An operating tool, e.g. a rotary radial roughing brush (698), is supported by a tool mounting (692) itself pivotally supported by a tool carrier (682) rotatable about a vertical axis, drive means (680) being provided for effecting such rotation. Height control means (716-724, 740, 742) is also provided, which utilises such rotational movement to vary the heightwise position of the tool mounting (692), and thus of the tool (698) supported thereby, in relation to the tool carrier (682). To this end the drive means includes a rotary spindle and the height control means includes a threaded shaft (716) on which a nut member (740) is carried. The threaded shaft and nut rotate together with the spindle, but the nut can be clamped against rotation; in this way rotation of the shaft (716) together with the spindle is effective to cause heightwise movement of the shaft also to take place.