Making kerfed linings with the BobCutter - video!

The sides of the guitars are really thin - just 3/32". So to glue the top and back to them, there are hundreds of tiny glue blocks around the perimeter of sides. They are triangular in section, about 1/4" wide and 1/2" deep. For convenience in handling and gluing, these are made in strips connected by just a hair of wood - no more than 1/100" or so. As usual, Stewmac sells these ready made, but I went to Forest Products Associates this morning and bought a small board of basswood and made my own.

Here is a short strip of the finished product:

It needs a light fine sanding to remove fuzz - I don't think I'll do this until after the linings are glued to the sides - they'll just fall apart from handling if I try to do it now.

Here's the jig I used to allow me to semi-automate all those delicate cuts on the bandsaw. First I milled 8 36" tapered strips on the tablesaw. Then I made the jig, which consists of a sliding board running in the slot on the bandsaw's table top. On the board is a long trough, perfectly fitted to the strips, which slide from right to left as I cut them. I made a hinged tab which slips into each just-cut kerf, as I move the strip gradually left, ensuring that each slot is equidistant from the last. The block of wood clamped to the back of the table ensures that the blade's cut stops exactly where I want it too, and no further.  This video shows it in action:

Here's the result: about 24 feet of nicely cut kerfed linings, which is enough, I hope, for 2 guitars. It took about 2 hours on the bandsaw jig to cut all the kerfs, which is about the same amount of time it took to make the jig and rip the strips.  Tomorrow I bend the second set of sides.

Bending the sides: First set AOK!

I have literally lost sleep over the possibility that I could not successfully bend the cutaway side of these guitars without fracturing the wood, in which case all the work on the tops would have been for nought.

But today I bent one set of sides, and they turned out perfectly! So I should get a sound nights' sleep, I hope. Of course, I may be jinxing myself for bending the next set on Thursday, but right now I'm pretty pleased and relieved.

As usual, I needed to make some tools; in this case, a boiling trough for the sides, and an add-on attachment for the bending iron.

In keeping with my idea of home-made tools, I made a 3 1/2" x 3 1/2" x 36" boiling tough out of a length of 6" galvanized stove pipe I had laying about.  I screwed two 36" 2x4s together as a "mold,"  and laid out the pattern for cutting with shears.

My high-tech sheet metal brake. Basically, folding and pounding.

First folding the sides, then the ends. I did this on a piece of paper first, as proof of concept. I used the Chinese takeout carton as inspiration.

Pinching and folding the ends. More pounding.

The finished trough, with a mahogany side resting on the "submergence clips." In use, these four clips go over the wood, to keep it submerged in the boiling water.

My boiling setup on my outside workbench. About 36 degrees out today - not bad. I made supports for the ends of the trough because I feared the trough, which overhangs the boiler. might buckle from the weight of the water and the heat.    Two strips of 1/4" steel keep the heat up the sides.

I boiled each side for about 20 minutes. 

To manage the first super-tight curve at the cutaway, I added a smaller-diameter pipe to the main one, and added a secondary table top with a holder for the side, so I could concentrate on pressing the strip against the heated pipe. This worked great - no fractures, and the strip bent quickly and cleanly. I let it "set" for a minute when it was bent, and the copper clip you see fit around the just-bent part, holding it tight to the heated pipe.

Bending the non-cutaway side over the larger-diameter pipe.  I had to keep the wood wet by squirting water from a squeeze bottle on the wood - the hot pipe produced steam when it touched the wood, which aided the bending significantly.  By the time this side was bent, I felt a little more confident.

As I bent each piece, I kept laying it over the original masonite top pattern, to see how I was doing. By the time I was done, the bent side was formed with no pressure needed to keep it in shape.

I don't know how I ever thought I was going to be able to get both sides in the same mold. After I bent the cutaway side, and clamped it in place with the turnbuckles and additional clamps, I couldn't imagine taking the clamps off to set the other side in. So I made a simple drying jig for the non-cutaway side. As I took this photo, I was breathing a sigh of relief that both sides had been bent successfully.

Tuesday PM, both sides drying and setting in molds with radiant heat from the wood stove. Scooter is annoyed because her sleeping spot has been preempted.  I'm going to leave them in the molds tonight and tomorrow night, too, then remove them and bend the other set Thursday. Tomorrow, a major shop cleanup and making the head and tail blocks.

Here's the finished product:

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How I spent a week lining the F-holes

The top of a guitar is visible. If there's a defect there, people will notice it for sure.

I could have left the f-holes unlined, but I decided to line them for a number of reasons. First, I have to admit, it's classy. Also, I really dislike the look of the end grain of wood. Finally, I think the lining will make the tops a lot more secure from damage. I kept thinking about those tiny softwood tips at the vortex of each of the curliques... had to do it.

Almost all archtops I see these days are lined with plastic strips sold my Stewmac and other places. They're what Bob Benedetto uses in his $40,000 guitars. So I guess there's nothing wrong with them, but I don't want plastic on my guitars at all.

Also, I don't want the guitars to be really "flashy." So I decided to line the f-holes with a single 1/16" strip of African Mahogany, same wood as the sides and back. When I made this decision, I had no idea how difficult it would be, but I remind myself daily that adding new skills is what this project is all about.

 Each f-holes has two tight curllique circles, so the wood would have to  be heat bent to fit. And, of course, I'm going to need a bending iron for the sides. Stewmac sells a bending iron for $189, but there are a couple of things I don't like about it. First, it's horizontal, and I'd rather have it with a vertical element. Second, it doesn't have a way to add small diameter elements like I need for the f-holes. And finally, of course, it's $189, which I hate to part with.

Looking around bins in the shop, I found a cut-off steel section from a lally column I used in the barn, and a heating element from an old electric paint stripper which I hated because it burned my hands and nearly set my old house on fire. Perfect fot this, though. I salvaged the heating element, and bent it in a vice. 

Here's the finished heating element, with a removable small-diameter curlique adapter in place. 5/4 rock maple top and hardware were all in the shop. Total cost $11 to Florence Hardware for the 600-watt dimmer. Notice the "limiter" on the switch. The heating element is 750 watts, and glows red hot after a few minutes. I only want 275 - 300 degrees, since the wood wil char above that. I experimented using the thermometer from my wood stove to find the right spot on the dimmer, then fixed it so it can't go any farther. My hunch is it's not drawing more than 200 watts or so.

I set up in my living room for steam-bending the mahogany strips, so I could use the wood stove to steam the pieces. To that end, I made a "steamer spout" for an old iron kettle. Scooter supervised. Ultimately, though, the steam bending didn't work, and I boiled each of the 8 curlique pieces  for 8 minutes to get it pliable enough to take the small-radius bend without fracturing.

I made 4 bending forms on the router jig out of 1/4" masonite, using the same router jog I used to cut the f-holes in the top. I got thin strips of brass to take some of the stress off the outside of the wood as I bent each piece around the copper pipe, then used these strips in the bending form to protect the wood strips from damage as I lashed them in to cool and dry. This is a closeup of one part of one of the strips, fresh from bending into place.

Here are all the bent strips in their forms, ready for a night in front of the wood stove to dry and set. The circles are for the less radically arced pieces, which still needed some persuasion to bend.

4 days work: the bent, cooled pieces of mahogany, ready for trimming and fitting in the f-holes. 

Before I could install the mahogany lining pieces, I had to trim sharp inside corners on the f-holes, where the 1/4" router bit from the cutting jig wouldn't go. The corner on the right is from the jig, the corner on the left is trimmed.

Gluing the first set of strips. I made little screw clamps to draw the strip tight into the inside corner, and little plugs for each of the holes, which I shimmed against toe strips to push each mahogany strip outwards firmly against the cedar.

Trimming the first strips down to the cedar, inside and out, with a sharp 1/4" chisel. Pencil marks on the cedar indicate the direction of the grain in the mahogany, to keep from digging in. 

Glueup part 2 - the adding the arced strips against the curlique strips. They had to be mitered on both ends, and fitted to be snug. Fussy work, but less risky than the first pieces. Actually a lot easier, since most of the pressure could be applied by little wedges.  I cleaned up most of that squeezed-out clue you see before it dried.

A completed, lined f-hole. I haven't sanded the insides of the strips, and don't intend to until after assembly - less chance for damage.

AI'm really pleased how these turned out. Not perfect, but up to my specs. Those sharp edges will be slightly radiused over when I'm ready to start the finishing.

Still building 2 guitars - no disasters, and looking good. the ops and backs are completed, and ready for gluing onto the sides, which I will bend as the next step. 

A whole new way to cut F holes

Frankly, cutting the F holes in the two fragile tops I had just spent a couple of weeks carving scared the shit out of me.

Everybody who writes about building archtops agrees, "using a pin router is the way to do it." I don't have a pin router, and haven't ever needed one so far, and I'm not going to add a homemade or expensive store-bought stationery tool o my shop, so my saga became making them cleanly without one.

I considered using a drill press with a pin in the table, but checking my machine, 2700 rpm was its top speed, and my router goes about 25,000 rpm, I think - so that probably wouldn't work without chattering. Also, I had a picture of the spiral upcut bit I wanted to use pulling the Jacobs chuck down out of the socket, destroying one of the tops, then bouncing up into my eye.

So I developed a low-tech router table template, and it worked just fine. In fact, I can't see why anyone would want o use a pin router. Here's how I did it:

Rough cut 3/4" AC pine plywood template base,  glued up with biscuits, room for pattern insets.

Cleaned up template base, routed ledges for pattern insets.

Blank pattern insets of 1/4" masonite, smooth both sides. I scanned full-size f-holes from Bob Benedetto's book, then used Indesign to produce mirror prints the same size as the insets, and spray-mounted them in place.

After cutting the pattern inserts slightly undersize, I cleaned them up. I use this odd tool only about once every six or eight years, but here it was perfect in the drill press.

Final filling he pattern inserts, right to the line.

Final pattern template, ready to use. The indent near the top is for the top braces, which lay slightly below the rim of the tops.

The point of no return - drilling a 5/8" hole for the bit to stick up through. Located it in the widest opening of each hole.

After a dozen different ideas, here is the router table setup I decided on. There simply isn't a top bearing router bit narrow enough for the "necks" of the f-holes, so I decided to use a 1/4" shank, 1/4" diameter solid carbide twin flute straight twin flute bit (did I describe that fully enough for you?) and let the pattern simply rub against the lower, uncut part of the bit. Frankly, I had fears of it smoking against the masonite pattern, but it worked just fine.

Test piece of cedar- worked great, so I went ahead with the actual tops.

This photo tells the whole story. Nice clean cut! I need to finish the inside corners with a chisel, then my next step is lining the f-holes. Everybody uses precut plastic strips for this, but I'm going to avoid plastic and use a strip of African mahogany (same board as the backs and sides) and a strip of tiger maple, which may be too difficult to bend without fracturing, in which case the center-facing strip will be rock or red maple - I have plenty of scraps of both.

Here's how a top looked when it was finished on the router table. So far, so good!

Cutting and fitting the top braces

Unlike flat top guitars of every kind, the backs of archtops are unbraced. Even though they're only 1/8" to 3/16" thick, their curve gives them a lot of strength. The top plates are strong, too, but the pressure of 6 steel strings means they need to be braced to keep from deforming. The bracing pattern I chose - parallel bracing - puts a substantial longitudinal brace on either side of the bridge, right under the pin supports. Both braces run the length of the top, ranging from about 1/2" thick under the bridge to about 1/8" at the ends.

Because these braces are so robust, the tops can be carved thinner, which makes a brighter, louder tone on the finished instrument.

I decided to make and add the braces before I cut the f-holes, disregarding Benedetto's instructions, for no good reason except that I just thought it might be better to have the top more rigid (with the braces glued in) when I cut through the top plates, which frankly scares the shit out of me.

These braces need to fit as perfectly as possible to the tops. 

Why I have a wood room: I found a perfectly quarter-sawn, dense cedar clapboard I had put away decades ago, which I planed to 5/16 for the braces. Couldn't have bought a better piece of wood, anywhere.

Rough, bandsawn braces, after scribing to fit. Gaps of about 1/32" on all of them, in several places. NFG yet.

Remember carbon paper? I think this package is from the early '70s. I cut strips to fit under each brace, one at a time, carbon side up, "hinged" with blue tape si it can be folded back, and rubbed the brace back and forth with tiny strokes, to show high spots (where the carbon paper meets the wood).

High spots. Next, light sanding on each dark spot with a sanding stick glued up with 80 grit paper. Repeat the process until the whole stick is basically in contact with the carbon paper.

Perfect fit! As I get closer to done on each fit, I shine a bright light looking for seepage under the stick none here, with no pressure on the brace - I'm done with fitting this one.

Oops! Good fit everywhere but the last 3/4", where I must have cut or sanded too deeply. I can fix this, though.

Where the end of that one brace was cut too deep, I added a little wood, then trimmed it to fit.

Nice fit. Next, trimming them all flat to 1/8" thick at the ends, then gluing them in. 

Homemade, zero-cost luthier's clamps. I had some 7/8" cypress left over from an outdoor project. I designed and made these clamps, and glued cork to the faces. Different length 1/4" carriage bolts ( I have a small bucket of them) let them expand to whatever size I need.

New clamps in action. I outlined he gluing area with blue tape, for a cleaner job and less question about exactly where the parts go. Scraping the glue when it's wet makes an easier, cleaner job in the end.

Final planing and chamfering the ends. I've had that cheap spokeshave since I was a child.  As an adult, I've improved it and reworked it several times, and I can't imagine wanting a "better" one.