How to resize y axis of a dendogram
If your're really only interested in distance proportions between the fusions, you could 

adapt your input linkage (cut off an offset in the third column of the linkage matrix). This will screw the absolute cophenetic distances of course. 
do some normalization of your input data, before clustering it

Or you

manipulate the dendrogram axes / adapt limits (I didn't try that)
I am using  scipy.cluster.hierarchy as sch to draw a dendogram after makeing an hierarchical clustering. The problem is that the clustering happens on the top of the dendogram in between 0.8 and 1.0 which is the similarity degree in the y axis. How can i "cut" all the graph from 0 to 0.6 where nothing "interesting" graphically is happening?