Monday, February 15, 2010
first tests building a powder-based stereolithography printer: part 1
i'm a bit sleepy, but i thought i'd post this while it's fresh:
after seeing really interesting powder-based printer designs like this one, that place down a layer of powder then "print" a binding material onto it, i began to wonder (as others have) if we could build a similar setup using ABS powder and a laser diode to fuse the material together. designs like this have a bunch of benefits, including the potential to use the powder as it's own support material. (and, after a few weeks of tinkering with building an extruder for a second printer that *constantly* clogs, i think i needed a break to think about better days when we won't need to rebuild extruders, or hope we build working ones in the first place... ). my goals for this tinkering are to build things with common off-the-shelf materials wherever possible, and so I went searching for some form of ABS powder, as well as a laser diode.
After some searching, it looks like ABS powder really isn't easy to come by, and it's most often found in pellet form. Zach had a similar idea a while back ( link ), and so I asked him if he'd had any luck. He said he never got past the materials research stage, but that polyester-based powders used as powder coatings sounded promising since ABS powder was so hard to come by.
I figured that if I was going to use a DVD burner laser, I'd need some black powder to absorb the radiation (since a 250mw red laser is relatively low power to melt plastic that isn't black). I sent an email to our local hackerspace in hamilton, thinkhaus, and folks were really encouraged by the idea. One of the folks there, jason, ended up finding a local place that manufactures powder coatings. I called up a fellow there and told him about the idea, and he was extremely kind and prepared up some samples of black powder coatings, one a polyester, and the other a polyester-epoxy hybrid. jason and i did some tinkering with both these as well as some laser printer toner (since it's carbon mixed with a polymer). jason tried both with the hackerspace's laser cutter, as well as just heating a bunch of the stuff up in a popcan. in both cases each powder (polyester-based, polyester-epoxy hybrid, as well as laser toner) fused, but the product was VERY brittle. the pop-can tests that melted material to be a few millimeters thick showed that the problem seems to be with the material itself -- unfornately, even relatively thick pieces would snap pretty easily. (though powder coatings do contain quite a few different materials in them for curing, flow, and pigment, so it's quite possible that some particular combination might work).
so, not much luck on that front. i would really like to get my hands on a good couple of cups of black ABS powder, or make some. (random thought: i think the size of the powder will be fairly critical -- ideally one would want to maximize the ratio of surface area to volume of each little ABS grain, such that the laser diode could more easily heat up relatively little volume).
so, i decided to work some on a little test rig to try out different powder materials (and, conceivably, with some better seals, you might even be able to use it for liquid stereolithography). i figure that you don't need a great deal of print volume to test if the material is viable or not, so i decided to make a "mini stereolithography" system -- infact, it's almost pocket sized, save some of the larger mounting bits.
here's my progress so far (in picture form):
(click on the thumbnails for much larger versions)
first i went out and picked up this DVD burner. it's a 24x (the fastest i could find), so the diode in it should be around the 200-250mw range if memory serves. (clearly here i should add in the usual warnings -- LASERS CAN BLIND YOU AND THE FOLKS AROUND YOU INSTANTLY, unless you know exactly what you're doing and take appropriate saftey precautions, you shouldn't attempt this!).
off came the cover
and here's the diode -- it's even labeled (the pins are DVD, GND, and CD). The CD one is likely infrared, and even with lightscribe likely only within the ~40mw range -- so not too useful. But still plenty powerful enough to blind me instantly, and invisible so I'd never know. So I left that pin alone! :)
i soldered some leads on the diode, and tested it out to make sure the pins were correct, and to get an idea of the voltage.
even though the diode was still in the focusing housing, i thought i'd give it a try to see what sort of heat it could produce on some black plastic. the focus of these lenses is on the order of about 1mm from their surface, so the material has to be up pretty close.
having the diode on for a couple seconds heated it up pretty well, and i tried moving the head back and forth a bit and it produced a really faint line. so, it works, but i decided to take the diode out and not deal with all the optics in the DVD burner that weren't really required for this.
there are lots of interesting beamsplitters and lenses and such in modern CD/DVD combination readers/writers, and i often save these bits for tinkering. the diode was epoxied in, so it took a little bit to get it out.
i put some wire wrap leads on the diode
and tested it out. for some reason i remember reading the current should be around 200-250ma, but i'm not sure where. this turned out to be about 2.5V for this diode.
a quick test with the diode right against the surface --
this worked *much* better than when the diode was within the DVD burner optics, and even quickly turning the power on and off yielded distinct melting.
being a laser, the beam should be coherent and come out in a straight line with some width -- so i decided to see if i could get the same results from a bit of a distance -- a few centimeters above the plastic. unfortunately the laser beam divered quite a bit, and this didn't yield any melting, even for quite a few seconds of exposure.
(as can be seen here -- no melting under the raised laser diode configuration)
i had wandered around home depot for half an hour or so for ideas to make the indexing build chamber for the powder. i figured that a simple idea would be to just make it round, and find two pieces of pipe that fit snugly within each other -- the outer one would be the chamber, and the inner one would have a little piece put over the top to act as a "table", and index down within the larger outer pipe by a small lead screw or some other mechanism. here are the various pieces of pipe that i found. i think the outer pipe (the black one) is around 1.25 inches in diameter.
here are the critical bits. there's the black outer pipe for the "chamber" (left), a smaller white pipe that fits right into it that's threaded on the inside to be the "indexing table" (right), and a third pipe that screws into the "indexing table", that acts as the lead screw (center). you could attach a stepper to this, or just index it down manually.
here's the "indexing table" piece (top) fitting right into the "lead screw" (bottom).
and here's the whole idea, where the "table" and "lead screw" fit with the "chamber".
they fit together something like this, where the "table" ends up mostly inside the "chamber", starting mostly near the top but being able to be pulled down quite a bit. the "lead screw" piece is always outside of the chamber, and doesn't move up or down. (the "table" would index up or down, while the "chamber" and "lead screw" parts would be vertically stationary).
i foraged around looking for something to build the actual "table" out of, and was thinking plastic or even cardboard, so that you'd get a bit of a very rudimentary seal around the edges (although it's probably not critical if a little bit of the material leaks out). one of the folks at the hackerspace offered me some dense foam, and it seems like an even better idea than the cardboard -- it's pretty stiff but also a bit flexible, and expands to form a seal while still making it easy to move the table up and down! i cut out a circular piece to fit the "chamber", about 5 to 10mm thick.
checking the fit, it was nice and snug, but easy to slide the table up and down. i epoxied it to the "indexing table", making sure not to get any onto the "chamber".
it was around this time i had a crazy idea, and noticed that the "chamber" happened to be around the same size as the hole for the spindle cap in the DVD drive! i was thinking about how to mount the table, and decided to give it a try, so i cut out the spindle cap cover.
and removed it, revealing a nice perfectly sized hole!
AND it looks like everything fits! the chamber fits right ontop of the hole without falling in, while the table slides right through it with a bit of space to spare.
look at that!
the indexing table needs some guide rails to make sure it only goes up and down, rather than spinning in place, when the lead screw is rotated. i found the rails used in the DVD burner, and made up some slides and holders out of acrylic.
from top to bottom, here's the foam table proper, epoxied to the "indexing table" piece. the indexing table has a plastic guide (two holes, drilled in a piece of scrap acrylic) superglued to it. the "lead screw" screws into the indexing table, and beside the lead screw at the base is a keeper for the rails, also made out of some scrap acrylic. everything is resting on a piece of scrap acrylic that's being used as a base.
and here it is with the chamber on top, too.
the bottom of the "lead screw" should be resting flat against the base, and after measuring everything when the table was indexed all the way up, i determined that the setup would need a bit more height than just the DVD drive cover would have, so I brought it up a bit with some L-brackets. (it actually needs to come up a bit more, but I didn't have any larger brackets, so I made up some little acrylic spacers for screws, too).
and, here it is all together. too cool! :) i drilled some holes in the metal DVD case beside the spindle holder aperture to act as upper keepers for the guide rails.
so, that's my progress so far, and now i'll have to forage for some tiny steppers to both index the table, as well as move the laser on the x and y axis. the travel is extremely small -- the build area will be about an inch in diameter, with a height of about 1cm. that's pretty tiny, but should be more than enough to test different powder materials to see if they can successfully build very small parts with sufficient structural integrity. the neat thing is that the whole thing can come apart pretty easily, so it can be washed out to prepare for a new material. hopefully once the steppers and axis are on there, it'll still be just as easy.
hope you've enjoyed my little story! (and i hope my supervisors don't read it -- i'm supposed to be working on my dissertation).
I am very happy to see someone working on this direction!
I am being always curious about laser and I will continue to look on your reports here on this blog ;-)
I like the re-use element - the more you can re-cycle, the less it costs.
If you can focus your laser in the 10cm away range, how about using two Galvanometer-mounted mirrors for the scanning instead of building an x-y table?
Seems to me like it would be cheaper and much easier to build, and maybe operate faster too.
You can get galvanometers from analogue amp-meters, then just strap them on to a couple of DACs
R-2R networks on a stack of digital outputs, or just PWM might do the job for a first test if you don't have any DACs handy (might need an op-amp follower though)
Building a plastic grinder could be simple enough too
Would be really nice if this got somewhere, good luck !
I have quite a few old CD drives but only some are writers.
In your pictures you can see the Infra red lazer light that he camera can see easily ~ is there any indication that the laser is on without a using a Digital camera?
Very creative reuse of DVD burner parts!
You can me ABS powder by dissolving it and oversaturating the solution. Forrest has experimented with this as well. You can find an example on his blog, I assume.
I also think that scanning with galvos might be a good option instead of mechanically translating X and Y. Though fro a proof of concept, go with whatever works for you!
@jonathan: at first i was thinking of making a little x-y axis instead of a steerable mirror, but i'm starting to think that if i can get the laser diode to emit a nice straight coherent beam with a width of ~0.5-1mm, then a steerable mirror might be a good, interesting, neat addition to the project.
i've never used galvanometers, so i'll have to google them. maybe also a solenoid or something that you could REALLY precisely control the height of would work, too?
@bodgeit: the diode contains both IR (CD, ~808nm, ~40mw) and visible (DVD, ~650nm, ~250mw) emiters. I'm using the DVD one (far more powerful), which is red, and visible to the naked eye (although you'd never want to see it, or it might be the last thing you ever saw...)
A CD writer likely would work, the laser isn't very powerful in those.
@Reinout Heeck: I think I'd need to make a block of ABS and then chew it up with the belt sander if I go that route. Unfortunately I don't think there's an ideal belt sander that I have access to to go that route, so I'll have to keep looking/thinking.
@Erik de Bruijn: Thanks for the idea. I had read that dissolving method with acetone on Forest's blog, and it looked like it both stripped the ABS of colour (it needs to be black), and one commenter had mentioned that it was stripping the ABS apart into its three component parts -- so it didn't seem partcularly ideal. :)
Also, if you ended up with stuff that was anything like what we used, the curing temperature is much higher than the melting temperature. Our powder was supposed to cure at 400F, but would melt (and presumably adhere) at a mere 200-ish Fahrenheit.
What precautions are you doing/using? If I want to follow your steps, what protective material can I use? what is yours, where did you get them?
1. Laser diodes give a light the has a single wave length - which does not necessarily mean that it is a bundled beam. That's what all the optics in the DVD drive are for. All lasers need lenses if the beam is supposed to stay bundled. Here it is probably much simpler to move the diod right over the powder.
2. to heat the plastic, you need much more eneergy than the laser provides. But all you need is getting the powder from the solid form to a liquid where it fuses. If you pre-heat your build chamber to just below the melting point and then use the laser to merely add the few more degrees that are required to fuse, your DVD laser will probably be good enough.
Simply shine an IR light at the top of you powder layers and control the temperature. Yourplastic pipes won't do though... .
I've tacked up the text and the first photo here:
(I hope the name and wiki page are ok?)
You may want to have a go at the wiki page if your supervisors aren't watching.)
False Data said...
Very interesting! For obtaining powder, I've been wondering for a while what a Surform rasp (also known as a Microplane) would do to ABS. It looks like rotary microplane rasps exist. If one could reliably produce powder of the proper size, it would also be useful for recycling old printouts.
We do need to try it; I've been kicking the idea around for a little while.
1000mW 808nm diodes for 20 bucks
Mycroftxxx: the powder was pretty easy to get ahold of (like you said), but unfortunately because it appeared so very brittle in our heating tests, even for 2-3mm thicknesses, i'm not sure that it will be useful as a powder print material.
Casainho: i'm not qualified to advise anyone on laser safety, but i took a number of optics classes and labs in my undergrad, so i have enough knowledge to keep myself safe, i think. i think legally the only advice i can give is not to attempt to do it, and that if you have to ask how to keep safe, then you probably don't know enough to work with high powered lasers. vision is so very precious, and not something to risk at all.
Matthias: 1) after some reading i found the beam isn't collimated, like you said. i think finding a complete module would be the best solution to this, rather than having to design a mount for a little collimating lense, etc. 2) i had that very same thought! while i think its fairly likely the laser will have enough energy to melt the plastic powder (it seems to melt black plastic pretty well), adding a heated build chamber might make this process much easier. even strapping a power resistor to the chamber to bring it up to ~70C would probably help out.
Sebastien: sounds great! i'm very happy to share the project information in the hopes that it will be useful to the community in general. feel free to use any of the pictures in the wiki!
Rjizzle: unfortunately those are invisible, which would make both safety as well as aligning the optics a bit difficult. too bad too, since they're so much cheaper than visible diodes!
Awesome project! keep it rolling.
Not really, the lasers actually alter the reflective properties of a Dye on the bottom surface of the 'top' layer of the CD:
The plastic CDs are made from is specifically designed to be transparent at the wavelength the lasers operate at, so the head can read the pattern in the dye, and therefore will be very hard indeed to melt with CD drive lasers...
Thanks for the overzealous interest nonetheless :D
Interesting project indeed. There is one thing to point out in my opinnion regarding laser safey: wear Laser Goggles al the time!
They cost around 150$ which is a lot and you need some matching the wavelength of your laser, but it is the only way to keep your eyes safe.
So, what if you tried sintering some polyester powder, heating it, then dipping it in some liquid wax (or other low-melting temp plastic)?
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