Hi Francois,
Thanks for your interest in Syncfusion products.
In multiple axes scenario, by adjusting the Range and the Interval property of the ChartAxis you can make the Gridlines and Ticklines of various axes to be overlapped giving the appearance that all the axes are in the single grid.
We have created a sample for your reference and you could download it from the below given link:
http://files.syncfusion.com/support/Chart.WPF/7.1.0.30/F80361/main.htmPlease let us know if you have further queries.
Regards,
Pavithra.J