what is cut off current in dc motor?
After 30 years working with motors, I've never heard that term. 

For fixed field (permanent magnet or shunt-wound) brushed DC motors, and BLDC motors without speed control, the torque is fairly linearly related to the current, but is offset by the mechanical losses from ideal i.e. the line doesn't intersect the torque and current axes at zero. Normally the offset is expressed as a no-load current, or a friction torque - the intersects with the vertical and horizontal axes respectively. The cutoff current you mention looks to be that no-load current.


The graph  (from here ) shows a small DC motor, with the torque line intersecting the axis at zero torque (that I've highlighted in red) at about 0.15A  (table shows a higher value, probably a maximum value rather than a typical on the graph).

What doesn't make sense is the notation "ideal" - the effective current that generates useful torque is the armature current less the no-load current.