Mendel90 Rapid Prototype Machine - 3D Printer

Mendel90 using Printrboard revision D electronics (maybe E - I forget)

AKA Reprap 3D printer

Instructions and information


  • The power for motors and heaters needs to be turned on via the web ui and physical switches on the printer.
  • The print will need a manual ajdustment at the start of each print.
  • Cura needs to be configured exactly

Get model

OpenSCAD Every 3D printer user should learn OpenSCAD.

  • Create your model using binary operations.
  • To preview model press F5
  • To compile the model press F6.
  • After compiling export the model as a stl file.

Meshlab - useful stl tool

netfabb - model repair tool. To download for free choose the Basic version.

To repair a model

  • Open model
  • Click the red cross in the tool bar. This will open edit mode.
  • Click the repair button
  • click apply buttons
  • Ok to replace
  • Export the model by right clicking on it and choosing export as STL.

Slice model into gcode

Cura One of the better fastest slicers. Drop the model onto the checker board, edit settings and Save the gcode. Cura automatically slices the model as you edit things.

Cura settings

All setting (except fill density) need to be as shown including start and end gCode. For things like walled boxes that are only a few mm thick leave the fill at 100%. For large solid items % fill can be reduced to 25% - or better yet edit your model into a walled configuration.

Configuration Ian uses

  • ; Start gCode
  • ; Sliced {filename} at: {day} {date} {time}
  • ; Basic settings: Layer height: {layer_height} Walls: {wall_thickness} Fill: {fill_density}
  • ; Print time: {print_time}
  • ; Filament used: {filament_amount}m {filament_weight}g
  • ; Filament cost: {filament_cost}
  • M80 ; power supply on
  • M109 ; wait for temp
  • G21 ; metric values
  • G90 ; absolute positioning
  • M107 ; start with the fan off
  • G28 X0 Y0 ; move X/Y to min endstops
  • G92 X0 Y0 E0 ; reset software position to front/left/z=0.0
  • G28 Z0 ; move Z to min endstops
  • G92 Z0 ; reset software position to front/left/z=0.0
  • G1 Z0.2 F{max_z_speed} ; move to layer height
  • G92 E0 ; zero the extruded length
  • G1 F200 E10 ; extrude 10mm of feed stock
  • G92 E0 ; zero the extruded length again
  • G1 F{travel_speed}
  • ; End GCode
  • G91 ; relative positioning
  • G1 E-1 F300 ; retract the filament a bit before lifting the nozzle, to release some of the pressure
  • G1 Z+0.5 E-5 F{travel_speed} ; move Z up a bit and retract filament even more
  • G28 X0 Y0 ; move X/Y to min endstops, so the head is out of the way
  • G1 Z-0.5 F{travel_speed} ; move Z back
  • G90 ; absolute positioning
  • M104 S0 ; extruder heater off
  • M140 S0 ; heated bed heater off
  • M107 ; Fan off
  • M84 ; steppers off
  • M81 ; power off

Connect to printer

  • http:\\10.0.0.Something - it keeps changing, currently I think it may be 23
  • Username: mendel90
  • Password: mendel90

Turn on printer

There are a couple physical switches on the printer they all need to be on. The front switch will kill the heaters and motors if need be. The rear switch will kill everything including the server. As long as the bed and extruder are off it is ok to leave the server power on so it is avaliable to others. Turn the power on using the web interface enter code M80 in terminal. M81 will turn if off again.

Set temp


  • Use a glass bed with green tape
  • The bed may be off or heated to 60 degrees
  • 180 is a good starting point for PLA.
  • If you need to change the temp move in no more than 5 degree increments.
  • Set the hot end in the range 170 to 210 degrees. Typically 180.
  • The tape needs to be flat with no missing sections or overlapping sections.

When hot and idle the head can drain and wont lay plastic until it refills. Just before starting a print you can optionally

  • Raise the head a few cm,
  • Extrude plastic until it clearly squirts out
  • Wipe clean the nozzle removing the excess plastic.


  • Upload the file to the server
  • Click the open icon next to the file name to select it
  • Click the print button.
  • To get the print to stick you need to manually turn both z axis rods by hand.

To adjust the Z height: Turn at the couplers between stepper motors and threaded rods. Anti clockwise goes down. Do not turn so far as to pull the support nut out - the large M8 nut on the threadded Z rod should sit snugly in the bottom of the bracket that connects the Z axis to the X axis.

While printing the skirt or brim - first thing printed, make sure:

  • Is a distinct slightly flat line - ie sticks well to the bed
  • Equal on both left and right sides - they are driven by separate motors and can fall out of sync
  • Not too flat or the plastic will bulge and make the next few layers messy.

Turn here

PLA prints better with an extruder fan. After 2 or 3 layers have printed turn it on for the rest of the print by using the code “M106”. This will happen automatically if cura is set up correctly.

Remove the part

When the print is complete let it cool and solidify. It you try and remove it too soon you can deform the print.

For PLA Push a knife under one corner of the part and use it to leaver it off the bed working around the edges into the centre. It will probably tare and mess up the green tape.

Trouble shooting

Plastic stops moving in the extruder:

  • Push plastic through manually until it catches, adjust hot end temp and tightness of spring-extruder screws.
  • Remove plastic and extruder idler. Use a knife to clear any plastic from the teeth of the hobbed bolt.

Extruder clogged:

  • While hot manually push plastic as far as possible. Turn off hot end and allow to cool to room temp. Heat Hot end gently to 100 degrees. Pull on the filament while slowly winding extruder gear by hand to remove plastic. Discard end of plastic below clean unmangled filament.
  • If really clogged extruder may need to be disassembled and hot end soaked in acetone.

Print dosn't stick:

  • lower the print head by turning the z threadded rods at start of print
  • make sure the bed and green tape is clean. The green tape can be abraded a little to make a more porous surface.

Printer dosnt move or heat up

  • turn power on, at both physical switches and via the terminal with the code M80
  • Make sure the printer reports online in the web UI, otherwise turn the main power off and on to restart the server

Maintenance info

Pressing reset on the printer will disconnect it from the server. It will be unusable until the server is restarted.

Build instructions - note the PDF at the top it is slightly different but a useful guide

Blog of the printer designer

Models of printed parts

Electronics - printrboard rev D

LCD panel instructions

ABS and the heated bed have not been tested. Doing so you risk breaking the printer.

  • howto/using_the_3d_printer/mendel90_rapid_prototype_machine.txt
  • Last modified: 2014/05/17 21:04
  • (external edit)