[sdiy] Tonewheel relics

[rsdio at audiobanshee.com]

I have minimal experience with fabrication, but I’ve seen some clever approaches at the local shop. They have a powder printer, a couple of CNC machines from tiny to room-sized, three different kinds of laser cutters, and countless 3D printers. The smartest thing I’ve seen them do is take the most expensive 3D printing technology and make a single mold, then pour ceramics, plastic, or other materials into the mold for mass production. 3D-printed material can be very rough surfaced, and rather brittle and fragile, but the imperfections can be polished out before making the mold. You’ll get much stronger parts from a mold.

Laser cutting would also be a great option, unless the thickness or material type is not compatible with the laser. Highly reflective surfaces are bad because they reflect the laser!

Good luck with your project, Rutger.


On Oct 24, 2017, at 10:39 AM, Phillip Gallo <philgallo at gmail.com> wrote:
> Reading Tim Burns post caused me to open Allen Douglas's 1962 "Electronic Musical Instrument Manual" , the "Experimental Methods" chapter where he describes ("for those with limited workshop facilities")  machining sheet-iron or mild steel tone-wheels by drilling and filing.  55 years later and DIY tone wheels  are still a topic. 
> 
> http://gallomagnetix.com/AlanDouglasEMIM/TWheelFab.pdf
> 
> Also interesting was his "pantograph" rig "for marking out the tooth profiles".
> 
> p
> 
> On Tue, Oct 24, 2017 at 9:53 AM, Timothy Burns <snrubmit at gmail.com> wrote:
>> Hi Rutger,
>> 
>> Have you looked into laser cutting either out of plastic or aluminum?  This might reduce the chance of things warping or changing over time, since it's a reductive process instead of additive.  Tolerances can vary depending on the 3D printer but resin printers usually are the best bet for accuracy and strength; unfortunately it's also the most expensive.  
>> 
>> tim
>> 
>> On Oct 24, 2017 2:23 AM, "Rutger Vlek" <rutgervlek at gmail.com> wrote:
>>> I thought about that. The gear ratio's are crucial to the tuning of the tonewheel generator, and I feel that varying belt diameter (tension related, temperature dependant) could become an issue. Though, I have no way to quantify this instinct.
>>> 
>>> As for 3D printing, this is really a nice case where it's not perfect yet, as far as I can tell. I've asked some experienced people, and what I heard was basically that the composite nature of 3D printed objects results in a not-so-homogene material, that has unpredictable wear properties during applications with friction. Polishing changes the surface a bit, but lack of internal homogenity is supposedly a problem for gears, especially when running at higher RPMs (more friction). From memory I recall the drive shaft of the central AC motor in the Pari runs at around 1200 RPM. It connects with a belt drive to the first tonewheel drum shaft, which then connects with gears towards the last (12th) tonewheel shaft, progressively slowing down each drum such that identical drums given a semi-tone tuning difference. The last drum connects with a belt to the vibrato scanner.
>>> 
>>> As for PLL loop: I've never designed one, but it has my interest. What amount of complexity am I looking at? Can someone refer me to an example circuit schematic? Each tonewheel drum contains several octaves, the highest octave as (I believe) 16 dents on a single revolution. So that would be the preferred source for PLL feedback, I guess. The other octaves automatically align. The drums are spring-coupled to the gear shafts by the way, so the PLL loop may be affected by that (bouncing at startup?).
>>> 
>>> I do imagine this would be a HUGE step forward for the Pari in becoming tunable and way more silent than it is.
>>> 
>>> Best,
>>> 
>>> Rutger