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Question - made bender - spring back question on walnut
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Author:  John A [ Wed Mar 13, 2013 7:45 pm ]
Post subject:  Question - made bender - spring back question on walnut
Hi everyone,

I made my Fox style bender. I am bending some walnut to get the hang of it - before I get to some nicer wood. I have been using a pipe for a while but wanted the more consistent results.

I bent the walnut at around 235 degrees, and it bent easily. It was about .08 to .085 thickness. Once completely bent, I turned off the blanket.
Once the blanket cooled down to about 100 F. I turned it back on and took it up to 235-250 degrees, and unplugged it. It sat there for a couple of hours.
I then removed one of my clamps and noticed a good amount of spring back. I plugged my blanket in again and "cooked" the side for about 4 to 5 minutes at about 240 degrees. I have not checked for spring back.

Any ideas why I got so much spring back ? Should I be cooking the sides longer ? I did moisten the walnut side a little with some water before bending. I am not using slats (yet), nor craft paper, but I have no objection to doing so.

Thanks in advance !

John
Author:  Alain Moisan [ Wed Mar 13, 2013 7:54 pm ]
Post subject:  Re: Question - made bender - spring back question on walnut
John A wrote:
Once the blanket cooled down to about 100 F. I turned it back on and took it up to 235-250 degrees, and unplugged it.

Hi John,

I "recook" twice after the bent (instead of just once like you did). I started doing so after noticing some wod specie were indeed more prone to springback. Recooking twice heloed a lot. I also wait about 30 minutes before taking out the side of the bender.
Author:  ChuckH [ Wed Mar 13, 2013 9:19 pm ]
Post subject:  Re: Question - made bender - spring back question on walnut
Well, we're all different I guess. I just bent two sets of black walnut. Started bending waist at 250 and front then lower bouts at approx 290. Brought heat up to 315 and let cool to 290. Did this two more times and left in bender for approx one hour. No spring back at all. Sides were .085"


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Author:  WaddyThomson [ Wed Mar 13, 2013 9:52 pm ]
Post subject:  Re: Question - made bender - spring back question on walnut
This is just a guess, but I'd bet you didn't get it hot enough to really get the wood to release completely. I would want to let it get to at least 340 t0 350 before starting the cool cycle. Not that I have much experience with it at all.
Author:  mkellyvrod [ Thu Mar 14, 2013 9:12 am ]
Post subject:  Re: Question - made bender - spring back question on walnut
Can't claim to have a lot of experience here. I built my first two using a pipe as well. I have since switched to the heating blanket and Fox style bender (for 4 sets of sides; all about 0.08 thick) and followed Todd's utube video as far as the procedure for bending (including foil lining and wet kraft paper). As the steam begins to be given off (at about 250) I begin bending the lower bout after bringing the waist in about half way; I then move to upper as temp continues to climb. Temp gets to over 300 by the time I bring the waist fully in. I lower temp to around 300 or slightly less and cook for an additional 15 minutes (got a 15 minute timer). I shut off the blanket after 15 minutes and leave in bender for an hour or so (longer if I can stand the wait). So far I've experience only slight spring back on one set of sides, with no scorching of any of the sides. I've also bent my bindings using this method, and am looking forward to having a much better fit between the binding and sides (the consistency you mentioned) which was lacking using the bending pipe. Seems like you're not getting the wood quite hot enough with a maximum of 250. Recommend you search out Todd's utube video if you haven't seen it.
Marty
Author:  ernie [ Thu Mar 14, 2013 10:01 am ]
Post subject:  Re: Question - made bender - spring back question on walnut
I bent my walnut .090 vy slowly on an older alum overholtzer bending form at 250 deg f. It took abt 15-20 min for a CL . I then used a walnut veneer at .022 with brwn veneer glue to make a laminate walnut side which is vy stiff in the mold and needs no cauls or spreaders , and aids in assembly. of blocks/ linings.
Author:  Fred Tellier [ Thu Mar 14, 2013 10:15 am ]
Post subject:  Re: Question - made bender - spring back question on walnut
I bend at 300 and turn the heat down to 250 once bent and allow to cook for 10 or 15 minutes, actually what ever time is left on my timer. After it cools I recook for 20 minutes at 250 and once removed from the bender I put the side in the outside mold and clamp to it until ready to assemble the rim, some woods will spring a little but not enough to be a problem. I sometimes need to touch up the waist on tight 000 style shapes with my hand bender when I assemble the rim. I used to cook at 300 after bending and found on some woods like Cocobolo the sides darkened too much so I now back off and it prevents this happening.

The PID controller really makes the bending easier and allows me to walk away and work on other things as it is cooking.

Fred
Author:  klooker [ Thu Mar 14, 2013 12:04 pm ]
Post subject:  Re: Question - made bender - spring back question on walnut
Fred Tellier wrote:
... I used to cook at 300 after bending and found on some woods like Cocobolo the sides darkened too much so I now back off and it prevents this happening.



Fred,

Temp, duration, or both?

Kevin Looker
Author:  Terence Kennedy [ Thu Mar 14, 2013 1:26 pm ]
Post subject:  Re: Question - made bender - spring back question on walnut
I'm like Fred. Start bend at around 260, complete around 320, cook at 300-320 for 10-15", cool and repeat the cook a few hours later at the same temp and time. I usually leave in overnight as there is always other stuff to do. Springback is acceptable. Todd the long cooking time at 250 is interesting, do you find that has improved things opposed to the short cook X2?
Author:  John A [ Thu Mar 14, 2013 4:14 pm ]
Post subject:  Re: Question - made bender - spring back question on walnut
I will look up the Todd's video - I never paid much attention to the Fox Bending videos - due to my happiness with the pipe... but now I need the knowledge. I was getting some smoke at 250 - but now I realize it must have been chemicals burning off my blanket. Cooking now at 290 for 15 minutes.
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