directed at the trim piece 16 the segment of the sensor beam a reflected from the reflector 32 is caused to be collinear i e aligned and coextensive with the segment of the laser beam b past the reflector 32 with both collinear segments then impinging the surface 14 at the same precise point fig2 a shows a second form of a beam combining device 22 a having an inclined reflector 32 a having coatings causing reflection of a beam having the wavelength of the cutting laser beam b while allowing transmission of the beam having wavelengths of the sensor beam a to be transmitted therethrough to reverse the relationship shown in fig2 fig2 b is a simplified diagrammatic view of another form of the beam combining device 22 b combining the cutting laser beam b and the first sensor beam a to produce collinear downstream segments thereof this embodiment includes a simple mirror reflector 36 having a through hole 34 the hole 34 is small in diameter relative to the diameter of the cutting laser beam b in order to minimize or eliminate the effect that the presence of the hole 34 may have on reflecting the cutting laser beam from the mirror reflector 36 to redirect the cutting laser beam b such a mirror does not require coatings that are wavelength selective such as those shown in fig2 and 2a in order to combine segments of the beams into a collinear relationship in this particular arrangement the first sensor 20 could be a ccd camera receiving beams reflected from.