Steve Albini notoriously hates the term “project” when applied to a musical endeavor. But that’s undeniably what Shellac has become: a complex undertaking that evolves over time, like a model-train layout that’s slowly spreading across the basement. Front man Albini, bassist Bob Weston, and drummer Todd Trainer have been a band for almost twice as long as Big Black and Rapeman combined, and they’ve developed a robust chemistry that lets them do a lot of onstage tinkering without compromising the basic Shellac profile: a lean, athletic rhythm section and a guitar that sounds like a boiler explosion in a chandelier factory. Sometimes the band stops playing entirely while Albini delivers a semi-improvised soliloquy (“Mama Gina,” “Billiard Player Song”), and other tunes sprout jarring new instrumental intros or codas (“Song of the Minerals,” “This Is a Picture”). Though Albini also notoriously hates jazz, his band is now shaping its material on the fly, just like a jazz combo–though these techniques overlap only with the mechanics, not the aesthetics, of the dread genre. Shellac returns to the workbench this weekend for a series of shows, including three at Martyrs’, where the band made its most recent Chicago appearance at Robbie Fulks’s birthday party more than two years ago. Albini no doubt appreciates the club’s excellent-sounding room, but at that concert I couldn’t stop picturing him painted on its mural of martyrs, next to Bob Marley and John Lennon, gripping a mike stand like a nervous hostage taker. The fourth Shellac album isn’t yet imminent, though the band has a bunch of new songs worked up, and there are no big tour plans. Albini took pains, however, to underscore Weston’s comment to me that they’re “thinking of getting Todd a cowbell.” Call Me Lightning opens Friday at the Bottom Lounge; see separate items under Saturday and Sunday for details on the shows at Martyrs’. Fri 4/15, 8 PM, Bottom Lounge, 3206 N. Wilton, 773-975-0505 or 800-594-8499, $10, 18+.