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Original Prusa i3 MK2/MK2S/MMU pinda probe cooler

by universaljoint, published

Original Prusa i3 MK2/MK2S/MMU pinda probe cooler by universaljoint Nov 9, 2017
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The PINDA probe on the original PRUSA i3 MK2/S has an achilles heel: when it heats up, it detects the bed too early. (This will be remedied by the soon to be released PINDA 2 which actively compensates for the temperature of the probe).

This is particularly a problem when printing materials requiring a high bed temperature in an enclosure, especially if a print is aborted and restarted soon afterward.

This cooler helps with this issue by blowing unheated air from outside the enclosure over the PINDA during the bed heating cycle.

1x EK1713 Limit Switch

1x 50X15mm centrifugal fan This can be either 5v or 12v, depending on how you plan to power it.

2-3 feet of 9/16" OD Vinyl tubing Commonly sold by the foot at most hardware stores

Power supply for fan
M3X10mm machine screws (x8)



Because the cooler is triggered mechanically, there are many options for powering the fan. The simplest is to repurpose a suitable AC to DC wall transformer.

Wire the limit switch as follows

  1. Positive lead of power supply -> Common terminal of limit switch (C)
  2. Normally open terminal of limit switch (NO) -> Fan positive terminal
  3. Fan negative terminal -> Negative lead of power supply.

ADVANCED OPTION: It is also possible to power the cooler using the Mini-rambo's outputs. I will not describe this process in detail since you could damage your printer if you don't know what you are doing.

On the V1.3 mini rambo, A 5V blower fan can be powered by pin 2 and pin 4 of the P3 expansion header

A 12 volt blower can be powered from the mini rambo by multiplexing the part cooling fan output. Use the NC and C terminals of the limit switch to direct power to the part fan when the limit switch is open, and the NO and C terminals of the limit switch to divert power to the pinda cooler when the limit switch is closed. You would also need to alter the startup gcode to activate and shutdown the part fan for this setup to work. (M106 S255 ; turn on part fan M106 S0; turn off part fan.)


Press the limit switch and wiring into the cooler nozzle. The free end of the limit switch arm must face away from the heatbed.

Place the cooler nozzle on top of the right Z axis stepper motor. Slide the bottom bracket under the motor, taking care not to pinch the stepper motor's wiring. Secure the nozzle to the bottom bracket using 4 * M3X10mm machine screws.

Insert the blower motor into the fan holder body, taking care to route the fan wires through the smaller hole. Secure the fan cover to the fan body with 4 * M3X10mm machine screws.

9/16" OD vinyl tubing serves as an air duct between the blower and nozzle. The blower must be mounted outside the enclosure.

Slic3r startup gcode to activate cooler

Startup gcode is used to activate the cooling fan by moving the tip of the pinda probe to the X and Z coordinates where it activates the limit switch.
IMPORTANT Some calibration of the exact X and Z position may be necessary. You may need to change the values in bold below to ensure that everything activates properly. May not be compatible with all fan shroud designs

M115 U3.0.12 ; tell printer latest fw version
; Start G-Code sequence START
M140 S[first_layer_bed_temperature];
G21 ; set units to millimeters
G90 ; use absolute coordinates
M83 ; use relative distances for extrusion

G28 X Y Z; Home X Y and Z axes
G90; Switch to absolute coordinates
G1 Z5 F2000; Raise nozzle to 5mm above bed
G1 X230 F8000; Rapid move to end of x carriage;
G1 X247.5 F600; Slowly move to limit switch
M190 S[first_layer_bed_temperature];
M104 S[first_layer_temperature];
G4 P60000; dwell for 30 seconds (gives extruder time to heat)
G1 X220 F600; back off to turn off fan

G28 W ; Mesh bed levelling routine with a cool pinda
G92 E0.0
M203 E100
M92 E140 ;(change if setting a custom esteps/mm value)
M109 S[first_layer_temperature]; If extruder not at temp yet, wait for it.
G1 Z0.250 F7200.000
G1 X50.0 E80.0 F1000.0
G1 X160.0 E20.0 F1000.0
G1 Z0.200 F7200.000
G1 X220.0 E13 F1000.0
G1 X240.0 E0 F1000.0
G1 E-4 F1000.0
G92 E0.0

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Amusing ! Indeed, I am amused to see all the issues you poor guys have with your overly complex auto bed systems when a well thought and made cartesian machine simply doesn't need all these "sensors".

All Cartesian 3d printers worth owning have a bed sensor of one type or another. The inductive sensor's advantage is that it can locate the bed in all three axes. Heat sensitivity has been addressed by an updated version of the pinda sensor which will be standard on the MK3 and available as an upgrade to the MK2/S. It is an issue that seldom bothers people who print PLA. I print mostly ABS in an enclosed printer, and it used to be an issue that frustrated me. This fixed it.

Of course, vendors prefer to offer this gimmick that is cheaper than to make their machines correct. When it is a must, like a Delta, the use of strain gauge, piezo or other kind of "switch" detecting the nozzle contact with the bed are far better solution. Of course, one has to design these to work properly and in a wide T° range. Not that complex, solved more than 50 years ago but often forgotten :)

Shrug - it was a clever solution and it worked well enough to make this "Printer of the year". There are better 3d printers in the world but this one offers amazing prints at an affordable price.

I didn't vote and I don't care. I am able to judge by myself. I reckon the Prusa is a good compromise, simplicity yet, good enough. fact is I bought a Geetech Prusa Al to get my hand on FDM because of that. BUT I knew from the start it is a dead end, not rigid, two Z steppers, no enclosure but the real killer, a Y moving bed.
So time to move on.

There is a massive difference between a cheap clone and an Original Prusa direct from Prusa Research.