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Hi all,

I've built a reasonable few flat tops, mostly l00 sized but nothing for a few years but I'm mulling an archtop. Not a jazz machine, more old time/ blues. I have zero budget but I think all I need to find are top wedges, a violin maker i know days i can borrow a couple of planes for top carving. Ideas so far

L00 sized
Carved spruce top with f holes
'Flat' 15 foot radius back
Back and sides solid mahogany
Bolt on neck accessed through sound port upper bout side

Basically sticking a close as I can to the l-00 design which I know well but with arched top and probably elevated fingerboard extension. Any plans, clues, dimensions for similar instruments, eg vintage l50 etc appreciated. I'm apprehensive as I've played many flat tops and know how they should feel but very little experience with archtops and most of the Internet information is the larger jazz instruments.

Thanks for any tips.

Sounds like a fun project. One thing that I did on the one I'm making now, 15 1/4 inch wide, or something like that; is I made the top of 6 pieces of a vertical grain Sitka board I found. The board had some color issues, so I had to fiddle some with placement, but I don't know if you notice it as much when it is carved or not. If I didn't have to move them around, it would have just been 3 pieces.

This will help with your zero budget. Violin and viola wedges are fairly reasonable. Archtop and Cello wedges are pricey. Quartered spruce boards are even harder to find than quartered hardwood boards, but you do come across them.

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Why be normal?

That's good thinking thanks. I'm mostly concerned about getting the neck angle correct and also the shape and thickness of the top. Should I scale down plans for a larger body so I have guides for the carve shape?

Maybe the martin c3 plans would help with the carve?

I found that the most reliable way to do arching on violins, cellos, guitars was from the inside out. My newest way is just with tapping and scratching, but it seems that it works easiest if you have some idea what you are going for. If you don't have an instrument in front of you, how do you know; unless you have sculptor vision?

I have a smooth 18" chain I got from walmart. Plated, it doesn't need to be gold or silver! I carve diagonal arches from upper left to lower right, and vice versa. Then fill in with horizontal arches that match up with the diagonals.

You can't finish the diagonals until the horizontals are roughed in too.

How deep you go is determined by how thick your top is. A 3/4" or 18mm board you have to stay about 6mm below that. Thicker or thinner the same way. You probably won't be 6mm thick in the middle; maybe 4.5 or so, but you can make it deeper, and you might find in refining the arch; actually a catenary curve; that you have to make it deeper.

You can't cut this all the way to the edge. You have to have a plan of some sort. Determine where the low point of the outside is around the edge. Unlike violins, and cellos; archtops don't generally have a low point, and a raised edge, but they do have a point where it is finally flat. Go in at least a 1/4" from there.

I like to draw my arch that I expect to get on paper, and then draw the thickness inside of that. Take your chain, tape your drawing on a window upside down, and hold your chain, and see how far out you can go, without going over the line. This distance will be different on the top, bottom and middle.

Where the diagonals cross will not be the high point. The horizontal arch will get higher between the diagonals. The diagonals drop, but for a while, the area below the crossing point, the final center arch will get higher, and then stat dropping.

Violins and Cellos have Strad (the magazine) posters that come with 5 cross arches for the back and belly. The new ones even have ct scans of them. This makes it EASY. Guitar makers don't have that. If your violin maker buddy has posters, especially the new ones, ask if you can borrow them for a while, and you will find what you need to know when doing your archtop.

Planning, and knowing what to expect is a good thing. Doing this, you will find where the bridge location will be. Neck angle isn't as critical as on an instrument with a glued on bridge. It has to be right, but right has leeway on an archtop, or like the viola I just finished.

Draw that out full scale. Know where your slot, and bolts are going to go. Do it the same way that you always do. See what sort of cantilever you can put on the overhang so it is strong, but doesn't look stupid.

Planning is one part I really like. I should take a while. I can go on for weeks.

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Why be normal?

Ok this is great information thankyou! I work 7 days a week until November so I may not actually pick up tools until then! I've mostly used a single bolt butt joint for the neck and relied on the glued fb extension to prevent movement without string tension but that's not going to work with the raised fb extension...

For an archtop bolt on neck the higher angle makes it better to use the Cumpiano barrel nut technique as they can rotate to be square with the headblock. I use two bolts and tighten them with a long Allen wrench through the endpin hole.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Mike, for what it is worth two years ago I built my first carved top archtop. I basically followed Benedetto's book but a slightly smaller body - 16 inches across the lower bout. I had a non cutaway arched back which I decided to use, that means I could eliminate the issues of bending the cut and making the geometry work out.

I considered a bolt on neck with some sort of access but in end just went with a dovetail and floated the fretboard extension.

I did the top carve in the usual way, started with big wedges of spruce, drilled the outside contour lines and carved the outside arch. Then drilled a fixed thickness (1/4 inch) from the inside and carved to that. Finally thinned the plate towards the recurve. I made templates from Bob's plans, shrunk them slightly for my smaller body.

I debated between X and parallel bracing, the literature indicates that parallel might be louder and X "will typically produce a softer, more mellow sound" (Benedetto), so I went with X bracing. I do have software that allows me to look at the spectrum of various tap tones, not that I know what to do with it. But for what it is worth I did take tap samples all thru the voicing process and they basically followed the predicted changes as I thinned the top, cut the f-holes and finally closed the box.

I don't know if any of this will help you but I did do a build thread at a different forum. Might be worth scanning thru it before you start yours

https://www.tdpri.com/threads/lets-buil ... p.1085372/

I'll add one more thought, I had built a number of flat topped acoustic guitars of various shapes and sizes and consider myself a flat top player. When I first strung up the archtop I hated it. It was almost shrill in its brightness (so much for X bracing), the string squeak was terrible, it seemed to accent all my bad playing. It took a full year of experimenting to find strings that I liked on it and another year for it to finally open up. I now think that its actually a pretty good guitar of its type, I just wasn't used to that sound.

Anyway, consider getting the Benedetto book even if you aren't building that guitar. Enjoy doing the carving, tap and see if you can hear the changes. Play a few guitars of this style so you'll know what you are shooting for. Have fun

I actually use hanger bolts as the tenon is square to the neck block. Works well with my extended allen wrench through the endpin hole. Barrel nuts would be fine as well. I just got Marionized way back when.

Nowhere near the experience of Alan Carruth and others here but my first guitar in the late 90's was an archtop built using Benedetto's book. I've built a dozen or so since before moving on to flat tops and ukuleles with the first four archtops having dovetails and the rest with bolt on necks. I haven't built any with smaller than 17" lower bouts but have built two bass archtops with 20" lower bouts based on Bill Moll's dimensions and advice. I draw the contour lines carefully by hand based on bridge placement being at the peak of the arch and drill to just above final depth on the lines using Benedetto's methods. I then use a Safety planer to establish ledges based on the drilled depths and then hand planes etc. from there. Same for the inside arch which is done after the top carve. I did use a Kutzall carving disc on an angle grinder for the two basses as it was a ridiculous amount of carving otherwise. The Safety planer also makes it easy to establish the 1/4" ledge around the perimeter. The neck angle is easily mapped out by drawing it out to scale, knowing the height of the highest point of the top plate and allowing for an 1" or so bridge height if you're following Benedetto's measurements for a 17". Scribing the fretboard extension based on the bridge height and then slowly carving it down to the "overstand" height using carbon transfer paper (mostly 1/2" skew chisels for me) to reach the desired fretboard plane to bridge height is slow but not difficult. Looking forward to seeing what you come up with.

Even though I’ve given up on building, I’ve built a fair number of archtops, and pretty much play them exclusively. FWIW, I’ll share my experience as principally a player and secondarily a builder.

First thing I would say is that an archtop as an instrument is not a cool looking dreadnaught. It is a different instrument best suited to a different musical purpose. Oversimplified, a dreadnaught is an excellent accompaniment to vocals. Compared to other stringed instruments it has boomy lows and sparkling highs giving a human voice space. A good acoustic archtop is more balanced in the midrange. By comparison it may sound harsh, especially if you are playing cowboy chords and trying to sing songs over them. If you are playing single lines or what jazz players call chord melody the purity of the notes and note separation is unmatched. A bit like a small bodied flat top set up for finger style, but with more projection, dynamic range, and way more volume.

But… archtops have a schizophrenic history. Their heyday also is the dawn of electric guitars. For many players, an archtop is first and foremost an electric guitar. As a result there is a wide spectrum of acceptable archtops. There is a lot of conflicting information on what makes a “good” archtop because there is a bigger spectrum of acceptable uses than you find among pre-war Martin D-28 copies. Benedetto built acoustic oriented guitars, a Gibson ES175 is meant to be plugged in. Build to your purpose.

When I gig (rarely) it is solo and without vocals. I like to mic a guitar rather than plug in. My building journey was for that goal. I discovered that, while Benedetto was building for acoustics, the book measurements are WAY over built. The rumor was that the publisher made him add 1/16” to the measurements to avoid complaints, but that’s probably just a tall tale. I kept going thinner and thinner to get a sound I was pleased with. Eventually, I departed from Benedetto entirely.

If you want an acoustic 15” archtop for solo acoustic playing you will likely carve it much thinner than Benedetto’s book and you will likely need very little bracing. I also think a small acoustic archtop defeats the point. For that an OO will do fine. The archtop is there to project and be heard. But that’s just my opinion.

If you just like the looks of an archtop and want a build challenge, I recommend you build it as an electric guitar. You may even want to extend the neck block to under the bridge to mount pickups and bridge posts in. What I think of as an “airy” semi. I built a couple of semis and LOVED playing them. My Tele never was loved the same again.

Whatever you choose, archtops are great projects and you will end up with a guitar people will always comment on and gravitate to. Good luck and have fun!


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We did a lot of solid-top and laminated archtop work at Greenridge, to include scale length conversions taking 17" bodies to shorter scale length (580mm) for conversion to 8 string guitar-shaped Greek bouzoukis and 3-4 arched top/flat-backed octave mandolins (I don't recall the exact number... was early days for me with that shop). The most important 'tool' for planning was the full-sized profile of the instrument, worked from known scale length and the top center-line profile. Unknowns with regard to neck attachment, truss rod integration, and such mundane considerations as tailpiece resign were quickly resolved once that initial profile was lofted... questions with regard to dovetail versus bolt-on access geometry, etc. were answered in a direct fashion.

Our bouzouki conversions on Ibanez Artcore archtops in particular were informed by use of these profile views, as we used a Martin two-way adjustable truss rod with access via a hidden channel through the semi-cantilevered fretboard extension. Working access issues out on paper (or these days in Fusion 360) allowed for that approach as well as the bolt-on conversion.

On the 00-sized guitar-shaped octave mandolins, I believe a scaled profile from Mr. Benedetto's book was used for both the center line top profile and the upper and lower bout top contours. The rim was deepened versus the usual shallower arched-top/arched-back practice with use of this developed profile view as well, and fit in a 00-sized case confirmed with a full-sized profile view template pasted to 1/4" MDF stock. Those instruments used red spruce 6- and 8-piece tops gotten out of some Canadian-sourced 2x4 stock... as mentioned, patience and diligence will turn up a couple suitable sticks over time, although be prepared to restack the culled wood if you don't wish to endure the side-eye from the people working in the lumber department.
Good luck with your project

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