Posted by Philip on Nov 11, 2018; 2:34am
URL: https://forum.librecad.org/Open-source-CAM-software-tp5716598p5716621.html

When cutting steel with the spindle turning CW and traveling to the right the bit will be making a cut that is pulling the bit to the right.  The quill is also traveling to the right so that the force applied to the bit is lessened.  This helps to reduce bit breakage but produces a rougher cut.  With a CW spindle rotation and a leftward travel side force to the bit is increased.  This also gives a smoother cut.  The way it was explained to me is to think of the drive wheels on a car.  As the wheels are turning the car is also moving forward.  Now think of trying to push the car backwards while the tires are trying to push the car forward.  Much more force is required to do so and the chance of breaking an axle is much greater.  I understand why the smoothness of the cut is different between the two cuts but I don't really know how to explain it.  I has something to do with the math of speed and distance, entry and exit point and other factors.

This all really doesn't make a difference with plastics because they are so soft.  For engraving is use a 1/8" 60 degree V carbide end mill.  I will vary the depth depending on the size of the letters and material being used.  I've never machined Plexiglass (also known as acrylic) but it is difficult to drill and chips easily.  Polycarbonate is easier to drill and cut but is much easier to scratch.  It's a tradeoff.

Now for something I've never tried so I'm not sure how this would work out.  In LibreCad you can type a letter using MText or Text.  Then select that letter, then use Explode to break it down into it's individual entities.  Then use the Mirror command to make it read backwards.  That part I know will work but this next one is a guess.  Use your gcode generator on this file to see if it will work.

Can't hurt to try.