Hi Bernard; are you talking about a OEM unit as supplied by the makers or a home built unit?. I have fitted a home built unit into my WM16 using a 12v.wiper motor & 240 – 12v power supply from china that comes with a variable speed pot, easily done, have a look in my album…. 'X axis drive … on the left hand side, as have many others.
Cheers.
George.