Not able to insert hobbed drive and filament in the extruder drive


I am building a AlfaMendel 3D printer (edited : The original question named it to be Prusa Mendel I2). I printed the extruder drive using PLA material from the STL available in the package but I'm not able to insert the hobbed drive as well as the filament in it. The dimensions of hobbed drive is correct.

Is the problem related to shrinking of print material while printing the extruder drive or something else.

I have included few pics of the extruder drive and hobbed drive.

Filament hole in extruder drive

Extruder drive

Close up of extruder drive

Hobbed Drive

This image shows the maximum possible insertion of hobbed drive in the extruder drive.

Trying to insert the hobbed drive in the extruder drive


Posted 2018-06-19T11:53:31.143

Reputation: 43

1The MK7 and MK8 hobbed extruder gears have different diameters. One is 12 mm and the other is 9 mm respectively, so the question is what diameter is your hobbed gear? – 0scar – 2018-06-19T13:10:41.480

Its MK8 with 9mm diameter – MSD – 2018-06-19T13:15:33.557

1You need to add more information; e.g. what material you printed, a photo with the gear (tried to fit) in the printed part, measured dimensions, STL model dimensions. – 0scar – 2018-06-19T13:19:29.477

I have used PLA to print the part, as much I remember the measured diameter of the hole in extruder drive was 7.9 - 8 mm (actually I don't have a Vernier Calliper at present) and I added one more pic in the edited version – MSD – 2018-06-19T13:35:18.753



Your parts are not in the Prusa Mendel i2 as found here or here.

Also note, quote:

Parts included in Github repository have the wrong dimensions for the nut traps! Download the correct version from [Thingiverse Greg's Hinged Accesible Extruder]

Are you sure you have the correct parts for the original Prusa Mendel i2? Maybe you have a different version? The original extruder mount uses an M8 hobbed bolt, not an MK8 hobbed extruder gear. The first is 8 mm in diameter, the latter is 9 mm in diameter.

Edit: After you updated your post to hint to the correct printer, it appears that my answer still holds. You did use the incorrect extruder gear. The 9 mm gear doesn't fit in the extruder part as it requires an 8 mm diameter extruder gear.

It might be difficult to find a 8 mm hobbed gear with a 3 mm shaft diameter, they are usually 5 mm (as in the stepper shaft diameter) or 8 mm (as in the diameter of 8 mm bolts that are frequently used for extruder setups). You could redesign the part (load STL in a 3D CAD program and make the changes). By the way, PLA should not shrink so much. As can be seen in the photo's, it looks like your current printer does not print very accurately, that may also contribute.


Posted 2018-06-19T11:53:31.143

Reputation: 25 570

Sorry for incorrect info. Actually the printer is not entirely Reprap Prusa Mendel but it is AlfaMendel AM1 which is similar to Prusa Mendel I2. The link for its manual is link. You may check page no. 126 of the manual for its extruder drive. Actually I didnot correctly read it, the printer requires a 8mm M3 hobbed drive, not the MK8 which I have. Buy the way, thank you for the answer :)

– MSD – 2018-06-20T18:09:39.223

Can I print a hobbed drive using PLA, instead of purchasing a metallic one ? – MSD – 2018-06-20T18:10:20.800

@MSD No you cannot print that to use it functionally. – 0scar – 2018-06-20T18:18:37.180

OK :)

Also, I am not able to insert the PLA filament into the extruder drive (via the hole in the very first pic), I think it has shrinked. What should I use to drill it to make it proper or some other way to make it correct ? – MSD – 2018-06-20T18:25:52.447