Raj's Minimalistic Extruder MK1 for Printrbot

by HammerFET, published

Raj's Minimalistic Extruder MK1 for Printrbot by HammerFET Aug 24, 2012
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A small and quiet extruder only requiring a three parts rather than the six parts from wades extruder as well as the printrbot extruder mount system. It can also be doubled up with a mirror version for dual nozzle printing.

Video: http://www.youtube.com/watch?v=4cJrrj41O5c
Video: http://www.youtube.com/watch?v=vcOqAKPWycM


I came up with this extruder inspired from the compactness of the makerbots Stepstruder. It uses pretty much the same printerbot extruder mount design, just replacing the different parts by one 2-3 plastic parts. It requires a stepstruder MK7 hobbed gear and a spring loaded bearing system of some kind. I used the Minimalistic Mk7 replacement by whosawhatsis.


The motor can be run cool enough to not require a fan, however a fan for the hotend may be required to stop the heat getting to the plastic.

Hardware required:

Nema 17 stepper
MK7 stepstruder hobbed gear
40mm fan
Bearing (623 size - 3x10x4mm)
Heavy duty spring (~30x8mm)
Hotend (16mm)
2x Linear Bearing (8mm ID, 15mmOD)
1x M3x10mm screw
6x M3x16mm screw

Possible problems & tips on use:
-SPRING TENSION! (you really need a strong spring, so strong that the PLA arm hyolding the bearing flexes a little.
-STEPPER HEAT will melt the filament passing though the gear and damage the extruder where the screws tighten! (Don't run the stepper too hot, you don't need to. My printerboard has the pot set to about 25%)
-Bearing alignment, use the correct size bearing. (The design of the bearing arm by whosawhatsis has the bearing a bit off centre, either edit the file or make sure you use the right size bearing.
-Bearing binds on plastic arm (Make sure you clean up the bearing arm so nothing binds.
-Keep speed under 125mm/m or whatever your hot end allows. (You'll get slippage from the gear and the gear will get plastic all over it)
-Prevent extruder overheating due to nozzle being so close.

  • I added some foil tape behind the hot end just incase the heat affects the plastic behind it, haven't had any problems yet with up up 2 hour long prints at 215degC.
  • I didn't have the right size spring so used 5 smaller springs stacked together. An M4 screw holds them in place but doesn't tighten, allowing the top spring loaded mechanism to be released for quick filament change.

I have this running at 100mm/min and just printed a 2 hour print no problems, all motors cool to touch.

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I noticed the X axis 2 barrel's space is closer than the http://original.dooriginal.do you have the design those x barrels holder on Z axis?

can you please link the the top part design?thanks

could you pleaseee upload the obj format?

I'm curious about the durability of this without a bearing opposite the hobbled bolt like thing. Is it just rubbiing on plastic? and how long has it lasted for anyone else?

There is a bearing the other side of the hobbed bolt. That part of the design is actually someone else's. I Only designed the lower part that holds the nozzle and motor to the X rails.

Hi, any idea where can I get the spring and Hotend, or their part numbers? A store with international shipping would be preferred!

BTW, would the hot end from the printrbot store work? http://printrbot.com/product-category/hot-end/http://printrbot.com/product-c...

The spring I got was just from a pack of random springs i got on ebay. I actually had to double up some of the springs to get the right length and tension. See whosawhatsis' extruder to see what spring he used. In terms of hot end, I used the J head hot end from here: https://www.hotends.com/index.php?route=product/product&product_id=83https://www.hotends.com/index....

If the dimensions of the other one is the same then it should work fine.

What was the calibration for the mk7 gear for the printrboard? I cant seem to get it right.

I have:

define MICROSTEPPING_RATIO 0.0625#define XY_MTR_STPS 200#define Z_MTR_STPS 200#define EXTRUDER_MTR_STPS 200#define PACKING_DENSITY 1.0#define BOLT_DIAMETER 10.56#define EXTRUDER_GEAR_RATIO 1