3D Design and Creation

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3D Design and Creation by MarkM

Contents

Introduction

When I was a little boy, I wanted to be able to create new figures and accessories for my toys. I’d spend seemingly hours drawing designs, then gluing scraps of plastic together trying to build a vehicle, or smashing parts together with clay to get a new accessory. More often than not, the result was a huge mess. I wanted a way to take my drawings on paper and turn them into real versions. 3D printing makes that a possibility.

3D printing is a new option quickly becoming available to customizers. Whether you buy a printer yourself, or design a piece then send it off to one of the printing services, you can now add pieces to your collection that would have been much more difficult in the past. It allows for creation of complex parts where sculpting or kitbashing may prove difficult, or when multiple, exact copies are needed. This article will help explain some of the aspects of printing, as well as provide some tips for printing. It may also dip into other, related, areas, such as design and milling. The article is definitely a work in progress and will be updated as I learn new things or find new information to share.

Definitions

#D

#Dimension, how many planes an item occupies (see Figure 1). In printing or machining, there are usually 4 types spoken of (although the differences between 2.5D and 3D, or 3D and 4D are not well defined):

2D

In 2D the item exists only on the XY plane. Think of it like writing on paper, or engraving on a nameplate

2.5D

In 2.5D the item exists only on the XY plane, but has some depth. An example would be a rubber stamp

3D

In 3D the item exists on all three axes (X (left-right, Y (front-back), and Z (up-down)). This would be a statue or other fully-formed item.

4D

In CAD, 4D means the item is 3D, plus includes motion (or time) - that is, it’s animated. In CAM, 4D means the machine is capable of movement along all three axes, plus adds a 4th axis of motion, rotation, usually along the X-axis. Without this axis, a 3D part with undercuts or detailing on the bottom has to be manually rotated before the machine can work with it.

3d design graph.jpg

Additive Process

A process that adds material to the item being created, building it up layer by layer. An additive process generally only uses as much material as is needed to create the item. Only generally and not always, because there are times when support material is needed for the creation of the item.

CAD

Computer Assisted Design, CAD is the process of using a computer to create a 2D or 3D model of an object on screen. This model can then be rendered for use in publications, websites, video games, animation, or CAM.

CAM

Computer Assisted Manufacturing, CAM is the process of using a computer to control a manufacturing machine for the creation of items in the real world. There are various types of manufacturing machines, including CNC machines, 3D printers, robots, and some others. the CNC machine and 3D printer are the ones of interest to us. (Note: CAD and CAM are also often combined as CAD/CAM, since the two are closely related, and there are some machines that can do both the design and manufacturing, which would be CAD/CAM machines. However, in the hobby world, the two processes are usually distinct and separate.)

CNC Machine

Computer Numerical Control Machine, a machine that uses a computer (either built-in or external) to precisely control movements of its motors to position the machining tool around the piece for material removal. Machining is generally a subtractive process. Some types of CNC machines:

CNC Mill

A machine that moves the tool about the material to create an item. Can create items that are 2D, 2.5D or 3D. Has movement in either 3D or 4D, with a wide range of motion along the Z-axis.

CNC Router

Similar to a mill, but has more limited Z-axis motion and rotation along the X-axis. Can create items in 2D, 2.5D, or 3D.

CNC Laser Cutter

Uses a laser to cut material. Usually only has movement along the X and Y axes, varying the intensity of the laser for depth (Z-axis). Can create items in 2D or 2.5D (some high-end systems can do 3D).

CNC Plasma Cutter

Same functionality as a laser cutter, but uses plasma to cut the material.

Build Platform

The platform in the printer on which plastic is deposited to build up the model. A good printer will have a heated build platform, which helps the first layer properly adhere to it, keeping the model from dislodging and moving around, ruining the print. A heated build platform also helps regulate cooling of the piece, so that the base does not shrink unevenly, causing edges or corners to curl.

Extrude

To move a material through a die (in 3D printing, just a standard hole, but can have shapes) to stretch it out. Think of it like a Pla-Doh factory or a pasta machine. 3D printing is an additive process.

G-Code

The software that tells a CNC machine or 3D printer how to create an item. An item can be created directly in G-code, but most users use a CAD program to create their 3D model, then use another application to convert the resulting model file to G-code.

Mold

A mold is a negative of an item to be created. This means that where parts of an item protrude, the mold recedes and vice versa. It is created by either machining or by casting a mold from an existing item.

Overhang

Material that hangs over a void, or empty space. If you were modeling a face, the nose would be an overhang, since it protrudes from the face, with it existing over a void. When creating an model to print, overhangs can be an issue and may require support material to keep them from dropping or warping. When creating a model to be machined, the opposite of an overhang, an undercut, becomes an issue.

3d design OverhangUndercut.jpg

Render

To convert the CAD model into an actual image. Some applications render in real-time, meaning as you draw the model, the application shows how the model would look in the real world. Other applications display a wire mesh of the model, requiring you to manually render it to see the finished product. (SEE Figure 3)

Slice

Slicing a model is cutting it up into layers that correspond to the printer’s capabilities. Slicing is a step in generating the G-code to actually produce a print.

Subtractive Process

Is a way of creating an item by removing material from a larger piece of material. A subtractive process always requires more material than the finished product will contain.

Support Structure

Material that is used during the creation of an item, then removed from the final product. Low-end 3D printers use the same material as the finished item for support material, while high-end printers will use a different material that is more easily separated from the finished item.

Undercut

A cut, or inset space, below an overhang. In machining, undercuts need to be carefully planned, due to the limitations of movement of the tool and/or material being machined. Undercuts are not an issue for 3D printing, since the item is built up. (SEE Figure 2)

Wire Mesh

A model that does not have finished surfaces displayed. Instead, it displays lines where joints and seams would be, leaving the surfaces empty, making the model look like it was made out of wire.

3d design WireMesh.jpg


Types of Printers

When talking about 3D printers, there are four types that exist, with two of them being what most people think of when they think of a 3D printer.

FDM Printer

Fused Deposition Modeling, this is currently the cheapest method, with hobbyist models available anywhere from $500 - $2,000, available as either kits or prebuilt. There are also DIY plans all over the internet for more adventurous types. These printers work by melting plastic (usually ABS or PLA) and forcing it out a nozzle, building up a model one layer at a time. The hobbyist models print at resolutions of .1mm to .3mm. Some printers offer multiple extruding heads, meaning the printer can print in multiple colors, or print the support structures in a different, more easily removed, material. Printed pieces are distinguishable from injection molded or resin cast pieces because of the “banding”, or visible lines where the layers are built up. At the .1mm setting, the lines are barely visible and with some finishing work can be all but removed.

ABS plastic

The plastic hobbyists generally use, due to availability and durability. For customs, this is what you would want to use.

PLA plastic

This is a biodegradable plastic, so this would not be a good choice for customs or other long-term parts.

Stereolithography

This method is almost in the realm of the hobbyist, but still finds cheap units still running more than $2,000. There are a number of groups working to create sub-$2,000 units, though. Stereolithography creates models by shooting a beam of UV light into a photosensitive resin. Resin that is hit by the light hardens. These printers can hit resolutions of .025mm or better, with banding being virtually invisible to the untrained eye.

Selective Laser Sintering (SLS)

This method is similar to Stereolithography, but it uses a laser instead of simple UV light, and a powder instead of a liquid resin. With SLS, models can be created in plastic, metal, and other materials, with a resolution of .1mm or better. (These are the printers sites like Shapeways generally use.)

3D Inkjet Printing

This method works similarly to your standard desktop inkjet printer, but instead of ink, the printer lays down a polymer dust that is bound with a pigmented glue. This allows for parts to be printed in full color at .1mm resolution or better. These are also the most expensive printer option, running in the tens of thousands of dollars.


Getting a 3D Model

Starting out, models can be found on various sites, such as [http:www.thingiverse.com thingiverse.com], [http:www.shapeways.com shapeways.com](only some models are downloadable), [http:www.cubehero.com cubehero.com], or several others. Printing pre-existing models is a good way to learn the capabilities of the printer, making it easier to determine if models you create don’t print properly due to the printer or to a mistake while making the model.

We wouldn’t be customizers if we were happy with off the shelf product or premade models, would we? So eventually, you’ll want to dip your toes into CAD drawing. There are several good CAD apps out there, too numerous to name them all. They can range in price from free to thousands of dollars, and licensing may or may not allow commercial use, so when looking at packages, pay attention to that, if you think you may want to sell pieces. Each will have its own pros and cons, learning curve, and documentation so I’ll not get into the technical side of drawing. I will say that the two apps I currently favor are SketchUp for non-organic designs and Sculptris for organic designs. SketchUp works a lot like other CAD apps, while Sculptris is more like working with modelling clay.

Another option for model generation that is quickly becoming affordable is 3D scanning. Out of the box, ready to use scanners are still quite expensive, but there are several DIY options out there, using either a laser line (such as a laser level) or depth sensing camera (such as a Kinect or Asus Xtion). With the correct software, one of these devices, and a little trial and error, you can create 3D models of real world objects. There are also applications and websites that can take a series of pictures you provide and generate a 3D model from them. Imagine printing out a custom of your head to put on a body, or sculpting the perfect head or part, then scanning it in and printing it.


Getting the 3D Model to the Printer

The models you download from a website should come to you in .STL format, which is the intermediary format between the CAD program and the G-code. For a real-world analogy, think of the CAD program model as a word document. It is in its program’s proprietary format (Such as Microsoft Word) that can only be read by certain other programs out there. To get that document into a format more readily viewable by other people, you may export it to a PDF, since PDF viewers are free. The STL file is like the PDF. If you want to print the PDF, you then select print in your PDF viewer, and the software automatically converts the PDF to a format the printer understands. This is what you do when you generate the G-code.

Models you create, either through CAD or Scanning, will need to be converted to STL format before it can be imported into your printer’s software (some printers may use another format, such as PLY, but most hobby-level printers use STL). This conversion is usually done in your CAD software via the Export function, but if your CAD or scanning software does not support STL export, then an intermediary program, such as MESHLab can be used to generate the STL.

Once you have the model in STL (or other appropriate) format, you can then open your preferred printing software and import the model. Then you can adjust placement of the object in the printer to make sure it prints out properly. Once you’re happy with the placement of the object, you can slice it and generate the G-code.


Finishing the Model

There are a variety of colors of filament available, so it is possible to print parts and use them directly out of the printer. However, you may not be satisfied with the banding, or you may want to add some painted details. To remove banding, you have a few options:

  • You can sand the item as you would any other part. If you choose to sand, just be careful to sand slowly to avoid deforming the part or creating too much friction and heating it, causing it to form melted spots, losing detail.
  • You can rub the item down with acetone on a Q-tip or cloth. Use caution when working with acetone and remember it can melt the plastic if left in contact too long. The part may form a white haze where rubbed with acetone, which will either require additional sanding or painting.
  • For the best finish, you’ll want to go with some sort of acetone vapor bath. The easiest way to do this is to put a paper towel or cotton ball soaked with acetone in a sealable non-plastic container (such as an old paint can) then suspend the item in the container for a few minutes. Carefully remove the item and let it dry (it will be tacky). Repeat the dip/dry method until the surface is to your liking. This method is less time consuming than sanding and is more uniform than either sanding or rubbing.

Once the model has the surface texture you desire, you can prime it, fill any blemishes, and paint it just as you would any other piece.


My Setup

Luckily, the printer I have, the Solidoodle 2, has a fairly small footprint of about 11 ½” x 11 ¾” x 11 ¾”, so I can put it away when not in use and set it up on the dining room table when I want to use it. Eventually, I will move it to a permanent location in my workshop. I can print up to 6” x 6” x 6”, giving a pretty good-sized object, and even larger items can be made by printing in pieces then gluing together. The only thing I would do differently if ordering again is order it with the case. I’ve found that the unit loses too much heat to the outside world while printing, which can lead to edges curling as the plastic cools at different rates. I’ve gotten around this by buying some acrylic sheets at Home Depot and fastening them to the unit with magnets. It works, but doesn’t have a finished look, which is a bit distracting since the unit comes looking quite nice. I use the Repetier Host software with Slic3r for printing and slicing models. There are better, more powerful software combinations out there that can yield better print results, but for ease of use and speed, I’m more than pleased with these two right now. This setup lets me import my models to print, arrange them on the build platform, scale them if they aren’t quite the size I want, and print them out.

For design, I use SketchUp and Sculptris. Sketchup works well, for me, for hard-edged things, like buildings or vehicles; whereas Sculptris does organics pretty well and feels more like working with clay. Figure 3, above in the Definitions section, is a model of a wing glider I designed in SketchUp. Figure 4, below, is a quick and dirty head mock-up I did in Sculptris, using the head template they provide. It took maybe 10 minutes to modify it.

Fig. 4

Speaking of clay, when it comes to design, I’m more hands on and can have troubles visualizing 3D concepts in a 2D space. This means that while I have ideas, I can’t always translate them from my mind to the computer. Because of this, I purchased an Asus Xtion Pro Live camera. This unit is similar to a Kinect, but is for PCs. It also runs a bit less than the Kinect for Windows. The goal is to be able to scan people or items and generate the 3D image this way. Then I’ll only need to clean up the image before printing, instead of completely generating the image on the PC. This will let me sculpt items in clay, as I am comfortable with, then scan them in for printing. It also has the additional benefit of letting me sculpt at a large size (even larger than 2-Ups) for better control over the model and detailing, then scale it down in the 3D software or the printer software. This is much better than my current method of having to sculpt at actual size, which leads to muddled and malformed details.

3D Printed Example

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