A fluid jet cutting head comprising: a nozzle body having an orifice mount receiving cavity; an orifice mount received within the orifice mount receiving cavity of the nozzle body , the orifice mount comprising an orifice unit having an orifice for generating a fluid jet during operation; a fluid delivery body having a fluid delivery conduit to supply a flow of fluid through the orifice of the orifice mount to generate the fluid jet during operation; a mixing chamber insert including: a mixing chamber ; an abrasives inlet conduit extending from an exterior of the mixing chamber insert to the mixing chamber ; an abrasives outlet conduit extending from the exterior of the mixing chamber insert to the mixing chamber ; and a jet passageway extending from the exterior of the mixing chamber insert to the mixing chamber , wherein the abrasives outlet conduit intersects the mixing chamber at an abrasives outlet port that is upstream, with respect to a flow path of a fluid jet through the jet passageway and the mixing chamber , of an abrasives inlet port where the abrasives inlet conduit intersects the mixing chamber ; a nozzle having a jet passageway from which to discharge the fluid jet from the fluid jet cutting head ; and a plurality of orifice mount adjusters configured to adjust a position of the orifice mount in a plane transverse to an axis defined by the orifice to align the fluid jet generated at the orifice with the jet passageway of the nozzle . a nozzle body having an orifice mount receiving cavity; an orifice mount received within the orifice mount receiving cavity of the nozzle body , the orifice mount comprising an orifice unit having an orifice for generating a fluid jet during operation; a fluid delivery body having a fluid delivery conduit to supply a flow of fluid through the orifice of the orifice mount to generate the fluid jet during operation; a mixing chamber insert including: a mixing chamber ; an abrasives inlet conduit extending from an exterior of the mixing chamber insert to the mixing chamber ; an abrasives outlet conduit extending from the exterior of the mixing chamber insert to the mixing chamber ; and a jet passageway extending from the exterior of the mixing chamber insert to the mixing chamber , wherein the abrasives outlet conduit intersects the mixing chamber at an abrasives outlet port that is upstream, with respect to a flow path of a fluid jet through the jet passageway and the mixing chamber , of an abrasives inlet port where the abrasives inlet conduit intersects the mixing chamber ; a nozzle having a jet passageway from which to discharge the fluid jet from the fluid jet cutting head ; and a plurality of orifice mount adjusters configured to adjust a position of the orifice mount in a plane transverse to an axis defined by the orifice to align the fluid jet generated at the orifice with the jet passageway of the nozzle . a mixing chamber ; an abrasives inlet conduit extending from an exterior of the mixing chamber insert to the mixing chamber ; an abrasives outlet conduit extending from the exterior of the mixing chamber insert to the mixing chamber ; and a jet passageway extending from the exterior of the mixing chamber insert to the mixing chamber , wherein the abrasives outlet conduit intersects the mixing chamber at an abrasives outlet port that is upstream, with respect to a flow path of a fluid jet through the jet passageway and the mixing chamber , of an abrasives inlet port where the abrasives inlet conduit intersects the mixing chamber ; a nozzle having a jet passageway from which to discharge the fluid jet from the fluid jet cutting head ; and a plurality of orifice mount adjusters configured to adjust a position of the orifice mount in a plane transverse to an axis defined by the orifice to align the fluid jet generated at the orifice with the jet passageway of the nozzle . <EOS>