15ml Tube Rack (Small - 8 x 6)

This simple tray was reversed engineered from existing 15ml test tube trays to support a request from a local testing company in need of more trays.

Standard trays and specifically standard size openings for 15ml test tubes did not support the thick stickers or improperly applied stickers on COVID tests and thus made it a challenge for lab techs to quickly and easily place tubes in the tray during testing.

This model was designed to be printed in PLA however almost any other material (i.e. PETG, ABS, ASA, Nylon) could also be used.  I would not recommend using a “silk” PLA since that specific type of PLA typically shows poor layer to layer adhesion with thin wall prints.

The model will load in the correct build orientation:
“Tube Holder v10.stl” - Release Date 1/25/2021

The design was printed/validated on a Prusa MK3S using standard PrusaSlicer 2.3.2 settings “0.3mm Draft” and “Generic PLA” with the only two(2) modifications being Infill = 0% and First Layer Speed = 15mm/s.

Additional improvements in print time can be made by increasing “External perimeters” speed.  Speeds up to 50mm/s where tested successfully with minimal reduction in as-printed appearance and no reduction of as-printed part strength/robustness.  Results may very depending on the your specific filament/printer combination.

If using other slicers OR making a custom profile I recommend the following parameters should be maintained:
First Layer Height: 0.2 or 0.3mm
Layer Height: 0.3mm
Default Extrusion Width: 0.55mm
First Layer Extrusion Width: 0.42mm
Perimeter Extrusion Width: 0.55mm
External Perimeter Extrusion Width: 0.55mm-0.6mm
Infill Extrusion Width: 0.5mm
Solid Infill Extrusion Width: 0.5mm
Infill: 0%
Elephant foot compensation = 0.2mm

Recommended quality checks include ensuring the test tube openings measure an inside diameter of 18.0mm +/-0.2mm and a common wall thickness of 1.0mm +0.1mm/-0.05mm. Any wall thickness at/below 0.90mm showed easy breaking/cracking with just simple handling when printed in PLA.  Both a STEP and Fusion360 file formats are attached to enable modification if a more robust design is needed for your application.

Bed level is key to the success of printing this part.  A calibration model named “Tube Holder Bed Level Check v1.stl” can be used to confirm proper 1st layer bed adhesion/thickness at the full extents of the part in the X/Y plane.  These following articles may assist you in correcting any bed level issues you may be having:

https://help.prusa3d.com/en/article/first-layer-calibration-i3_112364

https://help.prusa3d.com/en/article/bed-level-correction_2267.