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side purfling question
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=35952		 Page 1 of 1
Author:  coach [ Thu Mar 29, 2012 11:01 pm ]
Post subject:  side purfling question
Hey all,

I just bent some side purfling, it was bold, 10/10/10 .030" b/w/b. Anyway, it buckled at the waist. It wasn't horrible, just a few little wiggles that I don't want there. This is for a parlor guitar so the bend was kinda tight. I used my bending machine which has worked marvelously(I just made it and was very excited about how well it works).

I also used the technique that Todd demonstrated with the purfling sandwiched between the two scrap pieces. I kinda feel like it's maybe too thick to bend such a tiny radius without the buckling. Anyone ever try cutting a relief cut into the inside of the bend?

Any recommendations of how to avoid this or how to fix it?

Sean
Author:  quentinjazz [ Thu Mar 29, 2012 11:19 pm ]
Post subject:  Re: side purfling question
Hi Sean,

I have exactly the same problem with my purflings at the waist right now, I'd really like to have some advice on this issue, too.
Do you first glue your purflings to your binding, and then bend them? This is what I (try to) do, but the result is.. wavy...
Author:  Daniel Minard [ Thu Mar 29, 2012 11:20 pm ]
Post subject:  Re: side purfling question
Yeah... It does that in tight bends. Supersoft II helps a lot. A hot iron with plenty of steam can (sometimes) iron out the wrinkles, after the fact.
Almost make a guy want to build dreadnoughts!
I bent two narrow strips of 1/8" thick aluminum to fit around the "leading edge" of my bending iron. Drilled & tapped & screwed them in place with about 3/32" space between them. These pieces support the side of the purfling strips & spread the heat more evenly across full width of the purfling as you make the bend. For really tight bends, this is the only thing that works for me.
Others may have a much easier solution.
Author:  Tom West [ Fri Mar 30, 2012 7:09 am ]
Post subject:  Re: side purfling question
Sean: Wonder if the purfling is glued to bindings. If you glue first then bend in pairs with the purfling back to back and taped tight together it gives a lot of support as folks have said.
Tom
Author:  David LaPlante [ Fri Mar 30, 2012 7:24 am ]
Post subject:  Re: side purfling question
It's the relationship of the thickness (.010") to the width of each element thats the problem.
Even once glued or sandwiched, under heat the lay up still acts like individual pieces.
The outer edge has to stretch while the inner one has to compress. Wood does neither very well so it buckles.
Veneer of at least .020" (.6m) works better. I usually lay up veneer and binding stock together and strip out. Waist bends are made on a hot iron with the two purfling edges held together for support and without extra moisture.
Attachment:
binding.jpg

Attachment:
Maple Binding.jpg
Author:  Tony_in_NYC [ Fri Mar 30, 2012 7:54 am ]
Post subject:  Re: side purfling question
I don't know about cutting a relief in the purflings, because if you go too deep, you could sand or scrape into it when leveling. Then you have a worse problem than the ripples. Thinning it however, as suggested above, would be a good place to start. Make it only as thick as your binding. I tape everything together but do not glue the purfling to the binding before bending. Also, my bender uses a metal backing slat in the waist curve to keep tension on the inside part of the waist bend. It might be helpful to support the bend in a similar way on your bender. idunno
Author:  coach [ Fri Mar 30, 2012 8:58 am ]
Post subject:  Re: side purfling question
Thanks to everyone for your replies and advice. I have never glued the bindings to the purflings but that sounds like a good idea. I have lots of ideas to try...I do so love this learning process!!!

Appreciate the help. If you have time check out my blog for the progress of my daughter's parlor guitar at

bucketguitars.com

Sean
Author:  Fred Tellier [ Fri Mar 30, 2012 10:34 am ]
Post subject:  Re: side purfling question
When this happens to me, mostly in a tight cutaway I wet the area and clamp between a couple scraps of wood overnight. The heavy spring clamps apply enough pressure, if you are careful to maintain the radius it comes out fine. For the glued up before bending purfling it should also work bit probably will need more clamp pressure.
Author:  jsmith [ Fri Mar 30, 2012 10:40 am ]
Post subject:  Re: side purfling question
Another quick fix is to place the purfling on a flat surface, then run over the rippled area with an iron set on low. As far as gluing the purfs to the bindings before bending: In most cases I bend my bindings with the puflings glued to them. There is a little more of a challenge in getting the mitres nice and tight where they meet the tail wedge while at the same time getting a good tight scarf joint on the binding sections (I'm a scarfer, not a butter), but it's not that difficult.
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