This is a printable rack for holding test tubes or centrifuge tubes used in modern biochemistry. The design is parametric, so it can be remixed for any size tube, with up to four rows per rack.

All parts of the rack are designed to print without supports on an FDM printer, oriented for maximum strength and prettiness. The shelves slide into the stand uprights, and there is a tiny bump which registers and locks the shelf in place. If your tolerances are correct you should not need any adhesives and the rack can be disassembled again if required.

When assembling, slide the edge of the shelf without the locking bump into the rails first. It's much easier.

For tall racks that have a risk of tipping over if knocked, there are optional 'shoes' which clip onto the 'feet' of the rack stand. These are also removable.

Parts are arranged onto two 'platters', one which contains all the stand parts (the sides and shoes) and one which contains all the shelves. Or you can save the parts individually using the customizer.

Three tested variants are provided:

• A single-tube rack for 10ml centrifuge tubes, without shoes, intended mostly as a tolerance test. (but they're also kind of cute!)

• 1 row of 6x 10ml centrifuge tubes, with shoes.

• 2 rows of 7x 2ml centrifuge tubes, without shoes.

These are the examples shown in the image.

For other sizes of tube, or other grid arrangements, you can use the Thingiverse Customizer, remix your own version (the recommended way, so others can use your work) or download the model and use the OpenSCAD Customizer (available in the latest version) to create your own presets.

Use the "assembly" part option to design the overall rack, and hen use the "platter_stand" and "platter_shelves" options to print the parts in batches. Or generate each part individually and create your own platter arrangements, if you need to.

The layout is very flexible. You can have up to 6 rows, with different numbers of tubes per row, and you can even 'stagger' the rows by giving a positive or negative offset. This allows you to create either square or hexagonal packings of tubes depending on whether you want a regular grid for a typical work-bench rack, or honeycomb 'storage' racks with the maximum possible density and strength.

The design allows for 2 or 3 shelves, with 3 being the default used in all the examples. The size of the tube hole is provided for each shelf, usually the upper two shelves are sized to fit the tube, but the lowest shelf has a much smaller hole in which the end of the tube can rest.

For tapered centrifuge tubes, the lowest hole should be just bigger than the end of the tube so it fits snugly. For round-bottomed tubes this is less critical. Don't forget that holes have a tendency to shrink on FDM machines, so add 0.5mm to 1mm to the actual tube measurement.

For tubes that do not have removable caps (or have a flanged top) you might be able to get away with only 2 shelves, both with holes sized larger than the tube. In this case you should increase the "stand_height" parameter so the lower shelf is further up off the table, and remember the weight of the tubes will now be borne by the top shelf, not the bottom.

It's possible to use only one shelf if you hand-tweak the code, but I don't think it would be very mechanically stable, so it's not a selectable option.

In theory the size of the rack could have been calculated from the tube spacing and number of tubes, but that would have made the overall size of the racks difficult to control if you wanted a consistent rack size for storage of different kinds of tubes. So the "base shelf size" and "shelf height" are the main parameters to tune the overall geometry of the rack, and the rows of tubes are centered within that. (don't forget the stand sides add a couple of millimeters to the total width if you're trying to fit inside a box)

I printed my shelves in transparent Polymaker "PolyLite" PETG and the stand sides in black "PolyMax" PLA. Mostly because I thought it looked pretty, but the PETG shelves are also a little more heat-resistant than the PLA. Obviously you shouldn't be using these for high-temperate chemistry with glass test tubes.