touch plate, but setting the X and Y offsets are a bit more difficult. The touch plate (or a variation of it) can also work in these situations, but it can be tedious and time consuming depending on how the workpiece is clamped. This is fine for situations that require high precision, but when a tolerance of +/-0.5mm is acceptable then a laser sight is much faster and easier. It's especially useful for placement of cut out parts in sheet goods. Another great feature is that you can simulate a program by running it with the router up and watching the laser trace the path.
Constructing it is actually pretty simple. The 1530 extrusions have a hole in the middle that is plenty big enough for a laser (almost an inch in diameter). The FLA-100 uses a piece of 1530 vertically for the Z axis, so it's a perfect spot to hide it. I just drilled a hole a the very top and then ran the wires down the middle of the extrusion. The laser is held in place with friction by a piece of microcell foam scrap that I had lying around. It's not exactly permanent, but so far the vibrations haven't moved it. If it does start to move then I'll just thread a bolt through the back side of the extrusion to hold it more securely. The laser itself is a 1mW adjustable crosshair module (they're all over ebay). The adjustable part refers to its ability to focus, which was actually pretty important. Most fixed focus crosshair lasers are set for a few feet away, but in this case the target is only a few inches away. It runs on 5V, which I already had available for running the vacuum and router relays. The factory alignment was off a few degrees, so I shimmed it using some strips of electrical tape.
Once the laser was installed I needed to calculate the offset between the laser and the center of the router. I mounted my smallest bit (a 0.7mm drill) and drilled a hole in some scrap mdf that I clamped to the table. Then I zeroed the X&Y DRO's in Mach3 and manually jogged the machine so that the center of the laser was exactly over the hole. The X&Y DRO's should now show the OPPOSITE of the movement I should make during my "laser zero" macro. Then I added a button to the Mach3 screenset for "laser zero" and programmed the macro to perform this movement. After a couple tests for accuracy it seemed to be working properly.