A sander, comprising: a housing; an electric motor at least partially disposed in the housing and used for providing a power source, wherein the electric motor comprises a motor shaft that rotates about a motor axis; a fan assembly comprising a fan connected to the electric motor; an eccentric element driven by the electric motor, wherein the eccentric element has a central axis separated from the motor axis; and a base plate assembly comprising a base plate, a support for supporting the eccentric element, and a support base, wherein the support base is used for mounting the support, wherein the support base is fixedly connected to an outer race of the support and to the base plate, wherein the base plate includes an upper surface and a lower surface opposite to each other, wherein the lower surface is disposed on a side of the base plate facing away from the eccentric element relative to the upper surface, and the lower surface is used for mounting the functional element such as a sandpaper, wherein the support comprises a first end surface and a second end surface opposite to each other, and the second end surface is closer to the lower surface than the first end surface; wherein the motor shaft can drive the base plate assembly so that the base plate assembly can swing relative to the housing, wherein the base plate assembly is fixedly connected to the eccentric element, wherein the eccentric element surrounds the motor shaft; characterized in that, the sander further comprises a counterweight connected to the eccentric element and driven by the electric motor to rotate about the central axis; wherein a ratio of a distance from a centroid of the counterweight to the lower surface of the base plate to a distance from the first end surface of the support to the lower surface of the base plate is greater than or equal to 0.2 and less than or equal to 0.4; and wherein between the electric motor and the base plate assembly, starting from the electric motor and going to the base plate assembly: the electric motor, the fan assembly, the eccentric element, the support plate, the support, the counterweight, and then the base plate are arranged, wherein at least the fan is located in the housing. a housing; an electric motor at least partially disposed in the housing and used for providing a power source, wherein the electric motor comprises a motor shaft that rotates about a motor axis; a fan assembly comprising a fan connected to the electric motor; an eccentric element driven by the electric motor, wherein the eccentric element has a central axis separated from the motor axis; and a base plate assembly comprising a base plate, a support for supporting the eccentric element, and a support base, wherein the support base is used for mounting the support, wherein the support base is fixedly connected to an outer race of the support and to the base plate, wherein the base plate includes an upper surface and a lower surface opposite to each other, wherein the lower surface is disposed on a side of the base plate facing away from the eccentric element relative to the upper surface, and the lower surface is used for mounting the functional element such as a sandpaper, wherein the support comprises a first end surface and a second end surface opposite to each other, and the second end surface is closer to the lower surface than the first end surface; wherein the motor shaft can drive the base plate assembly so that the base plate assembly can swing relative to the housing, wherein the base plate assembly is fixedly connected to the eccentric element, wherein the eccentric element surrounds the motor shaft; characterized in that, the sander further comprises a counterweight connected to the eccentric element and driven by the electric motor to rotate about the central axis; wherein a ratio of a distance from a centroid of the counterweight to the lower surface of the base plate to a distance from the first end surface of the support to the lower surface of the base plate is greater than or equal to 0.2 and less than or equal to 0.4; and wherein between the electric motor and the base plate assembly, starting from the electric motor and going to the base plate assembly: the electric motor, the fan assembly, the eccentric element, the support plate, the support, the counterweight, and then the base plate are arranged, wherein at least the fan is located in the housing.