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.