scatter plot with discrete colorbar

Hi

I'm using the following code for insert a scatter plot in a figure in Qt.

vmin=min(r_time[:])
vmax=max(r_time[:])
valores=np.arange(vmin,vmax+1)
a1=self.ui.axes4.scatter(r_east,r_nort,vmin=vmin,vmax=vmax,c=r_time,edgecolors="none")
b1=self.ui.fig2.colorbar(a1,values=valores,format="%.3f",spacing="uniform")

The plot is ok and and the colors in the colorbar are ok, but for
some reason the ticks are missing. I tried

b1=self.ui.fig2.colorbar(a1,values=valores,ticks=valores,format="%.3f",spacing="uniform")

but still the ticks doesn't appear.

How can I get the ticks in the colorbar?

Thanks

German