I just began a new website for teaching-related articles, photographs, and videos. The Layman’s Institute will be at http://laymansinstitute.com and will have lots of teaching articles: whether math lessons, violin-making, or anything else.
No content is there, just yet: I will begin adding content in the next few days, I hope.
Gotta have a stand for the bass…can’t let it just lie around the house.
Heavy base-plate adds stability for the five-string double bass.
Travel Case Coming!
The next project has got to be a travel case for this bass. A “Travel-bass” with a removable neck is less than optimal without a case in which to travel. And such cases don’t seem to be readily available for reasonable prices.
So, it is back to the drawing-board for me. 🙂
Probably looking at a foam-core fiberglass case. Shouldn’t be too much harder than building a boat. 🙂
I began to build a bass bow! but other things intervened, and I had to set it aside for a bit. I posted about it back then on my other website: Bass Bow Beginning
But then I got another little block of time, and I made more progress. That was fine, but it was still not terribly high-priority, so it was again set aside while I did what life demanded. (I had gall-bladder surgery somewhere around that time…kinda captures the attention somehow… I had posted about that progress, and the surgery, as well. But it really set me back as far as productivity goes. Sigh…) Bass Bow Progress
Annnd, as luck would have it, the gall-bladder surgery disturbed the existing scars from bowel surgery four years earlier, so I ended up with three hernias along the old scar, (sigh…) and was back in the hospital again for hernia repair. (Getting reaalllly tired of this game!)
But now… Everything seems to be healed up and I am once again productive, at one thing or another. 🙂
Completing a Bass Bow
I built my second upright bass, a five-string, 5/8-size double bass with a removable neck for safe transport, and I was struggling to adjust the sound. The bow I had was annoyingly cheap, and soft, and the hair as fine as I would expect on a violin bow… so it was frustrating, and I kept thinking, “I need a better bass bow!” So, the time had come!
I knew where the Hickory bow was, which I had begun years before, and most of the things I had bought to go with it, so I got moving on it. I finished inlaying the second gold star on the side of the frog, cut gold Mother-of-pearl for the slide and the dot on the end of the adjuster screw, and started on a ferrule.
All you bowmakers are already shaking your heads, because you know (as I did not know, that I should have built the ferrule first, and then made the frog to fit the ferrule, instead of the other way around. It is much simpler to carve hardwood to match an existing metal structure, than to bend and braze (that’s what silver-solder is, technically) metal together in an attempt to match an existing wooden shape. (Ah, well, never let it be said that I passed up an opportunity to learn things the hard way…)
Anyway…the ferrule was a real pain to make, because I failed to do it first. The under-slide, by comparison, was a piece of cake.
I had to make a new metal bow-tip, as I had accidentally made the original one a tiny bit too small. Also, I had chosen to use stainless steel, because it was cheap, easily available, and very durable. (Another beginner’s error: Yes, all of the above is true, but it is also much harder to cut, solder, file, and drill holes in than silver would have been.)
At any rate, I got back on the project, and in a day or so, had what looked like a promising bow! But I couldn’t find the hair I had bought. (I remember seeing it, and I remember putting it somewhere so I’d be sure to find it again. Must have been a really special place…I have no idea where it went.)
I looked and looked for the hair I had bought, but had no luck: I finally decided to quit messing around, and just order more hair. Usually, there are specialist suppliers I would patronize, and I prefer to do so, but they all would take a week to ten days to deliver: so I ordered through Amazon, and had it the next evening! (Amazing!)
While I was waiting, I added the leather thumb-pad and the wire windings.
And…that is what the new bow looks like!
And it Works!
I am grateful to be able to say, it works well! I get better tone and more volume with this bow than I did with the cheap student bow I already had.
Undoubtedly, a bow made of Hickory cannot be expected to match a good bow made of Ipé wood, let alone one made of Pernambuco. But this bow is quite satisfactory, and I feel pretty good about the project as a whole. I may try making another bow of Ipé, or Bois d’Arc, though, before I attempt a bow of Pernambuco.
Fit and install the End Pin. (Already done on this instrument.)
Fit and install the Saddle. (Already done on this instrument)
Fit and install the Tuners (in the case of a double bass, that means “tuning machines.” Already done on this instrument.)
Fit and install the Soundpost. (already done on this instrument.)
Fit and install the Nut, file the string slots to the correct depth in the correct places.
Establish the correct length for the Tail-gut (or tail-wire in this case) and install it.
Fit and install the Bridge, filing the string-slots once the height is correct.
Install the Strings.
Play for sound adjustment, string clearance adjustment, etc.
On violins and violas, the end-pin (usually called the end-button) only serves as an anchor-point for the tail-gut. But, in cellos and double basses, it also must serve as a height-adjustment, so that the instrument will rest at the correct height for the particular player. In this case, I had chosen an Indian Rosewood plug with a tubular steel end-pin fully adjustable and locked by a thumb-screw on the bass side. I installed it earlier, so here it is, without details about shaping the plug or reaming the hole:
I cut my saddles with a large radius on each of the upper corners, where the saddle is cut into the front plate. There is a strong likelihood, historically, that cracks will eventually develop, emanating from the corners of the saddle. They are so common that they have a name: “saddle-cracks.” There are two ways to try to avoid such cracks:
The first is to make the mortise for the saddle (the part cut out of the front plate) a little wider than the actual saddle, by maybe a millimeter or so, so that, when (not if) the front plate shrinks during dry weather, it will not find itself up against the unmoveable saddle, and be forced to crack, to allow for the shrinkage. This is a good practice, and I try to follow it.
The second is to make the saddle with sound corners so that there is no “notch” in the plate at the “corners” of the mortise, but rather a smooth rounded curve, which eliminates the stress-riser and minimizes the chance of a saddle crack in the first place. (Round discontinuities essentially do not cause stress risers, hence, do not cause cracks.) I always do this, (since about my sixth instrument) and will continue to do so.
I already explained all this, including the purpose of the saddle, in a previous post. Suffice it to say that this part is already completed.
There is a wide variety of choices for tuning machines for a double bass. Some are better than others, some fairly plain, but fully functional and reliable, others beautifully engraved or ornate in some other way, and understandably far more costly. Someone had to spend the time and money to do all that “pretty stuff,” so, if you want that, you gotta pay. I chose plain but functional. (They are pretty, too, but not fancy.)
At any rate, they are already installed on this instrument, as of my last post:
The soundpost is a “dowel,” usually of fine-grained spruce, that spans the gap between the inside of the front plate and the inside of the back plate, just south of the treble bridge-foot. My understanding is that it transfers the vibration from the front plate to the back plate, and “couples” the two plates so that they work together to make the sound from the vibrations created at the strings (whether by bowing or plucking.)
There may be (probably is) more to this function: It is an important enough part of the set-up that in some languages, the soundpost is referred to as the “soul” of the instrument, and it is definitely one of the most important adjustments that can be made. It is held in place simply by the compressive force transferred through the bridge by the tensile stress on the strings. Adjusting the position of the soundpost has a profound effect on the character of the sound the instrument can produce.
I already installed the soundpost, but I fully anticipate that I will continue to adjust it as the instrument settles in, in an attempt to produce the best tone, volume and balance that I can achieve in the sound of the instrument.
The nut is the transverse piece of hardwood (usually Ebony, but in this case Ipé, ) across which all the strings are resting, directly above the fingerboard. It serves as a positive stop for all five strings, so that the strings are not in actual contact with the fingerboard when the player is not fingering a note, but are suspended about 0.5 mm above the surface of the fingerboard. the idea is that an easy touch from the player’s finger should put the string in contact with the fingerboard at the correct position for the desired note. The nut is glued to the neck and fingerboard, usually, but in reality, it is held in place by string tension, and the glue is “just a formality.” (I glue them so that they can’t fall off and get lost, during transport or a string change.)
I carefully laid out the string locations, so that they are spaced equidistant, center-to-center, and then cut the slots for the strings using first a small razor-saw, and then a round file of the appropriate diameter for the string in question.
Tailpiece and Tail-wire
I chose to make the tailpiece of Ipé wood, to match the fingerboard, nut and saddle. The tailpiece fret (transverse bar forming a positive “stop” for all five strings) is also Ipé, and after being heated and bent, it resisted being glued. I eventually took it off entirely, scraped off all the failed glue-layers, washed it down with acetone to remove the oils in the wood, and reglued with epoxy. But this time, I anchored it with six small brass rivets. It is permanent, now! (Besides, I like the look of the shiny little brass rivets!)
I also attached the tail-wire; a 1/8″ diameter stainless-steel aircraft cable. I established the length so that the distance between the nut and bridge would be as close as possible to being in a 6:1 ratio with the distance between the bridge and the tailpiece fret.
I chose a bridge blank that was tall enough to serve with the projection angle I had already established, and wide enough to comfortably accommodate five strings.
I fitted the bridge feet to the surface of the bass front-plate, so that it would have an airtight fit when placed between the inner “notches” on the f-holes, and centered over the centerline of the plate.
Once the fit of the feet was established, I marked the bridge for the approximate height, hoping to achieve a string clearance of about 11 mm above the end of the fingerboard, but erring on the side of “too high.” (I can’t very well “put it back,” if I remove too much wood.) I then marked the locations of the strings, giving them 25mm from center to center. I filed the string slots, so that the strings would stay put when installed, and I went ahead and installed the strings.
As it happened, I ended up with about 14mm under the B-string, ranging to 12 mm under the G-string…way too high. No problem: I simply re-marked the bridge, this time having a better idea of where things would line up, re-cut the top of the bridge, re-filed the string slots, and tried again. This time I had 11mm under the B-string, and 6mm under the G-string, with the strings in the middle at about 8mm. That is acceptable, so I finished trimming excess wood from the bridge, tuned up the strings, and I was ready for the final adjustments for sound.
It is quite a relief to me to finally have this instrument nearly complete. It was actually begun several years ago; but it was set aside for a variety of reasons, and only resurrected as a project, this Spring.
The sound, at first set-up, is satisfactory, but I hope to achieve a better balance, more volume, and better clarity as the instrument “settles in’ a bit, and with subsequent adjustments of the soundpost. But for now, I’m happy with it. It looks good and sounds good. For a brand-new instrument, that is a good start.
So, for now, that is it! There are a few “finishing touches” and re-touch of varnish, etc, as well as the aforementioned sound adjustments, but the bass is essentially complete!
I hope to make all the necessary adjustments, and then find a player or two to “test-drive” it for me, since I am not a player, and can’t do it justice.
I will post the “verdicts” from those players when they happen.
The color varnish, as you might imagine, gets the instrument looking the way we want, but the clear coats keep it that way…we hope.
So, after the color coats were mostly complete, I waited a few days for the varnish to cure a bit and then added two clear coats as a protection for the color coats, so that they will not experience undue wear.
There is still a lot of work left to do at this point: There will be endless “re-touch” of spots in the varnish that I wasn’t quite satisfied with, but they can wait until after the set-up is under way.
I usually wait until the varnish is complete, before installing the saddle. The saddle is the transverse piece of hardwood upon which the tail gut rests, as it crosses the edge of the front plate. (Ebony, frequently, but, as I had opted for an Ipé fingerboard, Ipé seemed the right choice for the saddle as well.)
I make my saddles with radiused ends, to avoid saddle-cracks. To some extent, saddle cracks are caused by the shrinking and swelling of the spruce plate against an essentially unmoveable ebony (or Ipé) saddle. However, the other factor (possibly more important) is that, for hundreds of years, luthiers have cut the saddle with sharp-cornered, square ends, requiring a sharp-cornered square-ended mortise in the spruce…which inevitably inclined itself toward eventual cracks. Sharp corners are extreme stress risers.
Round discontinuities (holes, for example) do not cause stress risers, and are far less likely to cause cracks. I try to leave the ends just a little loose, as do most luthiers, but the fact is, the sharp notch is the primary cause of the cracks. So I make round corners.
The next task was the tuning machines. There are many possibilities to choose from: I chose these tuning machines partly based on looks, partly on cost, but primarily because, with the curvy pegbox, I wasn’t completely sure that any other style could be made to work. (There are some multi-piece tuning machines, which, I would imagine, could be made to fit nearly any configuration, but I have no experience with those, so I opted for something I knew about.)
Anyway, I knew that this type of tuning machine has a tapered spindle, which is not designed to go all the way through the pegbox, so I designed and built a small reamer, all wood, except for the blade, which is spring steel (just because that is what I had available.) It works well, but I have to be gentle with it, and stop periodically to clean the chips from the reamer.
I made a template, laying out the hole locations with the hope that I could avoid the strings from the G and D tuners rubbing on the tuners below them in the pegbox. I used the template to lay out the holes on the pegbox, then drilled to appropriate depths and used the reamer to taper the holes to match the spindles of the tuning machines.
Finally, I installed the machines and secured them with screws.
It was amazing to see how much weight the tuning machines added. The bass no longer easily balances on the two bouts: it wants to rock down and put its head on the floor!
Ready for set-up!
I installed the nut at this point, as well, so the bass was really complete.
If you have sharp eyes, you will probably notice the hole above the tuning machines on the bass side. The pegbox was narrow enough there, that I actually went through the second side by accident, and was forced to create a plug for the hole, from some leftover rib material. I cut it to exactly fit the hole, and glued it in place, pressing it home, so that it was nearly exactly flush, then scraped the wood of the plug to exactly match the wood of the pegbox, and was ready to begin varnishing to complete the repair.
Anyway… that is as far as I wanted to go today. Some of you may have known from other forums’ content, that I had also had trouble getting the tailpiece fret to “stay glued” in its slot. So I eventually gave up, removed the fret, scraped all the layers of glue down to clean wood, and washed the Ipé with acetone. Then I reglued with epoxy, but this time I drilled and anchored the fret with six brass rivets! (It’s permanent, this time!)
Next time, I hope to complete the set-up of the bass and have it ready to play!
I begin with yellow varnish for a base coat at least…sometimes two or three coats to get it even all over, as some areas soak it up rapidly, and look “dry”. though they have the same amount of varnish.
After the base coat is dry, I rub it down with fine sandpaper, just to remove any bits that stick up–whether dust, debris, wood fibers that raised up earlier…whatever is sticking up needs to be flattened, or there will be a “cone” of varnish growing around it with each coat.
if I am going to do any “wear” or “antiquing,” I need to begin thinking of it now. It will affect how much color I apply to what areas, as well as whether I intend to add “dirt” in wear areas.
If I have induced the type of wear that involves “scratched areas” or “dents”, I apply them now, and rub dark pigment into those discontinuities, to imitate dirt in old scratches on old instruments. Then I rub off any excess pigment, so that the dark color only remains in the low areas of the “distress.” This would also be when I apply “dirt” in wear areas, where grain is raised and where a player’s clothes or hands would typically wear off the original varnish.
Next I begin applying darker colored varnish in the areas where least wear would occur (Or, of course, if no “antiquing” is planned, I apply the darker varnishes over the entire instrument except the “handle” area of the neck, which is left bare until the very end. I sand between coats, using 400-grit paper.
As the color builds, I have to watch, and make a decision as to when to stop: I do not want the grain to be obscured, but I do want enough varnish thickness to provide a moisture barrier against sweat, etc.
When I finally decide (usually after six or more coats) that the color is acceptable, I give it two more coats of clear varnish, to deepen the sheen and to protect the colored varnish from damage.
Finally, with the varnish complete, I allow it to dry thoroughly, then I can begin final fitting and set-up.
So, since we are effectively at step “zero”, and the last time you saw the instrument it had only the rosin sealer coat applied,
The first thing was to wash down the sealer coat with alcohol to remove any excess rosin from the surface. I wanted the rosin in the wood, not “on” it. Then I applied a full coat of yellow varnish. The result is always a little disconcerting, as it is veryyellow after that first coat. But the yellow mellows and calms down under the subsequent coats of colored varnish, and becomes the “inner glow” that shows through the darker varnish.
At any rate, here are several pictures of the yellow varnish:
And, that is pretty much what the base coat looks like. Step one is complete!
I chose to add a second coat of yellow to the sides, back and neck, but began adding color to the front, in order to balance the front color with the rest of the instrument.
About this time, a friend in Australia, who is a great bass maker, contacted me to point out very kindly that I had made my fingerboard too flat for a five-string bass. (Well, rats!) So I had to make a new fingerboard with the correct radius for playing a five-string double bass with a bow.
Here is the side view with the old fingerboard:
And here it is with the new one!
Without that tighter radius, it would have been next to impossible to avoid playing two strings at once. I am very grateful that my friend alerted me to my error before I had completed the bass. Not being a player opens me up to some “sins of ignorance” that a player would notice immediately. He had also pointed out that I had made the upper end of the Fingerboard unnecessarily wide, so the new one is narrower…but that meant re-carving the neck to match the new board.
The neck feels better to my hand, now that it is narrower and a little thinner.
I decided to go ahead and fit the endpin assembly as well, before pressing on with final color coats. I had a double bass reamer made for me by a friend, about 2006, and I made a shaper for myself about that same time. In both cases, the occasion was the building of my first double bass.
I had hoped to make an Ipé endpin plug, to match the rest of the fittings, but since I wasn’t sure either that I was able to do so, or that I would have time, I went ahead and purchased an endpin assembly with a plug made of Indian Rosewood, and it turned out that the color was so similar that I gave up the idea of hand-turning one of Ipé wood.
Final Color Coats
Then I sanded down the whole bass, and re-touched the whole bass, adding color in areas that I felt were too light, and filling in places where the previous coats had not been thick enough. when that was dry, I gave a second color-coat to the entire bass. This will be the final color coat, though I intend to add at least one clear coat, and probably two. The clear coats deepen the sheen of the varnish and make it look more transparent. while actually adding very little to the thickness of the varnish film. They also protect the color coats against premature wear.
I really like the deep amber color that is developing in the bass. The clear coats will accentuate it, but not make it much darker.
Wet down the wood,to raise the grain and accentuate “problem” areas
I wetted the whole bass down with coffee, mainly to raise the grain a bit, but partly to add a little color to the white wood of the Sitka spruce belly. The Oregon Big Leaf Maple is already pretty colorful.
Then I turned the lights off in the workshop and went over the whole bass, inch by inch, with a small flashlight, held at a low angle, to make shadows wherever there was a discontinuity in the surface. As I located them, I scraped or sanded away the problems, before moving on. It took quite a while, but I was pretty happy with the outcome.
The next step is to coat the wood with a mineral ground: a suspension of extremely fine particles of gypsum in water is what I use. I brush it on, one section at a time, rub it in vigorously, to get the tiny particles into the pores of the wood; then rub off any excess, with a rag. It always looks as though I took all of it back off, until it dries.
After the ground is fully dry, I sand all over with fine abrasive, to remove any dry patches of excess mineral. There will be very small discontinuities that have been filled by the mineral ground: this is desirable, and I am not trying to remove those places.
When the ground dries, the bass will be stark white, but when I apply the sealer, to lock the mineral particles in place, the mineral ground becomes completely transparent, permanently. It will never be visible again.
So, here is the bass, with the gypsum fully dry, mounted in my varnishing fixture, and ready for the sealer:
I am currently using rosin dissolved in turpentine and alcohol as a sealer. The liquid (alcohol first, then turpentine) evaporates, leaving the rosin in the pores of the wood. When dry, this helps prevent the varnish from soaking into the wood, so as to minimize the sound-dampening effect of excessive varnish penetration.
This is the part of finishing I like best: it seems almost magical to see the stark white of the mineral ground disappear instantly and permanently as the sealer permeates the gypsum and renders it transparent, so that the beauty of the wood is revealed.
After the sealer is dry, or just before it is completely dry, I rub down the surface of the wood with alcohol, to pick up any rosin that may have remained on the surface. When the sealer is fully dry, I go over the whole surface, lightly, with fine sandpaper, to pick off any bits of wood fiber that may have raised during the ground and sealer process.
I always begin with a yellow varnish: I like the way it shines through the darker pigmented varnish when all the finishing is complete. In this particular case the maple was dark enough that even the yellow varnish will end up looking pretty dark. So, though I will still begin with the yellow, I will have to add a good deal of darker varnish on the front, to balance the color with that of the back. This is just a type of “Judgment call” that the maker must always consider when finishing an instrument. As I add coats of varnish, I will pay attention to which areas need darker varnish, and which could use yellow or clear varnish.
The last time I posted, I had temporarily installed the neck, and (I thought) I had glued the neck heel root in place, as it was to be a permanent part of the corpus, glued to both the neck mortise and the back button.
So the bass looked like this:
The heel root looked like this:
I was so confident that everything was right, that I even sawed off the excess heel root, visible in the above photo, and planed it flush with the back of the neck block, in preparation for installing the back plate. But! When I broke the paper “break-away joint” (see the above photo) the heel root gently let go of the mortise and was completely loose. (Rats!)
It turns out that hide glue doesn’t stick to carbon fiber plate! Ok… so I had to start over, and this time glue it home with epoxy. I put a plastic bag around the neck heel to protect it, coated the heel root with epoxy on the bottom and two sides, and slid it all back into place, this time bolting the neck in solidly, and clamping the heel root tightly against it. It all worked this time.
Beginning the purfling of the back plate
While the epoxy was curing, I decided it would be a good idea to at least install the “purfling weave” portion of the back plate purfling, before installing the plate. I figured it would be easier while the plate was still loose. The reason I wait until the back plate is installed to do the rest of the purfling, is that the corpus often changes shape a little when the mold is removed, so I can’t guarantee that the overhang will still be the same. If I have already installed the purfling, then I am stuck: but if I have not, then I can maneuver the overhang to being as close as possible to what I wanted, and install the plate, then plane away excess all around until the overhang looks right again, and finally put in the purfling so that it looks as though everything just worked out right, to begin with.
This is a weave that I came up with for my very first five-string fiddle and which I have tried to incorporate on all my subsequent five-string instruments. It is just a modified “fleur-de-lis”…nothing really special, but I like it. I use the same design, upside down, in the upper end.
After cleaning the slots out, I used heat and water to bend the purfling strips to fit the curves of the weaves, and glued them in using hot hide glue.
I planed the weaves flush with the plate after they were dry, using a gouge, a small finger-plane, and a scraper. You can see the beginning of the rest of the purfling slots, how they will connect to the weaves.
Closing the corpus
I finished scraping the interior and then laid the corpus onto the back plate, positioning it carefully, adding spool clamps, and constantly checking the overhang all the way around. When everything was as close as I could get it, I removed a few clamps at the bottom block, used a thin palette knife to ladle in the hot hide-glue, and replaced the clamps, tightening them securely. I added more clamps over the glued area, then repeated the process for the next section on either side of the bottom block, and worked up around the sides that way: removing clamps, inserting glue, replacing the clamps and adding more…until it looked like this:
I still had not put the magnets into the cover plate, because, when I added the reinforcements to the cover plate, it changed the curvature, and it no longer fits cleanly into the access port flange. (Rats, again!) So I kept wetting and clamping the cover plate in different configurations until I got it to a close fit, then I added the magnets.
Annnd… it turns out they are too weak. (Sigh…) I will have to order some bigger magnets after all.
At any rate, I was now ready to correct the overhang all around, and begin the final purfling.
Carving the Channel
After the purfling was completed, I still needed to trim back the purfling and carve the plate channel. This involved marking the edge crest all the way around, about 2 millimeters inside the outer perimeter, and carving the channel to barely touch that line. I used a sharp gouge, in the manner of a drawknife, to carve the channel, then used a riffler file to smooth the outer curve, where it meets the crest line.
(I actually made a very short video of how this works, but I was unable to successfully link it to this post. Sorry.)
After the channel was complete, it was time to begin final edgework:
The goal is to make sure that the edge contour is correct all the way around, and that the plate channel fairs smoothly into the surface of the plate, without ridges or lumps. Getting the light at a low angle across the plate makes shadows which will show me where the lumps and ridges are so I can scrape them away.
It suddenly occurred to me that my bass-varnishing fixture requires that the end-pin hole be drilled, so I drilled the endpin hole but did not ream it to the taper it will eventually have. On smaller instruments I usually varnish before drilling the endpin hole, so that there is no likelihood of causing sags or runs where the varnish brush touches the hole. But on the bass, I have to have that hole as a place to attach the support for varnishing. (I can’t hold the bass in one hand, and the brush in the other, as I can with a violin!)
And, that is pretty much where it sits, for the moment! The bass is ready for final varnish-prep, which will involve wetting down the whole surface to raise the grain, so I can sand it smooth again, then repeating until the grain no longer responds to moisture. Then I will rub in a compound to add color to the wood itself (not a stain, which might “reverse” the grain colors) and a mineral ground to close the pores in the wood. Finally a sealer locks in the mineral ground, and I will be ready for varnish.
So there is the bass corpus, ready for final varnish prep!
One of the problems with creating a double bass whose neck is removable for traveling is that there has to be a way to connect and disconnect the neck. Thus you have a choice– will the fasteners be visible from the outside, or hidden inside?
I have seen several examples of both, and I really prefer the hidden fasteners approach. BUT! That also mandates that there be a way to access the interior to tighten or loosen the fasteners. I have chosen a 3/8″ diameter bolt (tensile strength exceeding 5,000 pounds) and a large flat washer embedded in Epoxy on the inside of the neck block. The bolt extends through the washer and the neck-block and engages the threaded insert in the maple wood of the neck heel (see below.) So…the next step is to consider a side-access port through one of the C-bout ribs,
I chose to make the access port through the bass-side c-bout rib: the player will reach up through the port with his or her right arm to access the single bolt in the neck-block. As an added bonus, the soundpost is also easily accessible, as it will surely need to be re-positioned after having the bass apart for travel. (In fact, it is so nearly guaranteed to be loose, that I intend to provide a pocket in the instrument case for the soundpost, as well as the bridge, the tailpiece, and the neck assembly, etc. That way there is no question: as you reassemble the neck, you will also re-set the soundpost, after the strings are on, but before it is up to tension.) Finally, as another luthier pointed out, if there is ever repair-work to be carried out inside the bass, this access port makes it a much simpler task, thus saving money and time.
So: how to carry out the access port plan? I positioned the proposed hole on the bass-side c-bout rib, roughly centered, and laid out a 5-3/4″ circle. I cut out the circle using an X-acto knife, then smoothed the cut edges with a file and sandpaper. I wanted to use that piece for the closure, as well, so I couldn’t afford any damage to either the rib or the cover plate.
Initially, I had thought I would employ a drawer-pull-type handle as a means to open and close the access port, but I didn’t care for the looks, so, after further reflection, I chose to make a simple “finger-hole,” instead. I reinforced the single-thickness of rib-stock with two more, especially near the center, so that the rib would be stronger, and so that the edge of the rib where the finger contacts it will be 6mm thick instead of 2 mm, thus much more comfortable.
I reinforced the actual c-bout rib by adding a second thickness of ribstock to the entireinside of the existing rib, and I cut a slightly smaller hole in it so that the closure plate had a shelf to rest against. Also, this is the surface into which the neodymium magnets will be inset, to hold the closure plate in place.
(I realize that the above photo looks a little as if there were a plexiglass cover on the hole, but those are not reflections: you are looking through the hole at some pads behind the bass body. I was using the pads to protect the front plate, earlier.)
I added the reinforcement to the cover plate and sanded the interior of the finger-hole to be very smooth.
Cleaning up the interior
While the glue was drying on all the above assemblies, I took the time to complete the shaping of the blocks and linings, so as to be ready to close the corpus, once all the interior work is done.
I used a knife a gouge and a small plane to shape the linings and blocks. Then I used a scraper to ensure that it all was acceptably smooth.
I had checked and re-checked the fit of the neck-heel into the mortise in the neck-block, until all the measurements were correct, and then I had drilled a pilot hole through the neck-block into the neck heel. That established the position and range of both holes, so that when I drill for the insert and r-drill for the bolt, the holes will still be in line with one another. I bedded the large plate washer in epoxy on the inside of the Sitka spruce neck-block, so that the bolt would not be able to gradually wear a hole deeper into the soft spruce.
With the neck temporarily in place, I could check to see how much of the excess neck-heel “root” would have to be sawn off and planed flat. You can see, also, that I had glued the heel-block “root” onto the neck-heel proper, using a sheet of paper between them as a “breakaway” layer, so that when everything was correct, I could easily pop the neck free from the root.
As it turned out, hot hide glue does not bond well to carbon-fiber plate. So, after I discovered that the neck-root was actually not glued home, I was forced to choose epoxy as a final bond for the portion of the neck that is intended to remain permanently in the neck mortise. I don’t like doing this, as epoxy is not reversible, but there was no viable option. After making that choice, though, I took a sharpie pen, and wrote, inside the mortise, a notice to any later repairers, that those three joints (bottom and both sides) at the neck root are epoxy. (Sorry)
But I can put the neck on and take it off and put it on again, and it fits correctly, and all the measurements have remained correct.
And it is looking pretty good:
Next time we will talk about the final work before closing.
There are five measurements to consider in setting a neck on any violin-family instrument:
Obviously, the distance between the nut and the upper edge of the front plate is a critical measurement. One has to know what is required for the instrument in question and make a mark on each side of the neck heel, as to how deeply it is to be inserted into the neck block.
The height of the overstand (distance between the top edge of the front plate and the joint between the fingerboard and the neck.) This measurement is taken from the front of the upper edge of the front plate, right beside the neck, vertically, to the top edge of the neck, proper (joint with the fingerboard.)
The last three are all angles: The plane of the “floor of the neck mortise” must be perpendicular to the centerline of the instrument, and the plane of the bottom end of the neck, proper, must be perpendicular to the centerline of the neck, laterally. If these are both correct, then the fingerboard should project directly along the centerline of the front plate. Any lateral variance from centered is not good.
The centerline of the neck mortise, from front to back, must be perpendicular to the plane of the plates, laterally, so that it literally “connects” the centerline of the back plate to the centerline of the front plate. Simultaneously, the “footprint” of the neck heel should be bilaterally symmetrical about the centerline of the neck heel. The result should be that the plane of the neck face (when viewed from the scroll) should be parallel with the plane of the plates. (No “twist,” or “roll” in either direction.)
Finally, the “Projection angle” should be such that the height of the “projected fingerboard angle” should be at the appropriate height for the instrument in question at the bridge line. (This can either be literally measured as a projection height at the bridge line, or, if you know how high the end of the fingerboard will be if all other factors are correct, you can simply measure it there. The danger in this is that if the other measurements are not quite right, and you simply measure the height of the end of the fingerboard, then the projection angle will be wrong, and you will not discover it until it is too late to correct it. (Ask me how I know!)
Planning the Neck-Set
In the case of a bass, with a removable neck, as well as all the other enormities of a double bass (as opposed to the smaller instruments) I had to not only consider the five measurements listed above, but consider how to achieve those angles reliably when removing and reinstalling the neck repeatedly. It all has to come together correctly without the customer having to “measure” anything, except to correctly carry out the assembly and minimal set-up.
Cutting the Neck-mortise
I had already cut the “footprint” of the neck-heel, so I took measurements and laid out the proper shape on the end of the neck-block, where the mortise was to be cut. I worked from the centerline of the neck block, so there was less chance of ending up with a skewed neck.
Then I turned the corpus over and began sawing the sides of the mortise, using a thin-bladed Japanese pull-saw:
Once I had the two sides sawed out, I sawed across the line between the two sides and separated the rectangle of the front plate wood from the neck block, to expose the neck block, allowing me to use chisels for most of the remaining removal of wood from the neck-mortise.
I checked the fit continually until all five measurements were correct, then removed the neck from the mortise, and began fabricating the “removable neck” apparatus that will enable the player to pack up his or her bass and transport it safely.
One of the things that concerned me was the possibility of wood changing shape through wear or stress. And, since the neck is to be secured by a bolt, how can I be sure that the bolt will not gradually wear into the wood, causing a loose fit?
After fitting the neck to the corpus, as outlined above, I inlaid 1/16″ Carbon Fiber plate on both sides of the neck heel, to provide smooth, stable fit every time and simultaneously guard against a heel crack, as the CF plate is not only inlaid into the sides of the neck, but it is bedded in epoxy, so it is a permanent part of the neck heel, providing support as well as a smooth surface to the sides.
I used screws and epoxy to mount bars of CF across the ends of the “joint” between the neck heel and the portion of the neck heel that will be permanently mounted to the corpus (and secured to the block and button,) so that a bar of CF on the neck heel slides under a similar bar in the mortise, thus providing an anchor of sorts.
Then I re-attached the two portions of the neck heel using a piece of paper glued between them, so that I could check the neck-set one last time, before gluing the root end in place and drilling the removable portion to receive the bolt. The paper provides a “breakaway joint” that will be relatively easy to separate after the heel root is glued home. it is only glued with a few “stripes of glue on each face, so the paper will tear apart and allow me to extract the removable portion the neck and finally complete the drilling, installation of a threaded insert, etc., and thus complete the neck set.