Designing Parts for Acetal on the Computer

This guest post is from Jay Doscher. Part 2 of this series will appear next Friday.

Getting Started

Designing parts for a custom project can be a daunting task if you've never tackled it before. There are many unknowns and unanswered questions- and there is a risk that things might not turn out the way you planned. This guide will attempt to answer many of those questions and help you get started. The first thing to realize is that there are many steps to do before actually placing an order. The first step is thinking of the idea or problem in your head that you want to solve. Some good questions to start with are:

• What material will I want to make the part out of?
• Does this part need to fit with any other existing parts?

Design Software

There are many CAD programs out there, and they vary wildly in price. I'm a big fan of going with what you already know and already have available, and for me that means Microsoft Visio. It's not the best or the cheapest, but the ideas and concepts will be the same for just about any design software you choose. There are many free tools out there, and you can find links to them here.

Rough Sketch

To start, let's say you have an idea for a part, and you're pretty sure you want to use plastic as your material. While there are many engineering aspects to part design, we're going to assume it's a plastic bracket for a hobby project. We also know that this part will have to fit onto an existing project frame. Here's a picture of the project frame that we're starting with:



Now we know that we're going to want a plastic part, and that it will be mounting to the corner or side of this frame. Let's start with some basic graph paper to sketch out the part. Don't worry too much about getting the measurements exactly right, but for this example we're going to assume one graph paper square is two centimeters. We start by drawing out the frame that we need to fit into:



Now that we have drawn the frame design in pen, let's sketch some ideas we have for the frame:



Now we have two ideas: one is a panel that covers the full side and another is a small corner bracket. Now we're ready to move into software.

Part Design

Instructions on how to use Visio or any of the other software tools is out of the scope of this tutorial, but we'll walk through the basic steps to get our sketch converted into a shape in software. First, let's draw a rectangle that is our outside shape; for this project, we know it's 18cm x 30cm.



An important lesson for ordering parts is that larger parts usually cost more than smaller parts. Additionally, it is usually cheaper to get multiple quantities of a part than it is to order individual parts. That's why for this project we're actually going with the smaller corner bracket rather than a panel for the whole side. If we designed a panel, we would have to order unique parts for each side, and we would find out for our project that only the sides are the same. The top, bottom, front, and back are actually different sizes. Since we're using a smaller corner bracket, we can actually order multiples and use them on all sides- even on other similar projects that have the same corner design.

For this project, I need to cut out a corner to make room for other parts; here you can see I've created a rectangle and a triangle in the corner for this part. Each is a basic shape in Visio.- notice I am using the triangle's 45 degree angle to set the shape for my corner. If you can't see it now, don't worry- it will make more sense in a bit. Note this is only for the corner part I need to design around.



Now that we have a custom shape for my corner parts, I can bring in the other basic shapes for my part, using the outside rectangle from the first step as a guide. Now my layout looks like this:



Now we are ready to draw the outline for the full panel part-- the larger of my two planned designs. I'll use the line drawing tool again to draw the shape, using the existing shapes as a guide.





Now we'll copy this shape to a new page, and you can see the basic shape below:



Now that we've gone through the basics, you can use this same simple approach to build more complex shapes. You can use this same approach for drawing drill holes or other holes of just about any shape. For this project, we just want some holes for mounting screws. You can see in the photo below I've made a small square with a circle in the middle. The circle is for screw holes. The square gets used to keep it in alignment with the rest of the shape. I copy and paste them together, then remove the square before ordering.

It actually took several hours and attempts with paper to check for errors, but this is what the shape ends up looking like. Be prepared to print on paper, cut them out and check multiple times. This is why we use paper for prototyping! It's cheap and easy to correct.



Now that we have a shape we're happy with on the computer, let's print it out. We can cut it out using some scissors and check to make sure it fits the frame. For larger designs such as the panel, they may not fit on a single sheet of paper, so we can draw a large "X" in the middle of the design. Then we can line up the two sheets of paper after we cut them out. Since I am using a smaller part, I can copy and paste so I have multiple parts per printed page. Note that when you place the order, you'd only want one. Then change the quantity on the order at checkout.





As you can see above, we've cut out the shape for the smaller part. This will let us use the same part on various places throughout the frame. On the bottom, the shape can even interlock to create a solid panel. Now that we've tried the part out for one piece, let's tape it to the frame. (3M painter's tape works great for this exercise.) Here's a picture of the whole project with all the parts taped to the frame. It looks a little bit messy, but it shows us exactly how it will all line up.





Let's go back into our software and make sure we have a clean drawing. We don't want any excess shapes or lines- just the part and any holes we want to have cut. Here you can see the part is on its own page. From Visio, we'll export the page as an AutoCAD Interchange (DXF) file. Note: Make sure that your drawing only has the shapes you want cut and nothing else on the page. You can see in the screenshot below we've done this. When you're ready to save it, first save your original in the Visio format, then click File, Save As..., and select a folder to save it in, then click the drop-down box and select "AutoCAD Interchange".





Now we're ready to order! We'll navigate to the Big Blue Saw website and click the button for Upload and Order. The next steps are pretty easy!

1. Click the "Choose File" button and find the DXF file you just exported.
2. After you've selected the file, click "Upload".
3. The part should upload and look like it does below: PIC
4. From here, we are free to select a material type. For our case, we're going to select "Black Acetal Plastic 0.125", or 1/8".
5. The next screen shows pricing, where we can choose our quantity. Because we are going to use the same part all over our frame, we will save money through a higher volume of the same part, instead of having unique parts for each part of the frame.
6. From here we can finish ordering our part.

You can see the full project build gallery over on the Polyideas website here.