[Glass-Giant]

Hello,
I'm considering building a machine to make "talking strips". These are essentially linear records, with a series of bumps on a long, thin strip of plastic. You drag your fingernail over the bumps to play it.

A movie of my test strip is below and a picture is attached. It's a bit hard to hear, the message is "Kiss me you fool".
http://glassgiant.com/talking_strips/talking_strip.mov

The stip is about 3/32 of an inch wide by 1/32" thick by less than 2 feet long. The bumps are very, very shallow: they appear to have been stamped. You can just barely see them in the attached jpg.

I was wondering if anyone has any general tips for how to constuct a machine to make these on a "one-off" scale? The one I have was manufactured in bulk. My background is programming. I have a growing workshop in the basement. Mostly my hobby work is with wood, but I have a retired shop teacher for a father-in-law who is pretty good with metal. I have a bit of experience with electronics and making pcbs.

My initial thought was to source similar plastic strips somewhere, have it on a spool, then feed it over a small platform then to a pair of rollers to grab it, take out any slack, and measure the distance. Over the platform I had planned on having a router that would take away all but the ridges. Seeing an actual talking strip now, though, I think the ridges are too close together. Maybe a solenoid to stamp each groove individually? I thought I'd take the audio from wav files and convert it to the series of bumps. There are several C packages out there that deal with audio. I may even be able to use Flash, though I'm not sure. Now I'm wondering if I'm complicating this too much.

Does anyone have any general tips for doing something like this?

[Stepper Monkey]

Remember the grooves or bumps can be either positive or negative and have exactly the same effect. In your case making them "negatives", or grooves, would be massively easier. No reason to emulate what you see there and feel the need to machine away all but the bumps and make a "positive". No doubt that this was done on your purchased example simply because it was was mass-manufactured using a roller die technique not suitable for one-offs but for mass reproduction of a single item. For it, "positive" was easier and "negative" was more difficult, but you are not using that method so to mimic the profile that way would be pointless.

At first blush, The entire mechanism for creating these could be as crude as two sets of rollers on either end of a two-by-four with a single stepper involved and one or two relays.
Imagine the spool of appropriate material would simply feed through a first pair of rollers on the infeed side with a simple screw and wave spring or something similar to keep them from free-wheeling and thus induce drag/resistance, keeping the string taut. The second set of rollers on the outfeed side would need one roller driven by a single stepper so as to meter feed rate and speed. That is it.
No rotary cutter is probably necessary or desirable for the grooving. Impressions impressed in by an edged tool or wire through either force, heat, or a combination of both would seem to be optimal.
If necessary, a rotary cutter would need to be small and pointed. I would recommend 3/32" or 1/8" shank rotary pointed engraving tools with tips in the .020 or smaller realm depending on material. It will be easy to cut a consistent width of groove, even with a light inexpensive manual handpiece - TIR doesn't mean a thing here, other than adding it in to your tip radius when figuring groove width!

The "Z axis" could be a single stepper by itself (no screw or bearings). I would just clamp the handpiece to the shaft at 90 degrees to move the tip up and down. Two or three steps should do it to move the tip up across a full cut, and another two or three steps down for another cut meaning very fast production, probably even in REAL TIME if attached to a microphone feed!!!

Yes, I do know that means the tip would actually describe a small arc instead of linear motion. Considering the piece you are cutting is 3/32" wide, and the handpiece is likely at least 6" long, does it matter? It is so shallow an arc relative to the depth of cut I am not going to do the Trig. Someone else can if they want, I'm allergic to arctangents.

Besides, if you want to be REALLY anal, the "stylus" playing these things are fingernails. Something with quite a bit of curvature itself, as well as irregularities in profile, thickness, and curvature.
Any discussion of real tolerances and linearity in the talking strings is a joke, as they are inconsequential when compared to this other half of the equation.
All you need here is consistency, and that is easy to do with next to nothing, so don't think you need to overcomplicate to get quality product!

[Stepper Monkey]

Come to think of it, you don't even need a "Z". Using a dremel cutoff wheel attached to a fixed "toy" electric motor mounted parallel to the string feed, you could have the string feeding along very close to the wheel but not touching it. A small solenoid could simply "bump" the flexible string fraction of as inch into the fixed wheel, much the same way a typewriter "bumps" the ink ribbon, thus notching the string.

This means no stepper needed at all, and no stepper driver, only relays.

Just remember you are modulating frequency of strikes, not amplitude. Your sound software should be able to handle this however.

You could control this directly from your computer with no CNC software necessary.

The software app to do this is probably MUCH easier to write than going through all the hardware to do it conventionally - both in building the unit and having the driver hardware, and all that entails to run it software wise, plus converting to g-code, plus getting your software output in a form a CAM program could read, etc.

Just easier to write yourself a direct driver and use discreet electronics to do a non-digital electro-mechanical system based on the waveform output.

Edisons people didn't even go that far to get this same thing done reliably in real time 100 years ago...

[Glass-Giant]

Hi, Stepper Monkey.

Thank-you for the detailed responses. I hadn't considered not doing a full-blown CNC setup. But a full-blown CNC does seem like overkill after reading your posts. I think you're right in that "negatives" will be much, much easier than positives. I do like the idea of the typewriter-like cutting stylus, but I'd have to do some testing to see how much oomph it takes to make a groove (Anybody have any idea where to find spools of plastic 1/32" x 3/32"?). I could do another one with a marker to show separations between different jobs, so I could run batch jobs.

I'm not interested in real-time performance as the intended source audio is intended to be from the web and the audio will likely need to be cleaned up some before it's put on the plastic.

[Stepper Monkey]

I would imagine you could source plastic of the dimensions you seek with some research, but I don't know of anything off the top of my head.
I don't imagine that you are stuck with those exact measurements though, there is probably some leeway there.

Just a random guess not having actually seen one of these, but is there the possibility that the material in your manufactured piece actually started out as 1/16" or so round strand, and was run between heated rollers with grooves engraved into them to create the final form? I have a sneaking suspicion...

Sometimes my old materials engineering past sneaks back out on me. Too long since I worked R&D. My job was essentially finding ways to make the products marketing guys imagined, but then no one had any idea what the actual machinery to make such a thing would even look like. Then they called me to figure it out. With a lab at our disposal, the crap we would make for fun over lunch breaks alone would scare any sane person witless.
I miss that job.

[Glass-Giant]

Yes, I think it could be almost any width, but I think the thickness would have to stay pretty thin to make the groove. I can't really tell if it started out from round, but I don't think so, as the sides seem very, very square. I don't know if that's much of an indicator, though. I did notice the back, smooth side is slightly deformed wherever there's a groove on the rough side.

That sounds like a really, really fun job.

[vger]

The thought just occured to me that one might be able to groove or lay a talking strip on a roadway and the tires of cars would play them. The faster you drive the higher the pitch of course. Just a thought.

[Glass-Giant]

Shhhhhhh... Don't give the marketing guys any ideas.

[Stepper Monkey]

The thought just occured to me that one might be able to groove or lay a talking strip on a roadway and the tires of cars would play them. The faster you drive the higher the pitch of course. Just a thought.

The concept has been dubbed "road music", and yes, it has been tried by several guerilla artist groups, none of which who have it quite right yet. The contact patch of a tire and the size and spacing of the ridges actually makes for a pretty good sample rate though. You can even get stereo imaging between the sides.
The thing you can't avoid is the muddying "echo/reverb" effect from the rear tires passing over the same grooves milliseconds later.
The other thing you can't avoid is the sheer number that you have to attempt to grind into the road, over very long distances, without anybody noticing! That, so far, has kept it from becoming reality.

Maybe if somebody in the South could just use weight to impress grooves into asphalt on a really hot day it could be done quietly and quickly, but up here in freeze/thaw climates its all concrete that would have to be ground out!