Official Luthiers Forum!
http://w-ww.luthiersforum.com/forum/

Questions about Double Sides
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=11884		 Page 1 of 2
Author:  BruceH [ Thu May 03, 2007 1:11 am ]
Post subject: 
I'm thinking about trying double sides on my next guitar and I have a few questions for those of you that build this way:

1. What are the thickness of the two sides? Are you epoxying two thinner sides together, or are both normal thickness, or just the inner layer thinner, etc?

2. What kind of wood are you using for the inner layer? Something light and resonant or dense?

3. What about grain orientation for the inner layer? It would seem to me that vertical grain would offer the most support, but I wonder about the differences in expansion/contraction rates. Then again, after bonding with structural epoxy maybe it doesn't matter.

4. Any hints for getting a consistent clamping pressure?

Thanks!
Author:  WaddyThomson [ Thu May 03, 2007 1:19 am ]
Post subject: 
Bruce,
There was a pretty extensive thread on this in the Archives.  Here
Author:  Andy Zimmerman [ Thu May 03, 2007 1:26 am ]
Post subject: 
For my double sides I use:
1. 0.06 outer piece
2. 0.04 inner piece
3. The inner pieces is lower grade EIR...I buy them from allied
4. After bending and gluing, (epoxy) I dye my EIR insides black!!!!!
5. I have a mold similar mold to my bending mold for my gluing.
    I use spring clamps and cauls for gluing.
6. I bend both pieces at the same time.
7. I use west systems 206
Author:  SimonF [ Thu May 03, 2007 1:34 am ]
Post subject: 
I do the same as Andy. Tim McKnight has a nice web page somewhere
demonstrating his clamping methods. I am doing my first batch with
double sides and they are SUBSTANTIALLY stronger. It is amazing and
absolutley perfect fit in the mold, no springback, etc...

However, I clamp my sides using what I think is the traditional method.
Classical builders have been doing laminate sides for years. I use a half
mold and clamp with thin wooden cauls. Visits Schramm's website for
some pics of his setup.

Peace Out,
Simon
Author:  BruceH [ Thu May 03, 2007 1:40 am ]
Post subject: 
Thanks, guys. Looks like most of my questions were answered, but I still wonder about running the grain vertically on the inner side.

I like the black dye idea, Andy.
Author:  Brock Poling [ Thu May 03, 2007 5:03 am ]
Post subject: 

I do it much the same way. I thin both sides to .045 (or so) and I bend them separately.

My epoxy brand mix is West 105/206 and I use blue tape on the sides to keep everything from sliding around during the clamping process.

I have experimented a touch with putting a strip of tyvek between the layers to further prevent cracks, but I am not convicinced that this is either necessary or a good idea.

I have noticed the following.

* 0 spring back.

* the resonance of the rims is unmistakable they tap like a gong.

* mega stiff

* there is no lumpiness in the sides requiring them to be sanded smooth and flat. They are very very close to perfect after they come out of the gluing jig.


Author:  Steve Saville [ Thu May 03, 2007 5:18 am ]
Post subject: 
I was thinking on my next build I would make double sides. I'm thinking about using fish glue for that instead of epoxy. It seems that there is less water content and there will be much less warping of the sides than using LMI white or Titebond. Does anyone have any thoughts about that?
Author:  Brock Poling [ Thu May 03, 2007 5:31 am ]
Post subject: 

I think it would tack up way too fast. I use the slow setting epoxy so I have long open times and it dries very hard.

Author:  Steve Saville [ Thu May 03, 2007 6:24 am ]
Post subject: 
Brock, have you used fish glue? It has a pretty long working time. Do you guys coat both sides? If you coat just one, I'd think you'd have enough time with fish glue. If you need to do both, I think you are right.

Is 30 minute epoxy slow enough, or do you need longer working time than that?

I think using Tyvek is a bad idea. The surface energy of the material makes it almost impossible to bond to. It is porous, but the pores are so small that I think it would be difficult for the epoxy to flow through.
Author:  Brock Poling [ Thu May 03, 2007 7:13 am ]
Post subject: 

Yes, I have worked with fish glue. I certainly am not saying it "won't" work. It very well may, but I work notoriously slow and by the time I coat both sides, tape them together to keep them straight, get it on the jig, and apply 28 clamps ... a fair amount of time has gone by.

I don't know what the open time is on the West 105/206 combination is, but it is the slow hardener. I usually leave it clamped up in the jig a full 24 hours before I take it out.
Author:  KenMcKay [ Thu May 03, 2007 7:35 am ]
Post subject: 
Silk would be a better choice for the middle layer. Carbon fiber cloth
works out real nice also. I made some laminated sides with two very thin .
02 inch thick layers of veneer with carbon fiber cloth inside and they are
fairly flexible but very strong both across and along the grain. I don't
think I would go this thin but it gives you an idea. You don't need to make
them too thick to get what you need.

You can orient the grain in a center layer 90 degrees to the face layers if
you want to increase the cross grain stiffness. Spruce would be a good
choice here. Certainlywood.com sells sitka suitable for this. But I wouldn't
make the layup too thick. Another good choice would be a nice face
veneer about .05 inch thick with a layer of carbonfiber in the center and
spruce inside. That might be the best of all now that I think of it.

A good glue besides epoxy is Unibond 800 urea formaldehyde glue.

Author:  KenMcKay [ Thu May 03, 2007 7:37 am ]
Post subject: 
When I say carbon fiber I mean the cloth.
Author:  Doug O [ Thu May 03, 2007 12:43 pm ]
Post subject: 

This may be a stupid question, but hey, that never stopped before. 


What about a nomex core for the sides?  And for that matter why not the same approach for the back, whether it be two piece and epoxy, or nomex core? 
Author:  Doug O [ Thu May 03, 2007 1:42 pm ]
Post subject: 

Hesh, the diagram below is from the thread on this subject linked above.  It seems that if you put a nomex core into this assembly, where this detail is showing a void between the inner and outer plies, you could potentially get a very rigid side, while solving the binding problems you pointed out.



Constructing back and sides using a "multiple ply" assembly provides incredidble access to exotic tonewoods (veneers) that are largely unavailable in solid wood.    There is a veneer dealer 30 minutes from my house that stocks tone wood species in quality of figure that's simply amazing.  Not to mention flitch cut Brazilian RW.


It seems that one of the largest hurdles is overcoming the "plywood" stigma.  But isn't a spruce double-top with a nomex core on a $12,000 classical just a plywood soundboard with a different name and a bit of high tech mojo?
Author:  Anthony Z [ Thu May 03, 2007 2:39 pm ]
Post subject: 
Ken, carbon fiber must be hell on a router bit when cutting the binding ledge assuming your CF cloth runs the full width of the side. How do you get around the problem?
Author:  SimonF [ Thu May 03, 2007 4:10 pm ]
Post subject: 
When evaluating ideas (and I have lots of far out ones), I try to examine
things in light of practicality. And what I have found is that some ideas
are only sensible to a certain degree.

Let's take laminate sides for an example. I am currently building my first
batch with double sides, so I don't know what the results will be.
However, the sides are substantially stronger and I believe will be a big
improvement over traditional single piece sides.

Taking two sides and laminating together with epoxy gives you very good
results. Practically speaking, I think this method has reached its peak.
Adding Nomex core or a carbon fiber layer, IMHO, unnecessarily
complicates the matter while not really producing a significantly stiffer
rim.

Peace Out,
Simon
Author:  TonyKarol [ Fri May 04, 2007 2:45 am ]
Post subject: 
Hesh .. I fail to see what the sides have to do with a top that is only .065 thick (and BTW , who is taking them down to that ??) moving with RH - the sides are not going to move much in either case - ie, the lower bout measurement wont be changing much no matter what you make the sides out of - the expansion is across the sides, not lengthwise. The top will move no matter what when RH changes - it will rise or fall, not get any wider (measuring across the arc when its domed).
Author:  Mattia Valente [ Fri May 04, 2007 8:24 am ]
Post subject: 
FYI, John Bogdanovich's beautiful new book on classical guitar making has a pretty detailed and illustrated description of how he does his double sides. Worth a read, and the book is worth it simply because of the pretty and the absurdly low price.
Author:  KenMcKay [ Sat May 05, 2007 1:02 pm ]
Post subject: 
[QUOTE=Anthony Z] Ken, carbon fiber must be hell on a router bit when
cutting the binding ledge assuming your CF cloth runs the full width of the
side. How do you get around the problem?[/QUOTE]

It is not too bad on the bit because the cloth is very thin.

Author:  KenMcKay [ Sat May 05, 2007 1:14 pm ]
Post subject: 
[QUOTE=SimonF] When evaluating ideas (and I have lots of far out ones),
I try to examine
things in light of practicality. And what I have found is that some ideas
are only sensible to a certain degree.

Let's take laminate sides for an example. I am currently building my first
batch with double sides, so I don't know what the results will be.
However, the sides are substantially stronger and I believe will be a big
improvement over traditional single piece sides.

Taking two sides and laminating together with epoxy gives you very good
results. Practically speaking, I think this method has reached its peak.
Adding Nomex core or a carbon fiber layer, IMHO, unnecessarily
complicates the matter while not really producing a significantly stiffer
rim.

Peace Out,
Simon[/QUOTE]

Maybe true but lighter or tougher sides can be made with equal stiffness
to your "double sides". I hate heavy guitars.

Author:  KenMcKay [ Sat May 05, 2007 1:16 pm ]
Post subject: 
Oh and one more thing, Carbon fiber cloth can add crack resistance.
Author:  KenMcKay [ Sat May 05, 2007 1:28 pm ]
Post subject: 
[QUOTE=Doug O]

Hesh, the diagram below is from the thread on this
subject linked above.  It seems that if you put a nomex core into this
assembly, where this detail is showing a void between the inner and outer
plies, you could potentially get a very rigid side, while solving the binding
problems you pointed out.


2007-01-10_155450_side-schematic.jpg">


Constructing back and sides using a "multiple ply" assembly provides
incredidble access to exotic tonewoods (veneers) that are largely
unavailable in solid wood.    There is a veneer dealer 30 minutes from my
house that stocks tone wood species in quality of figure that's
simply amazing.  Not to mention flitch cut Brazilian RW.


It seems that one of the largest hurdles is overcoming the "plywood"
stigma.  But isn't a spruce double-top with a nomex core on a $12,000
classical just a plywood soundboard with a different name and a bit of
high tech mojo?

[/QUOTE]

This is a good idea, but I think Nomex is the wrong product for the core. I
spoke with Randy Reynolds a couple years ago about this because he
knew I had done a lot of experimenting "composite tonewood". He was
going to laminate his sides and wanted to find a light core material that
would be suitable. He could not find the product that I suggested which is
called Airex R63. So he got some blue, closed celled foam from the home
center and sliced it into thin 2 mm slices on the bandsaw. I am not sure
how that turned out but is is probably a nice light, stuff layup. The skins
could be almost as thin as possible and still retain the stiffness required.
The stiffness comes from the distance that the skins are spaced apart and
their tensile strength.

After saying all this I would highly suggest sticking to good old wood and
don't even get into this stuff.
Author:  JohnAbercrombie [ Sat May 05, 2007 11:38 pm ]
Post subject: 
[QUOTE=KenMcKay]
After saying all this I would highly suggest sticking to good old wood and
don't even get into this stuff. [/QUOTE]

I know of one builder who is using balsa core in 'doubletop' guitars, so this might be an 'all-wood' option for sides which would be low mass, if one wanted to go to the trouble.
I've built a few double sides, and I like to use some 'meaningful' clamping, so I'd probably crush a delicate core anyway. Two layers that add up to perhaps .1 inch don't weigh much - if you bevel your end block corners a bit more you will reduce the overall guitar weight as much as you will by coring the sides.
My inclination would be to add some strengthening fabric to the core. It pays to test your fiber reinforcement- most 'natural fibers' snap easily after they've been epoxy-impregnated. Ask any boatbuilder who's used epoxy how his jeans survived....

Cheers
John
Page 1 of 2 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/