3D For A Draftsman Of Yore
February 21, 2014 4:49 PM   Subscribe

I learned mechanical drawing 20 years ago - but I would like to wear a CAD hat for a small project. 3D CAD, so I can print it on a 3D printer. Unfortunately, 3D CAD makes no sense to me.

Twenty years ago, they were just starting to teach CAD in college, but I didn't take those classes: I took drafting. I learned things the old way, pencil and scale rule and triangles and drafting tables and all that. I'm a little rusty, but I can still pull out the T-square and draw something up when I need to.

My problem: I have a small project -- a personal project, low budget, but the only way I think I'll get it to work is to fabricate it. Difficulty: gears, turny parts, etc. It would be an ideal project for 3D printing, because I've seen similar things. I haven't seen anything practical like I'd want, but people are making celphone cases with ornamental, working gears in them, so it can't be that hard, right?

For the life of me, I cannot grasp 3D CAD. I have downloaded SketchUp, tried 3DTin and 123D Design, got something called OpenSCAD, and it simply doesn't work. "I made a cube! Oh, look, now there's a cylinder next to it! Unfortunately I have no idea how big anything is or how to make any shape more complex than this!"

If I had a drafting table, I could put this to paper lickety-split. If I had a well-equipped shop, I could make it, too. I have neither capability at the moment, but this is what 3D CAD is for, right? Rapid prototyping and one-offs, straight from the design to a physical copy?

I have seen the recent 3D CAD for the complete beginner AskMe, but it's all focused on what software to use. It's not just you, though: other discussion areas and FAQs all recommend software, but don't tell how to use it.

What I need is conceptual understanding. Tutorials, what the terminology means, how things actually happen. For example, I opened a SCAD file in a text editor and that made some sense -- some shapes are negative space? It was like a light turned on! How do I actually make something like that? I have no idea. Software doesn't just do that, regardless of what program it is -- it expects me to tell it what I want done, and I don't possess that language.

So, Metafilter, please point me towards understanding, rather than tools -- where does an old draftsman like me learn to use 3D CAD to get things done?
posted by AzraelBrown to Technology (9 answers total) 8 users marked this as a favorite
Check into your local community college. An obvious step would be to take a course. They may even have courses specifically designed for people like you, who already know the theory, but just need some time with a teacher and the software.

If you don't want to take an entire class, you could ask if anyone does any short-term tutoring.
posted by SuperSquirrel at 4:58 PM on February 21, 2014

Best answer: I came to CAD from a tech drawing background.

First, pick your software:
a. pick something powerful (else you'll outgrow it and waste your investment of time in learning it).
b. Pick something that is a standard, used by lots of people, or the industry standard in your field. Actually, (b) takes care of (a) - whatever is industry-standard will be something that Does The Job, so you don't need to worry about inadvertantly learning a toy then hitting the limits of that toy.

Once you've picked your software, and you have your software, get a book.
Get a 2" thick tome that is aimed at beginners, and is written about exactly the version of the software that you are using.
Preferably with a CD-ROM in the back containing all the files for the tutorials pre-set-up for you to jump right into. If not a CD, then a website where you can download the files.
Get the best book, not the cheapest - read the reviews on Amazon, pay attention to the ones written by people most like you.

The book will introduce the concepts, walk you through using them in the software you're using, then build on them, combine them, and master them.

(You'll find that the same concepts are often called different things in different software, and in different industries, but the concepts are the same and people happily hop back and forth. Hence start by matching the book to your tools, which means picking your tools before picking the book)
posted by anonymisc at 5:26 PM on February 21, 2014 [1 favorite]

Actually, start browsing for books while deciding software - it's often the case that, say, the 2014 version of the software will have few books available, and also cost a lot more than getting the 2012 version of the software which has a wider range of books to choose from.

It's probably easier to learn 2012 from a great book then later upgrade to 2014, than it is to learn 2014 from a mediocre book.

And besides, for your initial purposes, you won't need any features that haven't been present in every version of the software for the last decade... :)
posted by anonymisc at 5:36 PM on February 21, 2014

Here is a trial version of Solid Edge It has a trial period of 45 days which should be enough to learn the software and do a small project. The help in Solid Edge contains ~14 tutorials which do a good job of helping you to learn the software.

You could also download a trial version of AutoCAD if you wanted to complete the job in 2D.

In addition there a a ton of CAD libraries online that may have most of the parts you are looking for and will save you a ton of time in finishing the project.
posted by troll on a pony at 5:45 PM on February 21, 2014

Hackaday is running an ongoing series called "Making a thing in ..." which sounds like it might be up your alley. They're running Making a thing with Solidworks right now, and have links to previous installments on OpenSCAD, FreeCAD, and Blender. Of course, the cheapest available Solidworks license is about $3500, putting it firmly out of range of ethical hobbyists. If you're a student, faculty, or staff, you can get a copy of Autodesk Inventor for coursework-related use through Autodesk's student licensing program.

As an aside about what set of tools to learn: I'm a big fan of parametric CAD (Autodesk Inventor, Solidworks, FreeCAD, etc). I like the approach of "specify dimensions in a 2d drawing, then extrude that out, then specify another drawing and cut some bits away, repeat, etc." (There are other ways to make complex shapes, but that's the bread-and-butter for me). These tools tend to be expensive but very intuitive (from my frame of reference, which includes some drafting and some 2d art, plus computer graphics). The added bonus: everything is defined by dimensions and relationships between dimensions, so if you realize you need to change one or more, you just do it, and (assuming you set your part up sanely), everything recalculates and Just Works.
posted by Alterscape at 9:08 PM on February 21, 2014

Best answer: What helped me learn Inventor and SolidWorks (which are fairly similar in the way they draw/extrude/cut) was just finding a simple drawing and replicating it in the program, then finding a slightly more complex drawing, and then something a little harder, and on and on.

Occasionally I would find a YouTube video to explain something (some projects I work on occasionally require FEA and that can get tricky), but mostly once you learn the basics, you can create just about anything you want.

Rapid prototyping is probably what you're going to want for something ornamental. Contracting out your assembly to a CNC job shop might be prohibitively expensive for a single prototype. It might make sense if you're going to do a higher production run.
posted by spikeleemajortomdickandharryconnickjrmints at 6:57 AM on February 22, 2014

Best answer: Yes! I understand what you mean. It would be helpful for you to clarify which conceptual aspects of 3D modeling/3D CAD you're trying to grasp. Tutorials and books only help so much. Here's a quick primer:

3D modeling software involves doing a series of operations onto geometry, the same way that each different machine in a woodshop involves doing a specific kind of operation. As such, knowing what each operation does is crucial to understanding how to work with geometry, the way that understanding what kind of things a drill press is good at vs. a belt sander will help you work with wood to make an object.

Making something in the shop involves knowing what you want, and then how to tease it apart into a series of processes. Let's say you want to build a stool. So you want a circular seat, with a pocket for the stool legs cut out of the bottom. In order to get the seat, you would cut out a circle out of a piece of wood with a router and a circle jig. Or maybe you make a shape out of paper, trace it out onto the wood, and cut the shape of the seat out with a bandsaw. Maybe you chamfer the edges of the stool seat with a router and a chamfer bit. Or maybe you just sand the edges off on a table sander. And then you flip the stool and use a spade bit on a drill press in order to make the circular pockets for the stool legs.

3D modeling is similar, in that there are many different process that do similar operations, and you can often get the same result many different ways. But you need to know what each process does in order to get there.

Often times these operations are command-based, like AutoCAD, and you need to know/remember the name of the operation: "extrude", "loft", "sweep2", "flowalongsrf", "fillet", "chamfer", etc. Alternately, they may appear, like Photoshop or Sketchup, to be icons on a toolbar. They may also be both (like in Rhino). For example, the "loft" command takes two curves, and connects them together, creating a surface in the process. Or: The "chamfer" command will take an edge and, surprise, chamfer it the same way a router bit would.

When you 3D model, you're dealing with curves and surfaces. When you draw a 2d triangle, that's three straight curves (or lines) that are 'join'ed together at the edges into a 'polyline'. Imagine a series of straight wire pieces, welded together at the corners. You could draw an almond shape and mix curved lines and straight lines and also join them into a polyline as well. You can "explode" or unweld the polyline triangle back into a series of separate lines.

You could also draw a square, and turn it into a surface, defined by the boundaries of that square. A box/cube really consists of six square surfaces that are joined into a 'polysurface'. Even though it looks like a "solid" box, it's not. You can "explode" the cube into six surfaces [1], that then you could move around and manipulate separately. There is no such thing as a "solid" object in (most) 3D modeling, the same way that a beach ball is not a solid object; you're always dealing with a series of infinitely thin surface with a void inside. No surfaces have thickness. But many operations (like the "chamfer" operation) treats boxes and objects as if they are solid, though, and will give you a chamfered edge, that itself is a surface. Imagine if you're dealing with objects that are all made out of paper, ala papercraft.

So: if you wanted to make the stool in 3d modeling software, you could draw a 2D circle on the XY plane (aka, a horizontal surface). You would then use the "extrude" command and extrude the circle in the Z direction (aka, upwards) and to make a short cylinder, or disc, that is a solid 3d object. (However, again, this object consists of a series of surfaces (the circular surface on the top, the circular surface on the bottom, and the curved strip along the side) that are joined together. You could then use the "chamfer" command to make a chamfer along the top edge of the stool.

How would you get the holes? Well, one way is to make a cylinder or a plug the size of the stool leg, move it 'into' the stool so that part of the cylinder is inside the stool, and use a 'boolean' operation to subtract the cylinder from the stool. That way, you'd be left with a hole or a negative space where the cylinder was.

The rest of basic 3D modeling is, again, like woodworking, knowing what kind of operations do what sorts of things, and knowing how to use them together in a smart way. For your gears, you could do a similar thing with the stool, except that you would draw the outline of the gear on the xy plane, extrude it upwards, and punch a hole in the center for the axis.

Of course, there are many 3d modeling programs out there, with many many exceptions to what I just described -- but that's the basic gist. I've found lynda.com to provide pretty good and comprehensive walkthroughs for 3D modeling. Your mileage may vary. Good luck!

1. Some technical detail: 3D modeling software usually falls into two kinds, depending on how it works with surfaces - Mesh-based, and NURBS-based. Mesh-based modeling involves having each surface being made out of a lot of polygons - usually tiny small triangular surfaces or rectangular surfaces. You can then manipulate these polygons to modify geometry. With some software (like Z-brush) you push and pull hundreds of polygons to model a form, kind of like pushing or pulling clay. NURBS-based modeling is more exact and more mathematical; it uses a series of curves to describe every surface. You can have a curved shape (like the glass of a car windshield) made out of the four curves defining the edges. Depending on the software, you'll be working mostly in one mode. Maya is mostly mesh-based. Rhinocerous is mostly NURBS-based, although it does deal with meshes a lot. I believe Sketchup is NURBS-based.
posted by suedehead at 12:26 PM on February 22, 2014 [2 favorites]

Response by poster: Thanks for all the suggestions, particularly suadehead for the thorough primer: I spent a bunch of time researching what it would take to just buy off-the-shelf parts and/or make what I need using basic shop tools, and decided that this is where 3D modeling saves time; yeah, it's not fast on a 'weekend project' scale, but it's swift on a manufacturing timescale, so I turned back to 3D.

I have gone with OpenSCAD, since it best combines my skills both as a draftsman and a computer programmer, it's well documented, and I did not find any GUI-based software that could do as precise work as I want. Then, I downloaded a handful of other *.scad files from thinkiverse, studied their code, and what I couldn't reuse as a module/function I adapted to my own use. After 4 hours -- the first three just breaking things -- I had this coded pretty much from scratch, and 6 hours later I had a bunch of gears (from others' libraries, I'm not that good) and other mechanisms worked out.
posted by AzraelBrown at 7:13 AM on March 23, 2014 [1 favorite]

I hadn't heard of OpenSCAD - sounds super interesting!

Just for reference in the future: if you're also a computer programmer, and if you're looking to do precise work with a GUI-based interface, then Solidworks might also be up your alley.

It's designed for industrial design, and deals with material thicknesses, manufacturing tolerances, can model bending sheet metal, or making holes, assembly tabs, etc; it can also be parameter-driven, so the width of a tab will affect the length of a cut, you can program formulas in, etc. You can lay out plans/elevations/axos on a drawing sheet super easily -- and you can even modify the dimensions of an object on a drawing, which will change the model! If you want to manufacture the real deal, Solidworks is the way to go. It's not crazy hard to learn - it comes with a lot of great tutorials. The only disadvantage is that a license = $$$.
posted by suedehead at 7:28 PM on March 27, 2014 [1 favorite]

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