BowTie Pulleybox / Gearbox

prusaprinters

<p>Improve the extrusion accuracy of your direct-drive printhead while making it significantly lighter too.</p><p>This is a spin on my "BowTie"-gearbox, but made to use a belt drive this time. It features a <i>very</i> <i>slightly</i> bigger gear ratio - but it's main advantage is that the printed spur-gear from that design requires a very accurate/calibrated 3D-printer while this doesn't.</p><h3>Features</h3><ul><li>NEMA17 gearbox</li><li>3:1 gear-ratio <i>(38/12T, so a reduction of 3.16 to be more exact)</i></li><li>Easy to print</li><li>Very lightweight*</li><li>The exposed pulley doubles as a visualizer and thumb screw for manually (un)loading filament</li></ul><p>(*) All plastic and metal parts weigh a combined 34g. Combined with a pancake motor (~120-150g), it allows for significant weight saving over the stock motor (280g). With it's compactness and thus minimal use of filament, it is pretty much as lightweight as a NEMA17 gearbox can go.</p><h3>Printing Instructions</h3><p>PETG. 4 perimeters, 20% infill, 5 top/bottom-layers, PrusaSlicer: “detect bridging perimeters" enabled for the body.&nbsp;</p><h3>Necessary hardware (BOM)</h3><figure class="table"><table><thead><tr><th>Description</th><th style="text-align:center;width:100px;">Amount</th></tr></thead><tbody><tr><td><a href="https://s.click.aliexpress.com/e/_ATpxJ5">M3x6mm (DIN7984)</a></td><td style="text-align:center;width:100px;">5x</td></tr><tr><td><a href="https://s.click.aliexpress.com/e/_AA9O07">M3 hex nut (DIN934)</a></td><td style="text-align:center;width:100px;">4x</td></tr><tr><td><a href="https://s.click.aliexpress.com/e/_A5eyIj">Square nut (DIN562)</a></td><td style="text-align:center;width:100px;">1x</td></tr><tr><td><a href="https://s.click.aliexpress.com/e/_A8UL3d">MR105 bearing</a> (10mm OD, 5mm ID, 4mm length)</td><td style="text-align:center;width:100px;">2x</td></tr><tr><td><a href="https://www.aliexpress.com/item/33021883302.html">M5 Nylon washer</a> (<strong>8mm OD</strong>, 5mm ID, 1mm length)</td><td style="text-align:center;width:100px;">1x</td></tr><tr><td><a href="https://s.click.aliexpress.com/e/_9ws1QV">45x5mm D-shaft</a></td><td style="text-align:center;width:100px;">1x&nbsp;</td></tr><tr><td><a href="https://s.click.aliexpress.com/e/_AO3eQZ">Gates 92-2GT-6RF belt</a></td><td style="text-align:center;width:100px;">1x</td></tr><tr><td><a href=" https://s.click.aliexpress.com/e/_ApjwKx">12-tooth, 5mm bore 2GT pulley</a></td><td style="text-align:center;width:100px;">1x</td></tr><tr><td>NEMA17 pancake motor, max shaft-length 20mm, measured from the base (Recommended motor: LDO-42STH25-1004AC or <a href=" https://s.click.aliexpress.com/e/_AKN4RN">OSM/OMC 17HS10-0704S</a>)</td><td style="text-align:center;width:100px;">1x</td></tr></tbody></table></figure><h3>Assembly</h3><ul><li>Pre-assembly:<ul><li><i>Check to see if the D-shaft fits the printed pulley. If it is very tight (some tightness is desired), you can carefully run a 5mm drill bit through it.</i></li><li><i>Refer to the images for orientation of the different parts.</i></li></ul></li><li>Insert the hex nuts into the body, using the “screw pulling” technique (With use of a 12mm screw &amp; preferrably a big washer too)</li><li>Press the bearings into the body.</li><li>Insert the square nut - with a screw installed - into the printed pulley.<ul><li>“untighten” the screw through the hole in the pulley, until it gets a little bit tight, this will make it stay put.</li></ul></li><li>Put the belt around the printed pulley.</li><li>Put the printed pulley in the body between the bearings.</li><li>Insert the D-shaft through the front, about halfway into the pulley.<ul><li>Make sure the cutout of the shaft matches the location of the square nut in the pulley. Otherwise the shaft will not fit.</li></ul></li><li>Put the nylon washer between the bearing and printed pulley.</li><li>Fully push the shaft up to the end - take it back very slightly so it won't touch the motor.</li><li>Tighten the screw of the printed pulley through the hole in the pulley.</li><li>Insert the 12T pulley into the belt.<ul><li>This is a bit tight, take care doing so, it'll fit with some playing around!</li></ul></li><li>Put the motor on (insert it into the 12T pulley), without tightening the screws yet.<ul><li>Make sure the orientation of the wires/connector is as desired.</li></ul></li><li>Put the motor-screws through the holes in the body, screw them in about halfway.</li><li>Press, and keep pressing the indent in the body with your thumb, to put tension on the belt. Tighten the motor-screws while the belt is under tension.</li><li>Finally, position the pulley on the motor, so that the belt runs in the middle of both pulleys. Then, tighten it down.</li></ul><h3>Firmware changes</h3><p>For this mod on the MK3(S), make a custom <code>.gcode</code>-file with the lines below (put it on the SD &amp; run on the printer) or run these over an USB-connection</p><ul><li><code>M350 E16</code> - Set microstepping to 1/16</li><li><code>M92 E445</code> - Change the E-steps to 445</li><li><code>M500</code> - Save to eeprom</li></ul><p>If needed, to revert back to stock MK3(S)</p><ul><li><code>M350 E32</code> - rollback to 1/32 microstepping</li><li><code>M92 E280</code> - rollback default esteps</li><li><code>M500</code> - Save to eeprom</li></ul><p>PS: Depending on the used motor/cable, the E-direction may need to be changed too. With the Prusa, this can only happen in firmware, so I recommend to change the direction through wiring.</p>