Hi folks - I hope I can clarify this for you:
We calculate a width in data terms for the bars or columns in a series by examining the minimum distance between any two datapoints along the Y or X axis, respectively. We also take the number of series of bar/column series, and any stacking, into account and add a little spacing by default.
You can configure the amount of spacing between bars/columns and sets of bars/columns (those which are 'on the same datapoint') by setting the interSeriesPadding and interSeriesSetPadding properties on the axis' style object, where 0.f is no padding and 1.f is all padding.
@tonyarnold as you've discovered, where the calculated width is very small and the axis range very large, you can run into issues with thin or invisible bars/columns. I've sent you an email in the last few minutes which I hope will help in your case.
@giebler wider-than-desired bars/columns are more easily fixed - increasing the padding values should allow you to tweak their widths.
Hope this helps!