Friday, March 12, 2010


first tests building a selective laser sintering printer: part 3

Hi folks,

This is just a quick post, but I thought I'd post some progress:

The ball-joint system that I'd thought up for the pan-tilt mirror in [part2] was a bit haphazard and didn't work very well, so I decided to rethink the whole thing. A gimble would be idea, but placing the steppers right on the gimble axes wouldn't yield a workable resolution, and would need some gearing to make it work. To keep things simple, I wanted to figure out a way to use lead screws (to get that extra precision), without having to worry about printing some gears out.

I was trying to think of a simple system that would allow you to use a lead screw with a gimble, but there are tricky issues where the motor itself would need to pivot. I left the idea with my dad for a week (especially so I wouldn't be tempted to work on it instead of my thesis), and I'm pretty impressed with what he made. There's still some backlash in the nuts, and ideally you could use even smaller steppers (or, servos, if you could find some really tiny, really high resolution ones), but I think it'll work just great for testing!

Right now I'm tinkering with ideas for how fresh material will be delivered over the build chamber. I'm thinking simple, inexpensive, and easy to make... make your mistakes cheaply, after all...

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this last one is a 2 second exposure, where the simple square that i coded into the dsPIC controller can be seen (though it's a little blurry). The test square is about 100 steps on a side, and that translates to about 1cm of travel from about 10-15cm high -- so if the mirror assembly is around 5-10cm up, there should (hopefully) be plenty of resolution for the ~1 inch diameter build chamber.

(ps -- still no luck on finding inexpensive thermoplastic powder, the consistancy of flour. happy to hear thoughts on this that haven't already been covered in the past couple posts).

thanks for reading :)

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Icing sugar?

Vik :v)
Hey Peter! Nice to read, thanks for sharing ;-)

Good luck, may the source be with you :-)
how about the plastic powder used for powder coating car parts? I think that it is expensive and I don't know the consistency but it must be fairly fine and comes in all colors
Cool great work.

The way I have seen laser stearing done (admitdly not for this particular app) is using:-

1. Galvanometers.
2. Microstepping steppers with the mirrors/prisms glued straight onto the stepper shaft. One for X and One for Y. The beam being steared for diaplay purposes (laser lighting effects)
3. Speed regulated motors running continuously witht the mirrors/prisms glued direct to the motor shaft. One for X and One for Y The beam was modulated and synced to the motion to raster scan a target area.

Don't know if this is of any help or not.

PS with the stepper drives the shafts were milled flat enough so that the reflecting surface of the mirror was bang on (orpretty close to) the axis of the shaft.

Maybe this could help:

Respect to Mr. ChaN. I am being using since a few time his FatFs (FAT file system for microcontrollers) and it's great. I remember to see his works wich seems very good.
I remember reading an article somewhere about freezing plastic before grinding to get finer particle sizes. Probably a liquid nitrogen thing so not really scalable to long term reprap use but applicable to prototyping. I figure freeze some pellets in liquid nitrogen and powder in an old coffee grinder. Frozen plastic is much more brittle and shatters far better. Also overcomes the heating/clumping problem which would occur with regular room temp grinding although you might have to keep adding coolant as you grind.
I like the gimble idea for directing the laser. Heres a link to a powder coating supplier that may give you a few options.
For the build area you could also use a "deodorant stick". They have a thread mechanism built into the bottom that you could use for raising or lowering the powder. I have seen them with quite large diameters and may work better than the threaded mechanism you have. Just use google images "deodorant stick" to see several types.
Deep-frozen ice may be a useful coolant.

d taking a deodourant stick apart. Mine had a rod smaller than M8.

Vik :v)
Some deodorant sticks, particualrly the large base ones have a multistart thread in them. I thought you could use the whole assembly as your build area as you have are currently using threaded pipe tubes. Just remove the deodorant, fill the cylinder with powder and you could index the powder down by turning the base screw. The diameters of some are in excess of 30mm so would give you an instantly made indexable pot for your trials.
Thanks to everyone who keeps suggesting powder coatings, but we tried them out in part 1, and they don't seem to work very well. They both have long cure times, and aren't pure polymers (maybe only 50-80%), and I think all that extra stuff in them like colours and flow agents is what is causing them to be particularly brittle when they're hardened.

@pallepirat: thanks for the link! it's really neat to see that setup. i would like to use off the shelf parts as much as possible, so unfortunately i don't think making galvanometers is going to be an ideal solution. :)

@vik: maybe brown sugar, if its really powdered and really dry so there's no clumping... it has to be dark to efficiently absorb the laser beam, remember? ;)

@deodorant sticks :) : that's a neat idea, but i think they'd be a bit flimsy, and the screw would be all the way up the build chamber, in the middle of where you're trying to build! i've actually replaced the piece of pipe i was using as a screw with a long bolt, so there's lots more travel on the chamber table and it's just generally a bit nicer to work with. I think the build chamber should be about ~30mm dia by about the same in height right now, which is plenty for a test! :)


right now I'm trying to think of different methods to get the powder onto the build chamber -- coming up with a powder feed mechanism. typically folks use two chambers -- one that indexes down where you build, and one that indexes up with new material. they will then use a roller to roll material from the supply chamber, to the build chamber. i'm trying to think of a simpler way though, maybe something with a feeder...
Not sure if anyone is still reading this (or if you've tried this idea already) but another possible source of plastic powder might be plastic blasting media for "sand-blasting". It's, relatively, cheap and can be gotten in assorted colors for, potentially, better light absorption. It, also, comes in pretty fine grades.
How about laser toner?
Laser toner is basically plastic + colour.
There is some health risks usig such fine powder
Hi Peter,

... i've made some tests with sil-rock-spheres from sil-trade:

That are mostly uniform spheres of molten granite around 0.1mm in size.

With a 2Watt-Laser @1070nm focussed to 30 microns i evaporated them and they recondensed to even smaller spheres ... a 1Watt-diodelaser @808nm melted them when focussed to 0.06mm, but hadn't enough power to fuse the droplets with the base.

Now i have 5Watt-diode-lasers @975nm i can control from 0.4 to 5 Watts, so this could be a good option for a restart.

A good material for fusing experiments could be toner from laser-printers or copiers ...

Hi Viktor,

That sounds interesting. Where are you picking up these lasers? I'm looking around for a laser to see what I can find, and while I've been looking in the 250mw range, I keep seeing lots of 1000mw 808nm diodes on ebay, and I figure these would probably have a chance of being able to fuse both black and (potentially) white plastic material too. The tricky part is that they're just bare diodes, and I'd have to build a collimating and focusing system around them, too (and, it'd be nice if it was just all one unit).

In my first post about the SLS printer I mentioned how we'd tried to use both laser printer toner and a few different kinds of powder coatings, but the test pieces were *very* brittle when we took them out. I'm guessing it's because the mixtures are only part polymer, and there's a lot of carbon and other things in them (including flow agents, in the powder coating case) that make them good for their particular applications where thin films are required, but probably not particularly good where you're trying to build something large and solid out of them.
pa-12 powder sources
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