But what if I don't have access to a laser cutter or waterjet, or can't hire it out? Don't worry, these next few sections are well-suited to garage builders, and much of it was how Yours Truly was able to build consistent robots for years.
Without a freeform 2D fabrication process, the square edges of finger joints are extremely hard and time consuming to make. Usually, it's not worthwhile at all because other methods of fastening exist.Nutstrip
It is fairly common for builders to attach 2 plates at right angles, contacting eachother (a Tee joint
). Most often, this is done with an angle stock in aluminum or steel. If the stock is thick enough, end tapping
, or drilling straight into the thickness of the material and cutting threads into it, is another common tactic.
Another method which can be versatile is known as "nutstrip". Typically it takes the form of an extruded barstock, for known square sides and size standardization, drilled and tapped at regular intervals. In the past, they were DIY items - literally made by hobbyists on mills and drill presses, but these days they can be purchased stock on sites like Kitbots
, among others. However, if you can obtain small barstock economically, they are still easily made on drill presses.
Nutstrip is the most helpful when the plates being joined are of roughly the same thickness as the nut's square dimensions. In this case, it can offer increased rigidity over using a thinner angle-stock-based right angle joint. In cases where the stock being fastened is very thin, then the angle stock is generally of a greater surface area and hence stiffer. However, watch out - the rest of the structure can be floppy!Uber-Nut
A nickname for a single-row-tapped nutstrip that takes the place of individual nuts. The highly increased surface area of an "uber nut" compared to multiple discrete nuts makes the joint stiffer. This is helpful in situations where the mounting substrate is very flexible (e.g. metal fastened onto plastic), or fiddling with individual nuts is difficult, such as a confined space.
These can easily be made from drilled and threaded bar stock.Corner Blocks
An offshoot of the nutstrip is a corner block
, tapped on many faces and used to secure a modular assembly to another. It's very commonly found on generic drive base robot kits because of its easily reconfigurable nature.
The corner block is usually made from a much thicker material into which threads can be cut on (usually) at least 4 out of 6 faces of a prismatic stock. Different situations might necessitate other thread configurations.
Besides offering high stiffness to otherwise floppy corners, designing with a regular bolt pattern makes for easy disassembly and swapping of modules. The ultimate example of this is perhaps the optical table
, also called the optical breadboard, for which myriad accessories and mounting kits for various implements exist across manufacturers.