When tightening a screw, firm will do. Do not keep tightening until the screw can no longer turn because this can damage structure, actuators, and eventually the screw itself. Simply secure the screw to the point that the pressure is firm.
The side with the small ribs will always face towards the extrusion when assembling, so that the ribs can help square the bracket to the extrusion.
When securing a bracket to extrusion it is recommended to pre-load the bracket with screws. When the screws are loaded on the bracket before it is even brought near the extrusion, it is less likely that screws will fall out or get misaligned. The bracket can then be slid into place along the slot.
Building “stud up” is recommended with the REV Robotics 15mm Build System. This means building with the screw head inside of the extrusion. Pay attention to the direction that screws go into the brackets, only the screw head will fit in the extrusion.
When using the nyloc nuts, make sure the beveled “nyloc” side is facing out.
Have a plan for where the brackets and other structure pieces will go before building. Once pieces of extrusion are connected together it can be difficult to go back and add things without having to disassemble the robot. T-slot Screws can be used occasionally, but it is not recommended to build the entire robot this way.
When building different mechanisms, your design may need a specific length of extrusion or channel. Cutting structure down to the correct size is easy to do, and is recommended for these applications. Here are a few tips when cutting down structure to the right size.
Measure twice, cut once
Use a straight edge, not a measuring tape, to get a proper length. Using a marker with a sharp point, like a sharpie, helps as the "inside" of the mark is where to cut.
Use painter's tape
Preparing the structure before cutting by applying painter's tape can help make straight cuts. Align the edge of the tape with the mark and wrap along the cutting plane to help identify where to cut.
Use the right tool
At minimum, use a handheld hacksaw with a vice or clamp.
If using a powered saw, REV recommends using a horizontal bandsaw with proper clamping and safety measures to prevent injury.
Make sure that both sides of the structure being cut are supported while cutting to ensure a straight cut.