In shaper m/c job is held stationary and cutting tools on the ram is moved back and forth across the job.
Whereas, in planar m/c exactly opposite happens.
Shaper m/c is used for shaping much smaller job.
But planar m/c is used for larger job pieces.
Shaper m/c uses only one cutting tool at a time.
Whereas planar m/c uses several tools to cut simultaneously.
Shaper m/c os less rigid and less robust and hence its accuracy is not so high.
But planar m/c is very rigid and hence it gives more accuracy on machined surfaces..