I solved this for a date x-axis on a line and clustered column chart like this:
1. Create another column in the date table that turns up a value of -1 in each place where you want a tick. So in my case I waned one on the first day of each week so I used the formula
Start of week = IF(WEEKDAY([date])=1,-1)
2. Add this column as an additional line on the chart (I had to use "Sum of start o week" here)
3. On the Shapes part of the Visulation window choose Customize series, then choose the name of the new line.
4. Set "Stroke width" to 0; Show marker to "on"; Marker shape to "+"; Marker colour to the same as the bars.
5. You may have to play around with the Y start/end figures if it tries to create a second axis
If depends on your type of chat quite a bit, but if you play around with the options, you can hopefully get something that works for you, even if a "tick marks" check box would be a lot easier.
Matt
PS This is the first time I've dared offer a solution so if you can mark it as a solution (and I'm not sure you can) then that would be great, and helpful for anyone that needs to find this on Google as this thread was the top search result when I was searching.
