Selectively-Underextruded Flowers

prusaprinters

<p><i>Please note that the license for this print is for the layer-change G-code only. The </i><a href="https://www.thingiverse.com/thing:1715093"><i>Roses of Unicofil</i></a><i> flower used as an example remains “Attribution-NoDerivatives” and is itself unmodified in this print.</i></p><p>&nbsp;</p><p>By dynamically adjusting the flow-rate to very low values (as low as 25% in this example), it is possible to create a lacy effect on a print.&nbsp;</p><p>I originally tried using a linear adjustment (based on the ratio of <strong>layer_z</strong> and the part's height), but I found that the laciness wasn't good enough. What I wanted was a gentler adjustment so that more of the print would have higher density while the laciness starts and increases gradually at the top.</p><p>The best way I found to do that was to use a sinusoidal function based on the ratio of the <strong>layer_num</strong> versus the <strong>total_layer_count</strong>. Unfortunately, PrusaSlicer doesn't support sin(x) in the G-code placeholders; it only supports basic arithmetic.</p><p>Then I discovered the <a href="https://datagenetics.com/blog/july12019/index.html">Bhaskara I approximation</a> that gave me a way to convert the sine function into a basic algebraic formula:</p><figure class="image image-style-align-center image_resized" style="width:20.11%;"><img src="https://media.prusaprinters.org/media/prints/60049/rich_content/f084ffd9-9a66-4fe5-871f-8470f561c9a5/image.png#%7B%22uuid%22%3A%22fa3896a3-64a9-4ee2-b808-28d82b1c8941%22%2C%22w%22%3A114%2C%22h%22%3A43%7D"></figure><p>where x is:</p><figure class="image image-style-align-center image_resized" style="width:20.29%;"><img src="https://media.prusaprinters.org/media/prints/60049/rich_content/af4aba91-56af-4307-8f69-b4d7d17240db/image.png#%7B%22uuid%22%3A%22eb3389ed-89f3-40fb-9cb5-8bd741c1a3f1%22%2C%22w%22%3A99%2C%22h%22%3A38%7D"></figure><p>(<i>l</i> is <strong>layer_num</strong> and <i>t</i> is <strong>total_layer_count</strong>.)</p><p>Substituting x in gives us (including the 100% → 25% flow-rate range factor):</p><figure class="image image-style-align-center image_resized" style="width:84.7%;"><img src="https://media.prusaprinters.org/media/prints/60049/rich_content/0b84dc17-552f-462a-9534-779c2fac43ad/image.png#%7B%22uuid%22%3A%2214f33062-bd80-45f4-8a36-b047d9c70941%22%2C%22w%22%3A666%2C%22h%22%3A79%7D"></figure><p>That's quite complicated, but fortunately WolframAlpha simplified that down to just:</p><figure class="image image-style-align-center image_resized" style="width:30.51%;"><img src="https://scontent-iad3-1.xx.fbcdn.net/v/t1.0-9/161091054_10158890583511469_8321898798756325784_n.jpg?_nc_cat=104&amp;ccb=1-3&amp;_nc_sid=dbeb18&amp;_nc_ohc=lySzZvBL79oAX9QpsJT&amp;_nc_oc=AQlc6h58TyHHk0zx1WEfk-3cCqgbmlHVUajVKZnAjRxC0zKAf34lMZYhw7mtYkLBnqU&amp;_nc_ht=scontent-iad3-1.xx&amp;oh=aa72b791704496593abb75bf0a50413c&amp;oe=6075A556" alt="No photo description available."></figure><p>That then translates to this G-code that does all the magic:</p><pre><code class="language-gcode">;AFTER_LAYER_CHANGE ;[layer_z] M221 S{min(95, 212.5 - (375.0 * total_layer_count * total_layer_count) / 2.0 / (layer_num * layer_num - 2.0 * layer_num * total_layer_count + 2.0 * total_layer_count * total_layer_count))}</code></pre><p>&nbsp;</p><p>This technique should work for lots of different items, not just flowers, although it may be possible to use this layer-change G-code as-is on other generally similarly-shaped flowers.</p><p>&nbsp;</p><p><i><strong>N.B. </strong>Hopefully this won't be a surprise to anyone. Due to the significant underextrusion, the top parts of the petals are fragile.</i></p>