The chain makes a circle of radius 1.3 m as it spins, so that 1 revolution of the hammer amounts to it moving a linear distance of 2π (1.3 m) = 2.6π m. Then the hammer's linear speed is
(1.64 rev/s) • (2.6π m/rev) = 4.264π m/s
and so the centripetal acceleration has magnitude
a = v²/r = (4.264π m/s)² / (1.3 m)
a ≈ 140 m/s²