Side bending problem

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krichards

Posts: 597
Joined: Jan. 14 2007
From: York, England

Side bending problem

Sometimes when I bend sides with my side bending jig the sides end up with a slight dish either side of the waist bend.
It doesn't happen every time but of course, its annoying. Its not so serious in the end because by the time the bindings have been scraped flush, its barely noticeable.
But I can't work out how its happenning.

I use an electric blanket with two spring steel plates. I damp the wood with a mist spray and wrap in metal foil. I leave the sides in the bender overnight. When they come out they are fine, but 24 hours later they sometimes, not always, develop this slight dishing.

Is it the wood- maybe not perfectly quartered?
Is it the moisture? Should I do it dry?
Is it too much heat or too little heat?
Should I remove the sides staightaway?

Anyone else had experience of this?

Any suggestions??

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 18 2010 0:30:17

Anders Eliasson

Posts: 5780
Joined: Oct. 18 2006

RE: Side bending problem (in reply to krichards)

Sounds strange.

I bend more or less like you and I have never had these problems. How thick are your sides. I bend at around 2,2 - 2,3mm

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 18 2010 10:40:00

HemeolaMan

Posts: 1514
Joined: Jul. 13 2007
From: Chicago

RE: Side bending problem (in reply to krichards)

perhaps you moisten them a tad too much when bending and then the unequal drying causes them to warp??? thats the only thing i can thing of. either that or maybe if you try to store them between two know flat objects with some compression it might help them to stay un-bowed...

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 18 2010 10:49:52

krichards

Posts: 597
Joined: Jan. 14 2007
From: York, England

RE: Side bending problem (in reply to Anders Eliasson)

I normally make my sides at 2.1 mm or maybe 2.0mm.

I think Hemoleoman may be right about the moisture. I use a bit of water because I assume it helps transfer the heat more efficiently.

But its not actually needed to bend the sides is it?

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Kevin Richards

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 18 2010 23:10:09

Anders Eliasson

Posts: 5780
Joined: Oct. 18 2006

RE: Side bending problem (in reply to krichards)

I just spray the sides VERY lightly with water.

When bending thicker objects like inner lining, I soak the wood.

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 18 2010 23:41:55

HemeolaMan

Posts: 1514
Joined: Jul. 13 2007
From: Chicago

RE: Side bending problem (in reply to krichards)

honestly i've never bent sides lol. I just happened to be watching that part of El Guitarerro. Anders uses a very very spare amount of water, literally about 7 sprays from a plant spray bottle per piece. it barely darkens the wood.

if that helps. because i'm sure he doesn't really count the number of sprays, figure i'd geek out on you guys!!

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 19 2010 12:41:42

Stephen Eden

Posts: 914
Joined: Apr. 12 2008
From: UK

RE: Side bending problem (in reply to krichards)

I think i know what you mean. What is your bending jig like maybe some pictures could help. In the past I have had this happen when using my jig. My old light bulb jig was obviously not solid in the middle so when the pressure of the waste block came down it distorted the metal eitherside of the block.

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 19 2010 14:03:37

Andy Culpepper

Posts: 3023
Joined: Mar. 30 2009
From: NY, USA

RE: Side bending problem (in reply to krichards)

Do you do any hand-bending with a hot pipe before fitting the sides? It's a good way to "iron out the wrinkles"

REPORT THIS POST AS INAPPROPRIATE | Date Jan. 19 2010 14:35:57

estebanana

Posts: 9378
Joined: Oct. 16 2009

RE: Side bending problem (in reply to krichards)

You might be having a problem with residual water in the ribs. Like Anders said only a little water. If you are too heavily wetting the ribs and heating them with a silicon blanket, you might not be cooking all the moisture out of the rib.

When you let the rib sit in the side bender all night with the rib covered in foil and the two steel sheets that can trap a small amount of moisture in your wood. It may feel dry to the touch, but the moisture content of the wood, especially inside, may be enough to cause a reaction with room temperature and even exposure to minimal heat sources like 20 minutes under 100 watt light bulbs. One side of the rib gets hotter and it dries faster or more completely than the other side and the wood cups.

Two things you can try is to use much less water and then do two cycles of heat with the blanket. After you bend the ribs and the first cycle has elapsed, wait a few minutes then then do another shorter cycle at lower heat.

The second thing is to run another heat cycle the next morning when the ribs have cooled all night. Then let them completely cool before removing them from the bender.

I bet your problem is residual water in the ribs from too much water application before bending. Unless you have some other issue with your room moisture or you are inadvertently cooking the ribs under your work lights and warping them.

One more thing you can try is to bend your ribs in plain artists newsprint paper. It's very cheap and does not have the potential hold moisture like foil. The water will steam out of the paper faster than it will steam out of the wood and then you will not have as much of a problem with the ribs sitting all night in trapped moisture.

When you spritz your wood, set the spritz bottle nozzle to the fine mist setting. If you don't have an adjustable mist setting in the bottle you might want to get one so you don't over wet. Garden supply places tend to have more sophisticated spray mist bottles for watering house plants. They work very well, in addition to being more dainty and stylish.

I hope that information helps. It sucks to ruin expensive ribs and we've all done it one time or another.

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 19 2010 20:29:47

krichards

Posts: 597
Joined: Jan. 14 2007
From: York, England

RE: Side bending problem (in reply to Stephen Eden)

My jig is not solid in the middle but it would be a simple matter to add a steel sheet onto the top surface.
Thanks for that

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 19 2010 23:34:31

krichards

Posts: 597
Joined: Jan. 14 2007
From: York, England

RE: Side bending problem (in reply to estebanana)

Many thanks for this long and helpful reply.

I think moisture is the key, as you say.

But I'm not convinced its even necessary.
And I'm not convinced its necessary to leave it overnight.
I only do these things because it seems to be the accepted wisdom.
Trouble is, sides are expensive things to experiment with!

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 19 2010 23:37:42

Anders Eliasson

Posts: 5780
Joined: Oct. 18 2006

RE: Side bending problem (in reply to krichards)

Ok, then some of my experiments:
You dont need to leave the sides the whole night. I add heat once, and leave until fully cooled down, lets say some hours.
Never mind what you do, rosewood always keep the shape perfectly and cypress will always have some springback.
With respect of water or no, you are free to experiment and share results.

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 20 2010 0:34:52

Stephen Eden

Posts: 914
Joined: Apr. 12 2008
From: UK

RE: Side bending problem (in reply to krichards)

You dont really need any water to bend the sides at all. I dont use a machine at all and just bend by hand. I got a dish on the upper bout a few times, moisture or no moisture. It's easier and actually faster to do it by hand.

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 20 2010 11:48:20

krichards

Posts: 597
Joined: Jan. 14 2007
From: York, England

RE: Side bending problem (in reply to Stephen Eden)

I used to do it by hand but I find its easier to get consistent results with the machine
I'm going to miss out the water next time and see how it goes

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REPORT THIS POST AS INAPPROPRIATE | Date Jan. 20 2010 23:34:01