Planning a twisted neck

TFM94

TFM94

Aug 24, 2020
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Finland
#1
Hi everyone,

In every build I try to include something that I haven't done before to challenge myself and keep it interesting. Usually these are little things like headstock binding, special inlays, contour carves etc. Now that I have built several instruments and no need to quickly finish another bass, I can take some time and have set my eyes on a bigger challenge, a twisted neck mostly for ergonomic reasons. I know that Torzal Guitars is offering basses with a "natural" twist, I think it's 35 degrees from nut to bridge.

I couldn't find any build documentation of a twisted neck (on purpose) here on tb, has anyone attempted this?

To make matters worse, I am thinking about a 5 string, headless and multiscale design, around 34-36" scale.

A neck-through construction seems to be the easiest choice here. I am not a CNC guy, so for creating the twist on the neck, I am thinking to do it with a router sled on a jig of two oppsite inclined planes on either side of the neck.

I need advice on two things:
1. The fretboard could either be routed as a twisted piece from a thicker block, or it could be laminated from 2-3 veneers (e.g. 2mm) using the neck blank as a mold.
2. The neck blank could be laminated the standard way as a straight and parallel multilaminate (easy to make, but might look awkward) or it could be laminated already with a twist. The latter would look insanely cool, but how do I clamp this properly?

Any tips and ideas are appreciated! And yes, I know, it's a bit crazy.
 
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#2
I have no idea how to build this, but really curious to hear from somebody who does. Multiple thin laminations seems the most likely solution. How was a “rope” twist done on a wood lathe, like chair legs or stair balusters? Maybe look up fancy lathe work first?
 
#3
TFM94 said:
Hi everyone,

In every build I try to include something that I haven't done before to challenge myself and keep it interesting. Usually these are little things like headstock binding, special inlays, contour carves etc. Now that I have built several instruments and no need to quickly finish another bass, I can take some time and have set my eyes on a bigger challenge, a twisted neck mostly for ergonomic reasons. I know that Torzal Guitars is offering basses with a "natural" twist, I think it's 35 degrees from nut to bridge.

I couldn't find any build documentation of a twisted neck (on purpose) here on tb, has anyone attempted this?

To make matters worse, I am thinking about a 5 string, headless and multiscale design, around 34-36" scale.

A neck-through construction seems to be the easiest choice here. I am not a CNC guy, so for creating the twist on the neck, I am thinking to do it with a router sled on a jig of two oppsite inclined planes on either side of the neck.

I need advice on two things:
1. The fretboard could either be routed as a twisted piece from a thicker block, or it could be laminated from 2-3 veneers (e.g. 2mm) using the neck blank as a mold.
2. The neck blank could be laminated the standard way as a straight and parallel multilaminate (easy to make, but might look awkward) or it could be laminated already with a twist. The latter would look insanely cool, but how do I clamp this properly?

Any tips and ideas are appreciated! And yes, I know, it's a bit crazy.
Click to expand...

Yes, your idea is a bit crazy, but that's a good reason to try it! I think it all can be done.

The main thing is that you have to build a special routing fixture that can accurately cut the twisted surfaces. As you are thinking, the two rails of the router fixture will need to be at an angle to each other, in the vertical plane. Then the base of the router needs to have three points of contact with the rails; two on one rail, and one on the other.

Picture a standard flat rectangular MDF base on the router. On one side of the base attach two round rods of something. Round aluminum rod 1/2" x 6" long? Those two rods mount on the front and back edges of the one side of the base. On the other side, a third rod goes right down the center. When you flip that base over and set it on the rails, it will be resting on three points. As you slide it down the rails, the router will tilt at a consistent rate, set by the angle of the rails. Do you understand my description?

Also, the router bit will need to be a shallow dome, not a flat end. The larger and shallower the better. It will cut the twisted surface as a series of round-bottom flutes. You'll have to hand sand off the ridges between the flutes.

Once you've worked out that fixture to accurately cut those twisted surface, you can cut all the parts to make up the neck lamination. You'll have to cut and fit all the left and right hand surfaces on each strip. And it all has to fit together tightly. Gluing it up shouldn't be a problem.

Then put the lamination back in the fixture to cut the twisted top surface. Use the fixture to cut the twisted underside of the fingerboard block. Put in the truss rod. Glue the fingerboard on. Then make up a three-point radiused base for the router, and use it on the same fixture to cut the twisted, radiused fingerboard surface. Slotting and fretting would be pretty much normal.

Crazy, but technically reasonable. A lot of work. But a good challenge.
 
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#5
Dang, Marko, amazing Torzal build. I could not picture the router rails until I looked at your photos, ingenious. The multiscale requirement makes my brain hurt a little, since at the more extreme fret angles, wouldnt the fret themselves have to twist?
 
#6
I was thinking about the frets as well. As for every multiscale, the effective fret radius will decrease for larger fret angles. For the twist I believe that a continuous twist of 35 degrees on, say, 35 inches of scale length would result in 1 degree per inch. For a 2" scale difference (e.g. 36-34" low B ->high G) and the neutral point at the 12th fret, the fan at the 1st fret would be 1", so the angle difference between both ends of the fret would be 1 degree as well. As the fret itself is about 2" long, i think the nickel silver fretwire should be able to follow the fretboard surface. Even if the fret would stay straight, such a small deviation could be fixed by recrowning.
 
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#7
Thank you all for the input and ideas, and also for sharing Marko's thread. A really nice build, too bad that it had such neck issues.

I am not sure if one straigth trussrod with carbon strips on either side or two trussrods with carbon in the center would be the better choice. As adjustability with straight truss rods will be a bit strange, I think some carbon fiber inside the neck would be beneficial to keep the need for adjustment to a minimum. Maybe two 1/4"x1/4" CF rods.
 
#9
The router jig rail discussion over at Marko's thread has led me to another question: string spacing! A normal guitar has a linear taper in string spacing between the nut and the bridge. However, a twisted neck should have a non-linear spacing along the neck. Consider this: In the extreme case of 180 degree twist the two outside strings would meet at a single point. For equal nut and bridge spacing this point would be at the 12th fret, for typical values 10mm spacing at the nut vs 15 mm spacing at the bridge would shift this point to the 7th fret. With the taper from string to nut, I will have to make sure that the spacing at the 7th fret is still larger than the nut spacing, because I think it would feel awkward to play otherwise. I will do the exact math later, but this will limit the possible twist for a given nut/bridge string spacing.

The more I think about it, the more interesting it is!

Also, I found an old (25 years) and relatively light maple neck blank 77x64x1050mm, that should be enough for this neck. This way I will not have to do the twisted multilaminate, which makes this build a bit easier.
 
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#11
Ok, here are a few more specs for this build. As I move forward with the design, I might still have to tweak them a little bit, but these are my parameters for now:

- 5 string, with spacing 10mm at the nut and 15mm at the bridge (center to center)
- Headless, ABM single headless tuners
- 34"-36" scale, 24 frets, neutral point at 8th fret
- Twist: +15deg at the bridge and -20 deg at the nut, that would put the neutral (vertical point) around the 15th fret. This is the same as Torzal uses and should be a safe bet.
- Maple neck (neck-through) with Wenge fretboard (2x2.5mm laminated) and ebony binding, chambered swamp ash body wings, maybe with some wenge strips for contrast.
- medium chunky neck profile (ca. 22mm@1st, 25mm@12th). I was first thinking endurneck, but that might be redundant in conjunction with a twisted neck?
- Body shape not yet designed, but I think it will be quite thin on the bass side and thicker on the treble side, according to the twist at the bridge.
- Electronics: One or two Nordstrand Big rig humbuckers, Vol, Tone, 3-way switch, probably passive.

I am no expert on patents, but I believe this one should be alright to build, as I am not planning to sell or export it, right?

More ideas and suggestions are always welcome! I'm happy to see that people are following this thread, and I will keep updating and showing the build progress, but it might take some time to get it all figured out.
 
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#12
I watched a few of the Torzal vids and though it's a very strange look (just hard to get passed that instinctive reaction of- OMG that neck is twisted), it a very cool engineering feat and a very function-oriented design,.... Which I always dig.
Definitely more ambitious than anything I would try to tackle any time soon, so I applaud you for going for it.
I may attempt some off beat, complex ergo body contours at some point, but a twisted neck is definitely next level. And fanned fret on top of that?
I'm rooting for you.
 
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#13
From my (very) limited understanding of copyright law, it's perfectly OK to make a single copy of a patented design , as long as your don't sell it. Even then, as long as it doesn't say Torzal on it, I can't see anybody bothering to go after the OP about. I've built (2) Ric clones, and have an Alembic clone in progress, and don't expect to get any C&D letters any time soon.
 
#14
RichterScale said:
I watched a few of the Torzal vids and though it's a very strange look (just hard to get passed that instinctive reaction of- OMG that neck is twisted), it a very cool engineering feat and a very function-oriented design,.... Which I always dig.
Definitely more ambitious than anything I would try to tackle any time soon, so I applaud you for going for it.
I may attempt some off beat, complex ergo body contours at some point, but a twisted neck is definitely next level. And fanned fret on top of that?
I'm rooting for you.
Click to expand...

Thanks mate, I guess I'm a glutton for punishment here ;) To be honest I think the unusual look is part of the attraction as well, it will always stand out as a unique instrument. At least that's the plan.

It think I will add some contour carves as well, like a forearm rest and a belly carve.

I checked out the Torzal vids as well, and I'm sure they're using a CNC, I just don't see how it could be commercially viable otherwise. Especially with the curved body sandwich, which I will not attempt.

I am wondering what the angled bridge (15 deg) will feel like when playing with a pick? For fingers it will most definitely be more ergonomic.
 
#16
Bruce Johnson said:
Yes, your idea is a bit crazy, but that's a good reason to try it! I think it all can be done.

The main thing is that you have to build a special routing fixture that can accurately cut the twisted surfaces. As you are thinking, the two rails of the router fixture will need to be at an angle to each other, in the vertical plane. Then the base of the router needs to have three points of contact with the rails; two on one rail, and one on the other.

Picture a standard flat rectangular MDF base on the router. On one side of the base attach two round rods of something. Round aluminum rod 1/2" x 6" long? Those two rods mount on the front and back edges of the one side of the base. On the other side, a third rod goes right down the center. When you flip that base over and set it on the rails, it will be resting on three points. As you slide it down the rails, the router will tilt at a consistent rate, set by the angle of the rails. Do you understand my description?

Also, the router bit will need to be a shallow dome, not a flat end. The larger and shallower the better. It will cut the twisted surface as a series of round-bottom flutes. You'll have to hand sand off the ridges between the flutes.

Once you've worked out that fixture to accurately cut those twisted surface, you can cut all the parts to make up the neck lamination. You'll have to cut and fit all the left and right hand surfaces on each strip. And it all has to fit together tightly. Gluing it up shouldn't be a problem.

Then put the lamination back in the fixture to cut the twisted top surface. Use the fixture to cut the twisted underside of the fingerboard block. Put in the truss rod. Glue the fingerboard on. Then make up a three-point radiused base for the router, and use it on the same fixture to cut the twisted, radiused fingerboard surface. Slotting and fretting would be pretty much normal.

Crazy, but technically reasonable. A lot of work. But a good challenge.
Click to expand...

Yes, I can imagine this router jig, it seems like a good design. With the two rods or tubes this jig could even be adaptable to different twists and scale lengths for future builds. I like it.

Regarding the router bit, as the router base will be parallel to one of the two rails (the side with 2 contact points). I understand that a wide, completely flat router bit wil create a deeper cut on the side where it is angled to the rail as compared to the parallel side. Two options here: This error will be very small for thin router bits, so maybe it wouldn't be noticable with a 1/4" bit, or I can use the "dome bit" like you suggested. The closest I could find locally is this half-spherical one:
klein-hohlkehlfraeser20b.gif
with D=19mm. Seems more efficient to me. It could also be helpful to turn the router jig around halfway through to have two contact points on the side that I am routing at, meaning that when I'm routing along the outside string paths, the router bit will be perpendicular to the fretboard surface on both sides.
 
#17
Alright, a few more decisions have been made.

For now I will focus on the router jig to get the twist right. Only after that is finished I will design and work on the body, because that body likely wouldn't fit any other neck if this attempt failed.

Went to the hardware store yesterday, and all rods or tubes that were stiff enough for the rails and >1m were really pricey, so I decided to build the router jig entirely from MDF. There will be two fences parallel to the neck with opposite slopes. I will make a router base extension that will ride on these two fences with three contact points, two on one side and one on the other. These contact points are just three flat strips of MDF (screwed underneath the base extension) to create a flat surface for the neck, and three strips with a radius cut to the underside to later radius the top of the fretboard. With a fretboard radius of 16" this should be a shallow cut. I have ordered a dome-shaped router bit as described above (thanks @Bruce Johnson for the tip), it should be suitable for both neck and fretboard with subsequent sanding. I think I can also use this jig with an offset bearing bit to create the binding channel. By having two contact points on the fence side where I am cutting the channel I should have the bit perpendicular to the fretboard.

I also have to think of some addition to the router jig that will create an angled but flat area for the single bridges to be mounted on. Any ideas?

The neck blank is pretty thick at 64mm, so if the first attempt is not good enough, there should be enough wood left to attempt a second or third pass.
 
#18
What's the work around for a truss rod or stiffening rods for a neck like this?
Or is it simply that those aren't possible with a twisted neck?
Does the twist itself make it so a truss rod isn't needed, or is it one of those things that neck flex has to be build in and accounted for?
 
#19
TFM94 said:
I also have to think of some addition to the router jig that will create an angled but flat area for the single bridges to be mounted on. Any ideas?
Click to expand...

For that, you need to add a short section of rail on the near side, which is parallel to the rear rail, but down at a lower height. That will cut a platform that is tilted in one angle, but doesn't twist. That extra rail section could just be a rectangle of MDF temporarily clamped to the near side rail.
 
#20
For truss rods and stiffening rods, you need to cut straight non-twisted slots. Lay them right down the centerline of the neck, ignoring the twist of the top surface. I'd probably line up the slot so it is perpendicular to the surface halfway down the neck. Make sure the slot is deep enough so that no edges stick up above the tilted surface. If you want to, glue a thin strip of wood down over the rod, then trim it flush with the twisting surface.

Basically, install the truss rod like you would in a straight neck, but with it leaning at an angle that's half of your overall twist angle. But don't try to twist the rod.
 
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