RepRapPro Mendel extruder drive assembly

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Introduction | Frame assembly | Y axis assembly | X axis assembly | Z axis assembly | Heated bed assembly | Extruder drive assembly | Hot end assembly | Power supply | Wiring | Commissioning | Printing | Multi‑colour/multi‑materials | Colour Printing - Slic3r | Colour Printing - RepRapPro Slicer | Maintenance | Troubleshooting | Improvements

A notice about these instructions!

Since 1st April 2013, the RepRapPro Mendel has been superseded by the RepRapPro Tricolour and Mono Mendel.
If you are building the new machine, use the official, and most up to date, instructions on the RepRapPro wiki here


Reprappro multi-materials-alternate-drives.jpg

There are two types of extruder drive available for RepRapPro Mendel, the printed parts for which are shown left and right above.

If you have the printed parts shown on the left, your instructions are on this page.

If you have the printed parts shown on the right, then go here.


By the end of this stage your extruder drive will be mounted on the back of your Mendel like this:

Reprappro mendel extruder drive fitted.jpg

But without all of the wires.


  • 10mm (M6) spanner
  • Adjustable spanner
  • Allen key
  • Phillips screwdriver
  • Tweezers
  • 2mm drill

Step 1: Motor and hobbed stud assembly

RP parts Quantity Reprappro-huxley-extruder-drive-components-1.jpg
Reprappro-huxley-M6 block.jpg 1
Reprappro-huxley-large gear.jpg 1
Reprappro-huxley-small gear.jpg 1
Hardware Quantity
M6 hobbed stud 1
M6 full nut 1
M6 nyloc nut 2
M6 split washer 1
M6 plain washer 2
626 Bearing 2
NEMA 14 stepper motor 1
M3x10mm socket set screw (Grub) 1
M3 nut 1
M3x8mm screws 3
M3x25mm countersunk screw 1 (Mendel only - not Huxley)

There is an alternate design to the small gear that needs a grub screw shown in the list above:。


This needs no screw and is just a push fit onto the motor's shaft.

If you are building a Mendel drop the countersunk screw through the mounting hole in angled section on the printed block under where the motor will go - head towards the motor. (Huxley does not need this screw.) You won't be able to fit the screw after you have attached the motor.

Use the 8mm M3 screws to attach the motor to the block. Put it as far from the centre as it will go in its slots. Don't do the screws up tight. The motor wires come out towards the bottom of the picture:

Reprappro-huxley-extruder-drive-motor-fitting mod MA.jpg

Push the M6 nut (plain, not one of the nylocks) into the hexagonal recess in the big gear.

Put a bearing on the hobbed 6mm stud (note the relative positions of the short and long threads), followed by two plain M6 washers, followed by the gear with its nut. The nut should face away from the bearing.

You are going to adjust things so the gears mesh.

If you have the grub-screw gear, put the M3 nut into the slot in the small gear and run the M3 set screw through it. The small gear may need reaming out by hand with a 5mm bit. Some motors have a flat on the shaft that runs all the way to the motor case. If yours is one of these, put the small gear on the shaft with its hub towards the motor. Then put the bearing in its hole so the big gear meshes with the small one. If the flat stops short of the case, put the bearing and the big gear on first, then put the small gear on the other way round (as in the picture below).

If you have the push-fit small gear, push that onto the motor shaft with its flange towards the motor's body.

Take things apart and put them together again, adjusting the motor's position in its slots, until the gears mesh nicely.


When you are happy tighten all the motor screws, reassemble everything else, and tighten the small-gear set screw. Make sure that the small gear hub is not rubbing on the big gear - there should be about half a millimetre clearance between them.

Put the other bearing in on the other side of the block.

Put the split M6 washer on the side with the big gear so it bears on the gear's nut, then put M6 nylock nuts on both ends.

Tighten the nylocks, while checking the hobbing against the 2mm hole down through the block where the filament will run. The hobbing should be centred on this. Undo or do up the big gear with its nut, and the two nylocks until this is so.

Don't tighten the nylocks so far that the gears, stud, and motor can't rotate freely.

Step 2: Idler

RP parts Quantity Reprappro-huxley-extruder-drive-components-2.jpg
Reprappro-huxley-idler.jpg 1
Hardware Quantity
M3x30mm screw 1
626 bearing 1
M3x45 screws 2
M6x20mm socket set screw 1
M3 washers 6
M3 full nuts 2
M3 nylock nut 1
Springs 2

Put the bearing on the M6 set screw and drop it into the slot on the printed part. Check that it rotates freely. If it does not, use a blade to remove a little material where it is binding.

Fit the idler to the drive with the 30mm M3 screw, two washers - one each side - and the nylock nut. Don't over-tighten it - it must move freely. The photo below is wrong - you want the head of the screw on the gear side and the nut facing you in the picture. You will find that if you rotate the gear you can get the screw through the holes in it. This makes the idler much easier to remove when it is mounted on the RepRap machine.


Put the springs on the long screws. Sandwich each spring between a pair of washers.

Put the screws through as shown. If you drop the nuts into their holes with tweezers first, then hold a screwdriver blade over them while you tighten the screws this is less fiddly.

Step 3: The Bowden tube

RP parts Quantity Reprappro-huxley-extruder-drive-components-3.jpg
Don't confuse the PTFE tube (shown) with the shorter
translucent heatshrink also supplied with the kit.
Reprappro-huxley-extruder-drive-tongue.png 1
Hardware Quantity
slotted brass retainer 1
PTFE tube 1

Use a sharp blade to trim a few millimetres off the end of the tube at right angles to get a clean square end.

If your kit has a 4mm diameter PTFE tube supplied (as opposed to 3mm) then make a small cone on the end with a pencil sharpener. Don't cut too far - PTFE is very soft. The cone makes it easier to start the thread.

Screw the tube into the brass retainer. Look in the other end (a magnifying glass is useful) to see when it gets to the end of the internal thread, then stop.

Screwing the tube in will have reduced its internal diameter slightly. Gently twist a 2mm drill by hand in the end of the brass to thin the tube where it is inside the screw thread. If you have a small hand-chuck this is made easier. The picture shows this being done for the other brass connector that you will install on the next page. The method is the same:


Push a short length of 1.75mm build filament down the tube from its free end to clear out any PTFE swarf.

Push the brass retainer into the drive, and secure it with the printed tongue. The thin end of the tongue goes to the right in this picture:


Note: the bowden start fitting (brass retainer) must be held centrally in the hole. If the fitting diameter is quite a bit smaller than the hole in the extruder drive block, wrap a couple of turns of masking (or similar) tape around the fitting before pushing it in.

Feed in the short length of 1.75mm filament. The compression screws should be done up just tight enough that when the filament is trapped in the drive you cannot pull it out by hand - no tighter. (Hold the big gear still when you tug to test this.) Turn the device by hand. The filament should feed slowly and smoothly down the tube.

Step 4: Fitting the drive

Item Quantity
Printed drive bracket 1
Printed U clip 1
M3 washers 3
M3 nuts 2
M3 x 35mm screw 1

Attach the drive bracket to the machine using the nuts on the top bars. It goes on the left of the machine viewed from the front, with the support cylinder at the back.

Reprappro mendel extruder drive fitted.jpg

This view is from the back of the machine.

Use the screw a nut and two washers to attach the drive to the bracket.

Fit the U clip on the frame to match up with the countersunk screw that you fitted to the drive before fitting the motor.

Use a nut and washer to attach the drive to the clip. You will probably find that you have to hold the free end of the screw with long-nosed pliers to tighten the nut - its head is inaccessible, of course.

Finally, use the long-nosed pliers gently to remove the tongue. Take out the PTFE tube and its brass fitting. You will need these separate for the next step...

Next step

Hot end assembly