Aspects of 3D Design: Backlash

Aspects of 3D design

In this blog I hope to chronicle the lessons I learn throughout my process of designing my own creations. My goal is to be able to help others create their own designs, while avoiding the same mistakes that I have made.

What is Backlash?

In terms of 3D design, backlash is the term to describe the amount to space between moving parts before they actually begin to touch. In other words, it is the gap between different pieces of your design.

Why is Backlash Important?

Backlash is a necessary component to creating a final product with moving parts or that must be assembled from what you have made.
This is because the addition of backlash into your design accounts for possible imperfection or errors in your parts, tools, or assembly. For example, 3D printers use plastic that slightly expands when it is printed, and because of this, two parts that are printed to fit "exactly" together will fail to correctly assemble because the pieces will be slightly larger than expected. It is important to recognize where possible errors can arise and to implement backlash to account for them.

Backlash applies to all forms of construction from 3D printing, to woodworking. Each material will use it in different ways.

What does Backlash Look Like?

For a project that I have been working on, I have been designing a robotic arm to be printed using a 3D printer and assembled afterward, and I have been using backlash for each part of it. 

When creating gears inside the arm, I need to add backlash in three places: once inside the gear to make the gear teeth further apart to account for the other gear's expansion. The second place is the distance between the two gears to make sure that the two gears do not overlap once printed. The third place is within the hole of the gear in which I made the hole larger that the peg it is fitting onto. I specifically needed to make sure that every gear could turn smoothly, without begin inhibited by improper fittings.