How to create a machine from scratch to detail

It’s like eating an elephant. One bite at a time.

I always start with a sketch pad and a pencil. I work out the basic design and major parts before I move to CAD. There is no substitute for a freeform hand sketch. I often return to hand sketching several times during the whole design process.

In CAD, you start with designing the important parts. As these parts are placed into an assembly they are often constrained in free space to each other. Often the locational constraints may be to the root X, Y, and Z workplanes. After the important parts are in position then move on to designing the framework or structure that holds it all together. Finally finish out the design of the smaller less important parts. It’s an iterative process. As you move from one section to another you often must go back and modify parts and assemblies you think were finished. There may be parts that need to be reworked into assemblies. You may create temporary parts and assemblies that serve only as placeholders until the design is further along.

As you are designing parts, consider what the process will be if you have to modify that design. Like stretching a part a little or moving a hole. Keep your sketches simple. Make sure your sketches are always 100% completely constrained from the very start. Unconstrained sketches are difficult to modify and may do strange things if edits are made to other features.

I see videos of software like Fusion where freeform edits are made to components. Stretching a little here. pushing a hole there. That's a totally useless design process. While it's fast and looks cool, if you're designing a machine, you need details constrained to exact dimensions. Parts in the real world need to be made to exact dimensions. You must design with exact dimensions.

I essentially do a top-down design approach. I work in the assembly environment, working on individual parts as they fit into the assembly. Sometimes I will develop individual parts outside the assembly environment but immediately place them into the assembly to check fit and function. Occasionally parts are developed in a multi-body part environment and then they are "derived" out into their own part file. This derived-multi-body process has some advantages and disadvantages that are too lengthy to mention here.

I like to make my machines modular. For instance in the box folding machine you may have an input module where the flat box is fed in. Several different modules for each of the folds. Then finally an output module. The idea is if one module doesn't work as intended or worse yet, must be completely redesigned, You may not have to make any changes to the other modules. This modular approach allows you to build the machine as a series of sub-assemblies that are then fastened together for the final machine. This makes it easier to design, assemble and maintain the machine.

Never think any level of detail is too small. Prototypes often have a few details that are worked out when the machine is actually built. But in the end, I always feel every single nut bolt and screw must be accounted for in the design. All parts should have all holes detailed. Avoid the “drill at assembly” conundrum. If the person assembling the machine has to drill a hole, you failed as a designer.

The detail and assembly drawings need to convey every possible piece of information required for construction and assembly. Avoid verbal instructions. Pretty renderings are nice but they’re seldom actually required to convey information to the builders. Not saying they shouldn’t be done since a picture IS worth a thousand words. But the detail drawings are much more important and are where you should concentrate your efforts.

You see a lot of rendered images here on GrabCAD. That may lead you to believe that's a normal part of the design process. It isn't. Even the people selling CAD software use those cool renderings to promote their product. Renderings are actually rarely needed or used. Time is of the essence and no company nor individual is going to want to waste time on a labor intensive process that usually isn't truly needed. Understand we are talking a mechanical design process for conveying information on how to build and assemble a machine. If the end goal is a rendering that you're going to hang on the wall then it's different story.

As you’re designing the machine, keep in mind the capabilities of the machinery and people that will be making it. Don’t create a design that they don’t have the ability to make. If all they have is a drill press, a saw, and a welder, then you need to design the parts accordingly. Don’t design parts that require CNC machinery if they don’t have it. Don’t design parts requiring a ultra-precision centerless grinder if they don’t have one, etc. This is where your design will shine. When it fits the capabilities of the people and equipment that will be used to build it.

Your first time through will feel very cumbersome. As you develop your skills you will get to know the sequence of design and what comes first and how to fit it all together.