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Is clamping bad?

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I have had this book, "Classic Guitar Making" by Arthur E. Overholtzer for years. He built a Grandchampion Classical in the late sixties and has a number of interesting ideas on construction. He made a big deal out of minimizing the use of clamps when building. His point was to fabricate the given part to fit perfectly, so any clamping that was needed was very slight. He contended that clamping pre-stressed the wood a certain way, instead of being neutral to vibrate freely when activated by the strings. I haven't built too many guitars, but I used this principal on a dreadnought I built in 1983 (Martin wood, scallop bracing) and it sounds like a howitzer. I was curious if anyone else has employed this strategy and what results they had. When I look at a photo of a typical go-bar set-up in action I always kinda cringe because it isn't hard to imagine the inconsistent pressures and stresses this could potentially impart to the top. Food for thought.

May 11, 10 | 7:43 am

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What kind of glue did you and Overholtzer use?

May 11, 10 | 11:11 am

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I used Titebond or Titebond II, not sure exactly. I don't have the book in front of me at the moment but Overholtzer used some form of PVAC.

May 11, 10 | 11:26 am

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I know that HH glue requires very little clamping pressure if the joints are prepared very well - in fact here is a quote from a Wiki article

Hide glue also functions as its own clamp. Once the glue begins to gel, it pulls the joint together. Violin makers may glue the center seams of top and back plates together using a rubbed joint rather than using clamps. This technique involves coating half of the joint with hot hide glue, and then rubbing the other half against the joint until the hide glue starts to gel, at which point the glue becomes tacky. At this point the plate is set aside without clamps, and the hide glue pulls the joint together as it hardens

I have always heard that the AR and PVA glues required at least moderate clamping pressure to, if you will, squeeze the glue out of the joint to minimize the amount left wetting the surfaces.

In some cases, applying clamping pressure is manditory - how are you going to form the dome shape of the back or top without clamping to the curved brace? Preferably in a dish or against a curved caul. I also believe that that it is very bad to force the wood into some sort of compound or unnatural shape - for example the rim of the back should also fit that radiused dish perfectly so you don't have to force some part unnecessarily.

Back to your original question "has anyone else employed this strategy?" I try to prepare each joint as accurately as I can, but since I still build with
AR glues, I apply moderate clamping pressure to force glue squeeze out all along the seam. Yes, I use a go-bar, and yes, I spend a whole lot of time building cauls to spread out the force.

btw - you can also get in some really interesting discussions about HH vs modern glues, there are some that argue that the sounds of the prewar Marties (and the Authentics) are largely due to the glues. I've heard a D18A played next to a standard D18 and yes, there is a difference.

May 11, 10 | 1:12 pm
Ken Hundley

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Teeter, I'd love to say I manufacture with that level of skill...but I don't. I get better every day, but its been a long road so far. I can see his point, but as long as you don't overtighten, I can't see using more or less clamps having a significant impact on the guitar until its dropped. My suspicion is that as long as you have two good mating surfaces, how much glue (with in reason) gets used or what type of glue is not going to have all that significant an impact on the sound of your guitar. Thickness and type of wood, braces, and finish I think will have a far greater impact.

My suspicion is that the sound of prewar Marties is what it is because they are prewar...they have aged in all aspects of the guitar, and we, today, try to build in a sound that has taken 60-100 years to mature in any given instrument. Sorry, Freeman, not pickin on you....;)

May 11, 10 | 2:30 pm

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I did check and Overholtzer was using polyvinyl (book written in 1974). I totally agree that many, many factors contribute to the sound "Thickness and type of wood, braces, and finish..." and a dished back would be challenging. His backs were flat as a billiard table. I imagine shaping with heat might be the approach for the back, not unlike prebending the sides, but I did do mild clamping when I did mine, back in the day. And my build is 27 years old so that surely is a factor. I also stripped off the lacquer about 5 years ago and did a french polish with shellac. Now that turned to volume "to 11". Anyway another thing to think about. I plan on starting another guitar in a month or two and I'll see how I can incorporate ore of the stress free principals with this new instrument. Thanks for your comments and insights.

May 11, 10 | 3:00 pm
blues creek guitars Authorized Martin Repair Ctr

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Clamping is a good thing , forcing a joint is not
john hall

May 11, 10 | 5:12 pm

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What John said.

May 13, 10 | 7:04 pm
JJ Donohue

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For me, I began using HHG right from the start partially because of it's ability to "clamp itself". With other glues, I often found keeping the slippery and squirmy surfaces together to be difficult and became frustrated that all too often the clamps themselves would force misalignment of the parts. As a side note...when I use carpenter glues to construct jigs and fixtures, I often fill pre-drilled alignment holes with dowels to prevent such misalignment from clamps.

When using HHG, I generally hand fit the surfaces and watch the squeeze out appear until the glue's natural tack locks them in place. This happens within a minute as the glue tackifies and gels. It's at that point that I apply force from gobars or clamps...and not much force is required. As in all joints, THE most important factor is that they fit together as perfectly as possible.

From prior forum experience, the topic of which glues to use seems to generate a high level of controversy. I actually think that's good because it get's as much knowledge, fact and fiction out in the open for debate. I use HHG for lots of measurable reasons... the least of which is superior sound. I don't claim to be able to hear such differences. In theory, it should be superior because it sets up glass-hard, which should more efficiently transmit sound. Basically, I subscribe to the idea that lots of incremental issues add up to create a superior-sounding guitar and HHG is but one small component.

The idea of a guitar based upon stress-free joints has also been debated. In general, I agree that we all need to form the mating surfaces as perfectly as possible and not force them into position. IMO, having the components of the joint remaining in that exact position over the long haul is critical (no joint cold flow). HHG does not cold flow. Carpenter glues do cold flow. That was the most important factor in my decision to use HHG. Just as we know that a drum head needs to be kept tight to perform optimally, I believe that a guitar's top joints need to be permanently locked in place and prevented from relaxing (cold flowing) over time.

It will be interesting to participate in similar glue discussions on this forum.

May 16, 10 | 6:37 am

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I agree. The better the fit of the pieces the less force would be needed to clamp them together. I have seen many force two pieces of wood together in furniture building and even construction work.The more precise the cut and fit the easier the two would go together. Making the job a lot easier and more precise. ...Mike

May 29, 10 | 3:45 pm

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