how to set vtkScalarBarActor title's font?

Support
3

I have tried the SetUnconstrainedFontSize(), It can change default font(bold), but

	    scalarBarActor->SetTitle("Z(m)");
	    scalarBarActor->SetVerticalTitleSeparation(10);
		scalarBarActor->GetTitleTextProperty()->SetColor(1.0, 1.0, 1.0);
		scalarBarActor->GetTitleTextProperty()->SetFontFamilyToTimes();
		//scalarBarActor->GetTextActor()->SetTextScaleModeToNone()
		scalarBarActor->GetTitle();
		//scalarBarActor->GetTitleTextProperty()->SetFontSize(20);
		//scalarBarActor->GetTitleTextProperty()->SetUnconstrainedFontSize(10);
		scalarBarActor->SetUnconstrainedFontSize(60);

is same as

        scalarBarActor->SetTitle("Z(m)");
	    scalarBarActor->SetVerticalTitleSeparation(10);
		scalarBarActor->GetTitleTextProperty()->SetColor(1.0, 1.0, 1.0);
		scalarBarActor->GetTitleTextProperty()->SetFontFamilyToTimes();
		//scalarBarActor->GetTextActor()->SetTextScaleModeToNone()
		scalarBarActor->GetTitle();
		//scalarBarActor->GetTitleTextProperty()->SetFontSize(20);
		//scalarBarActor->GetTitleTextProperty()->SetUnconstrainedFontSize(10);
		scalarBarActor->SetUnconstrainedFontSize(10);

It kind of weird. font 60 is same as font 10