PIKA Build Process
PIKA (Printable In-place Kinematic Assembly) is a µRepRap with the majority of the XY Table designed to be 3D printed in one piece without support on a conventional FFF printer using PLA filament. It marks a departure from the MAUS design in that it is designed for a specific purpose rather than a general μRepRap prototyping kit.
Click the links below for construction details on the major components of the system. Please read the general construction notes, tools required, and 3D printing notes below before starting:
- Optics
- CNC Control System
- Axis Drivers
- XY Flexure Table and Stage
- Probe Z Axis
- Consumables (probe tips and slides)
The prototype as built requires two USB Microscopes, self-illuminating, 30mm diameter cylindrical bodies. One should ideally have at least 8Mpixel resolution to observe the print area, the other can be of lesser quality and is used to gauge the approximate probe height. It is convenient if one of them can be obtained to fit a 16mm pole on a stand via a height adjustment system, but this is not essential. Test and measurements of output will require a bench microscope.
To view the video output of the microscopes, using the mpv video player was found more convenient than the vendor's app. One instance is run for each video device, and mpv supports keyboard macros for zoom/pan etc. It is uncluttered, free, Open Source, runs on multiple platforms, and integrates well with user-developed software.
The CNC Controller needs to drive 3 x NEMA17 400 step/rev motors with 5mm diameter output shafts approximately 23mm long. The shafts can be round or have a flat. If motors with a different shaft length are used, the 5mm thick NEMA Plate can be omitted, a different length Drive Screw used, the thickness of the Motor Pillar Mount's base changed in OpenSCAD (motor_base_thick, maus_axis_driver.scad) or a combination of those. Note that some adjustment of screw lengths will be required.
A caveat for large NEMA17 motors is that the Z Axis Driver only has limited room underneath it for the motor body. For very tall NEAM17 motors, 3-hole Metriccano strips are used as a shim to raise the driver assembly.
For I/O the CNC Controller needs to support Z Touch, Normally Open max & min limit inputs, and have one spare output capable of driving a 20mA UV LED.
Note that the NEMA17 motors in the assembly instruction illustrations are somewhat over-specified, and smaller ones will suffice.
You will require:
- Screwdriver to fit chosen M3 fasteners
- Pliers
- Needle-nosed pliers
- Small wire cutters
- Small, sharp scissors
- Fine blunt tweezers
- Electric drill
- 3mm HSS drill bit
- Medium flat file
- Fine awl or similar long pointy tool with blunt edges
- Lighter or similar heat source
- Masking tape
- Thread locking adhesive
- Cyanoacrylate adhesive ("Superglue")
You may find useful:
- Magnifying glasses
- Wire stripper
- Haemostat
- Dental tool with a hook and probe
- Adjustable clamp
- Portable bench vise
- Hot glue
- Soft-faced mallet
- Caffeinated beverage
The probe tip and the prepared glass slide used by RepRap are considered consumable.
Rough tips can be fabricated from hypodermic needles or acupuncture needles and are ideal for initial experience with the hardware when the chance of a probe being abused or accidentally destroyed is quite high. Fine tips are created by an amazingly simple electrolysis process currently documented on Printables where the jig for holding the wire in the electrolysis cell can be found.
The glass slides are standard cheap soda glass microscope slides. Coated in Sharpie Marker they form a surface that can be scratched and easily reused during testing. For more precise work a print bed is constructed on a glass slide with an aluminium foil resin reservoir from which the probe tip can be recharged like a dip pen.
Parts were printed on a Prusa Mk4 with a 0.4mm nozzle, taking approximately 25 hours in total and using less than 500g of filament. The parts should be printed in plain PLA or eSun PLA+, 0.2mm layers, 2 perimeters, 4 top/bottom layers, 20% grid infill. The majority of parts need no support or brim, with the exception of the Flexible Linear Coupling which needs brim only. PLA with additives to give unusual finishes such as matt, roughened, metallic etc. will definitely not work. Others might, but have not been tested. Cheap 'PLA' tends to have a very low actual PLA content, so stick with a reputable brand. Maus C print sheets are available here on Printables (but can be compiled from Github source) are:
- Axis Driver (three of)
- Maus Complementary plates A, B, and C
- Maus Probe
Names used in the assembly documentation will usually closely resemble the names used in the OpenSCAD design files.
Note: The prints may be tidied, but be careful with the Axis Driver as it has fine detail that you may remove thinking it is a defect. If you see loose filaments around any of the flexures on any part, just leave them. It is highly likely that the flexure will be damaged if you attempt to remove them.
Metriccano is a system of generic 3D printed parts perforated by 3mm holes on a 10mm grid that can be used for rapid prototyping. This is used throughout the Maus design, and is similar in concept to the English 'Metriccano' and American 'Erector Set' construction toys. It allows parts to be easily added, shifted, and replaced when developing prototypes as well as making an educational toy for children. It is available in the 'library' directory in the Maus OpenSCAD source code should you wish to customise or steal parts.
The gist of each section is to prepare any parts requiring hand tooling, insert captive parts, then assemble.
Not all sizes of M3 screw are available everywhere. In most cases a slightly longer screw will work, though some washers may be needed under the screw head to stop the screw shaft from, say, obstructing a moving flexure. In extremis, there's always the hacksaw but do not use any form of shear as you may distort the thread.
The easy way to insert M3 nuts into cavities
When inserting M3 nuts into cavities face first, it often helps to screw an M3 x 50mm screw into them for use as a handle. When inserting M3 nuts edge first, it is essential that the sides of the nut are in parallel with the sides of the nut slot - insert them with needle-nosed pliers or a haemostat if you have fat fingers. Push nuts the rest of the way into the slot with a small screwdriver or similar, then poke a pointed object into the screw hole and use that to align the nut.