5-String Carl Thompson inspired bass

[Prostheta]

It has been quite a while since I last started a project. I've always wanted to build (or own...drool...) a Carl Thompson style scroll bass however I've hung off until now. The design for the bass was derived from a six-string bass Carl made featuring his fishtail string-through and the 3D scroll. My own modern twists on the design have been to incorporate compound scales, materials Carl does not use and also the sacrilegious....paint....

In actuality this project is two basses for various reasons which will no doubt become clearer as I document the build further. The first bass is a basic single-scale version closer to a Carl Thompson style "no frills" instrument where the woods are simple and plain and there are no complications across the instrument. Unlike Carl's no frills basses, this will be a set neck as opposed to a bolt-on. The final instrument is what I have already named the "Black Rainbow"; a passing nod to the famous "Rainbow Bass" Carl built for Les Claypool and a more than obvious statement on the bass being painted black. Hmm. The design for the Black Rainbow Night Rainbow was - as always - drawn up in CAD to plan out the geometry.

The old sketch drawing:



The intended specifics for the first instrument are:

• 35" scale
• Sapele body
• either Sapele or Birch set neck
• Wenge fingerboard
• EMG 40 size pickup, possibly a simple DC or a P5 (CAD plan is wrong)
• Hipshot "D" style bridge
• Rear brass string retention insert
• Stainless steel fretwire

Since this is the proof of concept instrument the spec is being kept pretty bare. I considered resawing the body wood and chambering it slightly however the already svelte 35mm thickness will shave a significant amount of weight anyway. All of the bevelling will be done by hand except for perhaps the large consistent runs of 45° bevelling around the bottom of the body and around the forearm area.

The second instrument (CAD plan being tweaked) is the same as the first but with the following specifics:

• 35"-36" scale
• Black Alder body
• Birch neck (depending on the results of the first instrument) with Wenge laminations
• Wenge fingerboard laminated with carbon fibre veneer
• Seymour Duncan SMB-5a Music Man pickup
• Seymour Duncan STC-3M4 pre-amp/EQ
• Custom milled and powder coated brass bridge
• Carbon fibre neck reinforcement, truss rod cover, cavity cover and jack football

Hopefully I will get chance to get the body blank glued up tomorrow and bandsawn before the end of the week, letting it settle out for a few days. In the meantime I have plenty of pin router templates to be making....

[Geoff St. Germaine]

I can't wait to see this one go. I have a design I've drawn up for a 6 string multi scale Thompson type scroll bass. Don't know if I'll ever build it, so I may have to live vicariously through your build.

[Prostheta]

No worries! I'll do my best. What scales were you planning on yourself? I'm just making the decision in my own head whether to relax my higher strings with a shorter scale or whether the fret angles will become too extreme because of that. I'd prefer to reinforce the lower end but compromises are always the name of the game. I'll likely just have to figure out a reasonable set of strings gauges to provide the flex I prefer in the high strings. Excuse my mind waffle here.

None of this will affect the first bass however I am wondering whether to make it a four rather than a five. Whatever. The body specifics will be the same.

[Prostheta]

The main template for the body was printed onto four pages of A4 with reference marks to ensure alignment and that the printer had output 1:1. These were then glued to a piece of 12/15mm plywood which I threw through the thickness sander to help with adhesion. MDF can be a pain to glue up in this manner hence me using plywood for this template. After it was (mostly) dry a trip through the bandsaw removed the majority of the waste....



....after which a lot of shaping on the oscillating belt sander roughed in the major curves....yes, I know this is a jointer but I forgot to take photos since I concentrating on the dusty job :-D



Still plenty of shaping to carry out on the spindle sander before finessing by hand. Whilst the body template was still "in the rough" I used this to ensure that I avoid any inclusions in the Sapele stock for the body blank. Ideally the template should have been transferred to thinner stock such as 5mm MDF before copy routing to the "master" template stock however I couldn't find any MDF scrap suited to my purpose without breaking a new board. Can't go spending money whilst I am studying now, can I?

[ScottR]

Now, that's a band saw! I bet you are going to exhibit withdrawal symptoms when you graduate.

SR

[Prostheta]

Yeah, I already thought about that bit. By then I should have my business proposal refined and be ready to move forward. Either that or ruled out as a non-starter.

[Prostheta]

Today's progress. I didn't take any photos of the body blank prep and glueup which is a bad show by me, but there wasn't anything amazing to report. The pieces were thicknessed to around 36mm as I have decided to go for THIN on this body like a real Carl Thompson with a target body thickness of 30mm. Super slender slinky smooth. This gives me a target depth for the cavity depending on how I plan on fitting the cover....if it is recessed then I will need a "football" with a corresponding recess under the plate to give the socket extra depth to fit. If the plate is mounted directly to the front, a cavity depth of 27mm (at least, in the area of the socket anyway) with a 3mm back wall will be necessary. I plan on offering up a couple of alternative sockets to the side of the body tomorrow. No major issue, but one I need to decide on before I consider planning the bevelling.

The two halves of the blank were jointed on this beast (the better of the two jointers) after having used the thickness planer is in the background. I kid you not - a well set up jointer does not require any subsequent preparation of the edges before glueup. You can tell that the result is exception when you pop them together and you get that "clap" of air being excluded and the feeling that the faces are almost "sucking" each other together. I've not had that since I last jointed a blank using a hand plane. One sexy sexy feeling. The halves were glued using the obligatory Titebond I, popped once again through the thickness planer to remove any stepping down to 35mm. The blank was then passed several times through the immense thickness sander to bring the size to 32.5mm in increments of around 0.25mm each pass.



Although I neglected to take photos of the thickness sanding, this is the machine as used on my previous bass build which is going to be prepped for paint relatively soon:

[Prostheta]

After the thickness was in the bag, the rough outline was drawn out and the blank moved to the (larger) bandsaw which has a turning circle of about two weeks. No shaping of the outline was really do-able here other than in straight lines.

[Prostheta]

After coarse shaping, the outline was taken to within a couple of mm of the rough outline using the lighter bandsaw.

[Prostheta]

Next, holes were drilled in the template through the neck pocket, pickup rout and the bridge mounting hole positions as these holes will be drilled or routed out later in the build. The template was mounted to the blank using four 30mm screws ready for work on the overhead pin router (yläjyrsin). The bit I started with is a 12mm single flute carbide cutter which I knew was going to be more trouble than it was worth.

First pass at 2mm depth of cut:



....aaaaaand yes - as DemonX will attest - any attempt to climb cut with a carbide bit will result in death. Big noisy shrapnel-y death.


Having proved something to myself I replaced the carbide cutter with a dual flute 40mm long cutter instead. Result:

[Prostheta]

Although it is nice to have access to fantastic machinery such as this, it is only as useful as what you take away from it. Same as any learning experience. The primary reason I am making this instrument (remember, this is the practice model) is firstly to familiarise myself with working on machinery and learning their specific idiosyncracies (familiarity is important IMO) before "ploughing ahead" with real work and secondarily to help create working methods and processes in my head. I am mentally calculating the workhours and material costs on this one instrument with a view towards a feasibility study on manufacture rather than the "one-off" custom.

I certainly learnt a lot about the differences between your common or garden router table and a 4HP overhead pin router! If that beast wants to take your work and destroy it, then you are not the one to be making the decisions. Normally when using a small "DIY" sized router the story goes:

router: "are you climb cutting again?"

me: "yes, I think I am"

router: "okay, fine"

**pause for reflection**

vrrrrrrt*BANGBANGBANG*

me: PERKELE

This is not the case with a fast running overhead pin router. As soon as you approach a climb cut, there is not pause. The router instantly takes all, laughing maniacally as it does so.

Climb cutting is not impossible of course, however the only thing stopping the machine throwing the workpiece and yourself halfway across the galaxy is the lack of strength in the wood. After the carbide cutter incident, all cuts were taken counter-clockwise around the body with occasional climb cuts only to move ahead, cut backwards into corners and move back before advancing through to eliminate tearout. Endgrain was not even an issue. Amazing. The only slightly confusing element of the routing process was the internal part of the scroll where I had to cut clockwise since it is essentially an internal shape. The thin lower horn gave me nightmares when mentally preparing for this work. Normally, handheld routers in tables would happily grab this wood and smash it up, no questions asked. Surprisingly, the overhead pin router shaped this gracefully without incident. I was however taking about 2-3mm cuts. This is to be an oil-finished instrument and filler would kind of show itself I think.

[Geoff St. Germaine]

When I was gigging I played Dingwall basses exclusively (had a prima artist 6, prima 5 and a Z2 5), so I was going to run the scale the same as the Dingwalls, so 37" to 33.25".

Looking great so far... and what a shop!!!

Edited September 5, 2012 by Geoff St. Germaine

[Prostheta]

Wow, now that is quite a difference in scales....obviously a five-string will be closer to 34" if the high C is dropped which makes it feel more realistic. I think on the basis that Dingwall are obviously not making "bad" instruments with overly slanted frets I can afford to be more adventurous in my compound scale choice. Locking the long scale to 920mm (36.22") and bringing the short scale to 850mm (33.47") would be a much more useful range than just one inch of difference. I'll draught her up and see where we go from there I guess. My immediate concern is that the additional bridge offset will possibly detract from the body styling and maybe even require a very sharp break angle from the bridge to the string-through hole.

Thanks for the ideas Geoff! Any chance of seeing the design you had in mind?

[gpcustomguitars]

Good work so far! And a very nice shop

[verhoevenc]

Yeah P. You seem to have really upgraded shops... perhaps to the world of some school's?

Chris

[Prostheta]

Indeed Chris. Was that not obvious? ;-D

Since moving to Finland I have found that all of my qualifications and experience in the UK mean nothing here so I am automagically outclassed in the job market. I decided on that basis to retrain and change career rather than study something that I have been doing for a long time again. I see it as an opportunity of sorts despite me losing three years of my life to do so. The qualification itself is a degree in "woodworking" for want of a better term however as with any course you take from it what you put in....rather than just tick the boxes for coursework and all that I'm taking the bull by the horns and learning the practices of manufacture so when I graduate I could start a business or work in the wood product manufacturing industry, or even go higher and study for a masters degree is material technologies or other related discipline. Either way I want to move beyond the haphazard "DIY" one-instrument-at-a-time stuff whilst taking those skills into a work context. I neglected to mention the enormous CNC machine also. That could mill perhaps six or more one-piece basses at a time if that were in fact a practical thing to do. That is a specialisation in the third year however I need to work on my language skills since I am doing this degree in Finnish.

[Prostheta]

Not much progress today I am afraid. Other duties called.

The internal cavity template was cut in a scrap of 12mm plywood which needs a bit of cleanup and finessing before ending up being mounted to thicker stock and routed through. A piece of scrap wood was squared and cut the same dimensions as the pickup. This will be clamped within a set of straightedges before being removed to rout a negative template. I decided to go for the Seymour Duncan SSMB-5A in this bass also and fit a homebrew pre-amp to make the bass active. The body was thickness sanded down to 31mm. Next job is to mark up the contouring around the body.

[Prostheta]

Today's work was purely on the neck. Starting out with a piece of fairly straight Sapele from my limited stock (Sapele can be pretty twisty and tends to warp like a clock spring, especially after cutting) cut within a few degrees of the quarter, I surfaced one large face flat before jointing the adjacent sides square. The remaining face was thicknessed leaving a total depth of 32mm with a width of 86mm. The centreline and 24th fret position were marked up giving me a reference point to measure and mark up the nut break point plus 5mm for the nut's shelf. The 18° headstock angle was then marked from this point on one edge along with a parallel line 15mm down giving me the minimum position I could scarf the headstock at.

Removal of the headstock on the bandsaw:


Thickness sanding Wenge laminations to 6.0mm:

(NOM NOM NOM)



(BLEAURGH....PTOOEY!)


6.0mm my arse. I ran the pieces through a couple of times more after tweaking the depth slightly and got a hair over 6.0mm:



The neck was taken to the bandsaw after calculating a taper with a central piece of 10mm at the nut and 21mm at the 24th fret. Each piece was then run over the jointed to clean up the glueing face before being laminated with the Wenge and 2x 1.5mm Birch veneers either side. To prevent slippage from hydrostatic pressure during clamping I dowelled through all the laminations using cocktail sticks, placing them in areas that would be milled out during neck shaping. All glueup done with good old Titebond I. I had to work quickly as the open time for Titebond doesn't allow you to be disorganised with eight glueing faces. I would rather not consider having to use a different glue with a longer open time like II or III on the basis that Titebond I sets up quickly rather than as not. Just my little foible. My trusty plastic squeegee with toothed and smooth edges meant I didn't end up with Wenge splinters in my fingers like I usually do. No weekend sepsis for me thanks. Plus it ensures that I minimise the glue waste from slapping too much of it around:



After allowing the glue plenty of time to set up (lunch plus other work is a good distraction) the excess was shaved off on the bandsaw and the blank run over the jointer and through the thicknesser back into square. One more trip to the bandsaw after remarking the taper....



....and then repeat the glueing/setup/cleanup process with the other side. Again, because Titebond I is relatively speedy stuff it allows several non-stressing operations to be carried out in one day. Anything that requires the full cure to be complete should of course be left for a day or two. Should these pieces creep (unlikely but feasible) or the wood move from cutting there is still plenty of leeway planned in to counter this.



Glueing face cleaned up but not yet ready for glueup. Neck width around the middle of the first fret marked out:



Same applies to the 24th fret position:



Work on the neck was saved until the end of the week as it can be left alone to cure over the weekend to do what it will. I doubt that there will be any remedial work necessary as the wood was dry and acclimated, plus wasn't overly twisty or otherwise crazy. Still, Sapele can be a fractious wood and this piece is far from the best, however this bass is the practice build prior to making the actual Black Rainbow. Had to get that out before the faults in the choice of wood were pointed out.

Next week I plan on marking up the body bevelling and contouring so any downtime on neck operations can be spent with rasps and files on the body. Now where did I leave that truss rod? Hmmm.

[ScottR]

Nice work and documentation on that neck!

SR

[Prostheta]

Thanks Scott. I have a horrible habit of plowing on through with my work in full on tunnel vision mode so I hope I develop better documentation habits. Correspondingly if I bear documentation in mind this should help me refine and clarify my work practices also.

[Prostheta]

Okay, I could do with a little input here as I was unable to carry out a specific process on the body due to not having the appropriate tool to hand.

Originally I wanted to cut a grain-matched cavity cover using the "rout around template/remove with flush cut saw/plane flat" method but I do not have a flush cut saw and didn't have enough depth to use "any old" saw. The truss rod cover and headstock nameplate will be laminated Wenge/Birch to reflect the theme in the neck and I was thinking of doing the same for a control cavity also. I can easily cut a spare piece of Sapele for a cover, however I think that if it isn't grain matched it looks out of place and would just bug me. It is not 100% decided yet on whether the cavity will be front or rear so there is room for modification on the design in this respect. I do think that Wenge over such a large area would also look out of place too unless the right piece were chosen, and my stock of it is somewhat limited.

I do have a piece of Ebony which I was saving for making a baseplate on a shelved build which just happens to fit the width of the cavity cover perfectly plus I can maybe squeeze a rod cover out of it also. Too many themes confusing everything?

[ScottR]

Ebony makes a great accent, but i think you'd need it in one more place (for a total of 3) for it to work correctly. I do like the idea of recreating your neck lams in the places you mentioned and for the cavity cover. The sapele involved in that will look fine if you use a grain orientation totally different from the body grain. That will look intentional as opposed to mismatched. You could even orient your lams offset by 30 degrees or (pick a number) in each of the three locations: TR cover, HS nameplate, and cavity cover, just make them all point the same way for continuity. In other words if your neck lams run at 12:00 and 6:00 o'clock, the other 3 locations could run at 1:00 and 7:00 o'cklock. Just one option.

SR

[Prostheta]

I know what you're saying Scott but turning the Sapele around just feels like a bigger clash than non-grain matched. The Ebony would just sit there "like an island" on the front so I guess I should rule out whether or not I can fake a near match with any of the other stock. I have the negative template sorted so I can use that to visualise the candidate stock against a pencil outline on the body. Worst comes to the worst I can "hide" it on the back but I am somewhat set on having a recessed front-mounted cover. I guess it is because I've gone to so much trouble to nail this instrument's dimensions down to the thinnest possible for a front-mounted Switchcraft open chassis jack despite it being quite likely I will side-mount a Neutrik barrel jack.

The Ebony might still be used as a headplate with a trapezoidal splice in there yet. I have had a few ideas along these lines for which I need to see the build in the later stages to get a realistic feel for whether they work for me or not. I'm just dealing with this problem caused by not being able to cut the cavity cover as I originally would have wanted. "Drat, drat, and double drat!"

[ScottR]

When trying to get a near grain match for a cavity cover, I've set the template in place and drawn on it in pencil indications of what the grain should be in a perfect match. Then I lay it down on my stock, turning it every which to see how many grain lines I can get to match up.

SR

[Prostheta]

My stock is a little limited as I only bought enough for a couple of projects back when we visited the warehouses in Lahti. The Sapele I have left is enough for a few neck laminations, plus what I saved from scrap. I think that since I have a piece which is the same thickness as the body before it was bandsawn to rough I can check the grain and see if fits and if not, cut it in half and see if the grain changes for the better inside.