I have a computer file of a vector image. I would like that image to be scratched (not printed, not milled, but scratched) into a surface (which can be an appropriately-soft material like plastic). Is there any sort of machine that can do that? I’ve considered, for instance, using a CNC mill, but with the bit replaced by a stylus (I can get access to a ShopBot). Is that a thing that can be done? Is there something else that would work better?
I’ve already tried using a laser cutter, and that didn’t work for my purposes, since the scratches need to have a smooth edge.
More than you’re looking for, probably, but yes. In 1969 I programmed and operated a Gerber Autodraft plotter, a wet-ink device using Rapidograph drafting pens for paper and Mylar drawings usually. One fairly common job was creating etched masters for Lithograph presses. An aluminum plate, coated with a substance to mask the ink, had to be etched (scratched) precisely so as to not damage the aluminum. To do this, a scribing tool was used instead of the Rapidograph pen. It wouldn’t surprise me in the least to learn there are still some of these devices around. (http://www.gerbertechnology.com/about/fast-facts/)
Perhaps an engraving machine? My father-in-law ran a small engraving business, and he used a computerized engraver. He could engrave logos and rather involved symbols, so I imagine vector images would work.
The cutting tools he used varied by the material he was engraving – i.e., whether it was a brass plate or that coated plastic frequently used for desk plates or dial indicators. I suspect there’s a cutting tool available for the material you want to use.
How large is the image you want to “scratch”? The main problem with an engraving machine may be a size restriction. I suggest you try an engraving company in your area and see if they can help you.
In fact, goggling “Gerber plotter” or Gerber Cutter" provides links to a variety of machines that will cut soft (vinyl) or hard materials.
In the early 70’s we rigged up a wide bed Gerber Plotter to translate the very first CAD program outputs to ~4’X6’ Rubylith sheets (if younger readers are wondering why we would use area rug-sized sheets to produce microelectronic chips, follow the Wiki wormhole in the link).
For a first trial run, I’d be looking at something a few inches square, though if I get all the bugs work out, I might move up to as much as a few feet. There are no set size requirements I’m working to (it’s all just art), so if the machine I’m using has a limit, I can adapt to that. The depth is “deep enough to be visible”, with the ideal probably being pretty shallow, since I want the scratches to be very narrow (my current design assumed 0.12 mm, but narrower would be better).
Hm, I hadn’t even considered one of those. My sister actually has one, but the one she has can only be used with authenticated designs sold by the same company (a fact she regretted very soon after buying it). There’s probably some way to jailbreak it, but I doubt she’s interested. On the other hand, if I can get this to actually work and want to do a lot of it, that might be a good way to go (much cheaper than a Shopbot).
OK, so the folks at the shop aren’t likely to look at me like I’m crazy, and are likely to have the appropriate attachments. That’s good to know.
It looks to me like you want something like this. It’s a spring-loaded diamond drag engraver that fits in any 1/4" collet.
You would want a spring loaded tool for a Shopbot–those don’t have enough vertical accuracy to get a scratch with a specific, repeatable depth to it if there is no compliance. The spring allows some unevenness in Z (whether from the machine or the material) without an obvious effect on the scratch width.
A “real” CNC machine like a Tormach does have the needed Z accuracy, but that’s really getting into overkill territory.
The stylus wouldn’t necessarily need to be diamond. While I could use a hard material like metal or glass, I don’t need to: Anything smooth and glossy that’ll take a scratch would work, and it’s easy to make a tool that’ll scratch plexiglass or solid styrene.
Is “drag-scribe” the standard term for the attachment I need?
Drag scribe, drag engraver, drag etcher–something with drag in the name, to distinguish it from rotating tools.
The diamond is not really the part that makes the tools semi-expensive. It’s the precision in the shank and sliding portion that gives it some minimum cost.
I asked my wife about it and apparently the new ones have something called a ‘Cricut Design Studio’ that lets you modify your own designs. Might be worth looking into.
So I poked around on the website of my local public makerspace, and it looks like they don’t have any drag tools for their machine (I e-mailed them to be sure, but haven’t gotten an answer). They do say that users are welcome to bring in their own tools to use with it, but I’m not willing to drop fifty bucks on this, especially since I don’t even know for sure that it’ll work.
Still trying to figure out some other way to make this happen…
Find a retractable ball-point pen made from hard plastic. Take out the ratcheting mechanism from the rear so that the clicker is always pushed out. Ideally, add a spring from another pen to increase the force.
Find a scrap tool of some kind–HSS or carbide. Either something really small, or with a sharp point, or even something that broke in a way to leave a point.
Attach it to the pen clicker in some way. Heat it up and melt it in, superglue, whatever. It’s an engraver and doesn’t need too much force. Try to center it, but don’t worry too much if it’s off; it’ll just have a minor XY offset as long as it doesn’t rotate.
Mount the “tool” in the Shopbot collet (1/4", something like that). The pen is plastic so it there should be plenty of tolerance for just forcing it in, but if not you can find the next size up and wrap tape around the pen until the diameter is close enough.
The pen is long and wobbly, but if you move slowly and cut only soft things (plexiglas, etc.) it should be ok. You’ll have around a centimeter of travel; calibrate the Shopbot to use around half of that. Make sure the Shopbot doesn’t enable the motor. Wear eye protection in case it does and your hackery centrifuges apart.