A slightly oddball guitar (completed)

[profchris]

By popular request (OK, one person asked ) I'm documenting a guitar as I build it.

This won't be a standard dreadnaught beast, but is vaguely inspired by the US parlor guitars of the 1930s. The methods I'm using don't require any specialist tools, and indeed you could build one of these using 1.5mm birch ply if you were prepared to paint it (don't stain and finish birch ply for instruments, it always looks tacky!).

I'm starting on the body, most of which is a recycled Victorian wardrobe door. I'm guessing this is Honduras mahogany, and sadly it's flat cut rather than vertical grain. I can make that work for the sides and the back, but the top is also mahogany and that really needs to be vertical grain. So I've bought some expensively educated Brazilian mahogany from a luthier friend.

Yesterday I took a slice of the door and resawed it lengthways to make the back. One half cupped a little overnight, so I've planed the two saw cut sides flat and joined them bookmatched.

The process is simple once I've got a light-free joint. I tape the plates together, planed sides downward, put a small batten underneath to make a tent, and tap panel pins along the sides.

Then run glue into the joint and simply press flat. The panel pins push the plates together with enough pressure to get a perfect joint (if I planed it perfectly to begin with!). To make sure the planed sides come out pretty level I clamp a batten either side of the join (making sure It's clear of the glue squeeze out which I've wiped away).

Then it was just a matter of planing down the top (already joined) and sides to about 2.2mm (top) and 1.8mm (sides), and cutting a sound hole in the top.

Here is the back, now joined but not yet planed. This is at about 8mm, so I've plenty of planing to do!

 

[skipdiver]

Looking forward to this. Thanks for posting.

 

[Honest John]

I’m also looking forward to this. I often think of a Ukellele but there always seems to be something else to do/make. I am surprised how thin the top and sides are, but then that is probably just ignorance on my part :roll:

 

[profchris]

I mainly make ukes - harder than guitars to make sound reasonable and nearly as much work!

Either instrument is built just heavy enough not to collapse, otherwise it will be really quiet. A spruce top might be 3mm because spruce is less dense than mahogany.

I'll explain some of the structural problems as I go.

 

[AJB Temple]

Interesting thread. I used to make acoustic guitars (before I even heard of internet forums). I never had any success with acoustic tops out of mahogany or rosewood. Compared with Sitka the instrument always sounded muffled. I also preferred to have some belly on the back as well - but you seem to be going for a flat back. I shall be interested to see what bracing pattern you go for. I played around a lot with shaped braces and different materials. You may inspire me to build another one!

Are you building a mould for the sides? Or do you have a method that avoids this?

 

[profchris]

Bending sides and a lucky escape!

My bending kit is very simple - a piece of steel pipe into which I insert a heat gun. Once the pipe is hot enough for water drops to dance on its surface, it's ready for bending. Commonly I'll place a wet, clean rag on the pipe to generate steam, because this gets the heat into the wood quickly, and also reduces the chance of scorching the wood. However, some woods like to be bent dry, some don't like to be bent at all!

The technique is to mark where you want the bend and then place the wood on the pipe there, applying very light pressure as near the pipe as you can manage. Rock the wood gently until you feel it start to soften, then ease it into the shape you need. For wider bends "chase" the bend along the wood, slowly increasing it. It's something you can only get a feel for by practising, but isn't too difficult. Start with the guitar waist.

Except:

Oh Calamity!. My sides have runout (hard to avoid if recycling wood), and the outside of the bend is separating.

And the inside of the bend is creased!

Fortunately I spotted it quickly. Any more bending and I'd have snapped the side.

So I've attempted a save, by applying heat to flatten the wood again and then taking it down to around 1mm at the waist bend, and under 1.5mm elsewhere. I plane away the separation and then bend the opposite direction, aiming to pull out the crease.

And, reasonable success!

However, the upper bout bend is hard work, probably needs thinning even more. I'll do that before completing the bend (I use a little block plane on the outside of the bend, and will clean up by scraping once the body is assembled).

 

[thetyreman]

interesting project, thanks for posting it! I like the mellowness of mahogany guitars, they are quite under rated, looks good so far

 

[MatthewRedStars]

I love a murky mahogany guitar too, I play a Martin and a Gibson.... my girlfriend's spruce Taylor is so bright i can't play it. Different folks/strokes innit.

 

[profchris]

All the plates are now thicknessed so I can begin building the body.

I draw the body shape on the inside of the top and then cut the sound hole.

If I were making several guitars the same shape I'd make a mould for the body. But I find making a mould really hard (I think a spindle sander or perhaps a router is a must and I'm 99% hand tools), so instead I just glue some blocks around my shape. The plan is to get the body as close to that shape as possible - it is surprising how far off you can be without anybody noticing (except another instrument builder!).

Then I make head and tail blocks and glue the sides to each other. Here I've attached the head block but left the tail unattached. This lets me push each side into the blocks to find out exactly where the tail joint should be (hint: measure the sides too, to make sure they are the same length after cutting).

Once both blocks are glued in I can squeeze the sides between the blocks to see how close I am. The answer was, "Hmm, not so much" but that's OK - back to the hot pipe, increasing some bends and opening out others, until I end up with this:

That's pretty close, and I can use wedges against the blocks to ease it into an even better shape as I glue the sides to the top. You might spot that the waist on the left (as you look at the picture) is leaning outwards and raised up from the top, but I can push it into place with light finger pressure so that's what I'll do.

From this point onwards I need a firm base to hold the top in the correct alignment, otherwise I can introduce distortions as I glue it up. And if the top is distorted, it will be a nightmare to fit the neck and make the guitar playable. All the rest of the body can be as distorted as you like, but the top has to be accurate.

So I use a solid building board. I want to dome the lower bout slightly, and so I tape 3.2mm ply spacers down around the perimeter and across the upper bout. When I start building I'll screw down the edges (outside the perimeter, obvs!) through those spacers, and screw a batten across the soundhole.

To dome the upper bout I just use a batten over a block to push it down to the surface of the board. This creates a shallow dish, which I can use to sand my bracing to fit.

But before I attach the sides I need to shape and glue in my bracing, and I can't do that while the humidity is high. The top will shrink widthways as humidity drops, but the bracing won't shrink because it is glued cross-grain, and that is likely to crack the soundboard. But if I glue up in low humidity all I have to worry about is the soundboard expanding, and that will simply push up the dome a little.

Off on a work trip on Wednesday, so the next instalment will be next week if the weather is kind.

 

[profchris]

I'm back, and the wet weather has gone. So I can glue in the bracing for the top. It's really important to do this in low humidity - professional makers aim at around 45%, but I'm happy (for UK conditions) if humidity is around 50%. So outside humidity forecast at 55% and a little heating inside gets me close enough.

The reason this is so important is that the plates are very thin, around 2mm. Thus they will expand and shrink with humidity changes. The bracing resists shrinkage, and if I glue it on when humidity is above 50% then the top will almost certainly crack at some point.

I don't worry about swelling - the top has a very slight dome at its widest point, so any swelling will just increase the doming a little. And the top is vertical grain, so it won't move excessively.

Up to now I've used Titebond Original, but for the rest of the body it's Hot Hide Glue. Two reasons: First, I can reactivate it with heat (and a little moisture if needed) so I can adjust my joints as needed. Second, if the guitar ever needs repair (maybe a brace comes loose) there is no need to clean away the old glue as fresh HHG will reactivate the old.

Once the bracing is on I can attach the sides. I start by glueing the head and tail block in place. Then I glue each side, working HHG into the joint. A little heat from a heat gun on the outside until I feel the wood is warm inside, to liquefy the glue, and then snug up the clamps.

[The plane is just a weight, so that the clamps can hang over the side of the bench]

 

[Phil Pascoe]

Sunday would be a good day to work here for low humidity - it drops to 98%.

 

[profchris]

I had a gap, of course (the nice thing about HHG is that it dries nearly transparent, so you just look for light at the joint). Clamps, moisture, a little fresh glue and some heat, and all is good.

Good though HHG is, I don't think a 1.5mm glueing surface is quite enough, as I'll be putting string tension of 120 lb or so on the body, and it also has to stand up to musicians! So the joint needs reinforcement. Standard choices are either a kerfed lining strip, cut almost all the way through so it will follow the curves, or a solid lining strip bent to shape on the hot pipe. But both work best if you build the body in a mould, so you can plane and sand the lining to the sides.

For this kind of freehand building, dentellones (little teeth) are what we need. I just take a square stick of something (in this case a mahogany offcut) about 8mm square, and then plane it down nearly to a triangular section. Then I cut 3mm slices with the bandsaw. I could use square section, but that adds weight (there are building styles which like heavy backs and sides, but those also look for as much rigidity as possible in the top joint and so use solid linings or kerfed linings glued with the saw cuts on the inner face).

I only recently worked out the easiest way to glue these in. They only need light finger pressure for a few seconds, but if you place them with your fingers then inevitably you get glue on your fingers and HHG sticks nicely to skin. Thus the scalpel - use that to hold the dentellone while applying glue and to place it, then press with your clean finger and remove the scalpel. Easy! Nurse, the plasters please ...

 

[Phil Pascoe]

Sunday would be a good day to work here for low humidity - it drops to 98%.

Revised estimate - still dropping, but 99%.

 

[profchris]

Sunday would be a good day to work here for low humidity - it drops to 98%.

Revised estimate - still dropping, but 99%.

Ah, the sunny West Country. 20 degrees + and near 50% in semi-arid East Anglia.

Carve the neck, I guess.

 

[profchris]

Once the sides are on they need shaping. My neck block is 2 3/4 ins deep, my tail block 3, and the sides are 3 1/4 at their highest point. This gives me a nice curve lengthwise along the back.

Linings are glued in (in this case I'm using 1.5mm plywood, cut along its bendiest axis because it will then clamp easily into the curves), and the back braces are also shaped and notched into the linings. But not glued at this stage.

I want a curve side-to-side as well, and you can see here what I'm aiming for.

Because the braces aren't glued into their notches I can put HHG on them, clamp the back in place, and then 30 mins later remove back + braces.

I used a double application of HHG (leave 5 mins, then reapply) so I know there is enough glue in the joint. All I now need to do is to clamp down the unglued portions, painting a little warm water into the joint, then heat with a heat gun and snug up the clamps. The braces are now in the right position and will fit to the top!

And they did, so I glued the back on. Double layer of HHG along the rim as before. At this stage I'm only concerned with glueing the head and tail blocks in place, warming after clamping until the wood is hand hot so I know the glue is reactivated, and also getting the back glued down at the ends of the longer brace. This will lock the geometry of the body into place, so I know the neck end and the bridge location are lined up along the centre line. If not, I can't fit the neck.

Tomorrow I'll apply moisture and heat to the gaps and then clamp, working my way round a section at a time, so that I can see any gaps and force them into place. Then I'll trim off the excess and start work on the neck.

 

[profchris]

Sorry for the long delay! Lots to do at work, and last weekend I was away playing at a music festival. But progress has been made on the neck, in 30 minute bursts.

Step 1 was to create a neck blank, which is the width and length of the final neck (or a fraction more, probably quite a bit more in length) and as deep as the neck. I'm not tapering this neck from nut to body, or at least not much, so it will be the same depth throughout. In my case, 15mm (or just over, to allow for neck carving).

This blank is made from three pieces of mahogany cut from the same board, because that gives me vertical grain if you view the neck blank from its end. This means the neck is less likely to twist, and also gives the shaft a uniform appearance once carved. It also makes carving a bit easier. For a short neck, like a ukulele, I might not bother, but the longer the neck the more important stability is.

Once the blank was shaped I routed a channel for the truss rod down the centreline, and then planed an angle at one end for the headstock to be scarfed on.

There are two possible ways to do this - as here, to scarf the headstock at the end of the neck, or alternatively to scarf it at the underside of the neck. My chosen method gives me no join on the face of the headstock, but a visible join at the side of the neck. To cope with the visible join on the headstock simply veneer a faceplate on to the headstock, but I didn't want to to that.

The third method is to cut the neck as a single piece, but that means the headstock shows end grain on front and back, and is also at greater risk of breaking if the guitar is knocked over. The remedy here is to apply both a faceplate and backstrap, thus laminating the short grain between two long grain veneers.

On goes the headstock:

I'd previously made the fretboard blank and marked out the fret locations and the edges of the board. It's important to do this while the fretboard blank is square, otherwise it's almost impossible to get parallel frets (and players are so fussy about that!). Note that I've abandoned rosewood or ebony, the traditional choices, and gone for the far more sustainable option of white pearl celluloid. Known in the trade as Mother of Toilet Seat (MoTS). Cheerful without being gaudy, I always think, and fits with the 1930s parlour guitars I'm channelling.

I cut the fret slots while the fretboard is still square and then taper it to its final dimensions. In this build I will shape the neck to fit with the fretboard. But it can be done the other way round - shape the neck, and then make the fretboard fit.

Because I'm making up this guitar as I go, I don't mark up the neck until the headstock is on and at its final dimensions and the fretboard shaped. Then I place the fretboard in position and just draw lines around it. I'll carve to just shy of these lines, glue on the fretboard, and then finish to final dimensions.

Before any neck carving happens I want to fit the neck to the body. This is vastly easier if the neck is square, not carved. Getting the neck in line with the centreline of the body will happen later, but now I need to decide the neck angle and mark it out. I've chosen to join the neck to the body at the 12th fret (1930s again), and this simplifies the calculations. The 12th fret is the mid point between the nut and the bridge, and I know I want the bridge to be 12mm high. I also want the strings to be around 2mm above the 12th fret. The fretboard is 4mm, and 2mm above the 12th equals 4mm at the bridge, so if I attached the neck in line I'd end up with a bridge 8mm tall (the maths says 9mm, because the fret is about 1mm tall, but the string pressure will make the top sink a bit so I'm guessing that will be about 1mm). Thus to get 12 mm at the bridge (4mm more), I need the nut end of the neck to be 4mm below the plane of the body's top.

This is easy - tape a 4mm drill bit where the nut goes, place the body join at the end of my board, and then use a set square to mark a line on the neck. Using my sliding bevel, transfer that line to both sides of the body join down the heel (I forgot to add, I've glued wood underneath to give me a heel).

Coming next: fitting the neck to the body (including choice of attachment method) and carving the neck.

 

[marcros]

is it genuine celluloid that you use, or a modern equivalent?

 

[profchris]

It's brand new stuff but I'm pretty sure it's celluloid - the right smell when cut, and suitably flammable!

It comes from China as guitar head plates. I can't get full size sheets, so this fretboard is three pieces, with the joins set at fret locations.

The material you can buy as larger sheets tends to be three ply, usually a black and a white layer of what I think is ABS with a clear sheet on top, the pattern printed on the inside. I have made a fretboard from that stuff, but it delaminates really easily.

 

[profchris]

Progress in dribs and drabs, so I've moved forward quite a way. All about the neck.

First I had to decide what kind of neck joint to use. A tapered dovetail is traditional, but I've only done that once before and adjusting the neck angle is quite tricky. I also considered a Panormo style joint, which uses a tenon to keep the neck in line with the body but pivots the neck just under the fingerboard and is adjusted using a bolt at the heel. This requires routing into the body of the guitar, so the heel has somewhere to go when it pivots. In the end, I thought it was too complex for this build.

So I went for a simple straight mortice and tenon, which will be reinforced by a bolt through the head block into a threaded insert. The cheeks of the tenon will be glued in, using hot hide glue, and the main purpose of the bolt is to hold it all in the right place while the glue dries. But if the neck needs to come off for a later repair, the bolt can be removed and steam injected into the mortice pocket.

I cut the mortice first, then the tenon a fraction oversize, and then pared it down until the neck fit and lined up properly.

If you go too far in one spot (as I did) just glue a shim of veneer on and carry on paring!

Once the tenon fits in the correct alignment, the neck angle needs adjusting. So I shape the sides of the heel, and then undercut where it joins the body so I only have 2mm all round to scrape/sand/plane away.

The actual fitting is tedious, because you have to attach the neck to the guitar, measure (using a straight edge along the neck) how high the strings will be above the body at the saddle, remove neck and pare away some wood, then repeat. But this is critical - if the neck isn't on straight, or doesn't give the proper string height, the guitar won't play properly.

Eventually I was there, with a reasonable fit between heel and sides. Not great, because I'm not a very precise builder, but it will look OK.

Note the gap at the end of the tenon, to allow the neck to be steamed off later.

Now the neck fits, I can start carving it. I always wait until this stage because it's *so* much easier to fit the neck if it's square!

 

[profchris]

The first step in carving is the heel. My primary tool is a half-round rasp, and I begin from the corner where the heel meets the guitar top and sweep round the curve. I do the same from the other side until the two meet at the centre line I've drawn at the front of the heel.

Then I mark out the desire profile of the heel on its base (at the top in this picture) and rasp round as before.

Finally I join up the two carves by removing the wood between them, and end up with a rough-carved heel. It will be refined later, as I blend it into the neck carve.