Glues

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blackalex1952
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Glues

Post by blackalex1952 » Mon Apr 04, 2016 2:36 pm

I have been laminating guitar sides and backs with West system epoxy glue. I am convinced that hide glue is best for the soundbox work on non laminated builds, and also for the neck join, for two reasons. Firstly, as long as the join is a tight fit, hide glue, being the hardest glue I have found gives great acoustic response. Secondly, HHG joints are easily undone and reassembled, being the only glue I know of that re sticks to itself. I had some hide glue in a plastic cup, and some Tightbond in a similar cup, both of which had hardened. Dropping the removed samples on to a saw table demonstrated the difference between the two acoustically. The Tight bond gave off a thud when it landed and the hide glue sounded with a ping!
My thinking re laminated backs and gluing is this. Surely glue can have a damping effect on the laminate? I have found this to be an issue, I have toyed with the idea of having some heated metal presses made that will glue my backs and sides using HHG, accurately made of course to eliminate any joint gaps. But this would be an expensive industrial process to set up and one of the disadvantages would be the fact that each guitar shape would necessitate it's own individual press. I have been vacuum laminating my components, which ensures a close fit between the laminates and also removes air bubble voids in the epoxy. The problem using HHG in this process is twofold-keeping the glue hot during layup, and the fact that HHG doesn't cure easily in a vacuum. I am wondering if there are any epoxy style glues that have similar hardness/acoustic properties to HHG?
Here is a link to some experimentation that I found on the web, courtesy of McKnight guitars:
http://www.mcknightguitars.com/glue-hardness.html
"Everything I say on the topic is based solely upon inexperience and assumption!"

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kiwigeo
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Re: Glues

Post by kiwigeo » Mon Apr 04, 2016 9:07 pm

I can't see much advantage in using HHG for gluing up a laminated side.

HHG has a much shorter tack time than epoxy or AR glue. You're gluing up a large area of wood with a quick setting glue which is a pain in the ar*e. From your post I deduce that the only advantage you've identified is the "acoustic" properties of HHG. On my guitars the sides contribute little to the sound of the instrument.....I want a rigid side that isn't going to leak string energy fro the top and leave me with less string energy to drive the top. Without looking into the specs of the respective glues I'd say an epoxy glued laminate would be more rigid than one glued with HHG. For the record I use AR glue on laminated sides because its easier to clean up than epoxy.

I've heard many people waffle on about AR versus hide glue on body/neck joints. I've made a few instruments with dovetail joints and Ive used AR and HHG on the joint. Personally I cant hear any difference in the finished instrument.

The McKnight experiment....all he's proving to me is how hard glues are once they've set. He in no way proves that glue hardness has a significant effect on the acoustic properties of a guitar. McKnight is using a 1/8" (3.2mm) thick bead of glue in his experiment.....the thickness of glue between a brace and a top is nowhere near as thick as 3.2mm....

My ten cents worth anyway.....
Martin

Dave M
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Re: Glues

Post by Dave M » Tue Apr 05, 2016 5:52 am

The primary sound producing component is the top. If there was going to be an effect produced by the glue used it surely would show in the glue used for braces and top to side joints. I would be seriously surprised if such an effect could be demonstrated audibly.

The back and sides will be providing second order input to the overall sound and so any difference caused by the glues used have to be absolutely tiny.

I therefore think this is a track not worth following too far. For myself learning how to get top mobility up and bridge mass down, amongst other things, are the what I am chasing.

Dave
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garryalb
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Re: Glues

Post by garryalb » Tue Apr 05, 2016 8:19 am

I have been using the West system micro fibre blend filler with epoxy for some laminations. The intent was to minimalize bleed through and get better control over the amount of epoxy by using a very fine notched spreader. The epoxy with filler seems much stiffer and harder than without and the filler reduces the possibility of dry areas in the joint. The mix is around equal parts by volume (with Bote cote epoxy).I would be very interested in seeing your rig for vacuum laminating sides.

Garry.

blackalex1952
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Re: Glues

Post by blackalex1952 » Tue Apr 05, 2016 12:22 pm

Thanks for the replies guys! I use an internal side mold as distinct from an external mold that the guitar is assembled in. I bag the laminates and create a vacuum then clamp the whole thing onto the mold. This is the way suggested in the Michael Collins book Building the Selmer Maccaferri Guitar. I know that some of the high end Selmer guitar builders use HHG as per the originals. I have an epoxy laminated back and a solid back (the epoxy one is for a selmer build, the solid for an OM). The solid back has more ping, less damping. The Selmeroid guitars have a certain sound...many high end Selmer builders and players have an opinion re solid vs laminated and most say that there is a difference in sound between the two. It seems to have a bit to do with sustain, which may or may not be a desirable attribute, depending on the player, and the guitars use. Gypsy rhythm players like a "dry" percussive sound-GY guitar afficianados refer to such properties as "reverb". Some like a solid back. Another advantage of a laminated back is that the arching can be similar to a carved back-this affects the tone and the projection, arched backs don't need braces...arched laminated backs, unbraced, can be very strong across the grain and very light which may affect the attack, particularly the projection of the bass, which in the Selmer "petite bouch" small soundhole pushes a column of fairly directional air out supporting the highs and mids coming off the top. That's what I have heard these guitars do. The ones where the bass isn't quite working tend to sound thin from a distance, the good ones have a rich "thump" behind each chord or note and support the mids giving them what I would describe as "body".
My understanding of all this is not that evolved, I have not made a selmeroid guitar with a solid back. I understand the fact that the top produces all of the sound, particularly with a non live back as in the Selmer Macca design. But the neck is coupled to the tail block via both the soundboard and the back-to my imagination this must have something to do with sustain, opinions please? I also know the opinions of drum builders-the material in the sides has a great deal to do with the tone of a drum, and the mass of the sides has the same impact on the t1(1) mode of the drumhead.A high quality drum with solid stave sides, a high quality laminated drum and a drum made with cheap ply sides are all totally different as well. In the better builds, the timber has an effect on tone. I have also played lots of electric solid body instruments and the timbers and their density DO EFFECT THE TONE and the sustain. I have also played Selmer style guitars with stiff backs, ie. back resonance higher than soundboard t1(1) and GJ guitars with soft backs, ie. back resonance lower than t1(1). I was surprised that the one with the lower back resonance had so much projection.When I damped the back and played it lost a lot of its power (DeMauro,France). As a musician, my measure of a guitars projection and tone is how clear it sounds and how loud in a crowded pub acoustic session. All the players tend to bash, so a guitar with cutting power is essential for a soloist. The Selmer design is for acoustically cutting through horns and the noise of people dancing before the days of PA systems. 90% of the Selmer guitars and their main offshoots around Mirecourt, Paris, where they were all built, used laminated backs and sides. I don't believe that it was only because of the expense of solid material, that may have been the case during and just after WW11, but not the rest of the time when they were built. So I am curious re the type of glue in the backs when laminating just as I am with the kind of back timber for solid builds. Lots of makers talk about the different tone of different back woods. Having done a few neck resets, I much prefer HHG for necks-so much easier to deal with when repairing.
"Everything I say on the topic is based solely upon inexperience and assumption!"

blackalex1952
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Re: Glues

Post by blackalex1952 » Tue Apr 05, 2016 12:54 pm

PS: Apologies for not putting my name at the end of my posts-I keep forgetting until someone assumes my name is "Alex"-cheers! Ross
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auscab
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Re: Glues

Post by auscab » Tue Apr 05, 2016 2:05 pm

Hi Ross ,

If you wanted to use HHG with laminated sides or back couldn't you add a heat blanket into the bag and give it a burst of heat to melt the glue at the right time, for the right length of time ?

Also,for sides, there is a way of pressing over a form externally that can do solid with a blanket , or laminated cold / 2 pac, or Hot glue laminated , with a blanket. All over the same form .

Its by pushing a steel strap down into the waist and pulling it at both ends around the bouts. I made one, and tested it, and that's all so far . It works , same as it always has for laminated cabinet and chair construction .

Rob

blackalex1952
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Re: Glues

Post by blackalex1952 » Tue Apr 05, 2016 2:11 pm

I just found some data re the West system epoxy range. I will put it here to feed the discussion if any further interest is forthcoming.I don't have a measure of the amount in practical terms that the figures represent, but some interesting speculation presents itself. The West 207 Special Clear Hardener "has been specially developed for coating applications where an exceptionally clear, moisture resistant,
natural wood finish is desired." The figures show that the 105/207 combination gives an impact figure of 67.7 m-N/m which is greater than twice the "hardness" of the 105/206 mix. It is also the clearest and might be best for grain filling. The other figures say something but not sure how to interpret them-perhaps the engineers on this forum have some guidance for me. Wondering how the tensile elongation, modulus, flexural figures etc could be interpreted.I am also interested in "Thixotropic" resins and ones that are available in Aust, as I have heard that some of the CF soundboard bracing guys prefer it. I am keen to try CF bracing on a Selmer design sometime soon.

Ross
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blackalex1952
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Re: Glues

Post by blackalex1952 » Tue Apr 05, 2016 3:11 pm

This post is for Gary-attached pix of my vacuum set up-messy shed in need of a cleanup yesterday! The pump was purchased for a bargain price off ebay, the rest of the pump scrounged from the local tip, eg the pressure cylinder was an broken Supercheap Auto compressor tank. I only paid for a non return valve, the pressure guage and a few fittings. The vac switch is an old Holden vacuum advance, a spring and wingnut to control switch operating pressure and a microswitch. Rotary vane pump not the best for the job, but as I said-CHEAP! New vacuum bag on the way, this was my first bag to see how the whole thing would work. The forms are made so that the laminates already under vacuum in the bag can be clamped into place while they dry. I have clamping cauls for both molds, but only one shown. Bagging prior to shaping in the mold is the best way IMO. For some laminates I pre bend the cutaway side. The grain runs logitudinally on the outside and inside veneers, the core material is cross grain. The core pieces are cut to size then shooting planed in a clamp made from two lengths of timber. They are then joined using superglue and masking tape to clamp the join. So far I have used 0.6mm maple veneer outside, pearwood inside and a 1.2mm mahogany core. The original Selmers had three thicker veneers from what I have read, but these thick veneers are hard to come by these days. The reason I don't use the guitar mold for the job is that it isn't wide enough to support the full width of the sides. My backs are now laminated in a similar way, but within the bag I lay the laminates on a carved back form which resembles an archtop back carve. I then have a little hassle mating the braces accurately to the actual back shape but seem to manage. If I change the back mold in the future I will make it a concave form, which could also be used to sand and fit the braces more accurately and faster. One of the advantages of veneers is that the visual possibilities are not so limited by structural requirements-I have seen laminated burl and other attractive backs. Good gypsy jazz guitars are noted for their extremely light weight which has a lot to do with the back and side veneer construction and the fact that the necks are reinforced with no truss rod. CF is a good material for this these days, the originals used duralumin.

Ross
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garryalb
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Re: Glues

Post by garryalb » Tue Apr 05, 2016 3:46 pm

Hi Ross,

Thanks for the photos, looks like a good method, similar to the method some builders use to laminate arched doorways in situ.

It would probably be best to use the 207 hardener for laminating to avoid the bleed through resin blushing / turning white over time as is likely with the other hardeners, same as with grain filling (learnt that the hard way). This is the reason I am using the bote cote epoxy as it is intended for clear coating. The bote coat also gives a longer work time and the manufacturers claim it contains less harmful / allergy causing chemicals. It is certainly more pleasant to work with. The thixotropic epoxies have fillers added, you can do this yourself to any desired consistency with a filler like the west microfiber blend.

Garry.

blackalex1952
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Re: Glues

Post by blackalex1952 » Tue Apr 05, 2016 5:04 pm

My understanding so far of thixotropic resins is that they thin out under stress eg. when mixing and clamping, but thicken after that. This means that they don't run, they have gap filling properties, eg when laminating CF strands under a brace, and also butress the braces either side. Would adding a filler create these attributes, or only just thicken normal resin?
"Everything I say on the topic is based solely upon inexperience and assumption!"

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