Using a Laser Edge Finder on CNC Milling

Source:shengfe Date:2018-06-11 17:46

Using a Laser Edge Finder on CNC Milling
 
A laser edge and centre finder (Fig. 2-19) projects a beam from a laser held in the spindle on to the work and, in the basic model, this allows a ‘dot’ of light to be aligned with an edge or a mark on the workpiece. In other models, the beam produces a different pattern, such as set of crossed lines or concentric circles. The image can be seen even in quite bright light, making it an easy-to-use tool. The critical factor for accuracy is the size and clarity of the image on the work- piece, and currently available laser edge finders use lenses and polarizing filters to project a small, sharply defined dot or a narrow line pattern that allows considerable accuracy and repeatability. Figs 2-20 and 2-21 show the difference between a basic projected dot and a dot projected through a polarizing lens.
CNC Milling
 
When aligning with an edge, the technique is to split the dot on the edge by jog- ging the axes in small increments. As soon as the dot is on the edge and sheds light down the vertical face, it is right above the edge and that axis can be touched off. Other patterns suit other applications; for example, a set of concentric circles is ideally suited for locating the centres of existing holes. The various patterns
make the laser edge finder a versatile device for locating features and touching off. Figs 2-22 and 2-23 show the cross hairs in use to locate a position on a workpiece and to locate two adjacent edges.
 
 
Fig. 2-24 shows the concentric circle pattern (but note that this was pho- tographed from an angle; the circles appear circular on the flat face of a workpiece if the beam is projected on to the workpiece at right angles). Figs 2-25, 2-26 and 2-27 show the effects of changing the distance from the laser to the work and of focusing the beam, and Fig. 2-28 shows how the circular beam pattern can be used to align the axis with an existing hole, even where the edge of the hole has been chamfered. All in all, a versatile tool. How accurate is the positioning achieved using a laser edge finder? That de- pends on how accurately the eye can judge the coincidence of the dot with a mark or an edge, or how accurately the circular displays can be aligned with existing holes. Like the optical scope, the laser can be calibrated so that the axis of the beam coincides with the axis of the spindle, so this is, potentially, an accurate device.
CNC Milling