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I change gears dozens of times per day when it comes to adhesives applications... This one happens to be guitar related and requires the immediate defenestration of all thinking occurring inside the box. I thought some of you might enjoy this thought experiment with me.

The application is minimized assembly time from in house fabricated parts with the fewest workers attempting to maximize production within some quality parameters, which remain vague at the moment. I'm presuming the goal is a price point low enough that replacement will be preferred over repair for warranty fulfillment. All adhesive technologies are on the table, mostly consisting of reactive PUR hot melts and a few operations using water based wood glues with RF.

My ideas so far regarding installation of the lining:
1.) Vacuum fixture to maintain shape and position using a traditional kerfed lining.
2.) 1/4" curved plywood pre-bent to conform to the body.
3.) Pre-shaped graphite, or potentially a plastic (malleable plastic would be nice, but then creep will be unmanageable as well as fun stuff like plasticizer migration).

Using the method I've worked out so far, we're looking at parts to a strung up and playable instrument within a hour (aside from finishing). Thoughts/opinions are certainly appreciated, and I'll probably be writing a few production flow charts anyways. If nothing else, I found this rather interesting and at least wanted to share.

In a production environment, why would you string up the instrument before finishing?

Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

There is no reason to string up before finishing, I thought that might be an interesting point regarding production cycle times being investigated.

Plastic ? who are you making guitars for ?

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It's this new idea from recent decades that everyone gets a participation award. - MUX

Parts to boxed up & "in the white" within an hour? No way. You can't do a good job of sanding within that amount of time, much less everything else that goes into building an acoustic.

There is a builder up in Canada that molds a 'framework' that the sides, back & top are attached to. The name escapes me..but it seems like something along the lines of what you are talking about.

Trev

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http://www.PeakeGuitars.com

What's the hurry?

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JJ
Napa, CA
http://www.DonohueGuitars.com

FTW

http://www.designnews.com/article/15651-Guitar_assembly_with_no_strings_attached.php

Trevor mentioned them while I was looking for the link, but this is the company he's referring to. I'm not sure what happened, since they did really well for some time, but eventually Gibson bought them out. And then Gibson shut down the factory last year. I think I might try to track down some of the guys who used to work there; I'm really curious about the behind the scenes on all that and nobody could have talked while they were operational.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Chris Griffiths I believe, building a brand called Garrison guitars that made an injection molded graphite frame including all braces, bridge plate, linings etc. in one piece. Bought out by Gibson, and no longer active. (I think)

Guess not. Figures Gibson would do that.

Ahh, "production"...
More junk guitars using precious woods.
If you are building a guitar an hour, you should be making it out of popple too.

I can't comment on the identity of the client, and the rate of production is up to them. Realistically, I think from materials to finished and out the door in 3-5 days would make sense for this application.

Bob, thanks for the link and interesting read.

Again, I thought some might be interested and I'm not looking for opinions on what my client is up to. When I'm called on as an adhesives expert it's my job to provide guidance, not judgement. I've talked countless people down from using Titebond II/III, epoxy, and polyurethane for both building and repair work.

Understood Hugh, no offense was meant...best of luck with your project! FYI, the fasted production rates that I've heard of for acoustic guitar production are from Martin guitars, using their high pressure laminate material. I believe these guitars are built in somewhere around 13 hours, start to finish. For a solid wood guitar, I believe the norm for a factory is about 3 times higher...and most small builders are at least double that.

As an adhesives guy, what are your thoughts on RF gluing for acoustics? It seems like you could probably get away with it in certain areas. From my own experience, it seems like RF gluing does not result in as strong of a glue as air drying methods.

Best,
Trev

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http://www.PeakeGuitars.com

I actually spent a couple of days in Martin's DXM facility during my time with the company. Very interesting stuff indeed.

Some guitar companies use RF extensively, and it's not a bad practice if you need high volume. From a personal standpoint whenever the luxury of time exists while using PVA I would rather keep my glueline at room temperature to avoid thermal plasticity and scorching. Hopefully I'll get a chance soon to start running tests on adhesives as they relate to resonance. My hypothesis: that the best performing adhesives will, under perfect conditions, be infinitely rigid with zero mass. Whatever ends up wit th closest to those parameters will likely win.

I know of electric guitar factories using RF, but not of any acoustic folks who are doing so. I like RF glue...just not for structural joints (for the aforementioned strength issues). I think the problem is that it's hard to find something in an acoustic that isn't structural...! My experience suggests that RF glued joints have 50-75% the strength of the average room temperature joint.

As for the acoustics - I think you might have a hard time testing the acoustic properties of well glued joints (hot melt glues being the exception - it seems like they always leave a substantial glue line). I think that process time is a much more important issue when you look at the "business" of guitar building. The .1% of difference that you may or may not receive from glue X versus y isn't nearly as important as something like getting the right neck angle...setting action right...or even the amount of finish that is on there. I'll attest to the effect that finish has on tone - even on an electric - but I'd be hard pressed to do the same for glue. Just my $.02...your mileage may vary..

Also - it's great to have an adhesive expert on the board. Welcome!

Trev

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http://www.PeakeGuitars.com