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Side spring back?? More like spring forward . . .
http://luthiersforum.com/forum/viewtopic.php?f=10101&t=32765		 Page 1 of 1
Author:  StephenW [ Tue Jul 05, 2011 9:04 pm ]
Post subject:  Side spring back?? More like spring forward . . .
So, over the holiday weekend, I had a bit of time to myself and decided to try to bend my first set of sides. The sides are ovangkol, between 0.08 and 0.09 inches thick. I used a steel bending pipe, 2 3/8 inch outer diameter, ~1/4 inch wall thickness, heated with a propane torch.

I tried to bend dry at first, but got some scorching, so out came the damp rag to get a bit of steam going. The side seemed to be a bit tough to bend, but what do I know . . . it's my first effort at bending. I just tried to be patient and wait for the wood to relax. It did and I started bending, bit by bit, checking my progress against the plywood template shown in the pic below.

After a few bends, unbends and rebends, I got what I thought was a pretty decent side - it matched the template quite nicely. I put it aside and called it a day/night. Then then next morning, I come down to my workroom, fulling expecting to see some of the dreaded spring back that I have read about, but I see this . . . .

Attachment:
Bent side.JPG


Each bend is tighter than when I left it the night before. eek

Thinking about why this occurred, I come up with the following:

First, I left the sides too thick, I should have thinned them down to around 0.07 in. The thicker sides caused difficulty in bending, so I used some steam and I ended up using too much water to get them to bend. I didn't get all the water cooked out, and as the wood dried over night, it shrunk and pulled all the bends tighter.

But, that's just my guess. idunno

So, my questions are:
    1. What thickness should I have had the ovangkol at for a successful bend?
    2. Should ovangkol bend easily dry, or should I need steam?
    3. Would clamping in the form have prevented this?
    4. Is there anything that I am missing (sometimes the obvious can escape me)?
    5. Should I bend it further, get the ends to meet, glue them together to form a lopsided, heart-shaped object, thread some rawhide through it and convince my wife that it's a necklace that our 4 year old made for her as a late Mother's Day gift?

Just trying to salvage something here . . . . .
Author:  Ken Franklin [ Wed Jul 06, 2011 1:49 am ]
Post subject:  Re: Side spring back?? More like spring forward . . .
I've had that happen to me when I'm bending thick linings. The good news is it's easy to bend it back now to what you want. I wouldn't use much water.
Author:  Colin North [ Wed Jul 06, 2011 3:30 am ]
Post subject:  Re: Side spring back?? More like spring forward . . .
Looks like you got a fair bit of water/steam in to the inside of the curves, and as the wood dried out, so the wood shrank.
I don't know about the thickness, most of my sides have been bent about that, 0.08" /2 mm, no problem, but I clamp them in the mold to dry.
Even then I've had cupping of the sides, but yours doesn't look bad. Should be easy enough to bend back.
General advice is to bend using steam, not dry - but less is better, especially for figured woods.
Author:  DennisK [ Wed Jul 06, 2011 3:35 am ]
Post subject:  Re: Side spring back?? More like spring forward . . .
That's not too bad. At least it looks like they still lay pretty close to flat on the table.

I normally do sides in two days. First day just get the shape pretty close. No pre-soaking, just spritz as needed to keep from over-drying, and quit adding water when you're close to finished, so they're mostly dried out when you're done, to minimize warping. Next day, dry bend to final shape, and glue to soundboard as soon as possible (or clamp in form and glue blocks/linings, if building in the style of assemble rim first, then glue plates). I feel it gives a more stable and stress-free structure if you let them work out their warping after the major bending, so the final bend before locking them is only small adjustments. But you could try clamping them in the form next time, and see if they retain the shape the next day even if you take them out of the form. I suspect they'll still need a little touch-up, but probably less than if left sitting loose on the table.
Author:  WudWerkr [ Wed Jul 06, 2011 8:04 am ]
Post subject:  Re: Side spring back?? More like spring forward . . .
Were they allowed to sit over night like that , free and unclamped ? I keep everything that is bent clamped to a form from bending to assembly ! I have 5-6 side sets that have been bent for 6 months or so and they are still in a form and held to the shape.
Author:  StephenW [ Wed Jul 06, 2011 7:23 pm ]
Post subject:  Re: Side spring back?? More like spring forward . . .
Thanks for the replies. Looks like it's time to fire up the bending pipe and do some de-bending.

WudWerkr wrote:
Were they allowed to sit over night like that , free and unclamped ?

Yes, I did leave the side free overnight. In fact, I now plan to use that as a feature on my guitars - "Made with free range sides!!" :lol: It works with livestock, why not guitars?

Seriously, though, I'll clamp the other side when I bend it (less water this time) and compare the results. Probably thin it a bit before too.

Thanks again.
Author:  WudWerkr [ Thu Jul 07, 2011 7:19 am ]
Post subject:  Re: Side spring back?? More like spring forward . . .
Free range guitars huh , laughing6-hehe

And people say im nuts ! laughing6-hehe
Author:  gozierdt [ Fri Jul 08, 2011 10:06 am ]
Post subject:  Re: Side spring back?? More like spring forward . . .
I wouldn't go too thin with your sides. I leave my sides right in the range you have now-
I typically shoot for 0.085", unless its a tight cutaway, then I thin down to about 0.75"
just in that area of the one side. If you go to 0.075", I'd put a couple of extra support
ribs on each side to help protect from knocks and bangs in the future.
Author:  StephenW [ Fri Jul 08, 2011 10:46 pm ]
Post subject:  Re: Side spring back?? More like spring forward . . .
OK, so I "fixed" the side in the photo above this evening. It went fairly quickly and easily, and I am leaving that side "free range" for the evening.

While the pipe was hot, I grabbed the other side and went at it with very minimal amounts of water. I got it done and clamped that one in the form and will leave it there through the night. I left the thickness by the way. I had a couple of small cracks in that side near the edges, but I believe they are fixable or will be taken care of when I cut the sides down.

Thanks again for the replies.
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