Heat makes the wire expand and lengthen, so a fixed-length wire goes slack and sags the instant you power it. The fix is a spring tensioner: anchor one end and run the other through a spring (extension or constant-force) that pulls the wire taut and automatically takes up the thermal expansion as it heats.
Tension it hard while cold so that even hot it stays straight, and use a wire that holds tension well (stainless is stiff; nichrome is fine with enough spring). On long spans, more tension and a stiffer spring help. Always heat the wire after tensioning, never before, and re-check tension if you swap wire length or gauge.
Tension it hard while cold so that even hot it stays straight, and use a wire that holds tension well (stainless is stiff; nichrome is fine with enough spring). On long spans, more tension and a stiffer spring help. Always heat the wire after tensioning, never before, and re-check tension if you swap wire length or gauge.