Time to close things up!

First things first:

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:

Side view, showing neck heel break-away joint.

The heel root looked like this:

Heel root positioned and glued to mortise, using hide glue. — Heel root positioned and glued to mortise, using hide glue, with paper break-away joint.

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.

Cutting the slot for the purfling weave on the back plate for five-string double bass . — Cutting the slots for the lower purfling weave on the back plate.

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.

Picking the waste wood from the upper purfling weave.

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.

Both purfling weaves completed on the five-string double bass back plate. — Both purfling weaves completed on the Oregon Big Leaf Maple back plate.

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:

Closed Corpus for five-string double bass. — Closed Corpus.

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.

magnets in cover plate — Here are the magnets in the cover plate.

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.

Overhang corrected, beginning final purfling.

Tracing in the slots for the final purfling.

The bottom end of the back plate has the same design.

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.

Using a gouge as a drawknife, to carve the channel.

(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:

Beginning final edgework on back plate of five-string double bass. — Beginning final edgework on back plate.

Beginning final edgework for the front plate of a 5-string double bass. — And the same for the front plate.

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!)

End pin hole drilled for a 5-string double bass. — End pin hole drilled.

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!

Five string double bass corpus ready for varnish prep.

Thanks for looking.

Neck Progress

Reinforcing the Neck

When I last posted, I showed the garland with the Sitka Spruce front plate installed, and the completed Oregon Big Leaf maple back plate sitting on it (because I wanted to see it that way) with the neck block (also Oregon Big Leaf Maple) beside it. You can see in that photo that I had already installed carbon fiber reinforcement rods, bedded in epoxy, to stiffen the neck. But I didn’t say how they got there.

Completed parts for a five-string double bass. — See the reinforcements in the neck?

The problem with maple is that it is fairly flexible. Usually, that is not a concern, because the instrument necks also have a fingerboard added on (usually of ebony) which is very stiff, so that the flexibility of the maple is not much of an issue. But, when the fingerboards become thin, after years of being used, re-surfaced, and used again, the frequent “re-dressing” of the fingerboards thins them to the point they are no longer stiff enough to bear the stress of the string tension, and the neck begins to bow forward, under string tension.

Carbon fiber is very light and extremely stiff, so it makes an ideal material for reinforcement. Carbon fiber rods are available in a variety of shapes and sizes. I chose 1/8″ x 1/2″, and they arrived in two-foot lengths from the “Dragonplate” company.

I do not have a router table, nor even a table saw, so I used my hand-held circular cut-off saw (commonly called a “skill-saw” as “Skilsaw” was an early brand of this sort of tool.) I set the blade on the saw to 5/8″ deep, and, having already drawn the lines where the cuts should go, I clamped the neck block in the vise, with a block beside it to guide the saw, and simply sawed slots into which to fit the carbon rods. The slots did not fit well, as the blade was not wide enough, so I attempted to use a hand-held router to widen the slots, but I did not have the correct bit for the router, and they were very expensive at the local hardware store, so I carved out the remaining wood, using my knife and a small chisel.

Once the slots were satisfactory, I mixed my epoxy, filled the slots, and pressed home the carbon rods. The epoxy I chose to use was advertised as “15-minute” epoxy, but all it meant was that I would have 15 minutes of working time, in which to get the rods in place, the epoxy smoothed over the tops of them, where it had squeezed out, and be done tinkering with it. It turned out to achieve full cure in about 24-hours… by the next day, in other words. No problem: I had plenty of other work to do while I waited.

Neck block for five-string double bass with carbon fiber rods bedded in epoxy. — Neck block with carbon fiber rods bedded in epoxy, waiting to be trimmed.

So, I scraped all the excess epoxy off of the neck joint face, where it would be glued to the fingerboard, and waited until the epoxy had fully cured, before sawing off the excess carbon fiber rods, using a hacksaw.

Neck block for five-string double bass with carbon fiber reinforcement rods trimmed to length.. — Neck block with carbon fiber reinforcement rods trimmed to length.

The result is a five-string double bass neck that will never become bowed or warped.

Ipé Fingerboard and Tailpiece

I chose to use Ipé instead of ebony for my fingerboard and other fittings, as it is more readily available, it is not a threatened species, and I like the finished color (dark brown.)

Ipé is an extremely hard, dense, South American hardwood, similar to Ebony, in terms of hardness and durability. It is difficult to work, as are all the extremely hard, dense, tropical woods, but I like the finished product. Here is a fingerboard on a five-string cello I made some time ago:

Ipe fingerboard on five-string cello. — Ipe fingerboard on five-string violoncello piccolo.

So, I decided on the shape and size of the fingerboard and tailpiece, and then cut them out on my bandsaw. Then I used gouges and planes to shape them appropriately.

Fingerboard underside for five-string double bass being carved of Ipe wood. — Fingerboard underside being carved of Ipe wood.

The dust from sawing, planing, scraping or sanding Ipé wood is a bright yellow color, and it fills the pores of the wood, giving the wood a greenish-yellow look while it is being worked. But that color disappears entirely when the wood is finished, and the Ipé becomes a dark brown color.

I glued the fingerboard to the neck block when it was nearly complete, and then completed the shaping of the fingerboard with the neck as a unit. The tailpiece, too, is only partially completed.

Fingerboard and tailpiece for five-string double bass. — Fingerboard and tailpiece waiting to be completed. Fingerboard is glued and clamped to the neck.

My wife was a little perplexed about the odd color of the Ipé wood, so, after completing the preliminary dressing of the fingerboard, I used a paper towel, and rubbed the fingerboard down with turpentine, to show the color as it will look when finished. I also rubbed a small portion of the tailpiece, to show the stark contrast between the color of the Ipé when freshly worked, and when finished. (The turpentine is not the finish, obviously, but the color will be very similar, as a light coat of linseed oil rubbed into the wood probably will constitute the finish.)

Fingerboard and tailpiece for five-string double bass with turpentine. — Fingerboard and tailpiece with turpentine to show the true wood color.

I went ahead and began the shaping of the neck at the same time, so it is beginning to look the way it will be when completed. When the neck shape is correct, I can begin the neck-set procedure. This is the first time I have attempted a removable neck, so I am a little apprehensive about it. All I can do is press on, and see how it works.

Here is how it all looks right now:

Neck and tailpiece for five-string double bass. Notice the “fret” bent and clamped to the tailpiece.

When completed, the tailpiece will accommodate five strings, and have a “fret” inlaid across the upper end, to provide a hard “stop” for all the strings at the same point. The “Fret” is made of Ipé wood, too, bent to shape with heat and pressure, then clamped to the tailpiece to cool in that shape. Next, I will cut the slot in the tailpiece to allow the fret to be inlaid into the tailpiece, and drill the holes for the string-slots and the tailgut wire.

After that, I will begin the neck-set, I hope.