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.