re-cambering a bow weakens the stick

[Guido]

I was hoping for people to tell me the opposite and ideally have some good arguments to dispel this urban myth.

[Brad Dorsey]

I've never heard the “urban myth” that re-cambering weakens a stick, but I spend very little time in cities.

[JacksonMaberry]

Hadn't heard that one before either

[Guido]

Heard it a number of times now. Maybe it's a local myth :-)

[fiddlecollector]

Shouldnt do unless theres something wrong with the stick or the recambering is done badly.

[Wood Butcher]

I never heard this myth either. Maybe in your area, someone was doing them so badly it actually happened.

[martin swan]

Some bow restorers don't like to do recambering ... 

[Blank face]

I heard similar claims, always given by bowmakers/rehairers or dealers as an excuse for being unable to manage the job.

[fiddlecollector]

27 minutes ago, martin swan said:

Some bow restorers don't like to do recambering ... 

I can imagine ,its very risky if the bow is expensive, ive never broke one yet but some have terrified me when ive noticed some dodgy looking grain run out or knots.

[Blank face]

36 minutes ago, fiddlecollector said:

I can imagine ,its very risky if the bow is expensive, ive never broke one yet but some have terrified me when ive noticed some dodgy looking grain run out or knots.

Yes, the correct claim wouldn't be "it weakens the stick" but "it might break the stick".

[LCF]

It seems uncertain what the context for evaluating 'weak' might be but the obvious paradox is that if you recamber it's hard to understand how the stronger curve will make a bow weaker???

Weaker what? Weaker how?

[fiddlecollector]

13 minutes ago, LCF said:

It seems uncertain what the context for evaluating 'weak' might be but the obvious paradox is that if you recamber it's hard to understand how the stronger curve will make a bow weaker???

Weaker what? Weaker how?

It could make the stick weaker as in the bow wouldnt function properly  as a bow  but the actual stength of the wood itself shouldnt really be affected at all

[LCF]

7 minutes ago, fiddlecollector said:

It could make the stick weaker as in the bow wouldnt function properly  as a bow  but the actual stength of the wood itself shouldnt really be affected at all

I'm sure it's possible to recamber badly!

[FiddleDoug]

26 minutes ago, Blank face said:

Yes, the correct claim wouldn't be "it weakens the stick" but "it might break the stick".

That's my understanding. Any client that requests a recambering needs to be warned, and a signed acknowledgement that the stick might break needs to be in place. The sticks are cambered when they are made, and re-doing that shouldn't weaken the wood if done correctly.

[Brad Dorsey]

8 hours ago, Guido said:

Heard it a number of times now….

Do those who say that re-cambering weakens a stick say that straightening weakens it, too?  I think that it would have to be either both or neither, but not just re-cambering.

[IBK]

If the stick is weak to begin with (overly flexible) it may appear to be weak after recambering.  Also if you burn the stick you will weaken the fibers of the wood.  It has to be done slowly with the precise amount of heat and downward pressure.  It is an acquired skill. 

[Geoffrey N]

I had a not very expensive German bow at one point that was almost twisted around the camber was so bad. The bowmaker I took it to said there was going to be a 50/50% chance it would break but I had him do it and was happy I won the coin toss. Now it's a usable bow instead of a piece of kindling...

[The Violin Beautiful]

I’ve heard of this idea. The argument is that any time the wood is bent, it weakens the fiber structure of the wood. The same argument is used with straightening bows and bridges. I don’t know if the wood actually becomes weaker, but I have heard a lot of people suggest it.

I agree that a good recambering job should make the stick better and potentially stronger if it has flattened out over time for whatever reason. I think that it’s also significant that heat is being used in the process to make the wood pliable—it isn’t being bent cold. It’s possible to make a stick weaker through recambering if the curve isn’t established properly, but that’s more an issue of getting the camber wrong than degrading the wood. A good repair to camber will bring back the character of a bow. A customer of mine just showed me a bow he bought from the top maker in my area years ago. The bow had lost some camber over time and the player brought it back to the maker when he found it to be hard to control. The maker recambered the stick and the player said it brought it back to life completely.

[Mike_Danielson]

I think you will discover that increasing the camber will increase the bow strength--this is what I recall from finite element stiffness calculations based on the amount of camber.  Why not measure for yourself.  Set up the Stroup system that measures stiffness and do a before and after test--pretty simple.  

I was looking at some data on bamboo.  Bamboo for fly rods is heat treated.  Heat treatment dries the wood out and causes the modulus to increase, but as the bow rehydrates to its' equilibrium moisture level, this increased stiffness is mostly  lost.  

[Guido]

Of course a straight bow with a good camber is worth achieving and the better outcome compared to a stick that isn't straight or has insufficient or inappropriate camber.

The point of concern rather seems to be a physical degradation of the wood on a cellular level caused by repeated heating (and bending). Any effect would be small (each time) and the improved camber would outweigh any perceived effect. So it's easy to dismiss based on experience... However, It would be great to hear some counter arguments at a material science level for these wood cells/ fibres/ lignins.

[LCF]

3 hours ago, Guido said:

Of course a straight bow with a good camber is worth achieving and the better outcome compared to a stick that isn't straight or has insufficient or inappropriate camber.

The point of concern rather seems to be a physical degradation of the wood on a cellular level caused by repeated heating (and bending). Any effect would be small (each time) and the improved camber would outweigh any perceived effect. So it's easy to dismiss based on experience... However, It would be great to hear some counter arguments at a material science level for these wood cells/ fibres/ lignins.

I suspect that one of the reasons for pernambuco being a premium bow wood is that might bend more readily when it's hot enough than other woods, and take a good set cooling down. I don't have any experience of pernambuco to back up that thought but I have bent a lot of rib woods for diverse instruments, and some are 'sweet', and some are definitely not sweet. 

 

PS Abeille wood, porous and fibrous, looks like some of the 'unsweet' woods I have run up against. Pernambuco seems finer and more resinous. 

Edited August 12, 2024 by LCF
PS

[Brad Dorsey]

11 hours ago, Guido said:

…material science level…

I’m trying to imagine a machine testing procedure:  A stick of wood would be clamped in a device which would automatically heat it, bend it, allow it to cool, flex it and measure its strength.  This process would be repeated, perhaps hundreds or thousands of times, alternately bending the wood one way and then the opposite way, and the strength would be recorded each time to see if it changed.  The process would be repeated using different temperatures, bending forces, grain orientations and wood species.

I think this is the only way that the original question could be definitively answered.  It could make a good materials science thesis project.