DIY Laser levelling using webcam and laser level

[devmonkey]

Back to the job in hand.

I found a rather obvious flaw in my sensor setup for setting my routing jig into plane today. I have the sensor mounted in a nice true cube and this sits on the jig plate. I then alternate its position above the 3 levelling points bringing each up to the correct height with the jack screws. The problem is unless the sensor is positioned in exactly the same location at each point for subsequent rounds of this procedure you will get different readings. This is because the sensor is effectively rotated around the axis of the jack screw and since the plate is not yet planar to the laser the height of the sensor relative to the laser plane changes based on this rotation. This makes it bloody difficult to do, and it is not until the plate is planar with the laser that sensor reads the same height right across the plate.

To put it another way with the sensor sitting on a plate that is not planar with the laser if you rotate the sensor about any point that is not the vertical axis of the sensor chip itself then the reading will change since the height has changed, similarly if you slide the sensor up and down this plate the height reading will change. This means you can trick yourself into thinking the heights are zero'd by moving the sensor, which I noticed I was doing.

There are two options:

1. Machine up a new sensor mount with some mechanism (likely a dowel pin) inline with the vertical axis of the sensor to that can be used to relocate the sensor consistently at 3 points across the plate.
2. Use 3 sensors simultaneously (would need software change) each fixed to the plate for the levelling operation.

[Kitwn]

Thinking out loud, but is there a three-sensor option that works the the other way round? Set up three sensors around the router frame and firmly fix the laser in one position on top of the moving plate. only the plate needs to be moved and adjusted for constant numbers out of the sensors. No trailing wires from the plate to tread on either. This does require the design to allow the laser to stay in place during routing or to be accurately replaced between cuts.