Correct bow camber

[Nemo]

I have read somewhere that a bow if laid flat on a table with the string side down & untightened should have a camber that touches the table mid way and at least a 1/4 of the bow length. Is that true? I am looking at a good sounding bow but I notice it does not touch the table but does come close.

[GlennYorkPA]

We don't get much discussion about bows on this forum so I'd like to add a supplementary question about the position of maximum camber. In some bows it seems near to the middle of the stick and in others, closer to the head.

Can anyone explain how camber affects the bow properties?

[Craig Tucker]

Interesting question.

I know that I often prefer the maximum point of camber closer to the mid point of the bow than closer to the head or tip of the stick.

Locic would seem to dictate that the camber would be stiffer the further up the stick it is, as the bow diameter generally increases with the distance from the head.

My guess is that bows with the camber peak closer to the head would be a bit more live for bouncing the stick around, and bows with the camber nearer the center of the bow would be a bit more stable, and play long smooth notes with less effort and less tendency for the bow to bounce around.

Though I have been playing for years I never really have made a concerted effort to distinguish characteristcs of the camber in order to correlate them with the playing quality. (other than to be able to say "Yes, I like the way this bow plays" or "No, I'm not impressed with this one.")

Hopefully someone with actual knowledge will chime in. I may have it completely backwards...

When I recamber a bow, I always just put the camber back that the bow apparently came with, which is usually fairly obvious.

[GlennYorkPA]

If I remember correctly, maximum camber near to the head is a fairly modern trend.

I think the historical bows of Tourte had the camber in the middle and Dodd and Tubbs placed it closer to the head.

I like a bow to have it's center of camber closer to the head because I feel it compensates for the thinner wood thus giving more even spring along the length of the bow.

Surely the physics/engineering of this is a walk in the park compared to violins

[Andres Sender]

As I understand it, the camber interacts with the graduations to create the stiffness pattern of the stick. ONE approach to cambering is to use it to bring the bow's stiffness pattern more in line with the ideal implied by the typical graduation pattern, you can learn to see this in how the stick bends. But I suspect there are many ways of varying this to get different effects.

I think many makers just follow a model, but one hears sometimes of bow people who pride themselves on very sophisticated monkeying with cambers.

[Claire Curtis]

I put the camber in the middle, so that the curve is even to either side. Then I graduate the bow until the stiffness feels correct along the bow. When done, I like the bow, when laid so that it sits on the frog and head, to just touch or barely clear the table.

[Andres Sender]

Claire can you describe what the correct feel of stiffness is and how you look for it? Are you looking for particular pattern of movement as you bend it?

[Regis]

I'm not a bow maker but, when I have to re-camber, I make sure that when tensioning, the bow straightens over the entire length. If you put camber too far forward, you will simply pull down the tip end of the bow when tensioning. If you put too far toward the frog, the bow will tend to appear to have a slight hump (above the camber) when the bow is tensioned. Not real easy to get that straightening distributed in proportion to the bow's flex (usually relative to diameter). My hat's off to them that can do this quickly.

Regis

[GlennYorkPA]

At last, a principle I can relate to!

It can't be easy to devise a stick of diminishing diameter which will be perfectly straight under tension.

There would need to be a counterbalancing force to prevent the narrow (tip) end from dipping down but that would imply that the camber needs to be more towards the tip to prevent this. (The opposite of what you said).

I think in French bows, there is another factor, which is not to make the stick circular in section but oval or elliptical. That would be another way to control the straightness of the stick under tension so perhaps one camber does not fit all.

[Claire Curtis]

Quote:

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Claire can you describe what the correct feel of stiffness is and how you look for it? Are you looking for particular pattern of movement as you bend it?

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Oh, that's hard to describe. The feel is very much like the feel of the back plate of a violin when you flex it. It fights back, but not too much. If it fights too little, the bow will feel sloppy; too much and it will be unresponsive. For me, this is tactile, not visual. I can look down a bow to find a kink, but even there I usually do better feeling for it.

Sorry I can't describe it any better.

When testing the bow, I place the tip on a tabletop and hold the frog end, then with the other hand press lightly down the bow, starting at the tip. The resiliance should be even down the bow. Wait, maybe not exactly even -- the springiness decreases as you approach the frog -- but there should be no detectable jumps.

Mind you, while I've gotten good comments about the bows I've made, I'm not exactly an expert bowmaker, and I have a lot to learn. But I had a good teacher in the French tradition, which I think is a very good way to go. It teaches you to really listen to and work with the wood.

-Claire

[Andres Sender]

Claire that reminds me of how the late lutemaker Robert Lundberg used to thickness lute tops. These were spruce thinned mostly to either side of 1.5 mm, and he would run his fingers up and down the wood with one end supported by his hand and the other on a table and feel how the wood flexed 'locally' under his fingers.

[Claire Curtis]

Yes, that's the technique.

I just don't know how to describe what you're feelling for.

[Andres Sender]

We'll just have to start feeling bows. ;-)

[fiddlecollector]

Glen, your right ,i believe the oval cross section on fine old French bows is a very important factor towards their playing qualities , one of the most important things it helps is to prevent unecessary sideways motion which is almost unavoidable with a perfectly round stick.