IKEA Trofast: the rails that hold the tubs
The Trofast stores nothing on its own: it is an empty frame with a row of rails down each side, and the tubs that hang from them do all the work. Each tub sits with the lip of its two long sides on a facing pair of rails and slides like a drawer, in and out through the front. That one detail — the tub is held by its lip along the whole length of the rail, not by a base — governs everything you print for this unit. You are not designing against a hole or a leg: you are designing against a lip that rests on a wooden batten and slides along it. Before you draw a thing, the only two dimensions that matter are how far that rail sticks out and how often it repeats up the frame.
What it is and what it actually holds
The Trofast frame is an open box of laminated board with horizontal rails — wooden battens screwed or slotted in — running down the inner face of the two long walls at several heights. A tub does not sit on a base: it sits with the top edge of its two long sides on a pair of rails at the same height, one on the left and one on the right. That top edge is the lip.
The full weight of a loaded tub is spread along the line of contact between lip and rail — centimetres of bearing, like a drawer — rather than concentrated at a point. Only when you pull the tub out to remove it does it tilt and the bearing shift towards the front edge; fitted and at rest, the load spreads along the whole length of the rail.
That is why two dimensions matter, and both belong to the frame, not the tub: how far the rail sticks out towards the inside (the ledge the lip sits on), which fixes how much hook you need, and the vertical pitch between rails, which sets the heights at which you can hang something and how much clear space is left above a tub once it is fitted. Everything you print hangs from, slots into or rests on features fixed by those two dimensions.
The dimensions you have to measure
These are ballpark figures for a common Trofast frame. IKEA changes the Trofast dimensions by country and by year: there are frames of different heights, low and tall tubs of different widths, and the batten has changed section between versions. Treat them as a starting point for knowing what to measure, never as a standard.
| Dimension | Ballpark value | Why it matters |
|---|---|---|
| Rail overhang towards the inside | 10–12 mm | It is the ledge the lip rests on; it fixes how much hook you need |
| Rail section (height × depth) | ~12 × 12 mm | Defines the profile your lip or hook has to wrap around |
| Vertical pitch between rails | 60–70 mm | Sets the fitting heights and the clear space above a tub |
| Clear width between facing rails | ~340–350 mm | The tub body passes through here; the lip, a little wider, overhangs outwards and rests on the rail |
| Usable rail length (depth) | ~300 mm | The bearing length available, roughly the depth of the tub |
Why the whole tub almost never pays off
A small tub is roughly 42 × 30 cm in plan (the lip, overhang to overhang; the body that hangs between the rails is narrower). That will not fit on most print beds, and even if it did, printing a hollow box of that size is hours of machine time, kilos of filament and a part you have to split into pieces and join. The joint, on top of that, lands in the worst possible place: a box loaded with toys is loaded in bending across the long walls, and a glued or screwed seam between two halves is a line of weakness in the region of highest stress.
The move that pays is the opposite: not to reproduce the tub, but to add to what you already have. Lids, dividers, labels and hooks are small, quick, cheap parts, and each one solves a real problem without ever wrestling with the size of the bed. The factory tub keeps doing its structural job; you add what it is missing.
Lip clearance: it should slide, not seize
If you design a hook or a lip that mounts over the rail, the joint is of the clearance family — it has to slide — not the press-fit family. The part goes on and comes off, and while it is on it moves over the wood. That calls for a gap, and FDM works against you: as Real printed clearances explains, the process bias closes up internal gaps and fattens outer features, so a hook drawn to nominal comes out tight and seizes on the rail.
Design the gap per side. For a hook that wraps a ~12 mm batten and has to slide without rocking, start from 0.20–0.30 mm per side between the inner face of the hook and the rail: a touch looser than a fine sliding fit, because wood is not smooth — it collects dust and paint — and a rail is not a machined surface. In PETG, add another tenth. Better it hangs with a little play than it never goes on at all.
Orientation is half the battle. A hook is loaded as a cantilever: the weight of whatever hangs pulls the neck of the hook downwards, and that is where FDM is weakest — layer adhesion. If you print the part standing up, with the layers horizontal, the load pulls perpendicular to the layers and peels them apart — which is exactly how a printed part fails in tension between layers. Lay it down or reorient it so the layer lines run along the hook, in the direction of the load, and you will be pulling on the material, not on the bond between layers. A well-oriented neck holds several times more.
What is worth printing
With those two dimensions measured, almost everything useful is simple geometry. Lids that close the mouth of a tub so you can stack things on top or keep dust out: they rest on its top edge, not on the rail, so the critical dimension is the inner perimeter of the part, not the frame. Internal dividers that partition a large tub: side friction alone is not enough — the walls are smooth, low-friction polypropylene, and their draft angle means a straight divider only rubs at the top edge — so land it on the base and give it a tab that hooks over the top edge of the tub, or a small clip; let it be held by shape, not by friction. Labels clipped to the front lip so the child recognises each tub. And hooks that use a free rail — one with no tub — to hang headphones, a toy tape measure or bags — the one place where the rail system already being there really pays off.
If you have already organised another IKEA unit by the same logic of measuring first and translating the dimension into FDM clearance, IKEA Kallax: inserts, dividers and legs carries that method over to a cabinet of square holes. And to pin down the exact clearance for the rail hook on your printer, Real printed clearances gives you the tolerance stack that lets you stop guessing.