Liutaio Mottola Stringed Instrument Design

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Closing the Box - Attaching the Plates of the Flattop Guitar

Instructions for attaching the top and back plates to the rib assembly (garland) of the modern flattop guitar. With a completed top plate, back plate and rib garland in hand, the body of the guitar is ready to be put together.

Initially appeared: April 8, 2010
Last updated: Saturday, November 25, 2017

Tools and Supplies Needed for Closing the Box

  • Completed top plate
  • Completed back plate
  • Completed rib, blocks and lining assembly
  • The mold used to build the rib assembly
  • Rib jacks
  • Guitar body cradle (see text)
  • Pencil
  • Paring chisel and/or router w/ flush trim bit
  • Short ruler
  • Assorted clamps
  • Chisels and knives
  • Razor saw

General Description

For the most part the steps required to attach the top and back plates to the rib garland are straight forward. About the only real work that needs to be done here is to trim the ends of the braces that will be pocketed into the linings and to form those pockets. Just for the record, the state of the top, back and rib garland should be as described in those pages on this site describing their construction.

There are a couple of operations which could (or should) be done to the rib assembly before the box is closed up, however. These involve work on the neck end and tail end of the garland. Although you can inlay the end graft on the tail end of the rib assembly now, I prefer to do this after the top and back have been attached. The reason I prefer to put this off is that, if you end up with the center seam of either the top or back slightly off center, you can inlay the end graft so it still looks good and lines up with the seams.

You can also route the mortise in the neck end for attachment of the neck now, assuming your instrument uses a mortise and tenon (or dovetail) neck joint. But here too, I like to put this operation off until the box is closed up. The butt joint at the neck block probably represents the centerline of the instrument, and having this intact will make it easier to line up the plates when you attach them. Cutting the mortise now will obliterate that seam.

The instruments I am building in the pictures on this page use a bolt-on neck joint, and I do drill the bolt holes before the top and back are attached.

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I drill the holes at this time because now I can back up the neck block when drilling, which keeps the grain from being blown out when the bit exits the neck block on the inside.

Attaching the Top Plate

The top plate is attached to the rib garland first. We do this because the geometric relationship between the top and the neck block is critical. If the neck block is tilted backward or forward in relation to the top the neck angle will be wrong and a bridge of reasonable height will not fit. If the neck block is twisted even a little to either side then the bridge will not be able to be mounted right on the centerline of the top. To maintain the correct geometry between neck block and top we do all the work involved in attaching the top while the rib garland is clamped into the mold using rib jacks.

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The rib garland is inserted into the mold and pushed down so that an even 1" is left above the top surface of the mold as in the picture. Measure this carefully, going all around the ribs with a ruler and pulling the ribs up or pushing them down where necessary. Make sure you've got the top side up! Once they are in place, clamp them there with the rib jacks.

We need to make a trial fitting of the top and make some marks that indicate where the ends of the transverse braces intersect the linings. And we also need to mark those transverse braces to their proper length. The first step of this trial fitting is to mark the boundary of the top outline on the inside surface of the top at the center seam at both ends. You may still have these marks if you drew the top outline onto the inside of the top plate and didn't obliterate those marks while cleaning up the inside of the top during assembly of that plate. If not, transfer the line where the outline drawn on the outside of the top intersects the centerline, onto the inside surface of the top.

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Do the same thing at the tail end of the plate.

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Now the top can be temporarily fitted to the ribs. The centerline of the top is aligned with the centerline of the garland at the neck end, and then the top can be slid so the outline mark is aligned with the ribs. When everything is in place you can lightly clamp it with one clamp to keep the top from slipping around. Repeat the alignment process at the tail end too, and again lightly clamp if necessary.

Now the ribs and linings can be marked where the transverse braces cross the ribs.

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If you don't have enough room to mark the linings just put your marks on the outside surface of the ribs. The lines can be continued up onto the linings later, when the top is removed. As you can see in the picture, the location of each side of each transverse brace is marked. Depending on the bracing pattern of the instrument you are building there may be other braces that will end up being pocketed into the linings. Mark the ends of those braces, too.

After the lateral positions of the sides of the brace ends are marked, the locations of the brace ends themselves are marked. This is a two-step process. The first step it to mark the brace ends at the outside of the ribs.

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You may need a really short pencil to do this - there isn't too much room between the top of the mold and the bottom of the brace ends. Now the top can be unclamped and removed. Flip it over, and you can see the marks you made at the brace ends.

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Now draw lines parallel to the lines on the brace ends, the thickness of the ribs and toward the center of the top. We want to trim the ends of the braces that will be pocketed into the linings so they are long enough to just fall inside the ribs. The brace ends can be cut off at these new lines using a razor saw.

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Be careful not to nick up the top while sawing. After you've sawn through the brace ends, the waste can be knocked off using a chisel.

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What happens next depends on how the ends of the braces are supported in the design of the guitar you are building. There are three common ways to support the brace ends. The first is to cut small pockets into the linings to accept the ends of the braces. This is the method I am using for the instruments under construction here. It is also the most complicated treatment. The other two common methods of supporting the brace ends are so simple to explain that I don't have pictures of them here. One method is to saw out the section(s) of the linings where the brace ends are located. After the top is glued on, small chunks of lining material are glued to the ribs so the tops of these chunks are in contact with the braces at their ends. The other common method is to use specially made wood brackets to do the job. This latter method is common in some classical guitars.

But again, the method I'm demonstrating here is pocketing the brace ends. Note that there are really three ways to pocket the brace ends. The simplest way is to saw or route slots for the brace ends right through the linings and the sides, the idea being that the bindings will hide the ends of the braces anyway. The next easiest way is to trim the brace ends so they ramp to a rectangular cross section and then fit them into simple-to-cut rectangular pockets in the linings. The most difficult method is to leave the brace ends ramped and to cut ramped pockets to fit them. This is the method I am outlining here. I have not chosen this method because I think it is superior in any way. It is just that, as the most difficult method, if you see how this is done it will be really obvious how to do the other two methods.

The first thing I do is to make a mark on the side of each brace at a distance from the end that is the same as the thickness of the linings. Then I measure how thick the brace is at that point.

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I also measure the thickness of the brace at the very end. Although you can cut a custom size pocket for each brace end it makes for a neater job if all the brace ends are the same thickness, because this makes all the pockets the same dimensions. So at this point I will re-trim the ramps on the brace ends so they are all the same. I shoot for about 1/16" thick at the very ends of the braces, and about 1/8" thick at the points where the braces will exit the linings. Since the brace ends are already ramped it is quick and easy to do this work, using a paring chisel.

Now it is time to cut the pockets. We have lines on the ribs indicating where the outsides of each brace are located. These lines are extended onto the tops of the linings, and then they are extended onto the inside surface of the linings, too. We know how deep these pockets should be at the inside surface of the linings - if you are following my dimensions they will be 1/8" deep here. So a line is marked at that depth from the tops of the linings. Note that, as with other fitting work, you generally want to make the pocket slightly undersized at first, so you can trim it for a tight fit later.

If your instrument uses kerfed linings for the top you will sometimes luck out and find that your mark falls right on one of the kerfs. Congratulations, you win! But just as often your line falls near to but not right on a kerf. Trying to make a cut here is guaranteed to yank out the skinny remaining length of the lining "tooth" you are sawing. You can take two approaches in this case. The first is just to make the pocket as wide as you have to to avoid cutting through the linings at all. This works fine but is kind of messy looking. The other thing you can do is to fill the kerfs in the lining around where you are making the pocket with veneer.

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When the glue dries the veneer is trimmed back.

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Now the sides of the pockets can be sawn using a razor saw. I use a German hobby type razor saw with fine teeth and a thin blade installed to cut on the pull stroke. It is incredibly easy to rip out the wood of the linings when making this cut, because you are starting on a sharp edge. All in all, cutting the brace end pockets is incredibly tedious work. Use a light touch. Each cut is made with the saw angled as shown so the bottom of the saw kerf ends up at the depth line for the pocket, and the top of the kerf at the point where the lining meets the ribs at the top.

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In this picture you can see that I only made one cut (on the left) because the right side line ended up on one of the kerfs in the linings. I also scribed the line marking the depth of the pocket with a chisel. Now the pocket can be chiseled.

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Note that I am chiseling upward, toward the juncture of the linings and the ribs. To do this you'll need a short chisel. If you chisel from the top down, you risk blowing out the grain at the bottom of the cut. Remember, this is a very delicate operation. The resulting pocket has a slanted floor, and looks like this:

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Here's another view:

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In the next step to the process, a flat is chiseled on the top of the pocket. This flat section is as deep as the end of the brace. Finally, the floor of the pocket is scraped so it makes a clean ramp that will perfectly accommodate the brace end. The end result looks like this:

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After all the brace end pockets are cut, the top can be test fitted to the ribs. The process is the same as for the original trial fitting, only this time we are looking for a good fit between the brace ends and the pockets for them. Some final trimming of the pockets or the brace ends may be required. If the brace ends pop into the pockets but the center lines of the top plate and the rib garland can't be aligned, this usually means that one or more of the brace end pockets need to have their sides trimmed a bit. If you can't gently push the top down flush to the ribs and linings over the end of a brace, this means that either the pocket needs to be deepened or the brace end needs to be thinned. I usually do the latter. The top may be a bit distorted and may not simply sit flush to the ribs, so you'll need to actually hold it in place to determine if you've got a good fit. Use clamps as needed here.

Once you get the fit right, the top can be glued to the ribs. There are many different clamp and caul configurations you can use to do this. Any way that clamps the top to the ribs all the way around is fine. I have a lot of clamps, so I just use clamps, no cauls.

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To glue the top onto the ribs, remove it from the garland and apply a thin bead of glue to the linings and blocks and spread it over the linings. Gauging the amount of glue takes a bit of practice and experience. On one hand it is very important that you have enough glue to completely cover the tops of the linings and the blocks, and the edge of the ribs. On the other, you don't want so much glue that it seeps down between the kerfs of the linings and onto the inside of the ribs. Remember, there will be no wiping up of glue possible, because the garland is clamped into the mold while the glue dries. Clamp the top down lightly. Be sure the clamp pads only contact the very edge of the top, over where the linings are. The top is delicate and it is easy to crack it by over tightening a clamp. When the glue dries the clamps are removed. If the mold doesn't have a solid bottom you can flip it over to remove the rib jacks. If not, the rib jacks are removed through the soundhole. Then the body can be removed from the mold.

In preparation for gluing on the back, the overhanging material on the top plate must be removed. You want to trim the top flush to the ribs. This can be done with a router and flush trimming bit. If you use these tools it is a very good idea to use climbing cuts when you are cutting into the grain. Otherwise it is very easy to yank out a big hunk of top wood by routing into the grain.

Although I usually use the router for this purpose I am going to detail trimming the excess material from the top using a paring chisel here. Since the top is made of softwood this step is possible to do with the paring chisel. The work goes quickly. If the body has been removed from the mold, reinsert it and hold it in place with the rib jacks. Pare a little wood off at a time, starting at the upper and lower bouts and paring toward the neck block and tail block respectively.

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Then pare from the upper and lower bouts toward the waist. You'll need to alternate, paring from one side, then from the other. This is a little awkward to do at first, but after you gain experience with the paring chisel you will soon learn to use it ambidextrously and will be able to make controlled cuts with either hand. When paring right in the waist, it helps to flip the chisel over so the beveled side is in.

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You'll want to hold the chisel so the cutting edge is at a slight vertical angle. Do this by slightly raising the handle from horizontal. This makes the cut go downward a bit, which helps prevents splinters from being lifted out of the top. It is also a good idea to slightly twist the chisel as if you were trying to make a bevel. This will prevent you from gouging the ribs with the sharp bottom corner of the chisel as you get close to the ribs.

This is another one of those lutherie operations where all of your senses come into play. As you approach the ribs, the effort it takes to push the chisel will increase ever so slightly and the sound the chisel makes as it cuts will change as you begin cutting through glue as well as wood.

The end grain can be tough to get through with the chisel. What with discretion being the better part of lutherie as well as of valor, it is often best to use the block plane for trimming this area.

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When the top is all trimmed you can take the body out of the mold in preparation for gluing on the back.

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Attaching the Back Plate

The process of attaching the back plate is essentially the same as that of attaching the top, but there are substantial issues peculiar to the back plate which need to be discussed. The first is the method by which the rib assembly is held for assembly. The mold was used to hold the garland while the top was attached, but a full depth mold cannot be used to hold the garland to attach the back. If you try to insert the body into the mold top side first, you'll notice that it will not fit. The top is ever so slightly larger than the inside of the mold. This is a consequence of a bit of the ribs sticking out above the top of the mold during the gluing on of the top. The ribs kind of spread out over the top edge of the mold.

There are a number of fixtures that can be used to hold the body while the back is glued on. A shallow mold that can be split apart can be used. Some folks that build on a workboard (solera) in the Spanish style will use some big 'L' shaped pieces of wood that screw down to the workboard and support the ribs. And you can even simply sit the body top side down onto the dished workboard used to dome it, and then concoct some kind of 'L' shaped brackets that clamp to the bench and support the ribs.

No matter what fixture you use, the important feature of it is that it provides some support to the ribs that keep them straight and parallel to each other and perpendicular to the imaginary plane of the top (this is imaginary because the top is actually domed). This is necessary because the ribs tend to bow in or out a bit, and they must be pushed back into shape before the back is glued on.

I have a shop-built cradle that holds the body to present it to a stationary router for cutting the ledges for the bindings, and I use this fixture to hold the body while attaching the back.

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The cradle is adjustable for a wide variety of guitar bodies. Each of the six arms of the cradle is adjustable in location, and each has a depth adjustable block on which the body sits while in the cradle. The body goes in the cradle top down, and the position of the arms are loosely adjusted. Then the depth of the blocks are adjusted so that the top plate is the same distance from the base of the cradle all the way around.

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Of course, it can't be exactly the same distance from the base of the cradle all the way around, because the top is domed. Note that this measurement is taken from the top, and not from the edge that will contact the back plate. This is because the body of this guitar, like that of most guitars, has a taper from one end to the other. So the tail end of the ribs will stick up a little bit higher than will the neck end.

The next thing that is done is to adjust the arms so that they are tightly up against the ribs. As this is done for each arm, the arm will either contact the top edge first or it will contact the back edge first. Another way of putting this is that the ribs will tend to cave in a bit or they will tend to spread out. But we want them to be straight up and down, and in continuous contact with the arms of the cradle.

The two arms at the neck and tail seams are positioned first. If the ribs tend to spread out, you simply push the brackets in until they contact the edge of the top plate, thus pushing the ribs into place. If the ribs tend to cave in, the brackets are also pushed right up against the edge of the top plate, but some method of forcing the ribs up against the brackets will have to be devised. One thing you can do is use the rib jacks to do this. Another possibility is to cut some thin go-bars of scrap wood and fit them inside the ribs, up near the back linings, to spread the ribs into correct shape. Whatever mechanism you use, be aware that you are going to leave these in place while the back is glued on, which means you are going to have to remove these through the soundhole later. If you use the go-bars, make them thin enough so that you can break them into pieces to remove them.

Once the ribs have been made straight you can do a test fitting of the back. This goes about the same as the test fitting of the top, but the back has the center seam reinforcement, which first has to be trimmed. I like this to be tight up against the neck block in the finished instrument, because this area is visible through the soundhole. So the first thing to do is to carefully measure from the outline of the back down to where the inside surface of the neck block will be in the finished instrument. The reinforcement strip is trimmed to this mark.

Now a test fitting of the back can be done. Because the back is domed to a smaller radius than the top and because it (usually) is parallel braced, you'll find you have to bend the back a lot more to do this fitting.

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By the way, you don't really have any choice other than to cut pockets to support the ends of the back braces, because you have to do the work while the box is still open. The process of marking and cutting the pockets, and fitting and trimming is the same as described above for the top plate.

When you get a good fit for the brace ends in their pockets, the last step is to trim the center reinforcement at the tail block.

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This joint will be invisible in the finished instrument, so you don't have to fiddle with it too much if you don't want to. But do be sure that the reinforcement strip clears the tail block before you glue on the back.

Gluing on the back and trimming the overhang is the same as for the top. If the back is made of mahogany you'll be able to trim it with the paring chisel if you like, but all other wood species typically used for guitar backs and sides are too hard, so you'll need to use the router or plane. Again, remember to use climbing cuts when cutting into the grain.