DIY Laser levelling using webcam and laser level

[Kitwn]

A little earlier I was tempted to ask, tongue somewhat in cheek, how, once the long ( X axis in my case) rails are aligned, we now extend these techniques to setting up the gantry. After a little more serious thought I came up with the following. The required equipment is satisfyingly simple and inexpensive. Sorry for a lack of drawings, I'm not at home among all my toys at present and I'm thinking and editing this as I write it. All comments and corrections gratefully received.
-
Depending on your design, the same principles discussed earlier might be used to align the pairs of Y and Z axes rails when building the parts on the bench but we then need to square the gantry and tram the Z axis to bring everything together. Wanting to test for misalignment of rail pairs due to the stress of assembling the parts adds even more complication.
-
I'm thinking that two taught wires (one in front of and one behind the gantry) stretched across the now perfectly aligned X rails could be used with a simple threaded sensor probe mounted in an offset bracket in the spindle in much the same way as a single dial gauge is commonly used for tramming but without the awkward setting up and possible errors of a glass plate sitting on the machine bed. For machines with the rails mounted on high sides this might not work. Design your next machine with your chosen alignment procedures already devised.
-
One complication is that the wires must be perpendicular to the X rails and very close to the exact spacing required to give contact points with the probe arm parallel to the X axis or measured errors will be a compound of several possible alignment errors in the machine. By rotating the probe and adjusting it's height it is possible to use an ordinary multimeter to detect a setting where the probe just fails to make electrical contact with the wires at both front and back. If the spindle axis is not perpendicular to the X rails in the vertical plane these heights will not match. Unfortunately we can’t tell from these measurements if it’s the gantry feet that need shims or the spindle mounting.
-
Testing at either end of the Y axis travel will check for any twist in the Y rails plane and variation of height above the X plane (I'm calling this 'Y axis tilt' ). At least we know where the shims go for these last two. All these errors will need to be corrected before moving on.
-
I'm thinking of using a threaded probe rather than play with the software-driven Z axis height to do this as it's going to be quicker and easier.
-
Your chosen gantry design means it may not be possible to position the axis of the spindle in the ideal position directly above one wire and check for two matching contact heights at two points either side of the spindle along the Y axis but any two points on one wire found by moving the sensor over as wide an arc as possible over a wire as close to the spindle as possible should work. Height differences measured here are only due to errors within the Z axis/spindle assembly alignment if there is no remaining Y axis tilt.
-
Only after all this is done is it possible to skim the bed and then square the gantry by making the machine mark the corners of a rectangle on the bed and comparing the length of the diagonals.
-
Kit