Bow Terminology

[john fletch]

I was visited by a gentleman who is 76 years old and has been making bows and arrows for most of that time.

He has some amazing work and we had a good talk.  However he used some terms I was unfamiliar with.  I did not have time to write down his full explanations and he has not written his own book.

What can you all tell me - or what books are out there that may clarifiy what he was talking about - e.g.

Modulus - the properites of the woods and how they recover for flexing, compression and extension.  I am familialr with the term in fly rods, and maybe it is essentially the same.

Trapping - the working of wood laminations which includes thickness and width and the ratio to gain the best compression/tension throughout the limb

Heat Tempering - carefully controlling the heating of various woods to get the best tension and compression characteristics.  Especially helpful with bamboo

8:1 ratio - a thickness of limb vs. overall width trying to keep the tips slender working down to wider main limbs which will produce the best arrow speed.

He does self bows quite well using this science, but mainly does laminations of various woods trying to achieve great arrow speed in bows with smooth draw and little to no hand shock.

At 76 he can still fully draw the 65 to 70 lb bows.

Quite an education.

What can you tell me about this or any written sources.

I will not divulge his name without his permission, but he does live locally.

I have a lot to learn having been making self bows only about 10 years and just starting out in the laminations.  I am not too interested in getting into fiberglass or recurves - plenty of great folk been doing that a lot longer than I have left.  But still eager to learn the basics.

[Rick P]

Modulus, it's the same as for bamboo fly rods. Basically it's having lots of individual cells combine to form a very strong flexible structure.

Trapping Oh boy this one is a little tough, new bowyer don't ya know. There is a theoretical perfect ratio between the thickness and width of a limb that decreases along the length of the limb. Trapping is the process of removing material from both the thickness and the sides of the limb in an attempt to achieve said theoretical ratio.

Heat tempering is just as it sounds. You heat the back of the limb causing the leginin in the wood to melt slightly and cool harder. This improves strength under tension.

Not sure what he means by the 8:1 ratio. But I'd be willing to bet it's the ratio he likes the limbs to tapper in his bows. The theoretical fastest bows have a pyramidal shape. Fat at the fade outs tapering to a point at the tip, with the last 1/3 of the limb flexing very little. This greatly reduces overall limb weight and through the principle of conservation of angular momentum increases tip speed. The last 1/3 of the limb ends up acting more like a throwing stick than flexing like a whip or leaf spring. This general shape also produces a very long lasting, reliable self bow that is fast and lacks hand shock.

[Keefer]

You must of run into "Dean Torges" Sounds like his way of wording things ! Or WingNut !Ain't he about that age now and uses words that you can't find in the Webster Dictionary?  

[Pat B]

Trapping is shaping the cross section of the limb to a trapezoidal  shape, generally with the belly side the widest. This allows the compression side to be stronger than it would if it were the same width as the back.
  My take on heat treating(tempering) is to also increase the compression strength of less strong woods by heating it to a controlled charred condition. This works best with whitewoods that are normally weaker in compression but I have used it on osage as well with good results. For self bows I would not temper the back of the bow as it will make it more brittle and weaken its tension strength. With bamboo, it can be heavily charred to improve compression strength for a belly but also boo backings can be lightly charred to improve tension strength.
   TBBIV has a chapter on heat treating by Marc St Louis which explains the technique very well and another chapter be Steve Gardner on the Mass Theory of building bows which covers the width to length ratio but also the total mass of a self bow to get it to its optimum size for its draw length and weight.

[SCATTERSHOT]

Check out "The Traditional Bowyer's Bible" series for good explanations on these terms and lots more useful info.

[john fletch]

I have Bowyers Bible somewhere - looks like I might have to dig up the others also.

You guys seem to explain a lot like he said, at least now I have some things written down.

If the Trapezoidal shape with the belly wider than the back is faster, why is the classic English longbow 'D' shaped with the rounded belly?

Has it to do with the Yew wood they used?

[Pat B]

It all has to do with the wood used. Some woods are more tension strong and some are more compression strong. Most wood is stronger in tension than compression so a trapped cross section gives a more durable design. Most ELBs are made from yew and it is a compression strong wood that can take the compression stresses that are common with the deep belly design. Less compression strong woods can be made into ELBs but they will take more set because of the compression stresses of that design.