Nicholson #49 and #50 rasps, my pocket knife, (very sharp), a square furniture scraper, (also sharp), and a sanding block loaded with 150 grit sandpaper), I divide each limb into 3 equal parts.

Beginning with the tip 1/3 I take about 10 strokes,(you want to keep the last 4-6" thicker than the rest of the limb, the last 4" should not bend in the finished bow).  Then moving to the middle third of the limb I take approximately 20 strokes all the way to the tip. Lessening in pressure as I get to the last 6" of bow limb, and finally the handle third of the limb another 20 strokes all the way to the limb tip.

After repeating the process on the other limb, in an exact manner and number of strokes, I put the bow in a tillering string and give it a good 20 pulls, never more than 10 to 15 inches in a pull.  This teaches the limbs to bend.

Continuing with this when I feel like the bow is bending evenly, I will string the bow to about a 4" brace height and weigh it.  Never pull the bow so far that it exceeds the target weight or you will introduce string follow into the limbs.  This defeats the purpose of building reflex into the bow and weakens cast.

This is the bow in the tillering stick.  Using a tillering string.

Place the stick on a bathroom scale and pull the string progressively from notch to notch.  Looking to see that the bow is bending symetrically as you go.

Check to see that you are not exceeding your target weight on the bathroom scale.

If the bow is not bending symetrically go back to the vice and remove wood from the stiff places only.

Check again after bending the limbs 20 times if symetry is attained proceed to the next notch; if you're ok, go to the next notch and so on, never pulling past the target weight.

Continue in this manner checking progressively from notch to notch at the target weight only, removing wood if you are too heavy or the bow loses symetry.  Say your target weight is 50# at 28 inches and you have the bow pulled to 16 inches and have reached your target weight.  Then you need to return to the tillering vice and follow the steps outlined in the section above, never taking more than 10 to 20 strokes at a time and exercising the limbs before measuring.  One final note about tillering; the top limb when finished should bend more at the fadeout by 1/8 to 3/8 of an inch.  Measure this with a bow square just as you would measure your brace height.  If you aren't getting this measurement take a little more off, (slowly), from the top limb.

Remember to change from the tillering string to your bow string as soon as you can string the bow with a 4 inch brace height.

This will help you to more clearly see where the bow is bending and where it is not. Remember the trick to tillering, is to take off wood where the bow limb is not bending and to leave it alone where it is . . . . 

Bamboo as it comes, has a rather beat up back.  By scraping the first layer of the rind off you will have a pristine back without flaws, nicks, or scrapes that could weaken the bow.  The scraping, when done properly leaves a nice amber, waxy finish.

(Sorry I couldn't straighen my neck, broken vertebre wasn't feeling well this day.)

Set the Brace height at 6.5" form the back of the handle to the string.  I like the knocking point 1/8" above center but you may need to play with that a little depending on your shooting style.

After shooting in your bow, I like to shoot it at least 50 to 100 times no more than 10 to 20 times at a session.  I unstring the bow until the following day and the next 10 or 20 arrows are shot.

After this, you are ready to finish the bow.  If you would like to stain it; I like to use Fiebings Leather Dye.  If not, I use an oil finish like Watco Danish Oil (in natural for a matt finish), or Birchwood Casey Tru-Oil gun stock finish if you want a hard shiny finish (just about bullet proof.  If you use the Birchwood Casey Tru Oil you can rub out some of the gloss with a little 0000 steel wool or pumice stone with mineral oil.  I have an Osage self bow that was finished 10 years ago with Tru-Oil and it looks just as good today as it did the day it was finished.

Yes it's a lot of work, You'll see rather quickly the $300.00 I charge for building one of these bows doesn't even begin to cover the labor.     

The returns are huge, you get a fine hunting bow and an heirloom that can be passed down through your family, and something only the primitives fully understood.  A bow like this is mystical in many ways, they understood that it was the staff of Life.  It both gave life and took life.  Good Luck!!

If you should have any questions along the way email me at bowyer@cowichearchery.com I'd love to hear from you

Darryl

P.S. My next bow, (the model I hope to hunt with this year) "The Dragon Slayer" is nearing completion.  It is a 3 lam bow + the Bamboo backing, 66" AMO Cocobolo and Bacote Riser and overlays, @60lbs. @28"  Photos soon.  This bow will sell for $350.00