IKEA Ivar and Pax: pins and accessories

You've lost a pin. One shelf on your Ivar unit sits lopsided because one of the four metal pegs that hold it up has gone missing, or your Pax wardrobe came with just enough brackets and you want to fit an extra shelf it never shipped hardware for. The temptation is obvious: print your own. You can, but there's one non-negotiable condition: that pin is not a decoration; it's the part carrying the weight of the shelf and everything you stack on it. A badly oriented part in FDM snaps along a layer line without warning. That's what this article is about: the grid of holes Ivar and Pax use, how much clearance to give the pin so it seats without wobbling, and how to orient it so the load doesn't tear it off.

What they are and how they carry the shelf

The Ivar is the solid-pine shelving unit, with those tall side panels and a column of holes that lets you decide the height of each shelf. The shelf isn't screwed down: it rests on pins or brackets you've pushed into the holes at whatever height you want. You change the height by moving the pin to a different hole. That's the whole point of the system, and it's why the pin is a load-bearing part, not a decorative stop.

The Pax is the modular wardrobe, made of coated panel rather than pine, but the underlying idea is the same for its shelves and internal fittings: a column of holes in the side panel and a bracket that seats in the hole and holds the shelf, rail or drawer. The material of the furniture and the exact shape of the fitting change, but the principle doesn't: the weight travels down from the shelf to the bracket, from the bracket to the pin, and from the pin to the wall of the hole. Every link in that chain has to be sized right, and the one you print is the weakest.

The grid: vertical pitch and the 32 mm system

The holes aren't drilled at random: they follow a regular vertical pitch. The Pax, like most panel furniture, is built on the 32 mm system: the holes in its side panels are spaced at multiples of 32 mm, the same grid used by Besta and almost all industrial cabinetry. That works in your favour: if you measure one span carefully, you can predict the rest, because the spacing doesn't change from one hole to the next. The article IKEA Besta: the 32 mm system and its fixings breaks that grid and its hardware down in detail.

The Ivar has its own column of holes with its own pitch, different from the Pax and sized for the thickness of pine, not panel. Don't apply one unit's dimensions to the other. But watch the diameter: the vertical pitch tells you what height to set it at, but it's the hole diameter that rules the pin. That's the dimension you really have to get right.

The printed pin is a cantilever beam

Here's the physics that decides whether your pin holds or breaks. The original metal pin sits partly inside the hole, leaving the shoulder that the shelf rests on protruding. When you load the shelf, that weight pushes down on the protruding end, and the pin works as a cantilever beam: fixed in the hole and loaded at the tip. At the mouth of the hole a bending moment develops (the load times the protruding lever arm) that stretches the fibres on top of the peg and compresses the ones underneath. It's that bending tension, not plain shear, that breaks the part.

In FDM that's precisely the failure mode to worry about, because it takes far less to peel two layers apart than to break the material within a single layer. That's the weak direction. If you print the pin standing up, with the layers stacked across the axis of the peg, the bending stress acts exactly perpendicular to the layers and tries to separate them from one another. There, nothing resists it but the bond between beads. It snaps cleanly along a layer line, almost always the day you rest something heavy on it.

The right orientation is to lay the pin down: print it flat, with the peg axis parallel to the bed, so the beads run along the length of the peg. That way the fibres the bending stretches are continuous bead material, not the join between layers. You lose a little finish on the face that touches the bed, but you gain the strength you need. The article Real printed clearances explains why this layer direction matters so much in any part that takes load.

Orientation isn't the only thing, either: in a load-bearing part the walls and the infill count for as much as the layer direction. A cleanly printed but hollow pin fails just the same. Give it plenty of perimeters, four or more, and a high infill, 60% or more, or fully solid. A 5 or 6 mm peg has barely any room for interior infill, so raise the perimeter count until the section is effectively solid.

Clearance: the pin prints oversized, the hole stays undersized

The pin seats into a hole, so it's the male part of the joint, and in FDM male parts print oversized. It isn't shrinkage, either: thermal contraction shrinks; it never adds dimension. Something else adds the width. The perimeter is laid down outside the nominal contour and adds a bead width to it; and the first layer squashes and widens the base, the elephant's foot. The result tends to end up slightly larger than you modelled. If you model the pin at the nominal hole diameter, it won't seat: it scrapes, and if you force it, you split the mouth of the furniture's hole or crack the pin itself.

That's why you give clearance per side. Model the pin at the hole diameter minus 0.15–0.20 mm per side in PLA, that is, between 0.3 and 0.4 mm less diameter than the measured hole. With that it seats by hand, sits firmly and doesn't wobble. If you want it press-fit so it doesn't slip out when you move the shelf, stay at the low end, 0.15 mm per side; if you'd rather be able to pull it out and reposition it, go up to 0.20 mm per side. In PETG add another 0.05–0.10 mm per side, because it oozes and ends up wider still. These numbers are the starting point; the good number comes from your printer, and the honest way to pin it down is to print the pin in three stepped diameters, 0.1 mm apart, and see which one seats the way you want.

Remember to always reason per side and only convert to diameter at the end: 0.20 mm per side is 0.40 mm less diameter, double. It's the classic mistake: subtracting the clearance just once and ending up with half the gap you wanted.

What else to print for Ivar and Pax

The pin is the basic part, but the same grid makes room for other useful parts, and most of them take less load than the shelf, which makes them better candidates for plastic:

• Extra shelf brackets, to add a shelf where the furniture came with no supports. They spread the weight over more surface than a plain pin, so they fail later; even so, orient them with the layers along the load.
• Stops and limiters, to keep a shelf from sliding out or to mark a fixed position. They barely carry anything, print them however you like.
• Cable guides that clip into the free holes to route the charger or the LED strip behind the Pax without it dangling.
• Internal wardrobe fittings: dividers, hooks, small trays that use the Pax's 32 mm system holes to hang without drilling.

For any of them the process is the same as ever: measure the real hole in your furniture, give clearance per side to the protrusion that seats, and if the part carries load, lay it down so the layers work in the strong direction. The article IKEA Kallax: inserts, dividers and legs applies the same logic to another item in the same catalogue, in case your build mixes several.

The next step, before printing a batch, is that same stepped-diameter test: try it in the hole of your specific Ivar or Pax and keep the one that fits. From then on you stop guessing, and every pin comes out right first time.