# Onshape Tutorial for MASLAB

Tutorial courtesy of Brian Minnick and John Zhang.

This tutorial will get you up to speed with using Onshape to create CAD models of your robot. We highly recommend Onshape for MASLAB as this will make it easier to share your CAD models with the staff and sponsors.

## Getting Started

Please create an educational Onshape account using your MIT email. It is free with a .edu email. For the school website URL please use https://maslab.mit.edu

### Learning Center Tutorials

We recommend that you complete the two following tutorials if you are new to Onshape. If you are already familiar it may prove to be useful regardless. The more advance concepts are always good to learn.

## Designing for Laser Cut MDF

In this section, you will complete the exercise of designing a top plate for your kitbot that can be laser cut out of Medium Density Fiberboard (MDF) on the laser cutter in EDS.

### CAD for Laser Cutting (1/4 in MDF)

Designing parts for the laser cutter in Onshape is easy! Here are a few tips to make your CAD experience smoother.

### Setting the MDF Sheet Thickness as a Variable

Before starting to model your robot, make sure to measure the thickness of your MDF with a set of calipers. Each sheet is nominally ¼ inch thick, but each sheet can vary. Put this value into the variable table, located on the left side of the Onshape editor, shown below. It is better to overestimate this value slightly than underestimate it. 6.25 mm seemed to work well for us.

Name the variable something like MDF_thickness and give it the value you measured. If you do this, whenever you want to make an MDF part, instead of extruding ¼ inch each time, you can use this variable instead. This will keep all the parts the same thickness, and allow you to easily change the thicknesses of the sheets if you get a sheet that is slightly too large or small.

### Creating 3D Bodies

Creating a CAD model for laser cutting adds a few more constraints than with a normal CAD model. Since the laser can only cut from a flat sheet, your parts will be "2.5D," meaning that you can only design 2D parts and assemble them into a 3D shape. In short, to make good parts for laser cutting, try to draw the entire part in one sketch (to ensure that it can be cut with the laser) and extrude this sketch with your MDF thickness variable from the previous section. This will ensure your parts can actually be cut with the laser, but you can still make a fully 3D CAD model.

### Tolerancing using Variables

Tolerances are usually not required for laser cut parts. Especially with thick MDF, the kerf (or diameter of the laser spot) will allow parts to easily fit together. However, with some materials and thicknesses, or if you want a free/sliding fit, adding tolerances to your parts is a good idea. The easiest way to apply tolerances is to make a tolerance variable, as in the last section, then use the “Move Face” tool on any faces which should have extra tolerance applied. I have a few tips for this:

1. Put a negative value inside your tolerance variable, this will prevent you from having to flip the direction of the move face command every time (it will default to moving the face backwards, which is desired for making a fit looser).
2. Set a tolerance distance which will only require moving one face. If you have a box joint, for instance, you can move only one of the two coplanar faces at each interface, reducing clicks by 50%!
3. If you are unsure what values to use for each new material, CAD a small test patch with different (labeled!) joints and laser cut that before trying to cut an entire part.

### Exporting Parts

If you have a 3D part that you want to laser cut, simply right click on that face and find “Export as DXF/DWG” in the menu that appears. For almost all applications, this is totally sufficient. If you want to add engravings (laser cut features which do not cut all the way through) to the part: make a new sketch on that surface, add any geometry you want to engrave as sketch lines, and export that sketch as a DXF.

### EDS Laser Settings

From experience, it is better to err on the side of having the laser focus slightly higher (rather than lower) using the focusing tool. You will certainly need 100% power and the right cutting speed will be between 1-2% depending on which laser (there are two of different wattages). You should always cut a small pilot hole 3 mm diameter to test the settings, which will save you time and material. If this small piece falls out of the stock without you having to push it through, your settings are good to go! If you are having difficulty getting the laser to cut through with one pass, you can make two passes (running the same file twice in a row), but be absolutely sure you do not touch or move the MDF between cuts.

### Packing a Laser Cut

Pack and pattern laser parts as much as possible to save material. The MDF takes at least a full day to procure and we will only be do so once a week. See the example below.