Bad motor tuning,backlash or what?

[pajdoosijek]

When i live a cnc mill to work a relief it does't do it right but it goes diagonally, i mean it deform the picture so that it is not squared but rhombus like, and also if i tell him to make 30x20 it makes it 33x20 or something like this what am i doing wrong?
When hi finish a job ,return on home posicion is not right
before reinstalling mach3 everything was just fine i did Axisi Calibration
Working on 3 axis mashine

Here is a pic. on example



http://img855.imageshack.us/img855/5276/examplex.jpg

[KOC62]

I think it has two possibilities. There is a software problem or a hardware problem, or a 3rd option, both.

Try to do one thing at a time.
Jog 300mm in Y ony, then measure it. Now jog X 200mm and measure it. In other words can you jog the machine using the same dimensions around the rectangle and end up at the start position? This would check the mechanical behaviour of your machine.

Your diagram suggests that both X and Y axis are moving at the same time, or a small offset is added somewhere.

[H500]

Your motors might be slipping or missing steps under load. Try cutting the same shape, but in air. Does it still lose the home postion?