Building surfaces for the PurpleDrop requires spin-coating a hydrophobic coating. Many spin-coaters come with a vacuum chuck for holding the substrate, and this works well for glass plates. However, it does not work so well for the dielectric film, as it is not as rigid. Additionally, commercial spin coaters are expensive and may not be available, but it it possible to build one cheaply from hobby motors.
This chuck system allows for quick release of 100x74mm dielectric frame (the standard size used by all MISL electrode boards), 50x50mm glass plates, and 50x75mm glass plates. It is designed to be attached to this servo city motor hub but an adapter is also available to use this fixture on a standard vacuum chuck spin coater.
To build the chuck, you will need to print these components, and you will need M2 threaded heat inserts (like these) plus M2x5mm screws (like these) to attach the locking arms.
The part can be printed on an FDM 3D printer with PLA filament. The heat inserts are then melted into the holes in the part -- special "heat-set insert tips" for soldering irons exist for this, although it is possible to insert them using a standard conical soldering iron tip. If you've never used heat inserts, consider printing a small test part with some 3.2mm diameter holes and practicing on that first.
spincoater_100x74_chuck.stl - The main part
spincoater_chuck_lock_lever.stl - Two of these attach to secure the part in place
For coating glass top plates, there are two adapters (one for 50x50mm, and one for 50x75mm glass) which can be quickly attached to the main chuck. Flexure in the arms is used to secure the glass plate.
Both adapters use a common base. To build the adapter the base and glass chuck should be printed, and they can then be glued together with CA glue.
spincoater_chuck_adapter_base.stl
spincoater_glass_chuck_50x75.stl
spincoater_glass_chuck_50x50.stl
The vacuum adapter is two parts, which glue together (CA glue recommended) and then glue onto the main chuck component. It is intended to fit on a 40mm diameter vacuum chuck. Make sure that you get a good seal -- i.e. you can pull a strong vacuum -- with the face. I have found it to work, but this may depend on the surface quality of your 3D printed part, as well as the stiffness of the seal on the chuck. If you find it leaks, you may be able to glue on a small laser cut piece of acrylic or other plastic to provide a smooth surface to seal.
spincoater_chuck_vacuum_adapter_A.stl spincoater_chuck_vacuum_adapter_B.stl