Welcome to the development page for the prototype "RedBot" repstrap 3d printer. This 3d printer will be used to repstrap a more permanent 3d printer first by printing replacement parts for the repstrap in plastic and later by printing either a huxley or mendel. This printer will also be a test bed for testing a long list of potential modifications for mendel and will also be making use of its larger bed to produce larger parts as required. Check out the flickr set of photo's documenting assembly of the frame (so far)
About the RedBot
This repstrap utilizes an X axis upon which rides the y axis, and upon that, the extruder carriage. The bed will make use of trapped nuts to ride up and down a Z screw drive much like the mendel uses on the carriage assembly. The printable area is currently looking to be approx 360mm x 300mm with a z depth of approximately 193mm at the moment.
In the last week(?) i've dissassembled and reassembled the whole upper frame 3 times. This is due to friction issues on and between the 2 Z screws, one is driven by the motor and the other is connected to the first by a timing belt. Liberal use of bearings has reduced the friction to a level where the only issue now is getting the right amount of tension on the belt to stop skipping steps. The Z screws originally sat on the bottom vertex pieces with a bearings outer ring pushed up against the wood of the vertex piece and the inner ring secured between 2 nuts. These nuts should turn freely(and the holes drilled in the vertex piece allowed this) but the upper end of the threaded rod passes through the upper vertex piece and this led to friction which was fixed with more bearings. The way the Z assembly is set up now, The Z screws actually float just above the lower vertex pieces now.
I started off with a generic Arduino Mega 1280 and started ripping dead printers apart for stepper motors. I have 5 working Stepper Motors and 2 of those motors have prototyped stepper drivers, however in order to make more progress and to get around the fact my soldering skills are VERY rusty, i've opted for some allegro stepper drivers with voltage regulators from a uk based company. **UPDATE** just arrived, there pololu's so should do a very good job!
I've been through a lot of ideas for extruders and the prototypes i'll be testing are listed below :
HotGlueGunStruder - like it sounds, i'm taking a hot glue gun, ripping the outer housing and trigger off and replacing it with a frame, a gluestick feeder and a smaller nozzle. Low tech with low melting point plastic applications as well as possibly utilising for experiments with other materials that require lower melting points.
Generic Extruder - based on the existing relatively basic extruder design, Adrian's Geared Extruder cold end + geared extruder nozzle hot end, a relatively basic extruder design with a brass extruder nozzle, PTFE thermal barrier etc. I hope to make use of this extruder with PLA and ABS.
HotWaxSyringe WaxStruder - I've got some experiments to perform with wax and resistance wire before i'm ready to start extruding wax but if i can crack it, i'll have a potential support material and custom candle printer.
SandCastruder - An idea both myself and a member of the north devon model engineer society suggested to me recently, printing with sand and a fixative to create cores for casting work. Definitely useful longterm.
The printer itself will repstrap me a working mendel/huxley which i can use to print other stuff but once I have that, the repstrap will be used as a test bed for potential new printer ideas. The following are currently being mulled over while i build the redbot so i have a hope of getting to this point.
Heated Bed - been done to death but apparently its very useful in a number of situations...
Heated Chamber - not done as much but enclosing the square frame with some MDF panels will probably give the printer more stability anyway.
Multi-Head - an extra axis set on the Y carriage will give the printer interchangable heads. discussions of extruders on rails or set up like microscope multiplier lenses have been considered.
Spindle support - important for stress free prints.
Temperature sensor overload - nothing crazy, just an expansive set of thermal sensors all over the printer to try and give me feedback on everything from extruded material temp to bed and ambient temperatures. I want to know how this affects any given print.
External Links to Project Progress
The RedBot RepStrap looks very similar to the Columbus RepRap.