15mL Tube Megarack
A bench covered in twelve-place tube racks is a bench where half the racks are somewhere else. This is one printed slab with enough positions to hold an entire run of 15 mL conicals in order, in one thing you can pick up with one hand. It prints in one piece, so there is nothing to assemble and nothing to lose in a drawer.
The model isn’t posted yet. What is below is the bill of materials and the print settings this part wants — the STL will land in the download section at the bottom.
Parts
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- 15 mL conical centrifuge tubes — the part the whole rack is dimensioned around. Measure yours; see below.
- eSUN PETG filament, 1.75 mm — print it in this. Why, below.
- SUNLU PLA+ 1.75 mm, 4 × 1 kg black — for the fit-check print. PLA+ holds the model’s dimensions more closely than PETG, so it tells you about the bore sooner and for less filament.
- Neiko digital caliper, 0–8 in — measure the tubes you actually stock before you commit a multi-hour print.
- AFA deburring tool — one pass round the top of each bore. This is the difference between a tube dropping in and a tube being screwed in.
- Self-adhesive clear rubber bumpers, 200 pcs — four under the corners so a loaded rack doesn’t skate on a wiped-down bench.
- Solimo 99% isopropyl alcohol, 16 oz × 12 — cut it to 70% before you wipe anything, roughly seven parts alcohol to three parts water. Neat 99% flashes off the plastic before it has done anything.
- Brother P-touch Cube label maker and 12 mm laminated TZe tape, 4-pack — for numbering the rows, if you want positions to mean something.
- CA glue with activator — only if the footprint is bigger than your bed and you cut it in the slicer.
Before you print
A 15 mL conical is about 17 mm across the barrel and about 120 mm long, and it comes to a point at the bottom. It cannot stand up on its own, which is the entire reason the rack exists.
Two numbers come off the tube, not one. The barrel diameter sets the bore. The cap is wider — call it 20 mm — and it never goes into the bore at all: it stands proud on the deck, so it is the cap, not the barrel, that decides how close two bores can be. Brands vary by a few tenths of a millimetre on both. Put a caliper on the tubes your own store cupboard stocks first, because every bore in the rack is the same bore, and one wrong number is the whole print.
If the bores come out wrong, fix them in the model, not with the slicer’s scale box. Scaling the part scales the pitch, the wall thickness and the deck thickness along with the hole, and you will end up with a rack that fits the tubes and no longer fits the bench.
Print settings
| Setting | Value |
|---|---|
| Layer height | 0.2 mm |
| Walls / perimeters | 3 |
| Infill | 15% |
| Supports | None |
| Material | PETG |
| Orientation | Flat on the bed, bores vertical |
Bores vertical is the only sensible orientation. Every hole is then a straight vertical shaft with nothing to bridge, and the part needs no supports anywhere.
Three perimeters rather than the usual two. A full rack is mostly water — 15 mL is 15 grams a tube, and a megarack holds a run of them — and what carries that is the wall around each bore. Sparse infill in the middle of a thin deck does almost nothing.
Material
PETG. A tube rack lives on a bench next to things that are warm — a waterbath, a bead bath, an incubator door, a sunny window over a summer — and PLA starts going soft around 60 °C. A rack that sags is a rack whose bores no longer line up. PETG holds its shape through all of that and shrugs off being dropped, which is the other thing that happens to tube racks.
PLA+ is the material for the fit-check, not for the rack. It prints closer to the number in the model, so a block of four bores in PLA+ tells you the truth about your tubes faster and cheaper than a full rack in PETG will. Don’t keep the PLA+ one: on top of the sag, PLA crazes under repeated alcohol — fine cracks that start at corners and holes, which on this part is everywhere.
Do not autoclave a printed rack. An autoclave cycle runs at 121 °C and both PETG and PLA are well past soft by then — you will open the chamber to find a puddle. Printed racks are bench organisers, not sterile consumables: the layer lines hold liquid that you cannot get back out of them. Wipe it down with 70% alcohol and keep it out of the autoclave and the glasswasher.
Finishing
Run the deburring tool once round the mouth of every bore. Fresh off the bed the top edge of each hole carries a burr, and a burr is what a tube catches on going in. A quarter turn each and a tube drops in under its own weight — which is what you want when you are loading a rack one-handed with a pipette in the other.
Four rubber bumpers under the corners next. A full rack is heavy and the bench is usually damp; without feet it will slide the moment you pull a tube.
Then label it. A rack with numbered rows is a rack you can write positions down against, and the laminated tape survives an alcohol wipe where a marker line does not.
Files & downloads
The source files for this project aren't in the repo yet — there's nothing to download
beyond the notes. They land in projects/15ml-tube-megarack/ when they do, and this
section fills itself in.