3D Digital design joinery is right up our alley with our background, and we are looking at these 50 digital joints similar to wood joints over on Adafruit. Looking at and understanding these traditional construction methods apply to modern 3D printing technology in more ways than one. However, these might not be that feasible for actual use in 3D printed or plastic products depending on what you are doing with it.
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3D Digital Design Joints
Recently, there was a PDF created of 50 3D digital design joints. This is a couple years old. The poster is really nicely laid out by Meredith Scheff-King. It outlays the different types of joints, there are 50 3D digital design joints in this case, and I don’t think I ever counted how many joints we used in an actual wood products. There are several tried and true that work very well, there are more joints here than we have used in production. They each teach something. It is very important when it comes to STEAM education, it teaches different ways of joining different parts together.
It is important to understand that the joints in this poster are intended to be used primarily for wood. It is a wonderful to do to be able to print out those joints using 3D printing as an example to show students all the real geometric realities and principles of those joints – what makes them strong, what makes them work for certain applications. This poster doesn’t go into it as to what applications you would use with these types of joints. You also do not know which ones are appropriate for manufacturing or the efficiency that the factory is making. There are different joints that would work better for other factories. You don’t necessarily need a more complicated joint for a picture frame joining pieces at 45 degrees. You have a key or more of a spline joint perpendicular to that 45 degree angle.
Especially for STEAM education and any kind of industrial arts education, having a poster like this of these 3D digital design joints, and printing out a bunch of examples, students can take and put these together and understand what the physical principles are. It is also a slippery slope to me, the idea of how these are created is like an icon library that you would drop into your CAD program so that any time you need to use these 3D digital design joints, you would just pick one of these pictures. The issue with this is that it’s an aesthetic application of something you do not know whether or not it is the right functional part or joint for your material.
Specifying for the Expectations
You now have this rendering with one of the the 3D digital design joints in it. If you got a color change, you may have the color lines in your color change. The customer is expecting that. When it gets to construction, it is not feasible. We never show the joints in our product renderings. We just don’t bother because the resolution of looking at renderings is that no one ever asks for the construction of everything. We specify them or consult to the factories to what they prefer for the material and the manufacturing process. The concept of tolerance is also important. If you were to 3D print any of these 3D digital design joints, it would be a good educational experience for a student to learn about really what tolerance means.
When you would print out these 3D digital design joints, because of the extrusion process of most 3D printers – the 3D digital design joints you selected may not fit together. The tolerances of 3D printing are very different from what it would be in wood. Wood is a very hard material and you are cutting it with a bit or a cutting tool of some kind. These 3D digital design joints would almost make them line to line. The space left from one finger will be filled almost exactly by the same dimension of a finger from the mating piece. In plastic, you need to change that and have some different relationship between the positive and negative spaces for things to fit.
It also does not go into the idea that very often with most of these 3D digital design joints, they glue them together and make staples that are placed in various places on things. Except in the case of high fine end furniture, you have to include another part – a pin or a key, or something. Most of these joints would be glued together so that they fit together. In plastic, I would not recommend using glue to hold them because it is messy. Plastic does not absorb the glue the way the wood does. You need another mechanical fastener to hold those parts, these 3D digital design joints together.
There is a really good case thought, if you already that you are using a particular joint for just easily having a small group of these 3D digital design joints in your CAD system to be able to drop it in and put it in your file when you already know that you are using it. Your 3D print prototype visually will look like the original and real piece at the end of the day. It is going to take some model manipulation or adjustment in the slicing software to create an offset. You need to build in tolerance.
I also want to talk about the realities of applying a joint intended for one material to another material. We did this five years ago. This is when we made our chair base for trying to make something that would break down or fit in a smaller box. We made a ready to assemble chair base.
It was a fairly innovative thing to do, but also the reality of the forces on a chair base really shows you what kind of joints can take those forces. We designed it into a five star chair plastic base, a dove tail shaped joint to join the five spokes of the wheel on a base with the center hub. It actually failed testing. It did not work. We learned the hard way that the dove tail joint is very strong and functional in wood, but it really does not have the same kind of strength properties in plastic. We need to change that to more of a t-shaped or an I-shaped joint that did not have a taper or angle to it in order to get the properties right.
This is a good example where FEA analysis in CAD program came in play to help us helped us analyze what was the right and best shape to go for. The original idea was just, “Can we do this? Can we create this?” We didn’t think that it would go forward. As we realized, we thought that there is something more here. The reason why this is so vitally important, was the much lower shipping cost because containers can be smaller. They cost less and there is less of a carbon footprint. Overall, there was a great benefit to doing it.
This is a good example of where you are doing it on the computer in CAD and with FEA, at the end of the day 3D printing or any other kind of rapid prototyping would only show us the principle at full scale for what we were trying to achieve. This was an experiment. This was a development project to see if we could achieve it. We used CAD and 3D printing and other prototyping as much as we could. We then made a decision at some point that there is no way that we can actually test and prove that this is going to work unless we tool for it and injection mold it in the material. We made an inexpensive tool out of cheaper mold metal material than what you would use for production. It would probably last for 5 thousand pieces if you used it in production, not a hundred thousand pieces. This is to keep the cost down. We spend $4,000 on an injection mold in Asia to prove it out. It was critical in the process. That’s just an example where 3D printing cannot tell you everything about what you want to do. It was still a very important part of the process.
3D Digital Design Joints – A Basis for Creativity
We wanted to bring these 3D digital design joints up because it changes you making mind – the designing mind, in terms of opening these up. We want to give you a little dose of realism about it so that you have an understanding of it is great to design these things, but if your plan is to make something that is manufacturable, these 3D digital design joints may not work at the end of the day. Just keep that in mind as you are moving forward and as you are thinking about what and why are you making something.
These 3D digital design joints can be used as a basis for thinking about puzzles or brain teasers. There is a lot of great joints here that teach a lot of geometric and physics principles. It opens up some students minds as to how they might think about joining objects. That would be a really cool class project. You show the 3D digital design joints, you talk about their structural properties and how strong they are or how different they are. You are really teaching a test and then 3D printing tolerances at this point. That is the next step that you are teaching. They have to make the 3D digital design joints fit in plastics as you are printing them. How do you adjust the tolerances and how do you do that in your CAD system to make them printable? Now you’ve taught that concept.
Your project assignment on 3D digital design joints, for fun, is to get them creatively thinking and be artistic is to let them pick their favorite 3D digital design joints or combination of joints and create a 3 dimensional puzzle. When I think back to my education, I don’t think I learned about tolerances in manufacturing until I was in college. It might be somewhat of an advanced concept. The reality of 3D printing in STEAM education in the grade school level is that you cannot help but have to teach students at that level about tolerances. In order to really put different parts together, you are going to face this reality.
3D Digital Design Joints – Perfect Fit
This week is leading up to our interview with 3DKitbash. It is a high level way to test your printer with some of the kits that they have or the downloads that they have. It can test the tolerance amounts or the sizes that you are printing in. Look at that and think about that because this is a great way for you to test it out. I remember an interview we did a very long time ago, about making drones, MDAR is a very good example to this. I remember them because they made a mistake of printing all the parts out and then trying to fit them together. They then found out that this is bigger than it is supposed to be. Our 3D printer is printing at a different relative scale.
Parts did not fit because they had parts that were from an outside source, and they needed to be set and fit to the plastic parts. They realized that, “Wow, we wasted so much time because we just did not test one small piece to begin with.” This is a great way where you can print out a 3D digital design joint and really test that out for yourself and see what is working. Check your printer and see where it is at. Just don’t forget that when you go to real production to shift back to what you really want. They figured out that they need to print it at 103% of what the actual CAD file said it was on their 3D printer for it to end up the actual size that they wanted.
That is another concept that is great for students to understand: different machines are going to print it out in different ways. Same goes for materials, shrink rates or extrusion rates all affect this. We have this recently in our WTFFF?! printed coffee sleeve on Thingiverse. We deigned it to fit all the disposable paper and Starbucks coffee cup with the hot cups. Printing it on our own 3D printer is possible. We also let other people to print it in other printers with different slicers, they had different results. They need to print it to 110% to get it to fit. We wanted this to inspire you to let you think about what you want to do as you are going about 3D printing your 3D printer.
Final Thoughts on 3D Digital Design Joints
There are some of these things out there that can help you figure that out for you to get your tolerances in line for yourself. Just adapt in your process of designing and developing or making whatever it may be, some time and testing into making sure, like print one piece and measure it carefully and make sure that it ends up with the size that you want. That is a great thing to communicate to students. You may not remember this from other episodes, or in case you are new to the podcast here; one tool we highly recommend in every classroom, lab, or person gets, is a pair of calipers.
I recommend a good digital caliper if you can afford it. They are not cheap, they can be up to $100 to purchase. There are some that are made with plastic which are cheaper. Anything is better than nothing for accurate measurement. Calipers are really great tools to have. I highly recommend it when you can afford it. Put that in your budget if you are purchasing one for your studio or your school, put that in your budget as something that you want to have. Lock them up though.
You got to keep close watch of those and take control of them. I will put just in case you might be very new to that kind of tool as a listener. They last a really long time. This is our second pair in 20 years. You have to be careful with it, I bought another one because I dropped it and bent the critical parts that measure the holes and outside shapes. It was no good to drop it. It costs you more to repair than to buy new ones.
- Adafruit – 50 Digital Joints
- Flexible Stream – 50 Digital Wood Joints
- 3D Printed Robotics and Drones – MDAR
- Coffee Sleeve download on Thingiverse
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