[T. Brandt]

So, somewhere in the 1950s, the compound bow was formulated. Around 1900, the Penobscot bow made itself known to the world. And just recently, reverse-draw crossbows (and bows, oddly) are making their appearance.

Now, the question is... have any of these formats been seen before the twentieth century, even if only as bespoke or experimental pieces? Humans are no more creative now than they were a thousand years ago, after all.

[Timo Nieminen]

Medieval Chinese multi-bow artillery crossbows:
http://www.myArmoury.com/talk/viewtopic.php?p=284513
http://www.grandhistorian.com/chinesesiegewar...gzinu.html

Cable-backed bows, if you include them: http://en.wikipedia.org/wiki/Cable-backed_bow

When you include pulleys and cams, those add weight, and they add the weight at the ends of the limbs, where extra weight hurts performance. With modern materials, they can be made light and strong, and the benefits of the design outweigh the penalty of that extra weight. It would be harder to reach the break-even point with pre-modern materials.

We have a trade-off like this in the long-siyah reflex-recurve composite bow - the siyahs (the rigid ears at the tips of the limbs) work as levers, but they add weight to the limb tips. For designs with long siyahs, you don't get much benefit until you exceed 50lbs or so of draw weight (that's the approximate break-even point most often given by others).

Think about the weight in pre-modern pulleys, and the losses due to friction (these days, we have good bearings, but Medieval cams and pulleys did not (by modern standards)).

[T. Brandt]

Thanks for the reply. I guess I made the (sophomoric) mistake of assuming that just because it's more technologically complicated and produces better results now doesn't mean it would do the same centuries ago.

Kind of like how a steel bowstring, despite being more technologically intensive, is actually less ideal than a fibrous one (under most circumstances).

[Timo Nieminen]

There are two key elements in the success of the modern compound bow:
1. Modern materials. This gives us lightweight pulleys, thin strong strings, and durable bearings.
2. Modern precision manufacturing. This gives better quality bearings, and allows the whole thing to be made much, much more cheaply.

The individual elements were all there: pulleys, cams, roller bearings. It's a question of making them well enough and light enough. Those individual things all worked for many different jobs.

Somebody would still need to invent it. Maybe somebody did. And discovered that it didn't work very well. A lot of technology was passed down from master to apprentice, from craftsman to craftsman, without being written down. It's very easy for unsuccessful inventions to vanish from sight with that kind of system.

There are other technologies we have today where the pieces were there for a long time before they became good enough to be practical. In some cases, the invention preceded practicality by many decades. Slow and steady improvement in materials can make a big difference in the end. Revolutionary change gets a lot more press than evolutionary change, but evolutionary change matters a lot.

[Lafayette C Curtis]

Precision manufacturing to tight tolerances is far more important for compound bows than it may seem at first. A local bowyer in Indonesia experimented with making a compound bow out of wood and bamboo last year and it worked -- giving the desired feeling of let-off at the end of the draw and providing an improvement (albeit a marginal one) in arrow speed over ordinary bamboo-limbed recurves made to similar specifications. However, the alignment between the parts proved hard to keep consistent, and the bow had to be readjusted every few shots to maintain its speed and accuracy.

[T. Brandt]

Lafayette, I'm sorry, but I find that absolutely fascinating. What material was used for the bowstring?

[Timo Nieminen]

That's interesting! Do you have any further info or references?

Alignment would be easier if axles and bearings are made wider/thicker/longer, but then weight goes up a lot, and performance goes down.

[Lafayette C Curtis]

Not much. It wasn't that special as a bow -- if I recall correctly, the maximum draw weight was only 40 pounds or so, and the full-draw weight somewhat less than 30 pounds (but I don't remember the exact number of the latter). The limbs were of bamboo while the riser was made out of a tropical hardwood. I'm not sure about the type of wood used for the pulleys/cams but it was a good deal lighter (both in colour and in specific gravity) than the one used in the riser. The string was Dacron since the bowyer wanted to be on the safe side.