Why does steel plate move during flame cutting?

[CdotS]

We use flame cutting on low alloy steel plates to make 6 to 12 inch wide strips. The plate moves around 0.5 inch and therefore the strips are not parallel. Did any one experience this type of movement? Any comments on how to stop this movement?

 

[msandoval]

I would like to think that it moves because of thermal distortion specially when you are cutting long strips.