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Deflection testing Double Sides part two:

Since posting the first thread "Double Sides" … the facts revealed, I have squeezed in a few more tests based on questions that arose in the first thread. Since it was a rather lengthy thread I thought I would begin a new thread to discuss the second round of tests.

I prepared several smaller sample coupons, to reduce the time and materials on my end. The numbers are not comparable to the first test since it was a much large piece but the results will hopefully shed new light on some of your previous questions. Three different wood species were used in this round, Maple, Cherry and Black Walnut. Since the previous test only considered the laminating effect on an open pored wood (walnut) this test proved to be interesting to see what affect the glue would have on closed pore woods. There were some Cherry and (hard) Maple cut offs in my scrap bin so these became the new test samples. All of the wood used was aged and dry so moisture should not be a factor in the results. All of the woods used were successive cuts off of the same billets.



All of the samples were cut to the exact same width and length and then thickness sanded to either .090" or .045" thickness. The first measurements were on the .090" solid pieces that were not laminated. The next measurements were on the .045" samples. Then another deflection measurement was taken by stacking two .045" pieces together (with no glue between them) and measuring how much they deflected. Each of these pieces was success cuts from the same billet with the grain oriented as it came from the billet. All of the tests were done using the same weight and laying the pieces across two lengths of inverted angle iron. The angle was used to try to eliminate as much surface resistance as possible.



The last measurement was taken after the [same] sets of .045" samples were laminated together using the binding press pictured below.



The adhesive was allowed to cure for 24 hours.



There is a lot of data to look at below but it is quite apparent that there is a significant gain in the overall stiffness of the laminated pieces of wood, compared to a solid piece of the same thickness, regardless of the species. Unfortunately the sample pieces are too small to measure any changes in cross grain stiffness but there is an increase but I guess you will have to take my word for it or perform your own tests


Sample Thickness - Deflection
Maple 1 .090" .038"
Maple 2 .090" .039"
Maple 3 .090" .041"
Maple 4. 090" .040"
Maple 5 .045" .114"
Maple 6 .045" .114"
Maple 7 .045" .111"
Maple 8 .045" .119"
Maple 5&6 .090" dry .056"
Maple 6&7 .090" dry .048"
[COLOR="Red"]Maple 5&6 .090" glued .014"
Maple 6&7 .090" glued .018"[/COLOR]

Sample Thickness - Deflection
Cherry 1 .090" .063"
Cherry 2 .090" .067"
Cherry 3 .090" .065"
Cherry 4 .090" .065"
Cherry 5 .045" .162"
Cherry 6 .045" .188"
Cherry 7 .045" .163"
Cherry 8 .045" .171"
Cherry 9 .045" .181"
Cherry 10 .045" .168"
Cherry 11 .045" .170"
Cherry 12 .045" .169"
Cherry 5/6 dry .088"
Cherry 7/8 dry .075"
Cherry 9/10 dry .076"
Cherry 11/12 dry .086"
[COLOR="red"]Cherry 5/6 glued .023"
Cherry 7/8 glued .020"
Cherry 9/10 glued .021"
Cherry 11/12 glued .022"[/COLOR]

Sample Thickness - Deflection
Walnut 1 .090" .060"
Walnut 2 .090" .058"
Walnut 3 .090" .061"
Walnut 4 .090" .059"
Walnut 5 .045" .159"
Walnut 6 .045" .161"
Walnut 7 .045" .174"
Walnut 8 .045" .171"
Walnut 9 .045" .168"
Walnut 10 .045" .164"
Walnut 11 .045" .164"
Walnut 12 .045" .169"
Walnut 5/6 dry .092"
Walnut 7/8 dry .091"
Walnut 9/10 dry .087"
Walnut 11/12 dry .081"
[COLOR="red"]Walnut 5/6 glued .019"
Walnut 7/8 glued .021"
Walnut 9/10 glued .022"
Walnut 11/12 glued .021"[/COLOR]

We have to make a quick trip to Nashville in the morning, to deliver a guitar so I will be away from the computer for a few days. I will try to answer any questions you may have when we return on Saturday.

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tim...
http://www.mcknightguitars.com

Tim, Thanks for putting all of this together, good number don't lie. I'm going to have to chew on this a little while though. I understand the unglued stacked vs the original deflections, but I'm chewing on the glued deflections as it's glued along the neutral axis. Humm.....

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Jim Watts
http://jameswattsguitars.com

Very interesting results!

I'm assuming that you are using epoxy as the glue in this case. Why not use HGG? I would think that with the impact on the environment that we would be all using biodegradable glues at this stage in our builds. I just don't understand the infatuation with epoxy with everything that is happening these days. I would also guess that HGG has a lesser deflection that epoxy. Maybe Torres had it right the first time.

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Michael Lloyd

“I was born to ignorance, yes, and lesser poverties ...
I was born to privilege that I did not see ... I didn’t know it, but my way was paved” – John Gorka

mlloyd,
There is no way that you could use HHG on a set of double sides and get them clamped up in less than 30 seconds, well... at least I couldn't. That is the reason I have never used that adhesive. I know a few builders who use AR glues with good results. I have shyed away from those glues since the glue permeates the sides (under clamping pressure) and often seeps through to the outer sides, This would be a nightmare if you planned to stain the exterior wood if you used AR glue.

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tim...
http://www.mcknightguitars.com

Very well done Tim!

Do you use side supports or tapes with your double sided guitars?

Thanks.

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Hesh
Ann Arbor, MI USA
http://www.heshtone.com

Fish glue would give you the open time and properties of HHG.

If the glue is contributing to the extra stiffness then it would be interesting to see if different glues gave different results.

So many variables, so little time, so many guitars to build

Tim thanks for all of this - this is fascinating stuff.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

So, How much does the glue soak into the wood? If it is a lot, than that could explain the increase in stiffness. An interesting experiment would be to take one of your .090 boards and spread glue on one side, put waxed paper on the glue and put it into the laminate press. Peel off the waxed paper and measure the stiffness of the "treated" board. Epoxy can be quite stiff. Just try bending some carbon fiber plates sometime. The stiffness isn't caused by the carbon fibers.

So if I understand correctly the laminated is approx. 2.5 times stronger than the solid of the same thickness?
That's amazing!
One thing I don't understand is the difference in deflection between the single piece of .045 and single piece of .090 thickness.
The moment of inertia (resistance to deflection) calculation cubes the thickness which increases the result by eight times when doubling the thickness.
This is substantially more difference than indicated in the tests. I would guess that the mechanics of the test such as distance between supports, friction etc. might influence the results but wouldn't think it would be that much.
Tim, I certainly don't mean to detract from your time and effort in doing the test. You did a great job.
I'm just trying to understand and perhaps someone can shed some light.
Thanks
Nelson

I don't know how the cube rule fits into this, exactly, but there could be some difference in glues. However, I'm sticking to my main theory that much of the added stiffness comes from two pieces of wood which when placed together with something holding them in place, have a very high coefficient of friction, and that's where most of the added stiffness comes from. I think it would have been interesting to brad the pieces together - no glue- and see if similar results were achievable, not practical for guitar building, but for stiffness theory, maybe.

Fish Glue might be an interesting test too. It dries to a crystalline state, and might offer some rigidity of it's own, where epoxy might have a little flex built in.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Using glue with water in it on wide, thin laminations can cause wacky things to happen. I made some multi ply sides using titebond for a few travel guitars and two of the sides had to be thrown away due to some extreme twisting.

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http://www.chassonguitars.com

That's a good point!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

I believe this arises because the boards are supported at both ends. A measurement of Young's modulus would (I think) be made using a board clamped at one end with the other end free. But don't quote me.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Good on you, Tim! Guys willing to do a little science really helps things along in my book.

I've done some laminating with hide, and figured out ways to get it applied and clamped 'real fast', but the addition of water is always an issue. You have to hold the laminates really rigidly until all the water evacuates, which might be some time, and even then there's a big risk of warping with the amount of moisture introduced.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I have been using laminated sides (and backs) for a few years now. I use West system epoxy and three to four layers of veneer, depending on the thickness. I laminate the layers in the same order they were sawn. I laminate under low humidity conditions as this seems to allow the glue to be taken up better and the finished product seems to distort less. I do this primarily as a cost saving measure. It brings a nice "set" of Brazillian down to the $50 range (material costs). The backs and sides when glued up in this fashion seem to work and behave as a normal set does. I have had them crack under extremely low winter humidity conditions. They do not have the stability that plywood would offer, but I think they work better sonically.
Recently I have glued up a set with carbon fiber cloth interleaved between the rosewood. Instead of the nice glassy taptone I usually hear, when tapped it sounded like tupperware. Oh well! I am building with it anyway.

ClayS, That's pretty interesting because I've been recently contemplating using carbon fiber in my own back and side laminations. Please let us know how it turns out in the end. I'm not too worried about the tonal affects on the sides. Did the cloth add to the rigidity of the laminations? Seems like it might be a way to get increased stiffness w/o much extra weight.

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-Clint Beacock

This is another random observation about laminated sides.

Since our whole discussion on epoxy and using a wetting coat with a thickened center coat I tried that on 2 pairs of sides (both rosewood) and the problem I normally get of having the epoxy seep through the sides was noticably reduced. Not eliminated, but it was probably only 10% as bad as it is with no thickening layer.

That is a real plus in my book because it saves a lot of work sanding off all that epoxy.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Hi Clint,
To me it did not seem to add any stiffness over the all wood layup. I substituted the CF cloth for one of the thicknesses of veneer and used a little more epoxy to wet out the cloth, most of which is squeezed out by the clamping pressure of the mold. The CF does make the material harder to work with. Someone told me how hard it was on HSS tooling, but I had to see for myself. When I ran the veneer,veneer,CF,veneer sandwich across my jointer It immediately nicked the knives, I tried it two more times in a different spot and two more nicks. The thin layer of cloth is tough! After edgeing I had to sand off CF fuzzies from the back joint to get a tight seam. Carbide tools seem to hold up better and I had no problem sanding it on a motorized radius dish..
Hi Brock,
I use the 207 hardener and epoxy "fill" to deal with the bleed through from porous woods. I wait for the epoxy to fully cure before I remove it from the mold or do any sanding of it. It seems to give a more stabile construction and cured epoxy is less of a sensitizer than uncured epoxy.

It may be a totally stupid question, but what would be the downside with gluing the laminations with yellow or hide glue, especially if you use a form and caul?

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I have a question too please: Does the epoxy permeate the fibers of the wood or just soak through the pores and then sit on the other side? If the later - when you sand it off it is then just in the pores?

Thanks

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Hesh
Ann Arbor, MI USA
http://www.heshtone.com

Laurent,

I did mine the first time with LMI white and it worked fine except you have to get everything clamped so fast. The open time of the epoxy is my favorite part about it. Someone mentioned that gluing thin laminations with water-type glues can cause some funky twisting and that makes sense, but I had no problems when I did it. I have been using the smith all wood epoxy and it is pretty forgiving. It mizes up thicker than the WEST too, so I don't worry as much about the thickener coat. I would rather use hide glue if I could trust I could get it together and clamped fast enough and it wouldn't twist up. Maybe heating the sides first? I imagine the epoxy is more structurally sound, as it fills gaps as it bonds, but it does add more weight, although not a ton more.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

I wonder if the fire method would work for laminations? Coat the side with Den Alcohol and set it on fire to make the HHG set right, like for attaching a back to the body. Probably not the best idea!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Brock, is this with West Systems epoxy? What type of filler did you use?

Hi Laurent,
What I found with yellow glue using my method, was the lamination would cup or wrinkle slightly with changes in humidity. Perhaps If I glued it up like plywood it would not do this. related to this , I found that the drier the veneers were pre-layup the more stabile they seemed as a finished product. Letting the pieces cure in the mold also seems to reduce any warping and twisting.

Hi Hesh,
Sometimes the epoxy seems to just be in the pores and sometimes the wood seems to have some saturation. Much depends on the particular sample and how much epoxy is applied. Pore filling with epoxy seems to even out the surface quality. Early on I did not do that and top coating with Nitro gave an acceptable finish to the casual observer, but close inspection revealed some lighter and darker areas.