Mendel90 Build Manual

Bill of Materials

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. For multiple files the whole project can be downloaded as a Zip from GitHub.

Required

Quantity	Description	File	Picture
1	Bar Clamps	stl
1	Cable Clips	stl
10	Fixing Blocks	stl
2	Pulleys	stl
1	Ribbon Clamps	stl
1	X Carriage	stl
1	X Idler	stl
1	X Motor Bracket	stl
1	Y Bearing Mounts	stl
1	Y Belt Anchors	stl
1	Y Idler Bracket	stl
1	Y Motor Bracket	stl
4	Z Coupling	stl
1	Z Motor Bracket	stl

Modified Wade's Geared Extruder

Quantity	Description	File	Picture
1	Extruder Body	stl
1	Small Gear	stl
1	Large Gear	stl
1	Cable Mount	stl

Optional

Quantity	Description	File	Picture
1	Fan Guard-If you have a fan	stl
4	PCB spacers	stl
2	Z Pointers	stl

Non-Printed Parts ("vitamins")

All measurements are in millimetres.

 1 Sheet 468 x 432 x 10
 2 Sheet 170 x 324 x 6
 1 Sheet 224 x 224 x 6
 1 Sheet 468 x 324 x 6
 4 19mm bulldog clip
 3 624 Ball bearing 4 x 13 x 5, 1 for X idler, 2 for Y idler
 3 608 Ball bearing 8 x 22 x 7, for extruder
22 M3 cap screw x 10
22 M3 cap screw x 16
17 M3 cap screw x 20
 4 M3 cap screw x 25
 2 M3 cap screw x 30
 2 M3 cap screw x 45
 4 M4 cap screw x 20
 2 M4 cap screw x 40
 1 9 way D plug
 1 9 way D socket
 3 M3 grub screw x 6
 1 borosilicate (Pyrex) glass sheet 214 x 202 x 2
 5 M3 hex screw x 16
 2 M4 hex screw x 20
 2 M4 hex screw x 50
 1 M8 hex screw x 60
10 LM8UU
 5 NEMA17x47.5
 1 PCB bed
 1 polypropylene strip 373mm x 17mm x 0.5mm
 1 polypropylene strip 320mm x 27mm x 0.5mm
 1 polypropylene strip 275mm x 29mm x 0.5mm
38 M4 pan screw x 12
24 M4 pan screw x 16
 1 Smooth Rod 8 x 22, for extruder idler
 3 Smooth Rod 8 x 275, 2 for Z axis, 1 for Y
 2 Smooth Rod 8 x 382, for X axis
 1 Rod 8 x 428, for Y axis
 2 Threaded Rod 8 x 211
 2 Tubing OD 7 ID 5 x 16
12 No2 pan wood screw x 13
 6 ziptie 87
 1 belt T5x6x674
 1 belt T5x6x861
 4 hex pillar M3x20
 3 microswitch
 6 nut M3
 2 nut M4
 3 nut M8
45 nyloc nut M3
 6 nyloc nut M4
 2 rubber washer M3 x 9.7 x 1.5
 1 spring 12 x 0.75 x 10
 2 spring 7 x 1 x 10
18 star washer M3 x 7 x 0.5
53 star washer M4 x 9 x 0.9
12 washer M2.5 x 5 x 0.5
79 washer M3 x 7 x 0.5
78 washer M4 x 9 x 0.9
 4 washer M5 x 20 x 1.4
 1 washer M8 x 16 x 1.5
 2 wingnut M4

Printed parts

So far the parts have only been tested in ABS.

The latest STL files are on GitHub at github.com/nophead/Mendel90/tree/master/mendel/stls/printed. These are for the default "mendel" configuration. The STLs for the "sturdy" version are also there: github.com/nophead/Mendel90/tree/master/sturdy/stls/printed. 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.

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 which have holes in surfaces where there is nothing underneath have a support membrane that needs removing. The 8mm holes in the X ends and Wades block plus the rectangular hole in the top of the X motor bracket are best removed with a small knife. The smaller holes in the Y belt anchors, Z couplers and the X carriage are best cleared with a 3mm drill.

General tips

• All screws have a plain washer where they meet the plastic to spread the load and prevent the plastic being chewed up by the rotation of the screw head. Most fixings have a captive Nyloc nut to prevent them vibrating loose. You can use plain nuts but in that case you should add a star washer between the screw head and the plain washer. The screws into the panels have star washers for the same reason. The only exception is the cable clips, which should be under tension from the wires.

• If you are worried about the plastic nut traps being strong enough for Nylocs you can thread the Nyloc onto a spare screw first to loosen it. Nophead hasn't found this necessary.

• Washers tend to have a smooth side and a side with a burr from being stamped out. Make sure the smooth side faces bearings and belts.

• Chamfer the ends of the rods with a file to remove any burr, otherwise they can knock the balls out of the linear bearings.

Wiring

The motor wires should be tightly twisted in pairs to reduce RFI. The normal coil pairings for the recommended SY42STH47-1684A motors are red / blue and black / green. The easiest way to twist them is to tie a knot at the far end of the wire pair and spin it in the chuck of a drill with some tension on the wire.

The motors come with 2.5m of wire so it is best the cut them roughly to length before twisting them but leave at least 0.5m spare to account for it getting shorter when twisted.

The spare wire can be used for the limit switches, fan and thermistor. Use different colour pairs to make them easily distinguishable from the motor wires and each other, e.g. red / black for the fan and green / blue for the limit switches. They should also be twisted to reduce induced noise.

There are three sizes of cable clip, each with two slots. The largest is for the bed and thermistor wires. The smallest is for the Y axis motor and limit switch wires. The middle size clips are for the Z axis motor + fan wires and the Z - limit switch. The clips keep the sensitive input wires away from the power wires.