Monday, May 28, 2012

Our Own 3D Printer

Mary Lynn and I have finished building a Printrbot, which is a 3d printer that comes as an assemble-it-yourself kit. It's a pretty cool contraption, but I want to give a very important warning for anyone who reads this post and thinks it would be cool to build their own Printrbot:

This is not like a piece of Sauder furniture that anyone with an Allen wrench and an hour of two of free time can put together. The Printrbot kit is a nearly-complete set of parts that a sufficiently talented individual with all of the proper tools could probably put together and get working after several days of tinkering and adjusting and calibrating, with several trips to the hardware store in between. The online instructions are woefully incomplete. The kit doesn't come with enough screws or nuts, and some of the plastic and wooden parts are slightly out of true and will need to be modified. Furthermore, achieving a good print requires several modifications to the print bed, which include tape and glass and cleaning solutions and so forth.

So I would advise you to only go in for a Printrbot if you really want to get into a fairly involved and technical hobby. That said, if you're still willing, please take into account the following recommendations:

  • Yes, the Printrbot kits with the laser-cut wooden parts do look nicer, and the Plus version does have a bigger print surface, but you should really, strongly consider going for the basic model. The basic model (from what I can see) has fewer parts and is much better documented.
  • Be sure you know the hours of your local hardware store. You'll be going there frequently for additional screws and nuts, and possibly for new tools.
  • If you really have to have one of the laser-cut kits, be absolutely sure you spend some time finding videos and pictures of the various sub-assemblies. It's very easy to assemble some of the bits backwards, and you may not notice something is wrong until you've gone way too far to back out and reassemble without physically breaking something.
Here's a picture of our Printrbot, fully assembled, in the middle of a print:

What it's doing is laying down a thin layer of melted plastic in a specific calculated shape, upon which it's going to put down another layer, and then another layer, and so forth, until it has built up a complete three-dimensional object.

So far we've printed a wire guide, a six-sided die, and part of my company logo. We have future plans to print parts for Mary Lynn's aquaponics farm and parts for some of our games.

It's amazing to watch this thing in action. You start with a 3d model (possibly something you've whipped up in Blender) which you then convert to a set of pathing instructions. You feed the pathing instructions to the software that drives the print head, get everything to the right temperature, and let it go.

It's actually a kind of musical little device; the motors hum at different pitches based on their speed, and so when the motors are making a series of rapid tight turns, it sounds like it's playing a little tune. So it's functional and artistic!

Just to give you an idea about how complicated this thing was to build, here are some photos of the assembly process, as it occurred in our household:

Above, you can see all of the parts that came in the kit, fresh out of the box. Doesn't look terribly complicated, does it? Looks, in this case, are very deceiving.

Here's the base. We opted for the model with the laser-cut wooden parts, which still smelled faintly of scorched wood.

After adding some hardware to the base, and assembling the print head carriage and bridge, we had this:

Here's a closer picture of the bridge and carriage after we attached them to the base, with the hot end installed:

We actually built the carriage backward, left-for-right. The carriage is the thing that big gear is sitting on top of. Can't tell from the picture that it's wrong, can you? There's a slight difference in one of the two side pieces that is constructed to hold a screw that serves as part of the left-right end stop. We had it in the wrong place. Mary Lynn had to modify the end stop design to compensate.

Oh, and you see that spot on the gear where there's a black curve drawn in permanent marker? We drew that on the gear to help us resolve an issue caused by the fact that the gear wasn't printed quite perfectly. Some of the parts of the kit were actually printed by another Printrbot: basically any of the white plastic parts you see in the pictures. The gear gets threaded onto a big metal bolt; obviously the gear needs to ride perpendicular to the bolt in order to spin correctly. Our gear rested on the both at a very slight angle out of true, causing it to wobble slightly as it rotated. We had to sand down part of it so that it wouldn't rub against the housing, and then spent hours trying to modify the bolt and gear to get the angle correct. We never did get it perfectly perpendicular, but we got it close enough.

Speaking of problems with the plastic parts: the items printed by the Printrbot is reasonably solid and sturdy, but they're vulnerable to certain kinds of stress. Remember, they're built up of many thin layers of plastic. If you can get something in between the layers and twist, the layers delaminate and split apart. Normally this is not likely to happen, but some of the gears in the kit require you to insert a screw near one end, which you need to screw down in order to increase tension and hold the gear tightly to the motor axle. If you tighten the screw too much:

Can you see the split in the plastic, to the left and right of that little screw hole near the top of the gear? That's what happened when we tightened the screw too much. And, of course, the kit doesn't come with spares.

Fortunately, the ABS plastic can be dissolved and re-set with the strategic use of acetone. We applied a little to the inner surfaces of the plastic where it had split, clamped it down, and let it re-set overnight. In the end, the fixed gear looked like this:

You can still see the split, but the gear is holding together.

The bed, which holds the printed object as it's being constructed, turned out to be a whole project by itself. Here's what it looks like when just the parts of the kit are used:

That red square is a heated surface. It needs to be nice and hot so that the plastic will stick to it during construction. If it's not hot enough, the plastic doesn't stick, and will peel right off during the printing process, giving you a glob of plastic instead of a nice 3d model.

But temperature isn't the only factor. The bed needs to be fairly flat, and the hot end needs to start printing extremely close to the bed so that it "squishes" the plastic down onto the bed, and of course the surface needs to be nice and clean ... after some research, Mary Lynn wound up laying a sheet of glass on top of the bed, and then sticking a layer of blue painter's tape on top of that. If you go back to the very first picture of the Printrbot, near the top of this post, you can see what it looks like. She spent days getting this together, experimenting and adjusting and fiddling and so forth.

Mary Lynn has some good "action photos" of the Printrbot making various things on her Picasa page. You'll see various failures and successes there, showing what happens when the machine works the wrong way and when it works the right way. It's still not perfect; you can see in the photos where the plastic didn't stick down to the bed here and there, around the edges and corners, leaving the model looking slightly incomplete at those points. We never did get a complete print of that shark thing, but that was the first thing we tried printing; we could probably do that one again and it would come out fine.

Now that it's basically working, we're going to move it to a more permanent location downstairs so that we can have our kitchen table back. Then we'll have our own little custom manufacturing studio.

For anyone wondering what possible practical use this contraption will have, I recommend visiting the Thingiverse web site, which is a public repository of items that other folks have designed for printing on 3d printers. The items range from useless to artistic to "oh, wow, that's exactly what I've always needed!"

It's a long way from here to assembling our own robotic army for purposes of world conquest, but, you know, baby steps.