Many people assume that since the machine uses water, the waterjet cutting process is quite gentle. This is far from the truth. In actuality, a waterjet cutter uses a stream of water and garnet sand to blast through material at 60,000 or higher pounds per square inch. Here's what it looks like when the waterjet first starts.
Next, we've got a close look at the waterjet cutter in operation working on the same job in 1/4" thick aluminum 6061.
One increasingly popular CAD tool is Onshape, a new 3D design software package. It's free for many uses and can run in a desktop web browser without extra plugins, or as an app for Android or iOS.
Big Blue Saw can make parts which are designed in Onshape, as long as the designs are compatible with waterjet or laser cutting. I'll walk you through the steps to create a part for Big Blue Saw from Onshape's "Hexapod" sample design. To access the Hexapod, click on "Tutorials & Samples" from Onshape's main screen, then click the name "Sample - Hexapod".
Once this design is open, we will need to make a copy of it in order to make some minor changes. At the top of the screen, click the link that says "Make a private copy".
Onshape will show you a dialog box which allows you to create a name for the copied document. It also lets you set the new document as being Public (shared with all other users) or "Private" (only seen by yourself or people on your team). For this design we'll make it Public. Click the "Create public document" button to create the new document.
We now have a copy of the Hexapod which we can modify. The base of the hexapod looks like a likely candidate for waterjet cutting. Click the Baseplate tab to see just the Baseplate.
Now we can see just the Baseplate portion of the assembly.
Notice that it has a filleted (rounded) edge on the top face. Big Blue Saw currently has no good way to make this feature, so let's suppress it. Right-click the Fillet 1 feature in the Feature tree and choose "Suppress" from the pop-up menu.
Now we have a part in Onshape that's ready to be waterjet cut, as seen below.
To produce the 2D profile the waterjet needs, right click on the top face of the Baseplate and choose "Export as DXF/DWG" from the pop-up menu.
Onshape will show a pop-up dialog allowing you to choose the file type. Big Blue Saw accepts either DWG or DXF. We'll choose DXF on the drop-down and click the "Export" button.
After you click the "Export" button, Onshape will send a DXF to your computer with just the outline of the face we chose in the earlier step.
Once we have the DXF file downloaded, we can now upload it to Big Blue Saw's online quoting tool to get an immediate quote. You can choose a material and thickness as appropriate for the project. For example, we've chosen 0.5 inch thick aluminum alloy in the screenshot below.
Cody Armstrong conducted a webinar on 2D drawings in Onshape and specifically mentions our particular use case. The discussion of generating a DXF for waterjet and laser cutting begins at 51:22.
If you've been successful (or had any trouble) using Onshape with Big Blue Saw, let us know in the comments section below or drop us a line at firstname.lastname@example.org. To learn more about designing parts and assemblies for waterjet cutting, read our articles on designing for waterjet.
Join us this Saturday and Sunday, October 3 and 4 for Maker Faire Atlanta. Meet tens of thousands of enthusiastic and excited adults, teens and kids as they gather in downtown Decatur for a a family-friendly showcase of invention, creativity and resourcefulness. Big Blue Saw is a sponsor of the Faire and will have a booth you can come visit. We hope to see you there.
Recently I had the opportunity to compete at Robot Battles in Atlanta. When building with waterjet or laser cut parts, it is a challenge to make parts that fit together solidly without welding. My robot's chassis was mostly held together with t-nuts and tab-and-slot, but this wasn't adequate for the top cover of the chassis. You see, the top needs to be removable for quick access to swap batteries or do maintenance, and t-nuts just don't make that easy. With t-nuts, you have to keep the nuts aligned in their respective T's when installing them and you have to try not to lose the nuts when taking things apart.
There's a solution for this problem that I had been meaning to try out for a while. This solution had been developed by Fingertech and recommended to me by Mike from Near Chaos Robotics: nutstrip. Nutstrip, shown in the top image, is square profile aluminum bar machined with tapped holes at regular intervals on two faces. Using nutstrip allows me to install and remove the top of the robot easily, as the nutstrip is held in place.
Nutstrip comes in four sizes, from a 3/16 inch square profile up to a 1/2 inch square profile. I chose the "Medium" size, which is 3/8 inch square with 10-24 holes tapped at 14.5 mm intervals. I had already chosen 10-24 screws for the rest of the hardware in the robot, so this made a good match.
Below is a closeup view of the clear polycarbonate top held in place with red nutstrip. The nutstrip was cut to length with a hacksaw to hold two screws on each face. One of these sections of nutstrip was used in each corner.
The diagram below shows how the parts were designed together in CAD to mate using nutstrip.
One potential disadvantage of nutstrip is that it occupies the entire corner of the chassis, reducing the space available for other components.
The nutstrip pieces held up well during combat and I had no problems with the quality or finish. Nutstrip is available from Kitbots and FingerTech.