Share:
Notifications
Clear all

Composite/Double Tops  

  RSS

darrenking
(@darrenking)
Customer
Technician
Rep Points: 563
Joined:2 years ago
Posts: 212
06/12/2019 6:14 pm  

Hello folks! It's been a while since I've had any time to play with my guitar making but things have eased a little at work now so it's back to having fun again!

Any one tried making a composite or double top? It's the perfect way to get rid of all of those excess soundboards we all seem to end up with! To cut a long story, I had been thinking about constructing one of these soundboards for quite some time but just never seemed to get around to it. Then, earlier this week I found myself having to order some resin and carbon fibre products from Easy Composites and saw that they sell Nomex so I order a couple of piece of the 2mm material. I then had to go and buy some veneer for another project and whilst at the veneer merchants picked up a bundle of 1.5mm thick western red cedar. Originally I had though of using the 1.5mm cedar as the outer skins of the soundboard with Nomex in the middle but it turned out to be little short grained so I have taken a different initial approach. That is to make up a central layer of the 1.5mm cedar with the grain running outwards at 45° from the centre line and then laser cut a pattern of hundreds of small slots into it to reduce the weight. I then sandwich this between two layers of normal soundboard which I can then thin down after everything is bonded together. I had some C grade spruce and cedar blanks from Madinter and these have been employed for this project. To be fair to Madinter I must say that the cedar in particular is perfectly nice timber although one of each species was slightly cosmetically compromised so these have gone in the inside. For now I have made one with two outer layers of spruce and one with two outer layers of cedar but there seems to be some makers using a combination of materials.

I took the central laser cut layer down to 1mm prior to lasering and sanded each of the two outer layers to around 3.2mm before bonding, so I currently have two 7.5mm thick soundboards in my vacuum press waiting for the UF resin to cure overnight. I think my aim will be to reduce the overall thickness to about 2.8mm for the spruce and may a little thicker for the cedar but if anyone knows differently please let me know. I In either case the soundboard should end up around 20% lighter than a solid top of the same thickness or 1.7x stiffer that a solid soundboard of equal weight.

These are both for Maccaferri copies so I will have to press some more backs and sides next week when my new log of rather beautiful massur birch arrives from Germany. Pics of that to follow.

I will read up a little more on using the Nomex and hope to have a go with that over the Christmas break.

I'd love to hear any feedback.

Cheers

Darren

FwA%hfX2TBCONv1beFMGJQ
WckGqbrJSmuO1sq+0FyOSg
c9bw1zsNTZq10wJxGddO6g
umOK2npcQt6Do0kmZcBFbg
NgHY4x8sSLOUWC9vlCNRMA
ClsEp1zhTM+Euwr0HGiuBA
Vxq9sehjR72WM0V8PCmpiA
DoF6yttXQQWDV%2gfUMRow
hBXukI4+Q+C0GgAsqRUXNw
WDnW9qWfT7SlwykvNaa8BA
74vlxCXMTgiLCMiqfXNLHQ
Vbs55FKORz6WwQeVYSgh7A
sR4pEgjEQEW83O6dz+MvAg
yxPhBVPjTY2j3oDkbt2wWg
PXY4M02AQOCtVQq1Oycg9w
d+OI+J+uQ0a1EiMSpjBiYw
acSqapAUSumTqEiePKcMvA
QIxtUBLVTaqkVaZh0S6FVw
gdWLWWFCR0uRMZQczNHndg
bOkVT3QrSV6Htijxc+ZGEQ


cardiffborn
(@jonathan-auckland)
Adept
Rep Points: 127
Joined:2 years ago
Posts: 48
07/12/2019 12:46 pm  

This is really interesting, though I really have absolutely no advice to offer here. Having spent some time reading about the flame resistant properties of  a synthetic aromatic polyamide polymer, I am going to refrain from any puerile jokes....... 

I've just been asked what I want for Christmas, and I reckon a laser cutter would be fun, or useful, or essential.

After a coffee I shall attempt to tidy the shed, again. 


mark bailey liked
ReplyReplyQuote
darrenking
(@darrenking)
Customer
Technician
Rep Points: 563
Joined:2 years ago
Posts: 212
09/12/2019 11:52 pm  

 

Hi Cardiff,

Oh, essential - you just have to get a laser cutter! The problem is that there are just too many things that you can do with them that it’s almost impossible to know where to start!

Now that the soundboards are trimmed to +5mm of finished I would say that the cedar throughout is far and away the most resonant with significantly more sustain than the spruce/cedar/spruce example. The more I think about it the less appealing is the concept of mixing materials.

Many years ago I worked on some speaker cabinet components for (the now long gone) Mission and their cabinets were made up of a lamination of thin MDF and thin chipboard. The reason for this was that the two materials had different resonant frequencies and so, by combining the two, it helped to produce a ‘dead’ cabinet as each of the materials would kill the resonance of the other. In a speaker cabinet this is helpful as it means that the cabinet is not suddenly going to start vibrating at a particular pitch and give the impression of increased volume. Transposed to the construction of a double top soundboard I would assume that exactly the same would happen and, given the recognised difference between the resonance of cedar v spruce, surely this isn’t a good idea as we want the soundboard to vibrate to its hearts content! Certainly based on the two that I have made (and I know that a sample group of two cannot be the basis for any definitive conclusions) I would have to say that the cedar throughout soundboard is far more promising than the spruce/cedar composite.

Here are the latest pics of the soundboards showing the CNC routing of the rosette recesses and perimeter, the gluing of the rosettes and some back lit shots of the spruce version showing the internal voids. Interestingly, even though the cedar soundboard is only 0.2mm thicker (but lighter) than the spruce, it is pretty much impervious to the transmission of light (and I have some very bright torches).

Comments, encouragement, derision all welcomed in equal measure!

Darren

3F708010 93BE 4001 845A 3F1E919ECDA0
EE37701E CF62 4304 9D28 4244C5DC9FBD
B1A4D2DE 359B 4E31 9D24 95E54BE6D47E
CA5BF4DF 8E84 40F9 AB62 FF622635EFE9
9AF0FB0C 282A 4F68 A472 7E9F371B63BD
662DBDF3 8712 485C A2B1 0B51F6DDCD6C
609020D1 2864 48F0 8A1C FC5D3E2AE9C5
F1A2995C 36FE 429F 8C79 2F64ACDDC0CD
70061099 6732 4283 BB34 842B229EDAC3


ReplyReplyQuote
darrenking
(@darrenking)
Customer
Technician
Rep Points: 563
Joined:2 years ago
Posts: 212
12/12/2019 12:37 pm  

I have had a further thought about the construction of these double tops and that was that if I incorporated a narrow cross grain section down the centre line this would reinforce the central joint in the outer skins of the soundboard. I will have to modify the weight reduction machining in the central layer slightly but this change, along with the angled grain of the central layer, will mean that there are no defined lines of weakness anywhere on the soundboard due tot he coincidence of longitudinal glue lines. Got to be a good thing right?

As a one off Christmas special (first come first served (Was it Henry the Eight whose coat of arms included the latin phrase Primum Venire, Primum Raptae (points for spotting the historical inaccuracy here!))), if any of you are making a cedar topped guitar and want to try a double top soundboard I would be willing to supply a laser cut inner layer for it. In fact if you send me two jointed soundboards I'll stick the whole thing together for you as well. All I would need is a scale PDF drawing of the soundboard so that I can create the laser cutting file to match the outer shape, sound hole and bridge position.

DN02SsoWRNyb2Riq+ygCXQ
z7a8RXdjSJGW1dsAZKcBRg
540DzXDORv+B+klKo+BiUg
83dw+8%1Ro6%axmsipZ+Zw


ReplyReplyQuote
darrenking
(@darrenking)
Customer
Technician
Rep Points: 563
Joined:2 years ago
Posts: 212
12/12/2019 12:38 pm  

I should add that these images are pre-sanding


ReplyReplyQuote
cardiffborn
(@jonathan-auckland)
Adept
Rep Points: 127
Joined:2 years ago
Posts: 48
17/12/2019 2:01 pm  

It's raining again so I'm 'catching up' on the amazing builds from everyone.

I was thinking about what you said with regards to resonant frequency cancellation and then got a bit sidetracked. I was trying to remember what one needed to consider when looking for resonant frequencies. I seem to recall being shown what happens when one shortens a metal bar and how both length and mass change together..... then it all went dark.

After another coffee I ended up reading about Thomas Rossing ( https://ccrma.stanford.edu/people/thomas-rossing) and his book on stringed instruments ( https://www.springer.com/gp/book/9781441971098)

I'm sure I'm teaching my granny to suck eggs here, but it would be interesting to know whether one can sum resonant frequencies from different materials.

PS. My Missions are still working well thanks

 


ReplyReplyQuote