Project: Double Bass Build
By Steve Erling
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My 30 year old son wanted to buy a double bass, but the cost for a good one was in the tens of thousands. He asked me if I could build him one. The following article highlights the building process.
The first thing I needed to do was to learn as much as possible about the instrument. I bought two books, one had decent step by step information and half scale drawings in the back. There was too much lacking in critical details and information in that book, but enough to get me going. The second book was written for luthiers who want to learn about repairing and setting up the double bass to sound as good as possible. That book had a lot of the critical information in it. YouTube and online forums were also very helpful. Having worked as a architectural draftsman helped tremendously in redrawing accurate plans and understanding how everything was going to fit together.
The first thing that has to be built is a mold. It determines the thickness of the instruments body, holds the corner blocks in place, and is used for shaping the sides. Below is a picture of the back mold piece with a hinged section to create a sloped back, and the middle mold piece which is holding the rough corner blocks in place.
Below is the mold with the front piece attached. The corner blocks have been shaped.
This is the setup I use to bend the side pieces. A 4" copper pipe clamped to a vise with a propane torch blowing into and against the top side. The wood is kept wet on the pipe side and slowly bent over the pipe.
After a side piece is bent close to the desired shape it is clamped tight to the mold and allowed to dry over night. The clamps are released on the ends, glue is applied only to the corner blocks, and then re-clamped.
The six side pieces are planed flush with the mold top and bottom, and the four corners trimmed.
The top of the mold is removed and wood strips (lining) are added around the edges to provide strength and a wider gluing surface.
The back and front mold pieces are no longer needed as the center mold piece holds everything in place.
The pieces for the back are glued and clamped. The buckets keep the wood from buckling upward.
The back is rough cut to shape and needs to be bent. A V groove is made at the bend point.
The bend point is positioned at the edge of the table, covered with wet towel and aluminum foil. An iron is placed on the foil which heats up the wet towel, while pressure is applied to the edge which bends the wood.
The back is temporarily clamped in place and allowed to dry.
The back bracing is shaped and installed.
Cutting a groove around the edge of back to accept purfling. Besides adding a decorative edge, purfling adds strength to prevent splitting.
Gluing in purfling.
Detail of purfling.
Final shaping of inner corner blocks.
Gluing the back to the sides.
Slabs cut from a Sitka Spruce tree for the front of the bass. The thick end is the bark side and the thin edge is the center of the tree.
The two bark edges are glued together to form the full width of the bass. The thick wood in the middle is needed for the arch in the front.
Hardboard arch templates are made from the plan for carving guides.
Top to bottom arch template.
Carving depths established using templates.
Excess wood removed between depth grooves.
Front contours formed.
Cutting purfling groove.
Purfling is glued in a little high and then trimmed flush with the surface.
Jig to hold front while inside is carved out.
Interior depth carving contour lines layout. The thickness of the front varies from 4mm around the edge to 9mm in the center.
Actual thickness is measured with a caliper to determine how deep to drill depth holes.
Carving depth holes are drilled.
Inside of front is carved out to the bottom of the drilled holes.
Finished carving out of inside of front. Started with forty pounds of wood, ended with four pounds!
Cutting out sound holes with coping saw.
There is a support glued to the inside of the front called a bass bar. Its purpose is to distribute the downward string pressure from the bridge and sound vibrations. Here the bass bar is being fitted to match the contours of the inside using red chalk. It's like the dentist adjusting your bite.
The bar is rubbed on the chalk showing the contact spots. Those high spots are shaved off. The process is repeated over and over until the bar shows all red, indicating full contact and perfect fit.
Gluing the bass bar to the inside of the front.
After the bass bar is attached to the front, it needs to be tuned. The front is suspended so it can vibrate freely. When the center of the front is tapped, the tone it makes should match the tone the bass bar makes when it is tapped in the center. The bass bar tone is adjusted by shaving it to the correct thickness.
The final bass bar shape.
Gluing the front to the sides.
The bridge is fit to the curve of the front using a scribe and then fine tuned with the chalk technique.
The neck and scroll are made from a block of Maple wood. The plan is spray glued to the wood for a cutting guide.
The neck and scroll rough cut on a bandsaw.
Pine table extension for a long cut.
Rough shaping of neck.
Tenon cut on bottom of tneck to match mortise on bass body.
Finished shaping of neck.
Cut layout for rough shaping of scroll.
Vertical cut first.
Then horizontal cut. Repeat until you reach the top.
Carving the dip into the center.
Rough carving the scroll. Here's a tip: carving is much easier if you wet the wood.
Finishing the surface with very sharp scrapers and sandpaper wrapped around dowels.
Clearing out the tuning peg box with a Forstner bit in the drill press.
Carving detail done, inside of peg box shaped with a flat chisel.
Gluing the neck to the body. Blue tape is there to keep excess glue off the wood. A straight edge is clamped to the center of the neck to make sure it is aligned with the center of the front.
Final shaping of back button against neck.
The "rotisserie" setup I use to varnish the bass.
Final coat of varnish, brushed on.
Gluing the Ebony fingerboard to the neck. Blue tape protects finished surfaces from glue. The Ebony fingerboard provides most of the strength of the neck.
Cutting out an area for the saddle.
Gluing in the saddle. The Ebony saddle provides a hard edge for the steel cables to go over on their way down to the end pin.
The nut shaped and glued in. The nut spaces the strings evenly and guides them to the tuning pegs.
Installing the sound post. The sound post is a wooden dowel that is friction fit between the front and back. It provides support for one leg of the bridge and its location affects the sound of the instrument.
Inside view of sound post being set.
This is the most exciting part of the project, installing the strings and actually playing the bass for the first time!
The varnish is wet sanded with 3000 grit, polishing compound is used, and the bass is waxed for the final finish.
Ready to make music.
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