5 to 12 string PJ bass conversion.

[Conor Hartwell]

Okay, I've attempted to build a neck thru 12 string bass but have given up citing a lack of usable materials, and the fact that I am currently unskilled in such a task.
I still want a 12 as I play in a three piece band and there is a void which needed to be filled.
I live in Australia and currently I am having a hard time finding a 12 string bass, let alone buying one.
So here is the next best thing, this is a customer returned Artist 5 string bass I bought for just shy of $250 AUD.
This will be the bones of the conversion.

 

[Conor Hartwell]

I've already got an 8 string bridge on hand and I'm planning on swapping the neck, preamp and pickups (and maybe pickguard depending on pickups)

 

[Conor Hartwell]

This is the bridge in question, it was originally from a Schecter Stiletto 8 string bass, I bought the bridge off of eBay from the seller Stigatsu, imported from the US it costed me $141 aud, including shipping and taxes.

 

[Bruce Johnson]

You could just rebuild that neck, making the headstock bigger. It's not that hard.

Here's how I usually do it, converting a Rickenbacker into an 8-string:

I'll talk you through the details, if you want to try it.

 

[Conor Hartwell]

I'm concerned with the potential tension involved as it is a 34in scale with a single truss rod, I'm tossing up building a new neck in it's entirety ( I do have truss rods which I had harvested from other necks) or, if I'm going down the single truss rod route, it would be a short scale neck.

 

[Conor Hartwell]

You could just rebuild that neck, making the headstock bigger. It's not that hard.

Here's how I usually do it, converting a Rickenbacker into an 8-string:

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I'll talk you through the details, if you want to try it.

Besides, I want to keep the neck as is for a future build, if I can make it happen.

 

[Bruce Johnson]

I'm concerned with the potential tension involved as it is a 34in scale with a single truss rod, I'm tossing up building a new neck in it's entirety ( I do have truss rods which I had harvested from other necks) or, if I'm going down the single truss rod route, it would be a short scale neck.

Oh okay. A 5-string neck is usually going to be strong enough for a 12-string. You can test it quickly by tuning it up a note or two, and see how much the neck bends. You can even pull up some numbers from string tension charts, and work the math to figure out how high to tune the 5 strings to match the tension of the 12. See if it will handle the load, with a reasonable tightening of the truss rod and a workable relief.

But, yeah, building your own neck from scratch would be better. And more fun. Then you could make everything right, just as you want it.

 

[Conor Hartwell]

Oh okay. A 5-string neck is usually going to be strong enough for a 12-string. You can test it quickly by tuning it up a note or two, and see how much the neck bends. You can even pull up some numbers from string tension charts, and work the math to figure out how high to tune the 5 strings to match the tension of the 12. See if it will handle the load, with a reasonable tightening of the truss rod and a workable relief.

But, yeah, building your own neck from scratch would be better. And more fun. Then you could make everything right, just as you want it.

Now that you mention it, I did crunch some numbers in terms of string choices, for the fundamental strings, I'm going with Rotosound funkmasters, 90-70-50-30 gauge, that'll be approximately 107lbs of tension, or, 48.7kg. For the octave strings, I'm planning on using D'addario Piccolo strings, 52-42-32-20p, which has tension of 43.3lbs or 19.6 kgs, double it, and they'll be 86.6 lbs of tension or 39.9 kgs, the total tension being approximately 193.99 lbs or just under 88kg of tension (if that's how you calculate said tension).

Conversely for the record, a set of D'Addario nickel wound 5 string set with gauges of 130-100-80-65-45 has a total tension of 197.8 lbs, or, 89.7kgs, so in terms of tension, if my calculations are correct, almost much a muchness.
I have a warped P bass style neck which I thought could be sanded out on the fretboard (it's in the neck itself) that I might try to rebuild the headstock on as a dry run, if it's successful, I'll replicate that on the neck of the Artist, if it fails at least I have not ruined a usable neck and then I'll have a go at building one.

 

[Conor Hartwell]

I'll also do proper tests on the neck once the bass arrives from the courier.

 

[Bruce Johnson]

I'll also do proper tests on the neck once the bass arrives from the courier.

Yes, with those string choices, the 5-string neck will probably be fine. But definitely test it. Bring it up to standard tune, and adjust the truss rod to bring the relief in the right range. Then take it up one step, and see how much the relief increases. That will give you an idea how strong and stiff the neck is. And you can make your decision on whether to use it for this project.

 

[Conor Hartwell]

Yes, with those string choices, the 5-string neck will probably be fine. But definitely test it. Bring it up to standard tune, and adjust the truss rod to bring the relief in the right range. Then take it up one step, and see how much the relief increases. That will give you an idea how strong and stiff the neck is. And you can make your decision on whether to use it for this project.

Cool, I am interested in rebuilding the headstock, how should I go about it? If I ultimately decide to use the neck.

 

[Conor Hartwell]

I'm attempting to follow @Bruce Johnson suggestion to rebuild the headstock on this unused Pbass neck as a dry run, this will determine whether I can consider doing the same to the 5 string neck

 

[Bruce Johnson]

I'm attempting to follow @Bruce Johnson suggestion to rebuild the headstock on this unused Pbass neck as a dry run, this will determine whether I can consider doing the same to the 5 string neck

Hello Conor;

I'm sorry I didn't get back to you. Yes, you've got the idea. You want to trim the old headstock into some shape that has two straight sides. It can be a straight rectangle, a trapezoid, or a triangle. The straight sides just make it easier to fit the new blocks on the sides.

You'll want to plug the tuner holes before you saw off the outer wings. Maple plugs.

Make up a full size pattern of your new headstock, on posterboard or heavy paper. Figure out the tuner positions , so that the string paths are relatively straight and don't touch against other posts. You can do this on a computer in a CAD program if you like, Or with a pencil and a ruler. And an eraser. Get the tuner positions worked out before you start sketching out the headstock shape. With that many tuners on the headstock, you have to do that.

Place that template on top of the neck, aligned correctly, and draw the lines on it where the sides of the cut-off tang are. That'll show you the size of the blocks you need to add to get the shape.

Use a block of maple that you've planed to a little bit thicker than the tang. Saw the blocks out, leaving them rectangular. That will make them easier to glue and clamp.

Joint the edges of the blocks and the tang for a nice tight fit. No gaps.

I recommend gluing them with marine epoxy, rather than wood glue.

After it's cured, flatten the top and back surfaces with files and sanding blocks. Put the pattern on, tracing the outline and centerpunching the tuner holes. Drill the tuner holes. Then cut out the perimeter.

That's the process.

 

[Conor Hartwell]

Yeah, I think I did it wrong, fortunately, this is only a dry run.
I can nearly drive a Mack truck through those gaps.

 

[Matt Liebenau]

Yeah, I think I did it wrong, fortunately, this is only a dry run.
I can nearly drive a Mack truck through those gaps.

It’s not “wrong” you just need to go a little further. The edges of those boards need to be jointed which can be done with a jointer, hand planes, a router jig or a large flat surface and sandpaper.

 

[Conor Hartwell]

My uncle suggested to put some sandpaper on a pane of glass. It also didn't help that I didn't have enough tension in the blade of my bandsaw either.

 

[Conor Hartwell]

@Bruce Johnson does the plugs and wings have to specifically be maple? Or can it be any good quality hardwood?

 

[Dadagoboi]

6 string double truss neck to 10 string, I don't like butt joints. I use TiteBond as I have for over 40 years with zero failures. It does require good joinery.

First cut after plugging holes

Bass side wing

Second cut and Treble wing added

1/32" 3 ply craft plywood veneer FRONT and BACK

Shaped:

There's more info in my Multistring Madness and Current Cataldo threads. Good Luck with your Build!

 

[Conor Hartwell]

I was wondering if you were stepping in, I've seen some of your other threads and was blown away by the craftsmanship.

 

[Dadagoboi]

I was wondering if you were stepping in, I've seen some of your other threads and was blown away by the craftsmanship.

Thanks!. My day job was as a furniture designer, mostly high end wood chairs. Lightness and strength were very important. Chair breaks and lawsuit follows.