How to find the error of my CNC

[feldah]

Oh both are great ideas. Thanks guys. I will definitely use them. What I was referring to specifically is the z deviation. Sorry for my bad introduction. My idea was to take a long enough spirit level and put a small laser on it. The spirit level would be placed at one end of the table in parallel to my y axis. Now I would draw a line on the wall which lays behind the other end of the table. The further away the better. To find the exact same height I would use a long hose filled with water. Then I would make a mark every inch on that line.
Finally I would adjust the laser so that it's placed on one end of the level and pointing to the first mark on the wall. When that's setup I would attach a light sensor to my end mill. Beginning at one end of the x axis I would lower it until I get a signal from my light sensor. Now moving on I take several data points running down the x axis. When it finishes I would place the laser an Inch further on the spirit level and let it point to the second mark on the line on the wall. I hope that explains it better. What are you guys thinking about it?

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[mekanik]

I have no experiance with lazer levels. but from what i have seen you get a rather large red dot, and i think it would be difficult to acurately determin the centre of this. I do however have an optical level that is very easy to read your target (could be a rule on a magnetic base) the level will only focus if it is about 1Meter or so from the target but it does offer good magnification on the target, ideally you need a precision straight edge and precision level.
Regards
Mike

[routercnc]

I bought a precision level to do this. The 300 mm square frame type and accurate to something like 0.02 mm per meter?. Cost about £100.
Rest it on any piece of wood or box section that is long enough to touch both surfaces and measure any relative angle differences at any position you like along the beams where the rails will sit. Or start at one point and shim the level until it reads zero and check relative angles at other positions.
You need to do a bit of maths to convert the angle into the exact height differences based on your rail spacing but nothing too complicated. Then you can shim the rails level to each other and on the same flat plane etc.
I did this I one of my videos installing the Y axis onto the gantry. See YouTube channel.