In　this　article,　we　present　rapid　boundary　stabilization　of　a　Timoshenko　beam　with　antidamping　and　antistiffness　at　the　uncontrolled　boundary,　by　using　infinite-dimensional　backstepping.　We　introduce　a　Riemann　transformation　to　map　the　Timoshenko　beam　states　into　a　set　of　coordinates　that　verify　a　1-D　hyperbolic　PIDE-ODE　system.　Then　backstepping　is　applied　to　obtain　a　control　law　guaranteeing　closed-loop　stability　of　the　origin　in　the　$L＜^＞{2}$　sense.　Arbitrarily　rapid　stabilization　can　be　achieved　by　adjusting　control　parameters,　and　has　not　been　achieved　in　previous　results.　Finally,　a　numerical　simulation　shows　the　effectiveness　of　the　proposed　controller.　This　result　extends　a　previous　work　which　considered　a　slender　Timoshenko　beam　with　Kelvin-Voigt　damping,　by　allowing　destabilizing　boundary　conditions　at　the　uncontrolled　boundary　and　attaining　an　arbitrarily　rapid　convergence　rate.