DIY Laser levelling using webcam and laser level

[Kitwn]

2. Twisting the carriage hard on the rail can induce a few um of error.

To me this says a lot about the quality of your rails and carriages. It also makes the case for a well aligned frame if you want smooth movement without binding.

[devmonkey]

To me this says a lot about the quality of your rails and carriages. It also makes the case for a well aligned frame if you want smooth movement without binding.

I would say it says that standard hiwin rails and carriages are pretty good, would you agree? This is an artificial setup as carriages wouldn't be used singly in a machine. The related interesting fact is that with these 20mm hiwin rails, with a section bolted down hard, moving the microscope 60mm to the next unbolted hole, finger pressure is sufficient to deflect the rail +/-3um although a small contribution will be from frame deflection. As said before everything looks like jelly when you look closely enough.

Also torquing up the mounting bolts with light pressure on an allen key moves the rail 1-2um, I set the rail at -2um with the bolt snugged down, then tightened it with the allen key that brought it to zero. I've just redone the straightening procedure this way and I'm now +/-2um along the entire length, job done!

The rail I chose as the master had two 'bends' in it, it was 'S' shaped, with the two ends zero'd there were two intermediate points along the rail which were roughly +/-70um respectively. I verified this wasn't some artifact of the taut wire or the software algo by changing the wire twice, moving the wire guides and changing the end that had the hammer hanging on it.

This shows that you definitely need to straighten the rail, it is not sufficient to use it out of the box.

[Kitwn]

I would say it says that standard hiwin rails and carriages are pretty good, would you agree?

That was my meaning, ' a few um' detected by the microscope is not much movement at the carriage. These rails are known to be intollerant of poor alignment, non-straight frames etc. and that's what you'd expect where there is so little play. When I decided to go for fully suported round rails on my machine part of the decision was that I was unsure I coud make the frame accurately enough for the more expensive Hi-Wins not to bind.