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Cupped ends from new side bender
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=28614		 Page 1 of 1
Author:  Keith Lally [ Sat Aug 14, 2010 5:36 pm ]
Post subject:  Cupped ends from new side bender
My side bender from BluesCreek arrived yesterday so I hooked it up today and bent two sides. On both sides the ends came out cupped as if they weren't properly supported during the process. On inspection I can see where the support is lacking (pic below). Does anyone have any pointers for me to avoid getting cupped ends on the sides?

Here is the sandwich of slats, brown paper, side (black walnut), and blanket bowed in the machine while clamped for the cutaway.

Image

I'm sure its my poor technique and lack of experience with this tool but maybe someone has a suggestion that will save me some aggravation.

Thanks.
Keith
Author:  woody b [ Sat Aug 14, 2010 6:46 pm ]
Post subject:  Re: Cupped ends from new side bender
Too much water. (Especially with Black Walnut) Don't wet the wood at all. Just lightly spritz the brown paper.
Author:  Bobc [ Sat Aug 14, 2010 6:53 pm ]
Post subject:  Re: Cupped ends from new side bender
A spring clamp or 2 will resolve that. What gauge is the slat?
Author:  meddlingfool [ Sat Aug 14, 2010 6:56 pm ]
Post subject:  Re: Cupped ends from new side bender
I've had a similar problem with the same machine. I just made new bending patterns with the holes drilled more accurately so they just kissed the edges of the line you're trying to shape. It looks like the cross struts in your photo are inset from the edges. Also, it should be easy enough to flatten that portion showed with a clothes iron.
Author:  Bobc [ Sat Aug 14, 2010 7:28 pm ]
Post subject:  Re: Cupped ends from new side bender
Do you have another photo that isn't cropped so close. Tough to get a good perspective.
Author:  Keith Lally [ Sat Aug 14, 2010 8:49 pm ]
Post subject:  Re: Cupped ends from new side bender
Bobc wrote:
Do you have another photo that isn't cropped so close. Tough to get a good perspective.


Here is a picture looking straight on at the caul in the cutaway. If just a spritz is needed on the paper then I may have overdone the water. I sprayed the wood, then dampened the brown paper. I'm not sure what gauge the slats are - they are whatever size comes by default with the kit from John.

Image

Quote:
new bending patterns with the holes drilled more accurately


The picture is deceiving as this is a brand new mold I made this morning with the holes right at the edges. I cut a couple other sets of BW sides last week just for trying this out so will bend another set tomorrow with less water and see how it goes.

Thanks all for the assistance.
Author:  John Mayes [ Sat Aug 14, 2010 10:14 pm ]
Post subject:  Re: Cupped ends from new side bender
If it's just at the very edge there after the last cross support why not just add a piece of ply that is flush right at the edge? Simple solution, and shouldn't take more than 5 minutes to do.
Author:  Dave Stewart [ Sun Aug 15, 2010 8:36 am ]
Post subject:  Re: Cupped ends from new side bender
If that's a cutaway (looks like), I had the same situation ....think this is common unless you go with "full supporting" molds. As John suggests, I tried to get the last "bridge" as close to the exit edge as possible for support. (If I see cupping, I'll even jam a wedge between the support & the sandwich after all the "cranking" is done.)
Author:  Robbie_McD [ Sun Aug 15, 2010 9:23 am ]
Post subject:  Re: Cupped ends from new side bender
I had the same issue, so added a shaped solid block and extended it out a bit - works great!

Image
Author:  Daniel Minard [ Sun Aug 15, 2010 12:07 pm ]
Post subject:  Re: Cupped ends from new side bender
Yup! The extension trick works great on cutaway forms. Full support is the key.
Author:  TonyKarol [ Sun Aug 15, 2010 1:51 pm ]
Post subject:  Re: Cupped ends from new side bender
In the above posted pic .. only one of the cross tubes actually hits the form's edge (one looks to be off by about an 1/8 inch) .. you are asking for trouble .. it needs to be right on the form shape, or cupping and possibly cracking will happen right there ....

All my new forms are solid, as I employ spring tensioned slats ala John How's bender whenever I can ..
Author:  Keith Lally [ Sun Aug 15, 2010 9:00 pm ]
Post subject:  Re: Cupped ends from new side bender
As per all your suggestions I added supports at both ends of the form and used less water. No cupping on four sides bent today. The more support in the form the better so any new ones I build will be as near to solid as practical. Thanks for your help.
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