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bending cutaway issues
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=12929		 Page 1 of 1
Author:  Michael Dale Payne [ Mon Jul 23, 2007 2:14 am ]
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Ok, As you know I redesigned my cutaway and added it to the MJ plans. Well I did some test runs with quarter sawn straight grained Mahogany, Curly Cherry and Quilted Sapele. All orphaned or flawed sets I had laying around.

The quarter sawn Mahogany was no issue as expected.

The figured woods was an other issue.


One total crack and break through on the curly Cherry. So I thinned the cutaway area to .07" Still had cracking and curl more than minor figure separation.

The quilted Sapele un-thinned .09" piece was just like the curly Cherry. The thinned piece .07" had no cracks but a good bit of figure separation.

On none of the pieces did, did I have any clue things were amiss. every thing felt as if it was bending with out issue, no sound of cracking, no abnormal resistance. The figured woods were bent at 310-315 deg f.

I have not tried Supper-SoftII on High figured wood but have some on order

Any suggestions
Author:  Mike Mahar [ Mon Jul 23, 2007 2:23 am ]
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A lot of builders bend their cut aways by hand even when they use a bender for the rest. The best way to bend difficult wood by hand is to place it between two spring steel slats and then bend the sandwich over the pipe. That is how I bend the tight curves on my mandolins.

The curves in your plans do not seem to be too extreme. I'd wouldn't want to bend bee's wing bubinga to that shape, however.

In the end, there just may be limits that certain woods will not exceed.
Author:  Pwoolson [ Mon Jul 23, 2007 2:24 am ]
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MP, super soft works well. I'd recomend using it on the crazy stuff.
Also, are you keeping lots of tension on the slats as you bend it? Not sure of your setup but check out Taylor's factory fridays video on bending. They stretch the packet slats, blankets, wood and then introduce the bend when the tension is wanting to pull it straight. Makes the whole thing more reliable in a bend.
I think John How made something similar on his bender.
Author:  Glen H [ Mon Jul 23, 2007 8:58 am ]
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MichaelP,
I'm with ya. I've tried to bend venetian cut-aways three times and all three ended up flourentines!

Good luck on non-scrap.
Author:  Kent Chasson [ Mon Jul 23, 2007 9:43 am ]
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The tension idea that Paul mentioned works for me.  I spring load the bottom slat.  I also spritz lightly with water and wrap with aluminum foil.  Seems like I can bend hotter without scorching that way as the water can't evaporate.
Author:  LaurieW [ Mon Jul 23, 2007 9:44 am ]
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Very interesting - I have only bent one venetian (by hand) and it was plain black walnut and had no issues.  I assumed if I went slow and the wood was quite thin, I wouldn't have any problems.   A set of figured oregon myrtle is my next one, I'll let you know how it goes.   


I haven't heard of super soft, where do you get it? 


Laurie


 
Author:  Blanchard [ Mon Jul 23, 2007 9:50 am ]
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When I started out I built a fox style bender. It worked well until I tried to bend a cutaway. After breaking a few sets of nice culry walnut, I tried bending on a pipe and never went back. When bending by hand you can actually feel and see what is happening with the wood. For me, that was the key to avoiding breakage. I have probably bent 60+ cutaways in all kinds of wood with only one fatal break.

Oddly enough, I still use my Fox bender, but I put the sides in it AFTER I have bent them by hand over a pipe. This helps refine the curves, reduce cross grain ripple and assure symmetry.

The advice of using a sheet metal slat while hand bending figured woods is good. Pressure on the outside of the curve really helps.

Also, when bending curly woods, especially maple, it helps to only apply moisture to the INSIDE of the curve. Wetting the outside  reduces the tensile strength of the wood and makes it easier for it to crack along a curl.

Hope this helps,
Mark
Author:  Pwoolson [ Mon Jul 23, 2007 9:55 am ]
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Mark, is the side flat when you bend the cutaway on a pipe, or do you bend the waist and lower bout first? Also, don't you find it tricky to get it in the bender after bends have been made? That's when I tend to break things. Thanks, Paul
Author:  Blanchard [ Mon Jul 23, 2007 10:24 am ]
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Paul

I bend the waist first and work my way to each end from there. I usually bend the cutaway before doing the lower bout.

I don't have any trouble getting the bent side in my bender. On mine the whole waist clamping mechanism lifts off. I just drop the bent side on to the mold.

It shouldn't be a problem on a standard Fox bender either. If there's enough clearance to get a bent side out, there should be enough to put a bent side in.
 
Mark
Author:  tippie53 [ Mon Jul 23, 2007 11:50 am ]
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   Bob Gleason of Pegasus Guitars and Hilo strings of Hawaii taught me this trick. I have very few problems with bending cutaways.
    Highly figured woods can be a headache but this will improve your success rate . I use kraft paper that has been soaked in water for about 1 to 2 minutes so it is saturated.
   Take the heat on the blanket to 350 F and you will see steam coming off the machine like a tea kettle. Allow about 1 to 2 minutes of boil off time then check the paper before bending and re wet.
   The water is acting more as an anti scorch agent. This allows the wood fibers to plastisize throughly. If you dry out the wood it becomes case hardened and will crack.
     After that start bending and when you do the cutaway pull up as you crank the ram home In actual time you will be done bending in about 8 minutes or so. Once on the pattern blow off the water with an air compressor if you have one. Let the heat set about 220 degress for 15-20 minutes to help dry off the wood to set the bend. I let them in the bender overnight.
   To take them out I will first relieve the waist about 1 inch pull the lower bout and then start taking off the ram so that I can pull my pinning bolt.
     Then I take out my side and place it in the mold. That is all it takes. With this system I have lost 2 sides in 3 years and I bend a lot of wood .
      The most important thing is to keep going even if you hear a crack. Chances are if it cracks there us 1 of 2 things that happens
1 it is broken beyond repair
2 it it cracked and is repairable
   Try it you may find that this will work for you
john hall
blues creek guitars
Author:  JHerrick [ Mon Jul 23, 2007 11:52 am ]
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[QUOTE=LaurieW]

I haven't heard of super soft, where do you get it? 


Laurie[/QUOTE]


 


This link is to a site about applying veneer. They have some interesting testimonials and videos on the product. They also (obviously?) sell super soft.


I'm not affiliated with this site in any way...lol...was noticing the name!


Joe
Author:  WaddyThomson [ Mon Jul 23, 2007 3:05 pm ]
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Highland Woodworking has it too.  Here
Author:  Michael Dale Payne [ Tue Jul 24, 2007 1:10 am ]
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I have successfully bent lots of cutaways. even with quilted Sapele but avoided radius less than 1.5" when dealing with high figured woods. Even then figure separation has been an issue I have learned to deal with. Sometimes after the fact. I hoping the SS2 may help because my client really want this deep tight cutaway.
Author:  Michael Dale Payne [ Tue Jul 24, 2007 1:11 am ]
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I do my sandwich the same, in foil to trap the steam
Author:  Michael Dale Payne [ Tue Jul 24, 2007 1:12 am ]
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yep have some on order
Author:  Dennis Leahy [ Tue Jul 24, 2007 3:23 am ]
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[QUOTE=tippie53] I use kraft paper that has been soaked in water for about 1 to 2 minutes so it is saturated.
   Take the heat on the blanket to 350 F and you will see steam coming off the machine like a tea kettle. Allow about 1 to 2 minutes of boil off time then check the paper before bending and re wet.
john hall
blues creek guitars[/QUOTE]
Hi John,

Can you give me a little bit more detail about how you re-wet the paper? You evidently don't use foil, right?
I assume the initial 350° heating done on a flat sandwich? So, do you just quickly open up the sandwich, and spritz a little bit of water on the wood, or the inside surface of the paper, or...?

Sorry for all the questions!

Todd Stock mentioned breaking sides when removing from the bending mold. Thanks for that reminder, as I now recall that I promised myself to make a better way to slowly release that cutaway clamping caul. The outer piece of spring steel *sproinnnnnging* is a danger to life and limb, but when that inside piece of spring steel wants to quickly flatten out as it pops the cutaway from the mold, well I feel very lucky that the figured Bubinga cutaway side did not explode into pieces. I'm thinking of a way to gently release the pressure on the cutaway caul, and when it is released enough to just slip something between the side and the inner steel, then I'll capture the inner steel and get the wood safely away from the mold.

Dennis
Author:  tippie53 [ Tue Jul 24, 2007 7:42 am ]
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I use a spray bottle. The wood is in the bender and then I heat it there. A little misting is all you need as the steam will penetrate the wood a bit. You do need to let this set overnight to cool and dry out
john hall
Check out my website and the tutorial on bending
Author:  Michael Dale Payne [ Tue Jul 24, 2007 8:31 am ]
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[QUOTE=tippie53]After that start bending and when you do the cutaway pull up as you crank the ram home[/QUOTE]

Pull up on the end of the sandwich? Pull up on the cutaway caul? Please expand on this
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