Binding

The guitar with binding is pictured at left.  I mentioned that I wasn't happy with the way the binding went on my guitar, so perhaps a word or two of explanation.   I put it on in the standard way -- that is, I bent it to the shape of the guitar, and glued it in place using painter's tape as a clamping mechanism.   The channel cutter did a perfectly fine job of cutting the channel at a consistent depth around the guitar.  It's depth was shy of the thickness of the binding material (maple) or the binding material was proud of the guitar, and you can see the shavings where I scraped it down to be flush with the sides, soundboard, and back of the guitar.  All that works pretty much as advertised with a couple of exceptions.

Let me talk about the intersection of the back and the tail block.   Looking at it straight on, I think I did a reasonably good job of getting the two pieces of binding material to come together in a tight seam.  That too I did in the standard way.  I glued one piece of binding in place, then trimmed it back to the center of tail block inlay using a razor saw (cut at an angle) then a chisel.  The second piece of binding was glued in place up to the first, and I cut it away with the razor saw, then tweaked its fit carefully with a file.  I did the same on the soundboard side.  As I say, I am relatively happy with the way it came together.

 Looking at it from another angle, you can probably see the flaw that is annoying me.  I'm not entirely sure what I did wrong, but there was a gap that showed up between the back stripe and the binding.  I had cut the purfling channel not quite up to the back stripe, and then cut the binding channel.  I cleaned up the purfling channel to the back stripe with a chisel, and then glued the purfling in place.  I did the miters with an xacto knife.  The purfling was, or so I thought, flush with the binding channel, but when I removed the tape and scraped it flush with the back, there was a gap.  I filled it with epoxy and maple dust, but it is still visible.  Not completely happy with that.

There was another issue with the binding around the guitar.  I cut it too thick, and so I had difficulty getting it to set properly in the binding channel, and the tape didn't provide enough clamping pressure to keep it tight against the channel while I was doing the fitting.  Here again, I got a couple of gaps around the periphery of the guitar.  Again, I filled them epoxy and dust, but I can still see the gaps.  Not completely happy with that either.

My solution goes something like this.  Patience is a virtue, and one that I sometimes lack, but first, since I am cutting the channels with a rabbet bit and bearings, I should cut the channels for the purfling and the binding on the guitar body.  I can then use the channel itself to cut and finish the binding material to thickness.  I would still want it slightly proud of the channel to be scraped flush, but it would be considerably thinner, and the spring back after bending more amenable to adjustment with the tape's clamping pressure.

Side Bending

I have thicknessed and bent the sides for my guitar.  There really is no way of describing the bending process in words.  A person just has to do it to discover that it's not that difficult.  The tools I use for bending are pictured at left.   

The first step, however, is to mark the sides.  I put them side by side, as a book-marked pair, and marked the waist bend on both.  Do it with something that won't wash away as you soak the sides.  Because I begin with the waist, and I would encourage people to do that, if it's marked you will avoid bending two left sides and the two ends will align with grain patterns.

The stainless tray was fashioned for me by students at the college, and it has come in very handy because it is side sized.  I soak the sides to be bent in hot water and a cap full of Downy for about an hour or so before bending.   The Downy, or any fabric softner, does just that, it softens the fibers so they bend more easily.   The bending iron was a gift from my kids.  I had an elaborate pipe and blowtorch set up before, but I would encourage purchasing the bending iron.  I clamp it in my bench clamp, and let it heat up as the sides are soaking.  When all is ready, then just bend.  I wrap the bend in a wet cloth, press it against the iron, rocking it slightly, until I feel the fibers loosen and the bend taking shape.  I use the clamping jig as a template, and when it is right, I clamp it into place to cool and set.   I don't worry about a bit of spring back if the side can be clamped into the mold without excessive forcing.   I then clamp it in the mold, and mark the centerline to cut off any excess from each end of the side. 

You can see the sides in the mold in the photos to the left and right.  Before gluing up the sides, one needs to fashion the head and tail blocks.  The tail block is made from bass wood.  Other woods could be used, but I like bass wood, in part because it does not have a resonant overtone, and in part because it is light in weight.  The head block is made from mahogony.  Usually, I would use some left overs from the neck, glued up into a block of the right size, but this particular block I purchased from LMI.   You can see the mortise for the neck tenon in the photo below.  I cut it in multiple passes on the router table with a 3/4 inch straight bit.  I will cut away the excess side material later clear the mortise.

When I glue up the sides, I have the soundboard side flush with the top of the head and tail blocks.  That keeps everything at the right angles, no pun intended.   When the glue has dried, the next step is to arch the back.  In the photo below, you can see the preliminary arch.  I usually divide the guitar in half along the center line, and then plane along the side with my block plane, along each side, starting with short strokes near the block, then taking longer and longer strokes, until the side is planed flush with the block.  When I have glued in the kerfing, I will take away some of the peak as I level the kerfing. 

 

Back & Binding Jig

Last Sunday, I had some time, and the scrap left from my molds, so I began my binding jig.  The construction is less complex than it looks.  I began with the plastic that would serve as the router mount, and cut it to size.  In the picture, the router is mounted backward, and I still have some work to do on the mounting plate, but it's width is correct and that was the crucial dimension.

Next, work on the interior box.  On the material for the interior box (3/4 MDF) I cut the groove for the mounting plate on the table saw with a dado blade.  It took a bit of fussing with shims to get the width of the groove correct, but I wanted a tight fit.  Next, I cut the sides to width, about 2 1/2 inches, and length.  The drawer glides determined the length.  With the mounting plate in the side grooves, used that to get the measure for the width of the back.  I used a simple butt joint, then glue and brads to build the box.  You can use the mounting plate to keep things aligned.

The next step was the exterior box.  Again, I cut the sides to width, about 2 1/2 inches.  Again, the interior box and the drawer glides determined the height.  It is set so the router, at the lowest level, will not bottom out its bit.   A word on the base.     You can see in the photo above and to the left, that it is flush with the front, but extends back.  When the jig is in use, I plan to clamp it behind to one edge of my bench, and you can see from the photo that it supports the weight of my router without the clamps.

I built the exterior box in the same way.  The width of back was determined by the interior box, with the drawer glides.  I then used a simple butt joint with brads and glue.  I cut and installed the base last.  When the glue had dried, and I'd rounded over all the edges, I installed the drawer glides.  Make sure you get the orientation right, but basically the interior box slides up and down like a drawer in and out.

Next, I need to fuss a bit with the router mount, and build the guitar cradle, but on the whole, this project went together better than I would have anticipated.

I had ordered the back and side plates from LMI.  I was side tracked a bit.  Originally, I had intended to use mahogany, but got side tracked by the idea of black walnut, a domestic wood.  It arrived on Wednesday, so I was able to get a start on the back of the guitar.

I brought the thickness down some with my toothing plane, and my thickness sander.  With the toothing plane, I only worked the interior surface.  It's quicker than the thickness sander alone.  There was a bit of tear out, but the thickness sander removed it along with the toothing plane tracks.  

The center stripe is maple from the local hardwood store, with black/white perfling on either side.  The stripe, as you can see from the back view goes all the way through, and is not an inlay.  I prefer this to an inlay, particularly since the joint is reinforced.  The assembly needs a little fussing to get it all lined up in the lattice jig, but then I don't need to worry about sanding through the inlay.  I used scraps from the soundboard redwood to make the reinforcement strip.  Once I had glued it in place on the on the go-bar deck (using every go-bar I had to insure even pressure along the length) I planed it level, then planed a slight bevel on either side, which is rounded over when I sand it.  Today, I will work on the bracing for the back, which I intend to make from walnut, also purchased from the local hardwood store. 

A Bit More Progress

Another bad weather day -- about a foot of snow, but I was able to make a bit more progress.   In the photo at left, you can see the bending mold, now on a stand with the clamps installed.  I made them from scrap oak, but just about any wood will do.  The clamp at the waist has been contoured on the bottom to fit the waist snugly.  I did this on the bench sander, just rocking it back and forth, and checking it against the mold until it was about right.  Although it is not visible, the far post passes through a slot, not simply a hole.  When I had drilled the holes for the posts, I simply cut down with a gents saw into the hole.   This allows one to position it more quickly, a necessity if you are using the Sloan method of bending -- essentially boiling the sides until they are pliable, and clamping them into a bending mold like the above.  I have cracked several sides attempting it, and wouldn't recommend it, but then again Sloan has built more guitars than I will likely ever build. 

In the photo at right, you can see the completed mold.  I decided against the strap clamp for a couple of reasons.  First, they were too stretchy.  As I would tighten the extenders, it opened up the mold.  Second, the arrangement visible in the photos gave the mold greater stiffness.  Basically, it is simply a piece of 1/2 birch ply, tacked and glued on one side, bolted on the other with a 3/8th inch bolt.  Perhaps not the most aesthetically pleasing arrangement, but it works like a champ.

You can see the extenders below.  It is a simple arrangement as well, and a number of luthiers use something similar.  Essentially, it is a 3/8th by 16 threaded rod inserted into a 1/2 steel tube.  Both are available at the local hardware store.  At either end, the rod and the tube are epoxied into the blocks.  When the wing nut is tightened against the steel tube, it extends and puts pressure against the side in the mold. 

To make them, I laminated three scraps of 3/4 MDF, and from that cut six blocks to size.  Using the mold, I marked the contour on each block, and again shaped them on the bench sander to match the contour of the mold.  I then drilled the 3/8 inch hole on one side, the 1/2 inch hole on the other, about 2/3 of the way through the block. 

I then epoxied the steel rod into the 1/2 hole, and cut it off at about the center line of the mold, or where the two halves of the mold come together.  Since the holes were not precisely to the same depth, this worked well, and kept a sense of symmetry.
For the threaded rods, I did the same.  I epoxied one end into the block, then marked it at about one inch in from the opposite block.  In other words, the rod extends into the tube to about one inch in from the tube-side block.  This allows for enough rod in the tube to keep it straight, but also enough in and out play to remove the extenders when the kerfing has been installed on the side. 

The contoured end of the blocks were covered with cork.  The inside contour of the mold was also covered with cork.  It not only makes it all prettier, but smooths out some of the differences between the three layers of the mold and provides a protective cushion.  It's probably not necessary, but I do it regardless.  The cork comes in a roll and can be purchased in places like hobby lobby.  I cut the strips over-sized by about 1/4 inch.  Although the cork came with an adhesive, I still sprayed the interior of the mold with contact cement, waited for that to dry, and installed it carefully.  I then trimmed the excess away with a sharp exacto knife, and rounded it over with a file.        

A Wee Bit of Progress

Yesterday, I spent on yet another household project.  My wife does not like the arrangement of the living room, so I spent the day hanging a cabinet and the TV from the wall to free up floor space.   the challenge was not so much the hanging as the hiding of all the cords that support the electronics.  I have to admit, it looks much better, and she seems pleased, which is good enough for me. 

Today, however, is not a good weather day, so I couldn't move the vehicle out of the garage into the drive so I could get access to most of my tools, particularly the table saw.   I did make a bit of progress over last week on the bending jig.  In the picture above, you can see the hardware set for the upper bout and waist clamps, and the picture below, you see the hardware set used for the lower bout hold clamps, and in the last picture, the half-finished jig.  The stand is a piece of black pipe with two flanges.  The lower flange will be attached to a base.   I needed access my table saw in order to make the base.  

The upper and lower bout clamps are spring loaded, the waist clamp is shaped to fit the waist and is brought down with the two wing nuts.  As I said, I bend the sides first, freehand, then put them in the jig to rest, so speed isn't particularly crucial.  I do like to let the sides rest over-night, particularly if they are still wet from the bending process.

Next week-end, I hope I will have access to my table saw, and I will make the base, the clamps for the bending jig, and the spreaders to complete the mold.  More details to follow.

The Assembly and Bending Molds

I had a little more time to work this weekend, because my wife is out of town with the kids and grand-daughter.  She was a finalist in her school spelling bee, and grandma had to see it.  I'm a bit disappointed that I didn't get to see it, but we have an aged dog that doesn't travel well, so I am dog-sitting.  At any rate, the soundboard is as complete as I can make it for the moment, and I  don't have the plates for the plates for the sides and back.   So, wife away and at am impasse on the guitar itself, I decided to make the molds.  Since it involves MDF, it's also a hellacious messy, dusty job, something my wife fusses over the whole time.  What she doesn't see won't bother her, so long as I clean up well before she returns, all will be golden.  SAFETY NOTE:  wear a respirator. 

To be honest, I forgot to take pictures when I made the primary pieces of the mold, but the idea is fairly simple.  I used my router, a 1/4 upcut bit, and a brass bearing.  I took my initial template, clamped it first to a piece of 1/4 MDF on top of a piece of 3/4 MDF.  I clamped it my bench, tightly -- that's important, tightly -- and cut around the perimeter of the template.  I set the depth so it cut through the 1/4 inch MDF on the first cut, then another 1/4 inch into the MDF below.   Since there is a slight off set between the brass bearing and the initial template, the 1/4 MDF becomes the new template.  I set it aside, and cut around the template five more times, just 1/4 inch into the 3/4 MDF.

A couple of notes of caution.  When you cut left to right following the template, the router has a tendency to drift away from the template on the right side of the cut -- in the picture above, on the lower bout side.  Position yourself so you can keep good pressure between the brass bearing and the template.   

On the 3/4 MDF with the guitar shaped groove, I used my jig saw and cut along the groove, being careful not to cut outside the groove.   You should have twelve pieces, six for the outside perimeter of the guitar, six for the inside perimeter of the guitar.   Each of the six pieces should have a smooth contour left by the router bit, and a rough contour left by the jig saw.  I used my pattern bit, mounted in my router table, to trim off the excess left by the jig saw, running the bearing against the smooth contour, the blade against the rough contour.  I glued them up three at a time, trimmed the edges to make everything neat, and installed the dowels. 

Another couple of notes of caution.  My initial template extends a couple of inches beyond the center line.  Mark the center line.  When trimming the ends where the two halves of the mold come together, you want to hit the center-line mark precisely so the two halves of the mold come together symmetrically.  The dowels are there to keep things aligned and to keep the mold from folding up like a book when the band clamp is tightened around it.  There are a variety of ways that one can bind the two halves together, but after considerable experimentation in the past, this works well.  I have the band clamp.  It provides sufficient resistance for the extenders that hold the guitar against the mold.    So there you have it, an assembly mold.  Next weekend, I'll make the extenders. 

I did get a start on the bending mold.  I'll explain it in more detail, but you can see that it is basically the pieces that are cut out of the center of the mold.  You can see where I've drilled for the hardware.  Since it is six sheets of 3/4 MDF thick, I don't have a drill bit that will penetrate that far, so I carefully clamped two together, and drilled through them.  I glued up the bending mold, three sheets at a time, first using one drilled piece, then the other drilled piece.   Next week end, along the with extenders, I'll install the hardware and make the various hold down for the bending mold.  By the by, I do not actually use this for bending, though if one had a heat blanket, one could.  I bend freehand, but clamp it into the mold to finish drying and to rest.  It's also useful for holding bent binding while it's waiting for installation. 

Rosette

I finished the rosette, almost.  There is still a little tweaking that I need to do at the joints of the wafers, but it is essentially what it will be.  The tile at the top is there primarily as reinforcement and fill.

The first step, of course, is layout.  To do this, I used my template, which has already be scribed, and traced the outline on the sound board.  I am going for a parlor-type guitar, which I interpret to mean a steel string guitar with classical like dimensions.  It also suits me because I play finger-style, and find myself switching between classical and steel strings, so some continuity in the dimensions works for me.  Consequently, I am using a 25 and 11/32nd inch scale length.  There are all sorts of ways of coming at this, but I have found that one purchase has repaid itself several times.  Get a fret rule from LMI.   Again, I am going for classical like dimensions, so I placed the 12th fret line at the top of the sound board, and marked the location of the 22nd fret on the center-line (the glue seam).  With my compass set at 1 7/8th inch diameter, I scribed the circle for the sound hole.

Once I had the tiles set out in the working scrap, which you can see beneath the rosette, the whole process became rather simple.  I set the router so it would ride within the channel that I had cut to fit the tiles, set the depth to just a whisker (about 1/64th of an inch) shy of the total depth of the tiles, double checked (actually, quadruple checked) to make sure that I would not be cutting through the soundboard at that depth, and then made the cut, testing first where it would be covered by the fretboard.  Once the initial cut had been made, I eased it out and in using the precision adjustment on my router jig to accommodate the tiles and the perfling strips.  When I was finished, I gave the rosette channel a coat of shellac to prevent bleed out from the glue.

I put all the tiles and perfling in place, leaving slight gaps at the seams so I could lift them out, one by one.  Beginning at the bottom of the rosette, I would lift out one tile, run a bead of superglue along each of the perfling strips.  I then replace and quickly position the tile between the perfling strips.  I kept going I had worked up both sides of the rosette.  I wiped away any squeeze out, and pressed the tiles into place with my fingers until the glue set.    

Before I cut out the sound hole, I did a couple of things.  First, using my template, I transferred the outline of the guitar to the back of the sound board.  That was a simple matter of using the 1/4 hole for the router pivot, and a similar hole at the center of the sound hole in my template.  When sanding the back, make sure that you never sand away the lines that they cannot be retraced.  I also leveled the rosette.  Nothing fancy there, I just used my trusty card scraper, newly sharpened, taking light passes until the rosette was level with the sound board.   I then sanded it using 120 grit sandpaper on my sanding block.  A word of advice, never sand without a sanding block.  It's amazing how quickly one can cut shallow hollows sanding without a block.  Mine is just a scrap of cherry with a cork face.  I wrap the sandpaper over it and hold it in place as I sand.

To cut out the sound hole, I swapped the 1/4 inch bit in my router to a 1/8th inch bit, made the adjustments so there would be a lip of redwood approximately 1/8th inch wide, made an initial cut, then cut through.   Some have jigs to round over the edge of the sound hole.  I don't.  I just use a light touch with some hand held sandpaper.  I can't tell the difference.
 

Prepping and Joining the Plates

I re-sawed the plates for the sound board at the college before the Christmas break.  I ran them through the thickness sander until they were approximately the right thickness, then used my jointer to prepare the joint.  In the absence of a jointer, one could use a shooting board, and I know that some luthiers prefer the hand method regardless.  I do have a jointer, however, and it works perfectly fine.  I take the two book matched plates, and run them over the jointer together and I get a tight joint that stand up to the light test (holding the joint together and trying to see light through it).  My secondary test is that it squeezes out glue uniformly along its entire length.  That too tells me the joint will be tight.   


I used the lattice jig, pictured, left to join them up.  It worked precisely as advertised.  I glued the seam (using titebond) rubbed it until the glue began to set, then put it in the jig.  I wrapped the ropes in a criss-cross pattern loosely over the jig, then the loose ends I wrapped around one end, then drove the wedge shaped slats under the criss-crossed ropes.  It pulled the plates together sufficiently, and kept them dead flat while the glue dried.   You'll note there is no wax paper under the slats, but the slats themselves were well coated with wax before the glue up. 


The jointed plates are pictured at right, and you are looking at the exterior side.  After all the fussiness with the making of the rosette tiles, it was almost shameful how easily the plates went together with the jig.  You will note that there is a slight difference in color on either side of the center line.  The plate on the right has oxidized some, but as I do the finished sanding, that difference should disappear.  The next step will be the leveling of the top and the inlay of the rosette.  If all goes according to plan, I will tackle that in the coming weekend. 

Radius Cutter

I found a little time to mess around in my shop this morning, and I came up with this radius cutter that I will use to cut my rosettes.  I was able to get into the school shop, and we have a great band saw with a re-sawing blade.  It cut the redwood like butter.  I will begin work on the soundboard, beginning with the rosette.  I have something in mind, but don't know how well it will work.  I'll give it a whirl and let you know if it does. 

The construction of the radius cutter is fairly simple.  I had some 1/4 inch oak scrap left over from the bench, so I cut a 1/4 in dado in the sides of the cuter, and at the same time, cut for the end pieces and the slide, but did them on both sides.  The pieces are laid out on my bench.
 

The slide works fairly well.  I took a section of what I'd cut for the end pieces, enlarged the dado slightly.  I drilled a 5/16th hole for the blade, and squared it off with my 1/4 inch chisel.  I drilled a 1/4 inch hole for the carriage bolt, then cut it in half with my gent's saw, pushing the blade up against one side of the dado.  The slide is held in place by the carriage bolt, which pinches the two pieces against the interior slats, and the blade is held in place with a small shaped piece of the slat.  It all pivots on a 1/4 metal pin that goes in the hole on the right. 

The blade is made from an old jig saw blade.  I did some very preliminary work on the grinder, but it will need some additional shaping.  I have in mind a chisel point so I can turn it in both directions, and will work on some when I get up in the a.m.  I should be able to do that without waking my wife and our guests.  Even with the point only partially sharpened, however, it did cut a good groove in a scrap of birch ply, at about 1/32 of an inch wide.

Radius Dishes Continued

I have pretty much followed through on my plan for the radius dishes.  I had enough scrap ply left from the shop cabinets to build the jig that I used to cut the plates.  There are a couple of things that I should mention up front.  It makes an unholy mess of MDF dust.  Wear a respirator.  If I were making these dishes for a living, I would have figured out some method of dust collection, but for the two-off that that I'm making, I assumed clean up would be easier than rigging some elaborate method of dust collection.

Pictured, you can see the Xmas Tree Stand that serves as the base, the two end pieces to the right, the two rails for the router on the left, and the two sides on the foreground.  The 1/4 inch MDF attached to the one side is a template for the radius that will be cut into the side piece.  I have a nice one inch pattern bit that cuts such things like a champ and the template was an excuse to use it.  Since we're not talking a ton of material that has to be removed, you could join the two side pieces together, scribe the arch, then remove the material with a belt or bench sander.  Either way, it would work, but I recommend the investment in the bit.

Pictured, you can see the dish blank mounted on the Xmas Tree Stand.  It's a rather simple affair.  Use a wooden dowel.  I used a 1/4 inch dowel.  Your router bit is going to hit it, and you don't want to waste a router bit on this project.   To make the blank, I did as described.  I cut the MDF to size into two 22 inches squares.  I then used a very simple circle jig.  In a scrap of 1/4 MDF, I cut a hole large enough to accept a brass bearing on my router.  The measurement is to the outside edge of the bit -- in this case a 1/4 inch spiral upcut -- and I marked the location on the MDF for a 21 inch circle (10 and 1/2 inches from the edge of the bit).  I drove a finish nail through the MDF at the radius mark into the center of the dish, and viola!  A circle cutting jig.  It's pictured in my previous post.  I cut the circle in the MDF to a depth of about 1/4 inch, then used my jig saw to cut the majority of the scrap away.  On the router table, I finished the edges of the blank using my pattern bit running the bearing against the circle cut with the  router.  Since MDF chips easily, I rounded over the bottom of the dish with a 1/4 round over bit.

Pictured, you can see the router channel assembled.  It didn't work exactly as I had imagined.  With classic engineering oversight, on the length of the box, I had taken into account the width of the of the router base in determining the long end of the box, and so cut it only 3 and 3/4  inches longer than the 11 inch radius.  I didn't take into account the handles on my router base.  Also, I profiled the radius only on the long end of the box to the center marker.  In another well-duh! moment, I messed up the measurements on the first go round and didn't take into account the off-set of the long end.  I cut the radius from the center line of the side, not the center-line of the Xmas Tree Stand.  I disassembled, trimmed it off and started over, but you can easily see that you would want the center line over the center of the dish not the side and the 1/4 deflection (or 1/8th) should be at the edge of the dish not the end of the side.

Here you can see the whole set up put together and ready to rout.  Again, it makes an unholy mess of MDF dust, so use a respirator or something to protect your lungs.  On the router, I used a 3/4 inch straight bit.  The router wants to throw and spin the dish for you, but I could easily hold the router, hold and control the dish, and slowly advance the router from the outside to the center while turning the dish.  The rubber pads on the clamps helped with that.  I lightly pushed them against the dish and that too helped against the tendency to spin.  I had thought of taking the handles off the router to make it fit the channel better, but thought better of it, and was glad I didn't.

When the dish comes out of the jig, you'll want to sand down the ridge on the edge and take away the router marks.  But it worked, and I now have two radius dishes, one for the back and the other for the soundboard.  The stuff in the jar is a mixture of titebond glue and water at about 50/50 mix.  It's mostly just glue from nearly empty glue bottles.  I rinse out the bottles and save the remnants.  For lack of a better term, I call it sizing and I use it to harden MDF for sanding and just generally.  I'll also put a coat of poly on them.        

 

 

Shop Cabinets & Radius Dish

I did dig through my available plates, and unfortunately I didn't have one that would allow me to get a start on an actual guitar -- mostly scraps saved for various purposes, but mostly because I couldn't bear to throw out exotics, no matter how badly stained by the flood water.  So, I am still awaiting parts for my band saw.  I'll be able to re-saw some redwood for a soundboard, and I will probably buy the back and sides from LMI.

In the meantime, I have decided to go ahead and build a couple more shop cabinets.  I had gone to the Depot to get what I needed to make my radius dishes, but they had cabinet grade ply on sale for a little over twenty bucks, so I took the opportunity.  I will have scraps sufficient to make the router jig, and I did buy the 3/4 MDF that will be the dishes.   The shop cabinets are relatively simple affairs.  They are basically plywood boxes, joined with a tongue and groove -- that is, I cut a 1/4 groove on the sides of the cabinet, and a tongue on the top and bottom ends to fit the groove.  One will be used for my routers, and the other will be used for miscellaneous power tools.

As I was building the lattice jig, I did get a start on the jig to cut the radius dishes.  The plan is this:  I built what I am calling a Xmas Tree Stand, which is basically just a plywood X with each arm 22 inches long.  The MDF dishes will spin on this base.  The router jig will be similar to the one used to shape the drum for the thickness sander with a couple of exceptions.  My router base happens to be 6 inches wide, so two end pieces will be cut at 6 inches wide by about 8 inches tall.  The sides will about 6 inches wide as well (conservation of scrap) and about 25 inches long.  One end of the jig will be attached to the Xmas Tree Stand and the other will overhang about three inches or the radius of my router plate.


I plan to profile the sides with the arch on one side for the back using my router and a flush cut bit.  The first step is the creation of a template for the arch.  I use my metal shop ruler to create the arch.  I c-clamp a small block of scrap to the back-side of the rule, then clamp that down at the center of the arch.  I then deflect the ends up to create the arch, scribe it, then sand to the line on 1/4 inch MDF.    Remember, the low point of the arch should be over the center of the Xmas Tree Stand, and should allow enough clearance to attach the sides of the jig to the ends.  To accommodate that, I measure in 3/4 inches from one end of the side (where it will attach to the fixed side) then 11 and 22 inches from that mark.  The 11 inch mark is the center, and I deflect the rule up 1/4 inch on each of the other marks.  I then double stick the template to the side, and cut with the pattern bit.

The amount of deflection at either end can be easily calculated (though I had to be reminded of high school geometry and algebra to do it).  Take the radius of the dish (in my case, 11 inches) and square it (121 inches).  Take the radius of the back and square it (in my case, 20' or 240 inches, squared is 57,600).  Imagine a line tangent to circle 20' in diameter.  Now, imagine a point 11 inches out on that line from the point where it intersects the circle.  Using the Pythagorean theorem (a squared + b squared = c squared), you can calculate the distance between the point 11 inches out and the center of the circle (in my case the square root of (121 + 57,600) or the square root of 57,721, or 240.25195, which I rounded to 240.25).  The difference between the radius of the back (or the distance to the point where the circle intersects the tangent) and the distance to the point 11 inches out on the tangent line is .25 or 1/4 inch.  So each end needs to be deflected up 1/4 inch.  For the soundboard, I'm going with 1/8th inch.

When I have the arches correct, I will attach a 7 and 1/2 inch wide strip of thin ply to the arch with screws.  I'll clamp the ends to the sides so I can get the width exactly right, and then I will attach it to the Xmas Tree Stand so there is sufficient clearance for the MDF dish.  Before I cut the dish, I will cut the slot in the 1/4 ply for the router bit, put the dish in place, and cut up and back to the center mark while spinning the dish slowly. 

I finished the shop cabinets, but didn't get as far beyond that as I had imagined -- focus on one thing at a time.  So the dishes are a project for next weekend.  I will let you know how it really went.


    

Lattice Jig

Granddaughter and kids went home yesterday.  We went to Lowe's where Lora bought a white Christmas tree (something she has always wanted) and I bought a quarter sheet of birch ply (something I can always use).  I adjusted the platen on my thickness sander, and put a coat of poly on the drum.  I will put another coat on today, then during the week, I'll install the sandpaper, and all is for the good.

The lattice jig is really a rather simple affair, though it is somewhat ingenious, and I don't know who to credit for that ingenuity.   I took my design from LMI, and simplified it.   It is used for joining the plates for the back and soundboard.  I'll picture its work when I get to joining the plates for my next guitar,

It consists of two lattices, each of which consists of two rails (thinking of the rail road analogy again) and three ties (with a bad pun on ties).  It is assembled using standard wood-working techniques.  I cut 2 inch strips to length, then set up my dado blade to cut over-lapping notches.  I cut them slightly deep, at about an inch and an eighth, so I could keep it all perfectly flat during glue up.

The bottom lattice required the most work.  Between the notches for the two rails, I removed enough material to accommodate 1/4 inch MDF and some sheet plastic.  It provides the base against which the top rails bear, keeping the plates flat at the seam.

On one side, the rope is knotted into a single hole, and on the other, once it is crossed back and forth over the plates, it is snaked through the three holes pictured.  Drill the holes before assembly.  I glued and pinned it on my table saw, so it would be perfectly flat, threaded the rope and tested it on some scrap 1/8th ply.  It worked as advertised, so I can actually begin work on the guitar.  I will need to dig through my wood, but I believe I salvaged the mahogany for the back and sides, along with a book-matched piece of redwood for the soundboard.

If not, I will need to wait for the pieces needed to repair my band saw come from the manufacturer, and there is another project that I can tackle -- a circle cutter to define the rosette channel.  For that, I need a 1/4 inch brass rod (about 12 inches).  I have the necessary screws and inserts -- those I did salvage from the flood -- and the body I can make from oak off-cuts left over from the bench.  I could also continue making my shop cabinets.  I have in mind a router cabinet and another to hold my hand held power tools.  Never a lack of things to do.