Mendel90 Build Manual

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.