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More on bending cutaways
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=12945		 Page 1 of 1
Author:  Colby Horton [ Tue Jul 24, 2007 7:49 am ]
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I've been reading the other recent post on bending venetian cutaways and I still can't get good results so I wanted to ask a few more questions.
I've been trying to get to where I can bend cutaways in my shop made fox style side bender. I have bent them on a hot pipe before with EIR but I had a hard time with that, so koa on the pipe is out of the question.
Today I tried a test with some scrap mahogany thinned to .080(should be thin enough for mahogany). I wetted the wood and wrapped it in aluminum foil (because my test without it also failed). I got the temperature up to 250 degrees. I bent the waist first and then the cutaway part. I don't know whats wrong but I can't bend it for nothing. I always hear it breaking and I don't even have to finish the bending. I'm hoping maybe someone can suggest something that could be causing the problem. My problems are not as much on the horn of the cutaway as in the deep curve of the cutaway. Instead of bending it will just break right in the middle.



Could my wood be drying out too fast? It takes a couple minutes to clamp the waist all the way down. Maybe by the time I get to the cutaway it is too dry? Usually when I know I've broken it I will shut off the heat blanket let it cool to where I can handle it and take it out, it is usually bone dry at this time. Shouldn't it still be damp since it did not cook in the bender?

Could my cutaway pressing block be the problem? I've noticed some machines have a piece of pipe right there that looks like it rolls.

Does anybody use the stainless steel slats from LMI for cutaways? They seem almost to stiff. They also do not spring back very flat.

Any info would be appreciated.
Author:  Michael Dale Payne [ Tue Jul 24, 2007 7:57 am ]
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Too low way too low of temp. You might get away with bending the waist and LB at 250 but never the cutaway. I think I have been bending at too low on cutaways at 300-310 last night followed Johns advice and use craft paper that was pre-soaked in water for 2 min. then wet my wood and wrapped it in the kraft paper bent the waist 1/2way at 300 ran temp up to 350 re spritzed my kraft paper and moderately slowly bent the cutaway. It worked
Author:  Michael Dale Payne [ Tue Jul 24, 2007 7:59 am ]
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Stainless has memory and will not spring back to straight. I use spring steel.
Author:  Michael Dale Payne [ Tue Jul 24, 2007 8:05 am ]
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I know that if you take too long and too dry you case harded the wood, pretty much same heat treating steel. Then bending without breaking is almost out of the question. even taking the time to re-spritz the kraft paper in the cutaway section from the time my wood got to 300 till the time I finished the intire bend was less tha 7 min

Oh by the way I was bending Curly Mesquite
Author:  Brock Poling [ Tue Jul 24, 2007 8:18 am ]
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Are you putting spring clamps on the slats as it heats?

Author:  Colby Horton [ Tue Jul 24, 2007 8:25 am ]
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Michael,

Maybe my thermometer is not giving a good reading because I bend the waist and lower at 150 and with it on full blast by the time I get to the cutaway it is a 250 and it almost seems to stop there. I was just re-reading the bending instructions on John's site and I noticed he said to insert it in the sandwich. I had just been setting the tip of it on top!

So, when your waist is clamped half way, you just open the cutaway part of your sandwich and spray water right on the craft paper wrapped wood to re-wet it?

What is the cutaway ram on your machine like? Pipe, block?

Brock,
I do put clamps on the slats as they are heating.
Author:  Michael Dale Payne [ Tue Jul 24, 2007 8:54 am ]
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You can bend a typical none cutaway Mahogany between 250-300 all day long but not a cut away. Read John's(tippie53)post in my previous topic on bending cutaways you will notice he is suggesting bending the cutaway at 350
Author:  Pwoolson [ Tue Jul 24, 2007 9:36 am ]
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Colby, as Michael said, your temp is quite low. If you put the probe of the thermometer (assuming you are using some sort of meat thermometer) right next to the blanket in the sandwich you'll have pretty accurate results.
Is your cutaway tower flexible? Meaning will it pivot on the attachment blot? As you bend, you'll want to very firmly hold it "up" toward the waist to keep everything tight. That's important. Otherwise an option is to pull the slats "outward" away from the waist as you are cranking the cutaway tower. But that turns into a two person job pretty quickly.
Good luck. Paul
Author:  Colby Horton [ Wed Jul 25, 2007 12:42 am ]
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Thanks for all the info people!

I finally bent my first cutaway scrap using this machine. I put my thermometer in there better and got a more accurate reading on the temp. My only problem was when I took them out they were still slightly damp in a spot or two. And I cooked them real good. I didn't have any craft paper handy so I used wet paper towels. Would they be harder to dry out? Or did I just use to much water?
Author:  Michael Dale Payne [ Wed Jul 25, 2007 12:49 am ]
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Leave then in the press over night. If They are still wet after that then cut way back on how much you spritz them. Most wood it just takes a little on each side Maple takes very little as it just soaks up the water and the figuring may delaminate if quilted if it get too much water. Anyway a spray bottle and spritz each side with a mist. If you are using foil for your wrap the moisture will be trapped in the wrap so it takes longer to evaporate than kraft paper.
Author:  Michael Dale Payne [ Wed Jul 25, 2007 1:00 am ]
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If you take out a bent side while it is still wet they will cup.

If you used foil for your rap during bending and discovered the side to be still wet after you removed the foil, place kraft paper on both sides of the bent side. Place it back into the press with slats in place. re-heat to 220 for 5 min min. allow to cool over night.
Author:  Colby Horton [ Wed Jul 25, 2007 1:15 am ]
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Actually, I did let it cool over night. Apparently when I re-wetted it, I over did it. I'm going to perfect my technique a little more before I put a guitar side in there.
Author:  Michael Dale Payne [ Wed Jul 25, 2007 2:53 am ]
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Most woods really take very little added moisture. I bend even quilted Sapele and Snakewood with a very light spritz wrapped and in foil .I have been using Foil for my wrap but I think from now on I am going to do as John Hall recommends and use soaked kraft paper so that it would be easy to re-spritz the paper in the cutaway area. but I have to say that I had some handling issues with the wet kraft paper on my first two experiments with it.
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