不至于

不 = 丆 + 卜 : Bruno Bear (bu) is setting up a wind wheel (丆) with a voodoo staff (卜) in the space station's bathroom (Ø4). He also puts a "forbidden" sign (mnemonic symbol for 不) on it, to make clear that it may not (不) be stopped.

至 = 一 + 厶 + 土 : Mnemonic symbol: one of these conveyor belts from which you pick up your suitcase when you arrived at an airport. James II of England (zh) finally got the package he was waiting for! He picks it up from the arrivals (至) in the bathroom of the space station (Ø4). In it is a flute (一), which he sticks into his nose (厶). He blows his nose, and boy, does a lot of clay (土) come out! He's glad to have a free nose again.

于 = 亅 + 二 : Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.