T3P3 Kossel Mini Kit Release 2

Assembly Instructions

Chapter 9 - Extruder Assembly

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Think3DPrint3D Ltd


901 Extruder - Parts needed

Printed Parts: Motor spacers 2mm thick x 2 or 4mm thick x 1, big gear, small gear, extruder block.

NEMA17 stepper motor.

623ZZ bearings x 3

Pushfit pneumatic connector, M5 thread for 4mm tube

M3 x 12 socket capscrew x 1

M3 x 20 socket capscrews x 2

M3 x 20 hex setscrew x 1

M3 x 25 socket capscrew x 2

M3 full nuts x 3 (2 shown)

8mm hobbed insert (also needs an M3 nut and washer - see below)

Superglue (One-shot tube included, not shown) or Loctite 222 (not included in kit)

902 Assemble big gear

 Fit the M3 x 20 hex setscrew into the big gear, making sure the socket for the head has been fully prepared so that the head fits snugly. This is important because the hex bolt head transfers the full torque from the highly-geared extruder motor to the hobbed insert.


We have changed from the original hobbed insert shown on the left side of this picture to the replacement shown on the right. This requires an M3 nut and washer as spacers to make it up to the correct size, as shown. Some of the pictures which follow still show the old version of hobbed insert

Fit a 623ZZ bearing to the setscrew, add the M3 nut and do it up firmly, until the head of the hex bolt is drawn fully into its socket, then add the washer and finally the hobbed insert. Do up the hobbed insert finger tight only.

The new hobbed insert with nut and washer should look like this. (Picture courtesy of RepRapPro Ltd).

903 Check hobbed insert alignment

Fit a 623 ZZ bearing into the underside of the extruder block.

Turn the block over. Before fitting the big gear, fit an M3 nut in the nut trap, …...

…..fit the prepared big gear….

and check that the teeth of the hobbed insert align with the centre of the idler slot. If they do not align correctly then you may need add or remove a washer under the hobbed insert to achieve correct alignment.

Carefully prise the big gear off the extruder block using a screwdriver blade or similar between the two. Do it a little at a time, rotating the gear to apply the force evenly around the centre of the gear.


904 Fix hobbed insert to setscrew

Once you are satisfied that the hobbed insert lines up correctly in the extruder, partly unscrew it, then add a small dab of Superglue or preferably Loctite 222 to the thread of the screw, and screw up again finger-tight

NOTE: If you don’t lock the insert onto the thread with glue, it will unscrew itself when reversing filament.

905 Fit extruder block to motor

Use both 2mm spacers or the single 4mm spacer between the motor and the extruder block, and orient the block and motor as shown: the motor plug should be on the right side with the bearing for the big gear and hobbed insert at bottom left of the extruder block.

Fix with 2 M3 x 20 capscrews (to make alignment easier you can start by inserting the screws into the extruder block, followed by a spacer. Then fit this assembly onto the second spacer sitting on top of the motor).  

Double-check you have the motor-plug on the output side of the extruder - it should look like the picture on the right  (Thanks to customer JoeB for the picture)

906 Complete the extruder assembly

Fit the 623ZZ idler bearing with the M3 x 12 capscrew. This cuts its own thread in the plastic - do not overtighten.

Fit the small gear so that the top is flush with the top of the shaft.  Note that neither the hole nor the motor shaft is circular! The gear has been pre-prepared on a heated shaft so should fit on tightly.

Double-check that you have fitted the M3 nut in the nut-trap next to the small gear - it is missing in this picture.

Fit the big gear and hobbed insert, turning it as necessary so the gears mesh together. Rotate the big gear one or two turns by hand to ensure it is fully seated and turns smoothly.

If there is a rough point, turn the gear forwards and backwards a few times until smooth. The extruder gears will wear in and get even smoother after the first few prints. At this stage they should be lubricated with a little lithium-based grease

Fit the pneumatic hose connector in the pre-tapped M5 hole in the extruder base and tighten by hand.

Finally fit the 2 M3 x 25 capscrews and nuts that tension the idler. Tighten just enough to close the gap very slightly.

906 Test the extruder

Cut a 150 to 200mm length of filament from the sample supplied and cut a point on it.

Insert the filament into the hole in the top of the extruder while rotating the big gear clockwise until you feel the hobbed insert teeth begin to grip the filament. Continue turning the big gear slowly to feed the filament all the way through and pull it out.  Note: If you feel any resistance as the end of the filament reaches the pushfit connector, this could be because it is snagging on the “teeth” of the connector. Remove the pushfit,  complete the test, and then refit it.  

Examine the filament. You should see clear even tooth marks from the hobbed insert along the full length of the filament.

Put the extruder aside until it is required during final assembly.