The Mantis CNC is a well thought out and very easy to construct PCB mill. Unfortunately, as it was originally designed as a PCB milling tool its build area is very restricted both horizontally and vertically. Because of this, and a few other small problems I have encountered over the past week of playing with a mantis inspired repstrap, decided to build a new repstrap with a few improvements.
The design scheme for this new repstrap require that it:
- Has a print area of 200x200x100mm.
- Has a heated print bed.
- Has an precision of 0.1mm
- Has a manually quick swappable extruder/cutting tool heads.
- Does not use any bearings (extruder excluded)
- Is constructable with only basic tools.
- Only requires parts found in domestic printers and scanners.
- Is easy to access for cleaning and maintanance.
- Has a viewable window that can be opened.
- Has a entirely contained heated build chamber with a maximum temperature of 100 Degrees C to increase part quality.
Obviously it is the last dot point which will be the hardest to achieve. At 100C any thermoplastic components will be softened enough that creep will become a real problem. Also it will put real stress on the stepper motors, which are rated to only 40C.
In order to (hopefully) solve these problems the build will go against the reprap theme and not be constructed using low temp thermoplastic. Even the Wade’s extruder will be a polyurethane resin cast, which is usable at 100c. To try and protect the stepper motors they will be contained outside of the build area and exposed to the ambient temperatures only. This is of course all stepper motors apart from the extruder stepper, which must be within the build chamber.
To protect the extruder stepper motor it will be insulated and then cooled with a peltier(wiki link). If you find the wikipedia entry too heavy going, then take a look at this less physics based description instead. On ebay there are currently Peltiers rated for 230C , however I cant find much detailed information on them. This is far from the most efficient design, but I think it should work maintain a safe temperature for the stepper motor. Though more research is required though before I commit to this idea.
This is the design so far (to scale) as compared to the current mantis inspired repstrap:
The x, y and z stepper motors are located outside of the build area. Like the original repstrap, it will be constructed from plywood. The glass doors on the front will open by folding up on hinges until they lock into place on the top with felt covered magnets.
If more access is needed to remove printed parts or swap out an extruder then the sides with handles will also fold down on hinges to open up the print area completely.
However, even when closed up there will still be a 20mm wide gap where the Z extension bars move up through. My hope is that I can use bristles from a brush to stretch across the gap but still allow the rods to move freely from side to side.
The heated bed will be based on nophead’s 290W proven design using this aluminium clad resistor. My hope is that the combined heat from the extruder and the heated bed will be enough to heat the chamber alone.
Here is a close up of the extruder and z-axis. I havent drawn in the sliders in this image. The extruder was imported directly from the stl files and scaled so it should be the correct size and shape. The heat sink and fan is coupled directly onto the hot size of a Peltier and the cold side would be directly coupled to the stepper housing, which would be insulated.
I’m not sure if the fan cooling for the hot side of the peltier heat sink will survive for long at 100C+. If not I will need to build something custom.
If you want to take a closer look at the model you can download a copy from the google 3d warehouse.