Sunday, April 1, 2012

Archtop Guitar Build - Opening thoughts...

I am tooling up to build an archtop guitar based upon the design from Bob Benedetto's book "Making an Archtop Guitar."  I first read this book many years ago and was struck by several of the cool ways that he goes about solving the many interesting problems presented during the building process.  Over the years I've often thought about the drawing in the book that shows how to use a drill press to make a series of holes at different depths in the top surface of the guitar top plate and then using these holes as indexes to guide the contour of the carving process for the top.  This is just one of the many interesting ideas presented by the book.  I recently worked on an archtop (see the Harmony post on this blog) and this is what got me re-started thinking about building an archtop.

It is telling that the last chapter is about marketing and I must say that Benedetto is unashamed about marketing.  The only color photos in the book are a gallery of shots of photos of his guitars and many pages are devoted to showing the "who's who" of people who own and play his guitar.  Be warned, you cannot make a guitar using just the book, you also have to buy the set of plans for the guitar since there is no full sized body template and there are no directions for exactly what contour the top should be carved to.  Oh, there are a set of templates but none are on cardinal locations for the top or even show a uniform baseline to work off of.  They are essentially useless.  Did I mention Bob is a good marketer?  Oh by the way he describes tapping the top and body at various stages of the build but how do you explain what to listen for in a book?  Did I mention that there is a video series also for sale?  I don't know what is on those DVD's since the library doesn't carry them and I don't want to pay the $130+ to find out...  Don't get me wrong, the book is great and the plans are worth the price but don't think you can get by with just the book.

There are subtle differences between the book and the plans, and I am going to stick with the plans in the case of any variation.  One of the tools used in construction of the guitar is called a "Safe-T Planer."  I'll post a photo once mine arrives but they are no longer in production so you will have to look to the secondary market for them.  They are currently between $130 and $220+ on E-Bay and they originally listed for around $50 so there must be quite a few people building archtops looking for them.  They look anything but "safe" but from those that I've talked to who have used them, they work really well so we will see...

There are three key goals to building a guitar: good looks, good sound and playability.  Of these three, the first is the easiest to achieve and the least useful if you plan on using the guitar for anything other than ornamentation.  Good sound is going to be a matter of building a bunch of guitars and learning what works and doesn't work.  Since I don't plan on becoming a full time archtop builder, I'm going to have to rely on Benedetto when he says that if you follow the plate guides "even a first time builder can make a surprisingly good sounding guitar."  Lastly playability is something that I can do something about.  A guitar can be thought of as a series of strings suspended between the nut and saddle.  Everything else (neck, body, bridge, fingerboard, frets, headstock...) is aimed at making these strings sit low enough to the fingerboard/frets to make for easy playing yet not so low that they buzz on the frets.  This is what makes a guitar easy to play and feel good to the player.  With that in mind, lets look at the archtop guitar as a whole.

First off, the archtop is an acoustic guitar that has a resonating chamber to amplify the sound.  We know that arches are stronger than flat surfaces so it would seem logical that an arched top should be stronger than a flat top.  What is really surprising is just how thick an archtop is!  A standard flat top acoustic will have a fairly thin top (well less than 1/8) that is reinforced with braces on the rear.  An archtop has just two braces that run in an "X" or "parallel" to each other but the archtop can be up to 1/4 inch thick!  This is massive for an acoustic guitar top.  How is this thing ever going to vibrate enough to make any sound, especially higher pitched sounds?  A thin 1/8" thick rebate is carved around the perimeter of the top to free the center section of the top so that it can move sort of like a drum head that is suspended by it's perimeter.  Very clever. 

It is also very important to keep the geometry of the final guitar in mind while working on the various stages of the build.  For example if you look really closely at the plans for guitar and make a contour map of the top, you will see that the highest point of the top arch sits just in front of the bridge position.  This is absolutely critical and if you mess up on this, I bet you will ruin the guitar because the bridge must sit on the upslope of the arch and cannot teeter totter on the crest.  If you messed up on this in the carving process (one of the first things you do) you will be in for a very rude surprise when you try to set up the guitar at the end of the build.  Trying to fix this at the end will change the arch and body/neck geometry and might not be possible fix.

Most guitars have the neck coming straight out from the body with little or no set back angle to it.  The large hump of an arch that we just talked about requires the neck to have a fairly substantial 4 1/2 degree set back because the bridge sits so high relative to the neck/body joint.  Again, everything depends upon that nut/saddle string relationship and this is a part of that equation.  Once again, because of that arch, the neck extension must be carved to clear the arch and the finger board must sit fairly high to reach the strings  You need to understand every process described in the book before you begin because if you don't, you might easily make a mistake early on (like the crest of the top described above) and not be able to fix it later.

I plan on using this guitar to play out with so I will put a pick up on it.  Benedetto's pick up mounts under the pickguard and the wires to the end jack run through the "f" hole.  His pickup is really spendy so I will try winding my own and encase it in a wooden mount just like his.  I also plan on standing up with the guitar and I don't like strap buttons mounted in the heel of the neck so I will have to add a reinforcing block on the inside upper bout to accept the strap button.  Since there is no access to the inside of the body (because of the small f holes) I'll have to do this before gluing the top and backs on.

I hope there is nothing else I'm missing here.  All in all this is a really cool project and should be quite a challenge!

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