Lessons from 3DPrinting multiple objects simultaneously

The 4 simultaneous copies being printed

When I started printing these mini-product-logo icons, it seemed sensible to print more than one at a time. The Slic3r App I use for creating 3D Printing gcode (the instructions which the printer understands to control every layer) has this simple "duplicate" button which made it super simple to make a "4-up" version of my model of the Google Forms product icon. BTW, The Google Forms icon was necessary , since I already did Google Docs and Google Sheets - and it was timed to be done while I had green PLA loaded :)

When I printed these - each of which is 30mm X 22mm X 4mm - I had some unexpected quality issues, which I am attributing to the simultaneous multi-item printing method. The issues simply do not occur when I print one at a time. This is a lesson worth sharing.

The Quality issues:

Curled bottoms after printing

• Curling at the bottom of the models (in spite of a heated bed). I've never had curling on prints before.
• "Globbiness" (there must be a technical term for this) on some edges which make them stick up or out over the edge.
• Gaps in the top layers which make the surface not only rough, but look more like a weave than a solid.

Gaps and Globs visible in top layers

I decided to print another version of the model just one at a time - just to be sure that something else didn't change in my printer that I didn't notice. As suspected, the one-at-a-time version came out good again. Flat on the bottom, smooth on the edges and almost no gaps on the top.

COMPARISON - one printed alone, vs. one of the bad 4

Watching the printing process on both versions, I'm concluding the following: With multiple items to print, and the print head doing one layer at a time - doing layer 1 on object 1, then layer 1 on object 2, then layer 1 on object 3, etc - each object layer has too much time to dry and cool before the next layer is extruded on top. That reduces adhesion and the hot layer being laid on a too-cool layer causes the prior layer to pull up a bit. The "globbing" seems to be caused by simply too much movement between objects, whereas when there is one object, the movement of the head is always close by with less starting/sopping on extrusion. The gaps on top I can't explain too well.

I recommend trying multi-item printing in two's - figuring out an optimal level of efficiency without sacrificing quality.

COMPARISON - one printed alone vs. one of the bad 4

Project Details:

Printer:  LulzBot TAZ4
Model:  Google Forms Product Icon
Filament:  LulzBot 3mm PLA Green
Print Time:  4-copies: 85 min. 1-copy: 23 min.