Mendel90 Buyers Guide

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Mendel90 Documentation

A complete kit of parts for the latest Dibond version is available from nophead, see RepRap Forum For Sale Section.

There is a lot of supplier information for general RepRap parts in the RepRap Buyers' Guide. This page gives Mendel90-specific information.

Auto-Generated Bill of Materials

The latest version of the Bill of Materials (BOM), with a detailed breakdown of what is used in which part, can be found on GitHub (mendel, sturdy) or generated by your local compiled version. The below is just to give an idea of what is needed (for the "mendel" version).


 1 Acrylic sheet 468mm x 432mm x 10mm
 2 Acrylic sheet 170mm x 324mm x 6mm
 1 Acrylic sheet 224mm x 224mm x 6mm
 1 Acrylic sheet 468mm x 324mm x 6mm
 5 Aluminium foil tape 50mm x 234mm x 0.05mm
 3 Ball bearing 608 8mm x 22mm x 7mm
 3 Ball bearing 624 4mm x 13mm x 5mm
 4 19mm bulldog clip
 1 PCB bed 214mm x 214mm
 1 Belt T5 x 6mm x 674mm
 1 Belt T5 x 6mm x 866mm
 1 Corrugated cardboard 200mm x 224mm x 6mm
 8 M3 cap screw x 10mm
30 M3 cap screw x 16mm
11 M3 cap screw x 20mm
 4 M3 cap screw x 25mm
 2 M3 cap screw x 30mm
 2 M3 cap screw x 45mm
 4 M4 cap screw x 20mm
 2 M4 cap screw x 40mm
 1 9 way D plug
 1 9 way D socket
 1 Fan 80mm x 38mm
 3 M3 grub screw x 6mm
 1 Glass sheet 214mm x 202mm x 2mm
 4 Hex pillar M3 x 20mm
 7 M3 hex screw x 16mm
 2 M4 hex screw x 20mm
 2 M4 hex screw x 50mm
 1 M8 hex screw x 60mm
 1 PSU e.g. KY240W12L
10 LM8UU linear bearing
 5 NEMA17 x 47.5mm stepper motor
 6 Nut M3
 2 Nut M4
 3 Nut M8
45 Nyloc nut M3
 6 Nyloc nut M4
 1 Polypropylene strip 402mm x 17mm x 0.5mm
 1 Polypropylene strip 320mm x 27mm x 0.5mm
 1 Polypropylene strip 275mm x 29mm x 0.5mm
18 M3 pan screw x 8mm
38 M4 pan screw x 12mm
24 M4 pan screw x 16mm
12 No2 pan wood screw x 13mm
 1 Smooth rod 8mm x 22mm
 1 Smooth rod 8mm x 270mm
 2 Smooth rod 8mm x 275mm
 2 Smooth rod 8mm x 382mm
 1 Smooth rod 8mm x 428mm
 1 Electronics e.g. Sanguinolou
 4 Microswitch
 1 Spring 12mm OD x 0.75mm gauge x 10mm length
 2 Spring 7mm OD x 1mm gauge x 10mm length
 2 Threaded rod M8 x 211mm
 2 Tubing OD 7mm ID 5mm x 16mm
12 Washer M2.5 x 5mm x 0.5mm
87 Washer M3 x 7mm x 0.5mm
74 Washer M4 x 9mm x 0.9mm
 4 Washer M5 x 20mm x 1.4mm
 1 Washer M8 x 16mm x 1.5mm
 2 Wingnut M4
 2 Rubber washer M3 x 10mm x 1.5mm
26 Star washer M3 x 7mm x 0.5mm
53 Star washer M4 x 9mm x 0.9mm
 6 Ziptie 87mm min length

"Cap screws" are those with hex heads that take an Allen key. "Pan screws" have Pozidriv (like, but not the same as, Phillips) heads. "Hex screws" have hexagonal heads, to be driven with a spanner.

Printed Parts

The STLs are links to GitHub, so they are always the latest version. Follow the link and then right click on "Raw" and do "Save As" to download an individual STL. To get multiple files the whole project can be checked out or downloaded as a zip file from GitHub.


Quantity Description File Picture
1 Bar Clamps stl Mendel90-Bar clamps.png
1 Cable Clips stl Mendel90-cable clips.png
10 Fixing Blocks stl Mendel90-Fixing block.png
2 Pulleys stl Mendel90-Pulley.png
1 Ribbon Clamps stl Mendel90-ribbon clamps.png
1 X Carriage stl Mendel90-x carriage parts.png
1 X Idler stl Mendel90-x idler bracket.png
1 X Motor Bracket stl Mendel90-x motor bracket.png
1 Y Bearing Mounts stl Mendel90-y bearing mounts.png
1 Y Belt Anchors stl Mendel90-y belt anchors.png
1 Y Idler Bracket stl Mendel90-y idler bracket.png
1 Y Motor Bracket stl Mendel90-y motor bracket.png
4 Z Coupling stl Mendel90-z coupling.png
1 Z Motor Bracket stl Mendel90-z motor brackets.png

Modified Wade's Geared Extruder

Mendel90 uses a Wade's_Geared_Extruder whose design has been tweaked by Nophead.

Quantity Description File Picture
1 Extruder Body stl Mendel90-wades extruder.png
1 Small Gear stl Mendel90-wades small gear.png
1 Large Gear stl Mendel90-wades big gear.png
1 Cable Mount stl Mendel90-d motor brackets.png


Quantity Description File Picture
1 Fan Guard (if you are adding the fan) stl Mendel90-fan guard.png
4 PCB spacers stl Mendel90-pcb spacer.png
2 Z Pointers stl Mendel90-z screw pointer.png

You may also get a 7.5mm M8 ring, which can be used to space the Wade's big gear off from the block instead of washers. However, it depends on where the hobbing is on your hobbed bolt as to whether you can use this or not..

Print Parameters

So far the parts have only been tested in ABS.

The STL files are built from the OpenSCAD definitions. The latest built STL files are on GitHub for the default, "mendel", configuration and the "sturdy" version. For other configurations build the STL files from source using the scripts provided.

Nophead prints the gears, pulleys and cable clips with a 0.35mm nozzle using 0.3mm layers. The pulleys don't fit the belt well when printed with a bigger nozzle, even at the same layer height, because the teeth become too rounded. The gears can be printed with a 0.4mm nozzle but the M8 nut will be tight to press in because the corners of the hexagon get too rounded.

All the other parts are printed with a 0.4mm nozzle and 0.4mm layers. The W/T ratio is 1.5 in both cases. These parameters are defined in the config.scad file and affect the minimum horizontal and vertical feature sizes. Changing them will affect all the printed parts and sheet drawings slightly.

The relationship between nozzle size and maximum layer height depends on die swell, which in turn depends on the plastic and the length of the nozzle hole, so your mileage may vary.

It is worth printing the Y bearing mounts without support material - it isn't needed, and the unnecessary material tends to block the channels the cable ties go through.

The recommended infill density settings are as follows: -

Fixing blocks, Wades block, Wades idler block, Wades small gear 95%
Y bearing mounts, Z couplings 75%
Z motor brackets 75% hex
Bar clamps, Y belt anchors, Y idler bracket 50%
X carriage, Y motor bracket 50% hex
X idler bracket, X motor bracket 25% hex
Everything else 25%

Printed with these setting the parts weigh about 400g, a little less than a Prusa. There are a lot more parts, but most are a lot smaller.

Most of the holes are polyholes, so they should come out the right size on a well calibrated printer. The pulley and small gear holes are deliberately undersized to allow them to be reamed to exactly 5mm. cal.stl is a calibration object for testing hole sizes.

Parts Not In The BOM

Some items you need are not in the BOM because they are not modelled. These include:

  • Ribbon cable (22-way or wider)
  • Thermistor (may well come with your heated bed package)
  • Hot End
  • Reel of plastic
  • ...?

Tips For Sourcing Specific Parts


DIY stores such as B&Q in the UK can often cut MDF to size for you. When you have found the size of the sheet you are buying, work out a cutting plan so they don't have to adjust their machine between cutting two items of the same width, such as the base and gantry. This'll make sure they match exactly.


As the main page notes, this design requires a lot of different fasteners. To keep the cost reasonable, you will need to order them from a supplier which does small quantities. Try hard to find one which supplies in labelled bags - Orbital Fasteners and Bolt World are such sompanies such company. As the fasteners are so cheap, it is suggested that you order 2x the amount for anything in quantities of 4 or less, and "a good few extra" for anything in larger quantities. This will prevent you having to panic if you drop one on the floor, and give you flexibility for later fixes and additions.

If you plan to hob your own bolt, it would be a good idea to order several so you can practice. That's the 60mm M8 hex screw.


See if the company supplying your smooth and/or threaded rods can cut them to size. It makes life so much easier. Zapp Automation in the UK will cut their smooth rod to size if you specify it in the order notes.

If you buy the smooth rods in 1 meter lengths you will need 3 rods as there is 2034mm in total smooth rod length. The following is one layout you can use to cut the rods.

Rod 1: 22mm / 382mm / 275mm /275mm

Rod 2: 428mm / 270mm

Rod 3: 382mm

This will leave you with the longest waste, which might be useful to have for other projects(RepRaps).


Springs are hard to source at a reasonable price. Getting the right spring is more crucial for some than others.

The big one is not critical at all as all it does is stop the M8 nut vibrating off. You could use a Nyloc or two plain nuts instead. The spring allows you to remove the nut with your fingers.

The extruder springs are more critical in terms of length and wire gauge. For example some which were 12mm long and 1.15mm gauge were too strong and crushed the filament. The force is proportional to the fourth power of the gauge and the distance compressed. The length of the bolts means you can't use longer springs. Longer bolts stop the carriage meeting its endstop. The outside diameter is not important, but the inside diameter has to be bigger than the bolt inside and it is OD - 2 * gauge.

Hot End

To be filled in. J-Head Mk IV is what Nophead uses, but they are no longer in production.

Other Sourcing Tips

The big ticket items are the electronics, the motors, the hot end and the set of printed parts. Nophead supplies printed part sets, or if you have a friend with a reliable existing Reprap, you could ask them to help you out. Different electronics come at different prices, but if you want one that will power the fan (which is optional) you'll need a more expensive set. Gerv's parts cost £500 in total.

10cm is actually a tiny bit too short for the zip ties; get 12cm or more. (This needs to be fixed in the BOM generation.)