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Correct camber

 
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Mat Roop
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Joined: 24 Mar 2007
Posts: 911
Location: Wyoming Ontario

PostPosted: Sat Mar 08, 2008 9:42 pm    Post subject: Correct camber Reply with quote

Can anyone point me to a resource on the correct camber for a violin bow... ie... where is the low point, and how is it measured? Or is it a function of each maker?
Thanks, Mat
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Mon Aug 17, 2009 11:22 am    Post subject: bow camber Reply with quote

This is an old post but it ought to have an answer in case a newbie walks in.
With the frog fitted(all the winder etc) The bow on a flat surface should curve down till the middle of the wood just touches the surface.If there is a gap the bow has lost some of it`s spring (left with tight hair---or parked in a hot car).
That`s the camber.
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Thu Aug 20, 2009 7:49 pm    Post subject: bow camber Reply with quote

If you have a pernambuco bow that`s lost it`s curve you can put it right quite easily.
A heat lamp ( 100watt reflector lamp and not infra-red )will be enough to warm up the wood instead of using an alcohol burner.
Draw out the desired curve on a strong piece of plywood.Copy the shape of a bow in good condition.At the thick end fix a few wooden blocks to hold the bow steady(on it`s side)so that the "good" outline is showing up the "bad "bow shape.The screw and hair can be disconnected and tucked in a clean plastic bag.
More blocks should be fixed below the bow curve so that as the stick is adjusted small wedge blocks will hold the new curve in place. Above the stick fix blocks to give the final shape.
Work out how to position the lamp over the bow to get it as hot as a car seat on a hot day.A bit too hot for the palm of your hand.Work from the middle towards the tip of the bow , gradually adjusting the shape with very gentle pressure on the stick.
Don`t try to rush the job. It is best to put reflective foil beneath the stick as this will get the bottom of the wood hot as well.
The lamp will be 5 or 6 inches above the stick.Arrange for a moveable support to edge it along as you work.Take roughly 20 minutes as a starter.By then the wood should be ready.
You will be surprised at the gentle control you have with a normally risky process.
Before you begin have a look at pictures of good bows to guide yourself. When all the adjustments are done keep everything in place and switch off the lamp.Allow a good half hour for cooling down.With the frog fitted you should have a straight line from bottom of frog to bottom of tip,and curve of stick just touching that line.Always a great surprise when the stick is a good one.
Save the Pernambuco!


Last edited by John Cadd on Thu Jun 02, 2011 8:12 am; edited 1 time in total
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Janito
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Joined: 08 Oct 2007
Posts: 114
Location: USA

PostPosted: Sun Aug 23, 2009 9:45 am    Post subject: Reply with quote

@ Mat Roop

The camber of a bow and its location can be a distinctive feature of a maker, especially in the 6-9" behind the head.

This is because the camber and the shaft thickness scheme determine how the stick will straighten when the hair is tightened. I was taught that the optimal balance should be built into the stick by making it straight in all directions when it is tightened by a wire from head mortice to frog.

@ anyone else who is interested in DIY

Bending wood with heat is not particularly difficult, but it is easy to mess up a bow by introducing a twist in the shaft between head and frog. The gun-barrel view has to be perfect as the camber is being altered, and before it is finally allowed to cool.

Here are a couple of other points to consider:
- check to see if there is a coating on the bow. Heat will mess this up. On cheap bows this can look very ugly if it contained pigment to darken the shade.

- The wood has to be heated to the right temperature: if too low - crack; if too high - burn.
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Andres Sender
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Joined: 23 Mar 2007
Posts: 275
Location: N. CA

PostPosted: Thu Aug 27, 2009 4:17 pm    Post subject: Reply with quote

amezcua how often have you used the heat lamp process?
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Sun Aug 30, 2009 5:13 pm    Post subject: bow camber Reply with quote

Andres Sender I have answered your question but once again (mysteriously ) it has disappeared. Maybe somebody doesn`t like me.
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Sat Sep 05, 2009 7:33 pm    Post subject: camber Reply with quote

How many?About three.No problems so far.It was so trouble free even Mr Tourte would have tried it.Any volunteers to make a new bow this way? Risk free!
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Sat Sep 05, 2009 7:36 pm    Post subject: camber Reply with quote

Just testing the system here.If I mentioned a town in England would the internet delete it?----Scunthorpe.A seaside resort.
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Sat Sep 05, 2009 7:37 pm    Post subject: camber Reply with quote

Sorry ,back to topic now.
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John Cadd
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Joined: 23 Jul 2009
Posts: 819
Location: Hoylake

PostPosted: Mon Oct 12, 2009 8:55 am    Post subject: correct camber Reply with quote

Some good tips mentioned above by Janito.
The important idea is to keep eveything straight and not bring distortions in. The idea to do this with an electric heat lamp came to me because the Violin Shop owner wouldn`t waste his time on it.(That was his attitude).As an alternative to the dustbin I tried a new way.
The other influence was the number of players referring to bows going out of shape due to hot cars putting the wood back to it`s original shape.Also leaving the hair tight in the case.
As the wood warms up turn it side to side to make sure the heating is even.
Because the process takes place flat on a thick piece of straight plywood there is no danger to the overall shape.
To emphasise---The bow lays flat on it`s side.
It is not necessary to heat near the very tip.The pressure to adjust the shape is just a few ounces using your fingertips, absolutely nothing dramatic at all. No forces are used which can twist the stick.
There is no actual clamping ,just a few "holding "blocks towards the "blunt end" and a few moveable blocks towards the " sharp end".
If you worry about burning the wood put your hand under the lamp for half a minute continuous.Then compare that with half a minute over an alcohol lamp.The varnish will only be in danger if you use an alcohol lamp.
Bowmakers are incredibly skillful people to be able to work with the traditional techniques.Don`t think this is all a criticism. If the man in the street tried the accepted way at home they would not enjoy the experience.
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