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3D print figurines have inherent stability issues because they are made of different materials that are often moveable such as the arms and head of a doll. Disney research has come out with a white paper that provides a stability solution to these 3D prints through inserting weights to the product as it is being printed. Tom and Tracy talk how to address modeling the inside of the part and some of the complexities of creating stable 3D prints or even prints that are meant to sink if thrown in the pool.
Listen to the podcast here:
Stability Issues in 3D Printing
We’ve got an interesting discussion today, sponsored by the folks at MakerBot, around a white paper that’s been published on the internet having to do with inserting weights and movable masses within 3D prints. It’s quite intriguing and looks at stability issues in 3D printing figurines and other objects that are meant to be moveable.
It’s from Disney Research, that sounds cool, Disney Research Labs. Predominantly, they’re talking about a lot of 3D models that have movable masses. You can imagine they’re making figurines with movable arms and legs and things like that. You’ve got a lot of issues with stability and how it stands, falls, sits, does whatever it supposed to do. You’ve got a lot of issues in dealing with that.
A lot of times, when we make toys and other things, when you’re making them, you make them out of many materials. Dolls’ heads are typically made out of a more rubbery material. Because they’re made of multiple materials, they have different stability properties, different weight properties. When you’re 3D printing and you’re 3D printing in one mass or one piece, you can’t quite deal with it the same way.
It looks like they spent a lot of time figuring out various methods to enable the design models, to have that complexity, but still have a balancing behavior that they were looking for. I think that’s really interesting that they’ve managed to come with that. They have a lot of issues where they want to suspend things, make them stand, they also want to immerse things in water and other things like that. They have a lot of objectives that they want to achieve and they’ve done a lot of research on how to make that happen.
It presents some interesting challenges though for 3D modeling and 3D printing when you think about it, because most of the models that we all create for 3D printing, we’re creating a solid model, the outer shape of it. We’re not paying any attention what’s going on inside because the slicing software takes care of that for you. We don’t really think about it as much anymore.
You don’t model the inside of a part typically, you model the outside of a part. The outside is what we all care about. The slicing software takes care of the inside with whatever percentage of infill you want. Maybe you decide whether you’re doing a hexagonal infill or just a grid or more of a diamond shape. You have a few options. We don’t typically model the inside.
That actually can also be tricky. I’ve experienced it actually where I’ve wanted to create a hollow region inside a model. Some CAD software actually has trouble doing that unless you were to make it not just hollow inside but also have a dimensional path bringing that internal cavity to the outside as well. It becomes a part of the outer shell of the model but going inside as well. If you just try to put an open space inside, on certain CAD softwares that doesn’t work well. Some CAD softwares are better than others at it. It really present some unique stability issues in 3D printing or challenges but very interesting ones as well.
In this white paper, they talk about having some things that would be submersed in water, let’s say. Maybe you’re making a bath toy or something. If you were 3D printing a bath toy, PLA, ABS, it’s also lightweight. It would just float on top of the water. If you wanted to make a submarine or a dolphin or a fish and you want it to not sink all the way to the bottom either but not float on the top, you could put a little weight in that and offset the displacement of water that it would do and find the right balance and suspend it. It’s a pretty cool idea.
We should reference back to our pausing 3D prints episode that we had in the past where Vicky Somma shared with us her method for inserting mirrors as she was printing. You’re pausing the print and then you’re inserting something. That’s a great idea here, being able to insert that weight in there and it’s completely trapped. In a predictable way, actually build it in your G code, in your slice settings, that it’s going to pause at the right point so you can insert whatever it would be. In Vicky’s case, it was a mirror.
It could be ball bearing in the case of some of the things they’re doing in this white paper. It’s interesting because these cavities, when Vicky was doing it, she was inserting a mirror and just capturing it tightly. It wasn’t a movable object. That’s where this white paper and this new thought of inserting a movable object inside a 3D print is really cool and interesting. You could have let’s say an animal figure, a dancing bear, whatever. You have a figure and you have a ball bearing that there’s an internal chamber where it can move. You want it to balance on one leg and it looks like it would topple over, but because of the weight of the ball bearing or whatever’s inside of it, it won’t.
It could slide from one leg to the other or maybe up to an arm and then you flip it completely upside down. Maybe it’s a diagonal path from the left leg up to the right arm. You can then tip it over on the right arm. Looking at it proportionally, the thing should fall over but because of the weight, it won’t. It’s cool stuff.
I’m thinking back to the minion chess set that we made for our nephew Tyler. It would have been really smart if we had 3D printed the bottom piece and then inserted the weight because they may fall out. Although it’s probably great because he can rip off the quarters when he needs some money.
It didn’t really occur to me to do that. It probably would’ve saved us quite a bit of time removing some support material inside of there. I could’ve modeled it and printed it. I guess some of the outside portions needed support. If they didn’t, you have to make this interior cavity. If you only got it up to that height, you might not have needed it. You probably could’ve gotten away with it before you put stuff on top of it. Then you needed weight for that next piece.
Those chess pieces needed weight. I looked at washers and some other things. I ended up using quarters. I’m sure somebody who’s really patriotic is going to be unhappy with me for doing that. Tyler will be happy one day when he tears them apart and uses the quarters. I don’t think that matters.
It was really necessary on those chess pieces. Some of them got pretty tall, like the queen and the king and some of those. The plastic we 3D print with is pretty darn lightweight. You needed to make sure it wasn’t going to fall over so easy and give it a little, the quality of having little more weight to it.
That’s a really good point. It’s one thing if you’re about to do 100% infill or something like that in places and it’s then just heavy enough. In this particular case, it wouldn’t have been heavy enough. You really needed that weight because of the way you were using it. Some parts that you would be able to get away with for doing 100% infill on other areas more open, it just depends on what you’re making of course.
It depends on the material. I think if you were using one of these metal infused filaments that would work better or there was another filament we saw I think at a trade show quite some time ago. This particular filament that we saw that it was not glossy, it was very matte finish. It came with only three colors. It had some purpose for it but it was very heavy. It had a lead feel. It was a really heavy filament. That was like almost two years ago. It was a long time ago. We’ll have to look it up and we’ll refer to it in the show notes at 3DStartPoint.com. I’m sorry we don’t have that for you right now. It was cool material.
If you had a dual extrusion machine, you could then print part of it in one material and then a heavier weighted part in a different material. In this case, if you didn’t like the color because it was only available in limited colors, you could still skin it in the original color and you could put that weighted material on the inner portions only.
I’d like to throw in another thing for our listeners to consider. As I was reading this white paper, looking at it, it’s fascinating stuff on stability issues in 3D printing. You read about action figures and things that have ball and socket joints for moving parts. All the parts are so light, to have some weight in there, help keep it where you put it once you put it there may make some sense.
Stability Issues in 3D Printing with Magnets
I had another thought as I’m looking at this. I’m like, not just having weighted parts and balancing them in interesting ways is intriguing. To me, taking very small magnets and embedding those in. Not to be movable inside the part, but like Vicky did with the mirrors or something, to embed a magnet. You could then make a refrigerator magnet. It’s always very frustrating to me. It actually happened today on our refrigerator, believe it or not.
As I’m fixing dinner for the kids, a magnet … Not the magnet, the ornament I guess that is what we want to see on the refrigerator came delaminated from the magnet itself. Happens all the time. Why not 3D print a cool refrigerator magnet but embed the magnet in the plastic so it’s captured, it would never separate. Some of these magnets, those more ceramic magnets, if they drop to the floor, they can break anyway. You’d protect that from happening too.
Even making an interesting little puzzle toy or something 3D printed where the magnets hold them together. We have those magnetic construction block type things that the kids play with. The girls love those. We’ve had some that are made of wood that have magnets embedded in them. We had some others that are plastic where it’s more architectural, like they’re building structures. The magnets are only outer corners of it.
Magnets are not that expensive. You could easily plan an interesting 3D print and embed magnets in there. I think if you’re an educator and you’re dealing with principles of physics, some of these issues of weighted 3D prints or magnets and building structures, I would think there’s some great lessons there that could tie into an interesting new project for course curriculum.
That reminds me, I don’t think I’ve seen anywhere out there on Instagram or anywhere else, where I’ve seen somebody creating 3D printed accessory type pieces to go with that magnetic block set. The girls are always like, “Oh, I want to window here. I want this there.” That would be very cool. I haven’t seen anybody doing that. You could embed the magnets, so maybe that’s why nobody’s thought of it before. We’ll put a pic of the set we have, because our daughters build it all the time. We have this cool set and I really like it. It’s really well made.
I remember that our daughter, our seven year old was trying to build a structure that spanned a larger distance than it was really intended to or meant to span. What she wanted to construct, she really needed to do it, she needed it to stretch or something. It didn’t have the right kind of pieces to be able to do it. Why not? We’re always working with her. She’s doing her projects this Christmas of 3D printing bookmarks with people’s initials on that stuff. Oh my God, they’re adorable too. It’s really cute.
I think that she would get into that project, we could do that together and have a lot of fun with it. As we were talking about inserting weights, I think you’ve got to consider magnets. Because they’re always making them into castles and towers and they’re not really tower-y. They don’t have that turret look to them, which would be very cool.
One important note I want to mention, if you’re going to 3D print and insert a magnet, I don’t want anybody to hurt their 3D printer or hurt what they’re doing. Most FFF 3D printers use a brass nozzle. That’s great because brass is not a ferrous material and a magnet will not stick to it. But I have had one or two 3D printers, like when we had the Airwolf 3D Printer, those nozzles were not made of brass.
Before you go and do it, just take a magnet that you’re interested and touch it to your nozzle and see if it sticks to it before you go and do it. Double check. Because you’d hate to have it be all right, you pause your print and you place the magnet in there and you start printing again and also the magnet lifts right up out of the part and then attaches to you nozzle or your print head or anything. Just beware. I don’t anyone to damage their equipment.
Stability Issues in 3D Printing Objects with Hollow Insides
I was also thinking as we were talking about this a little further, just the idea that you could even do something where you were creating sound on the inside of the thing as you turned it over. We had been talking about the puzzle-y type thing or just having the ball bearings flip from one side to the other. Those sticks that make like rain sticks and they make sounds as you turn it over, the sound of the ball bearing shifting or something like that, or seeds or beads or something like that. You could make some really cool toys that have sound.
You get weight and sound. Weight and sound rattles. A lot of the time too, if you were making a solid volume form and you put it with a really low percentage of infill, like ten percent or something, usually those infill chambers, the spaces in there are completely vertical spaces, going from the top of the part to the bottom of the part. They really don’t close any of those interior spaces or make chambers that are less than running completely from top to bottom.
They’re making columns of spaces. You really could do that. You could put in some bird seed or you could put in beans or rice, really even if you wanted to, really small ball bearings if you wanted to give it weight. You could create something that does make noise, rattles whatever, or maybe it’s something for Halloween and it’s meant to make a funny noise. That’s a pretty cool idea.
Stability Issues in 3D Printing – Design Considerations
I want to just touch on something though, back to the idea of creating figurines, things like that. This is one thing that we found out when we were printing the minion ones. They were horrible figurines to print. It’s not because the minions weren’t cute or anything like that. It’s just like, it’s one thing to create a model in a computer and it’s another thing to create a model in a computer that is meant to be printed, meant to be cleaned up easily and then used. The minions were not easy to clean up at all.
I think there’s a lot of thought and design process that most people don’t think about. This is your manufacturing process. It’s no different than the restrictions we have on when we create injection molded tooling or if we were to create a rotor mold or something like that. We’re doing some type of manufacturing process. There’s restrictions but there’s also good design that happens with those. Things that you don’t do, like funny undercuts and other things like that.
Because it makes finishing difficult, it makes removing the part difficult. That’s the same thing here. Just because you can create in the computer doesn’t mean it’s a good print. The minions were an existing print. I certainly didn’t model them myself. I just wanted to give my nephew a chess set as a gift for his birthday.
I ended up giving it to him late even though I planned ahead and printed all the parts on time. It took me such a long time to remove support material that was necessary the way these were designed. There also were a few fragile areas, like some of the hands were very fragile. I ended up breaking a couple of them and having to glue them together before I sent it to him.
Which the reality is, they’re going to just break again. That’s really where we talk about safety of toys. Tyler’s old enough and there are no babies in their house to be sticking them in their mouth or anything like that. It’s fairly safe there. In a lot of homes, that’s not the case. Really, as you’re making toys, you have to think about this thing lipitor medication. It has to be designed properly.
If that means the arm can’t be in that particular position … I have the same problem. I have a statue of the Virgin Mary that was on my grandmother’s night table. She passed away, I kept it. Her hands are broken because the position of her hands are outwards instead of being crossed or in prayer or something like that. It makes it so that the minute somebody knocks it over on your vanity or on your marble countertop, the hands are gone. In that sense, it’s not a great design for its use.
We’ve seen this. Obviously, we went to art school and we’ve studied art history and sculpture. Ancient sculpture is full of statues that have missing hands, arms, legs, etc. or other appendages that were just naturally susceptible to either the material not being able to hold up long term. It crumbled and toes fell off or they’re just invulnerable structures or parts that are easy to get hit.
That’s unfortunate reality of trying to model natural life figures out of materials that normally wouldn’t be sculpted that way. You can rethink the positioning of the hands and how things work. That’s a design problem, and you need to really seriously think about that as you’re designing and printing.
One I want to point out with the minions that drove me nuts is that these are chess pieces. There was some sort of a geometric structure at the bottom, whether it’s primarily a cylinder or a cube or whatever that the minion is standing on, and then its feet were separated. There was a space between the minions’ feet. Sometimes there were other parts near that, like a shield or a sword or other things.
Getting the support material out from between those feet was just a nightmarish task to go through. I did it because it’s my nephew and I didn’t have the time to create new minion models myself. I did it. But boy, was it a pain in the neck.
Just because that’s the way it looks in real life doesn’t mean that’s the way it needs to be sculpted and modeled. You wouldn’t have done that if it had been in some other material. Honestly, they probably would never have molded it that way either. That’s something in the thought process and the design process that you really need to really think clearly about and plan.
Stability Issues in 3D Printing – Final Thoughts
I’ve really enjoyed thinking about all these different things. It’s giving some great ideas for some projects going forward. I think also as an educational exercise for those that are trying to hone their 3D modeling skills, creating interior cavity where you’re going to put these things presents some unique challenges and opportunities to learn. I’m interested, I’m excited to do it. I think as we’re doing projects we’re planning to do in 2017, we’re going to have to include some and do this.
The other thing I just want to briefly mention too as you’re working on these types of projects and working on this types of things is leave yourself enough time to actually test the prints. We were under a deadline to make Tyler’s birthday. That didn’t give us enough time to print some and say, “Ooh, I wish I had time to change all these models and fix them so that they’re lasered together.”
Give yourself enough time when you’re working on a project, especially on something new like this or you’re designing completely from scratch. Print it, check it out and go, “Ugh, this is going to cost a lot of problems.” Redesign, give yourself that time.
We’ll also make sure we have a link to this white paper on stability issues in 3D printing where you can find it and get it if you’re interested. This is, I would say, had a little research and academic. It’s not the easiest read in the world. There’s a lot of physics formulas thrown in here that I don’t think mean a lot to most of us. But there are some diagrams and the principles in there are worth checking out and studying. Hey, we have some physics teachers who listen to this podcast. No question. They may be extremely interested.
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