A Major component of or Liminal mass project was designing a sub system for the 3D printed structure to hang off of. This structural system contains all the mounting points for the other components. It is the base for the electronics, provides the structure for the printed components, and attaches to the hanging devices from the building.
The system is constructed using waterjet cut aluminum sheet, aluminum tube, and angle brackets. This was our first experience with cutting large thin sheet goods with the OMAX so there were some tricks we picked up along the way!
Step 1: Design+Prototype Your Hanging System
OMAX water jet cutter
OMAX Layout/Make software
3D Modeling software (Fusion, Inventor, Rhino/Grasshopper)
1/16" aluminum 4x4' sheet
Conceptually our system consists of a set of ribs attaching to a milled spine on which electronics are are mounted. that spine is then attached to the structure of the building.
Design your waffle grid structure using a 3d modeling software, such as Fusion 360. We used a combination of Fusion360, Inventor, and Rhino/GH to design various components of the system. We found that working in STEP and going back and forth works well.
The first step was to design a detail for connecting the diagrid members to each other. Our initial attempts focused on welding since we would need the rigid moment connection to resist racking. After a few failed TIG welding attempts on thin aluminum we decided to go with a mechanical fastening system.
With the precision of the waterjet we were able to design a permanint cam system. A notch and locking pocket is cut into the deeper transverse member. The matching notch and cam is cut into the thinner lateral supports. The pieces fit together with a tight enough tolerance to maintain 90 degree angles.
After the parts are seated a screwdriver is inserted into the cam to lock the structure in place permanently.
Step 2: OMax Water Jet
Upload your file into the OMAX software and prep your bed for cutting.
- Load your material into the bed
- Clamp it down securely. Also, because used such thin aluminum, we had to use some heavier weights to keep the material from having too much torque and breaking the water jet tip. We kept a careful eye on the path and moved around the weight as we needed to. Thanks to the Pier 9 staff to assisting!
- After you have focused the water jet tip on the material, and measured to make sure you won't run into any clamps, it's time to cut!
- Because our tool paths were complicated, we did a mix of raised water and low water cutting.
Using OMAX Layout, start to toolpath your part on the water jet. Make sure to add tabs to keep your parts from falling into the bed of used garnet and dirty water.
Once your piece is cut, carefully unclamp and remove the sheet from the bed. Take the parts to the prep area.
=) be stoked!
Step 3: Tips for Cutting Thin Aluminum on the Omax Waterjet
Start cutting with the water down, this will ensure you can see if your parts are flipping up.
As you move across the plate follow the toolpath closely, use the large black plastic weights to hold down part of the plate that might want to get flippy.
While we were cutting this it was a dance with the Omax, it was cutting slowly enough that we were able to place the weights then move them as the Jet came closer. This is a not a risk free operation and requires a pretty good idea of how the jet moves and where it's going next.
In general we were constantly bouncing back and forth from the control console, to the arm pause button, to moving the weight around.
Also when tool-pathing consider the side and floppiness of the pieces after they are cut. Since we had a large flat sheet of mostly cut pieces it was very difficult to remove. Adding relief cuts into the toolpath would be a good idea.
Step 4: Clean and Prep the Parts
Once you have the piece off the waterjet it's time to remove the parts from the leftovers. Use you hands or pliers to bend the tabs out and release the cut parts. This takes some practice to get right, especially since it was set up all the way back at toolpathing!
Don't worry too much about getting the pieces out cleanly for now, we'll take care of those tabs later just make sure to not bend or warp the pieces.
Once the pieces are out of the plate, you can go after the remaining tab nubs with pliers. The aluminum should shear off right at the base of the tab leaving a clean cut.
If there is a flat area use a metal sander to zip the tabs right off.
Step 5: Drill and Tap the Main Spine
Now that the ribs are ready to go it's time to prep the spine.
The ribs are connected to the spine with a series of tapped holes. Mark off the distances from hole to hole with a sharpie and speed-square. You could use a Bridgeport to be absolutely precise about these holes but there is no need so I just used the drill press and vice with parallels. The holes are just going to be tapped so as long as they are centered they will work.
Drill the holes one at a time, make sure the drill press is set to high speed for aluminum. The walls on this tube are thin so no need to peckdrill. Consult a Tap Drill chart to get the correct size hole for the tap you are using. I'm using M4 bolts so my drill size is #30.
Coat the hole with tapping fluid, there is a different type for aluminum and steel. For small taps you can use a power drill, for larger taps it's a good idea to use the hand tap handle.
Step 6: Assembly 1:Grid
- Metal grinder
- Bolts and screws
- Angle brackets
- D rings
Now it's time to put it all together! Start by laying out the pieces, we engraved the number of each piece into the side when they were being cut so that it would be easier to keep them in order.
First we assembled the crimp connections. The small ribs fit into the larger ribs to make up the grid. Once we got all the ribs seated we went back through with a screwdriver and crimped closed the rib cams.
The 2 grid sections match up along the long thin ribs, these has to be broken into 2 parts to fit on the waterjet stock. They are connected by a set of clamp plates connected with through holes to make a rigid connection. We used Nylock nuts to ensure that the screws will stay tight.
Step 7: Assembly 2: Spine and Final
After the 2 grid sections were connected we moved onto the spine. We attached the angle brackets which connect the spine to the grid using red locktite. This locks the threads to make sure the arn't going to come out.
After the angle brackets were installed we added the electronics mounting plates. One minor problem with the design was that we had to install the power supplies onto the mounting plates before mounting the plate to the structure. We used countersunk bolts to attach the PSUs then attached the assembly to the spine.
Once the spine was completed we added in the connecting ribs with connect the spine brackets to the ribs. These were secured with Nylock fasteners.
With that the structure is completed, time to move on to mounting the prints and setting up the electronics system.
Check out the Finished Project here.
Other Instructables in the series are here.