The Mysterious “Twang”
Wes Winfree from Gloucester, VA has these questions:
I hope you can help me with a couple things. My last “twang” bow was an effort to get the arrow speed of my 50# bow with a lighter weight stick. I lengthened the upper end of the handle to make both limbs the same length, added some reflex, and tillered it to have more bend at mid limb. Didn’t really know what I was doing, but it was good experimenting. I also made it perfectly center shot in an attempt to get more accuracy (I need all the help I can get). It does improve my aiming quite a bit and the speed is almost as good as my 50# bow. I am 64 years old, 5’3”, and 125# so the 50# bow is near my outer limits for comfort and not easy to hold on target; although I dearly love it. My question is where did the “twang” come from? Was it the center shot design, the greater mid-limb bend, or what? Oh, I use standard multi-strand packaged bow strings since I haven’t yet started making my own.
A different issue is tools. To work down the bows, I use an old rasp my grandfather had. It is completely different from any others I have seen that can be purchased and nothing like a Nicholson (which I hate). With it I can take wood off fast in long easy curls or I can take it off slowly, precisely, and smoothly. No scraping at all is needed to produce an almost glass like surface. All I need to finish is a little hand sanding with 200 grit sandpaper and that isn’t completely necessary. I’ve checked woodworking catalogs and countless stores to no avail. I’m worried that one day it will either break or become too dull to use. I finally did find one at a flea market that the guy had gotten from an estate sale. The teeth are curved and go all the way across the blade…see my drawing. This is a fantastic tool for bows. Do you have any idea where I can find new ones or do you think it possible to get someone to manufacture them for bowyers?
To increase the performance of your lower weight bow, you had to increase its efficiency. You did this by adding reflex and, by adding the reflex, you have increased the string tension at brace height. The increased string tension in turn makes the string, as you say, twang when it comes back to brace height on release; this is the major cause of the noise that you hear. Having the bow near center shot also means the arrow leaves the bow more cleanly which allows the string to vibrate.
As to your tool question, I was recently looking through the latest Lee Valley tools catalogue and saw two versions of the rasp that you like so well. One has straight teeth that go directly across and the other has the curved teeth that your tool has. They also have a flexible variation of this tool.
Bending recurves can be daunting to some people. Some wood species do bend into relatively sharp curves easily with wet or dry heat, such as Osage and Black Locust; others will only take sharp bends with wet heat. Most wood species will bend to some degree with wet heat; even the tropical hardwoods. Here are some tricks I have used for bending the curves in the static recurves I make.
The first thing that one should do is work the belly down to one ring making sure the wood is smooth; sanding with fine sandpaper is a good idea. Next you want to round the edges of the belly to a good radius, sanding that as well. If a splinter is going to pull up, it will do so on a square edge. Another thing is to leave the wood a bit thicker than necessary so that if a splinter does pull up you can still work the recurves down without making the bow too weak. A metal strap on the belly will help to keep splinters down, especially if you are aiming for a very sharp bend. The strap needs to be used properly though; if the strap sits too loosely, it will not hold any splinters down. It must be placed in such a way that when the wood is bent the strap is drawn down tightly onto the wood.
Another method I have used is a tightly wrapped string to hold down splinters. A natural fiber string with sufficient strength needs to be used here so that it can be wound tightly around the wood. You need to make the belly of the recurves slightly round when using this method, so that the string sits tightly around the belly with no loose spots in the middle. The string needs to start and finish past both ends of the recurve being bent with a space of about 1/8” between the windings. Starting at the tip and working back towards the limb is the best way to do this, as then a spring clamp can be used to hold the end of the string without it getting in the way.
Send your questions to:
Marc St Louis
P.O. Box 1132
Mattawa, On. Canada
or email Marc