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Lumi Custom 1951-5 P-bass


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I've had this one bubbling under the surface for a few months and I've decided to hash it in with my degree study's CNC module.

The design spec is a slab-bodied (no tummy cut, no forearm contour) P bass more or less in line with the design of a '51 P bass. Unlike '51 P basses this one is a 5-string with specific modernisations, however the visual presentation is to be as clean and '51 P bass-ish as possible.

First of all, the CAD plan:

Currently this plan shows that I designed in a Hipshot TransTone bridge however this will feature a vintage-style bridge instead. I feel that the TransTone is not in keeping with the vintage aesthetic I am attempting to maintain with this bass.

The neck pocket is longer than your standard Fender-style bass and extends through to the pickup cavity. This area is completely covered by the pickguard so to all appearances it resembles the original design. To maintain more of the original's appearance, four wood screws and a neck plate secure the neck from the rear whilst two additional bolts sit at the rear of the neck tenon to provide additional anchoring and neck-to-body coupling.

The pickup will be a modified five-string version of the original. No changes are really necessary at the basic level as authenticity is not the aim, only passing appearance. The pickup will be fed into a differential pre-amp which in essence amplifies only the voltage difference between the two ends of the coil. Although this would work better with a dual coil pickup actively bucking hum, it serves to buffer the output of the pickup and lower circuit impedance. Most importantly it performs a ground lift which certainly helps reduce the majority of hum. The pre-amp is powered by 2x batteries which supply a balanced +9v/-9v.

As usual with most of my builds, the neck features a zero fret. RestorationAD will hate me for this one. Truss rod access is available via a recess in the body end of the neck. I may modify the pickguard so that access does not require its removal, however I currently like the idea of hiding this design aspect. The nut itself is 45mm with bridge string spacing set at 18mm. The guide nut will be slotted by CNC to dial in perfectly equal string-to-string spacing. The rear neck contour will be relatively fat to give my thumb better guidance rather than how it errs around the bass side of the neck for anchor on thinner necks. The profile taper will run straight to the flat portion of the heel with a concave V style transition. The neck-to-headstock transition is an asymmetrical curve based around the headstock shape.

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The basic component layers were exported as a DXF file and imported into SurfCAM. Frankly, I hate SurfCAM. The drawing tools are ridiculous and what....no undo feature? Seriously Mr White? I'll endeavour to drop some screenshots of my CAM work and toolpaths when I get chance.

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Agreed. I thought of not making this one a slab however I really don't want to change the vintage aesthetic. I'll save that for the 2051-5 where I don't need to stick to the "sleeper" idea. I just wish I could pop an ashtray and pickup cover over this but they're not large enough.

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  • 1 month later...

This project is currently waiting for me to get back to the shop. I'm on work placement for about another two months so yeah. The plan is to CNC two neck blanks and fit them up, one with a Rosewood board and the other with either Ebony or a composite material. I'll also be cutting a bunch of bodies from different woods to make an objective comparison in their contributions to the sound. I'm hoping to compare Sapele, Aspen, Swamp Ash and Alder however I may have trouble sourcing the Swamp Ash at the moment. I got word that there is some Korina going so that might well end up in the shortlist also.

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Not really. I have a number of woods readily available where I am so I thought an objective test between them might be useful. I tested Sapele vs. Khaya a few months back and by far I really love Khaya. Sapele is far too heavy but I find Khaya less commonly.

This project will be somewhat of a first for me in many ways if all things turn out to plan. I'm going to re-draw the design and make it freely available via the site downloads section. In fact, I intend to do this with most of my large repository of CAD plans.

I expect Aspen to be relatively similar to the lighter woods like Basswood, etc. It reminds me very much of the wood used in my Korean Aria Pro II bass from '87. Fluffy. Smells like olives boiled in pee. Interested in the opportunity to make a Korina bass.

For what it's worth, I am going to try to make up 4-5 identical bodies and 2 necks. Being on super-limited budget as always, there will only be one set of hardware so no direct side-by-side comparisons. Should be fun, but any comparisons will purely be subjective compared to your work, pan_kara!

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unless you record a few samples and send me wave files :)

but I need to first demonstrate that I can indeed "test" anything... we'll see how that goes.

one set of hardware only makes the tests cleaner, you can always record and do "side by side" in post production. for sure thats what I'm planning, I try to keep as much as possible constant (hardware, electronics, body, neck - depending the test)

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That isn't really why I decided to use a few different woods though. I doubt I will record them in a controlled environment, if at all. I'd like to both do a direct working comparison for my own experience and pass that onwards. Tervaleppä (black Alder, Alnus glutinosa) is a viable alternative to the more common red Alder (Alnus rubra) so I'd like to work this one in. I have craploads of this stuff on tap. Aspen is also a common wood here and it is relatively similar to Poplar from what I am aware. It's an odd wood in use (currently constructing a log cabin from it, milling logs, scribing and dovetailing them) because it is so fluffy and awkward. Certainly one to try rather than as not. I'd like to extract some practical usage information from them I guess.

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  • 1 month later...

Bit of an update on stock preparation. Funds are limited so I am currently making two bodies rather than a variety. I wasn't happy with the price of the Zebrano (well, it is difficult to acquire here) plus the Aspen was too wet as it stood. I've prepped on large 43mm body blank from Alder plus one Alder/figured spalty Karelian Birch top.

Firstly, I glued up the top ensuring that the bookmatched faces were as well aligned as possible. This avoids the appearance diverging from a semblance of a match. The more you sand the top after bookmatching the more the wood changes, especially in smaller trees such as Visakoivu. The top was left deliberately thick as I want to paint the back. The thick top also means I can fake a drop top by just carving the forearm contour.

After drawing the body onto the blank, I drilled a set of holes outside of the outline large enough for screws to drop through. The back was cleaned up to remove any splinters blown out with a countersink. This ensures debris doesn't prevent a good glueup. The screwholes were made large so that the thread only bites into the bottom wood to cinch up the mating surfaces. They also keep the two pieces aligned across the centreline.

The top was laid over the Alder, and the screws tapped through to mark their locations. I pre-drilled these to a couple of mm and countersunk them also.

A thin layer of Titebond was added to the Alder whilst I spritzed the corresponding face of the Birch with water to ensure bonding. The glueup was screwed together and clamped to hell and back.

Next job is to get both the bodies and the necks cut on the CNC. I might hold off on the pickup choice for the Birch-topped bass. Maybe a 5-string split P is in its future.

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  • 1 month later...

Gah. Bad update. Was meant to have some time on the CNC last week but the tutor "in charge" of the CNC fed me a load of lies about why he couldn't (be bothered) to help me out. King furious doesn't even begin to describe my feelings on this, since this was meant to form the basis of an entire tutorial for the summer.

So anyway. Back to square one. The strategy now is going to be to produce one bass manually. That in of itself is a good thing perhaps. I'll write a separate photo tutorial on every step of the process using the plan from the Downloads section as the basis, uploading any auxiliary CAD files as I go.

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It's actually a longer story than that. He's a proper jobsworth and won't do anything that doesn't specifically interest him or fall within his specific job remit. I do question his worth as a CNC teacher sometimes. Those that are wanting to learn and to put in extra time to their education should be supported an encouraged. A teacher's job is one of dedication, not of ticking boxes and shipping kids off a conveyor belt with their piece of paper.

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A few work process shots....
Routing strategy. Start point from the exit of supported straight grain to the entry of unsupported straight grain. Draw your router bit direction on the blank! You'd be surprised how often you forget which way to rout. Big cuts done well. Better to cut less though.

Since I was completely screwed over about the CNC time (I would have had these basses completed by now otherwise) I planned the neck template by hand.
Extracting dimensions from AutoCAD 360 via the tablet and drawing the neck taper:

Once this was done I jointed a piece of scrap to make a temporary straightedge. This was screwed to the template stock and copied on the table router to both sides:

To create the neck pocket template, three straight-edged pieces of scrap (the last straightedge cut into two with one additional scrap piece) were screwed around the neck, butting up to all three edges. The neck was then removed, waste removed by bandsaw and routed flush. Although you can't see the tape, I added a layer to make the neck template slightly larger to allow for finish thickness. This is a bolt-on after all.

Finally, the template was screwed to the body via the eventual pickup location and the pocket routed 16mm deep into the workpiece.

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Truss rod channel and access recess routed on the table router whilst the blank was still square.

Rearmost hidden bolts recessed and drilled through. Need to take them through another 4,0mm yet because I forgot that this part of the neck will be cut flush with the body and hidden under the pickguard.

Checked for fit after fitting threaded inserts into the neck pocket.

Four "normal" bolt locations drilled through and inserts fitted.

Checked for fit. Centreline is on the money.

Day's work done. Forgot to take photos of the headstock shaping and tuner recessing work. Will cover that at a later date.

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I have no idea how; I'm usually as disorganised as anything! That 6,0mm router bit used for the truss rod channel was bugging me. Left an awfully rough edge. The bit for the recess burnt the far end too. Time to purchase new bits methinks.

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Creating a pickup template. Two 20,0mm holes and two 6,0mm drilled in precise locations and joined up using a temporary straightedge and bearing up bit. Low tech but effective and great practice. Good template-making practice means that the thirty seconds of routing that you DO do is immensely gratifying.

Firstly, knock out the corners that the radius of the router bit can't reach. Again, precision is paramount. Check the drill bit's spur for centredness and mark the drilling location with good awl or scribe.

Next, locate the template. A small hole was drilled at the back end so I can view the centreline through it and ensure that the pickup rout is perpendicular to it. The template is upside-down in comparison to the previous photo. This allowed me to carry the centreline mark over the edge of the template better than carrying it all way over to the other side, potentially drifting in errors. Knowing how tolerances can start creeping in is important in figuring out how to prevent them.

Ka-ching. One 18,0mm deep pickup rout. A quick slicing with a chisel and light sanding removed the very corners between the drilled holes and routed faces.

Headstock thicknessed to 17,0mm with 2,0mm recesses for the tuner bushings. This may be taken down to 16,5mm-16,0mm dependent on how the tuners look when dry fitted. Recessing too far be be detrimental and a bit of trust in your eyes in needed.

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This is pretty much where everything will be left off until the autumn. Colour choice was PPG Deltron 64033724, or Nissan AX5 "Merlot Red Pearl". It looks like this:

39285038.jpg

Dry fitting hardware to check that everything is cool. It is. Hipshot Ultralight HB6Y with clover keys in satin chrome.

The body was sealer with a 1lb cut of dewaxed blonde shellac. Alder is thirsty wood so don't skimp on this step! Application was done using the usual spit coat stage of French polishing. Nothing spectacular but it's important to know you are adding shellac rather than melting the previous layers and making no progress! After the shellac was hardened, I lightly sanded it back with 400 grit paper and applied a couple more coats of shellac. Over this went a red oxide primer which was again flatted back when dry.

Awful photo, I know. In sunlight the pearl flop is AMAZING. I chose this straight from the chip because it just had that vibe I wanted. Very cool. I can't wait to get the final coat on and bury it under clear....
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  • 1 month later...

Right, so where were we anyway?

Neck profile roughed in. Still needs fettlings into perfection. The main things is the 1st and 12th fret thicknesses, profiles and transitions.

Frets pressed....haven't had a fret press for at least six years....forgot how easy it makes things!

Fret ends nipped and filed flush plus 30° back bevel. Slight fingerboard edge rolling for a smoother feel in use.

Fingerboard end shaped, plus the truss rod access hole. Slightly deeper than I wanted by a few mm however I want a longer nut made anyway.

Lazy way to leave paint drying. I did however go to the trouble of measuring the gaps in the grate.

Orange peel happens. Unless advised otherwise, I'll just bury this in clear and pretend it never happened.

The colour looks so much better in person than in these photos. The final finished instrument shoot will be done in whatever daylight remains! The metallic is spectacular in bright light and the sun.

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