[endgrainguy]

I've spent most of the last couple months building myself a CNC from Ebay bargains, striving for a professional quality machine. Ball screws , THK rails, heavy 80/20 frame etc. Had huge problems building the controller,mostly related to limit switches and spindle start relay, but finally worked it out after simplifying the design.
But now I'm having difficulties executing programs in the right place. I"m getting inconsistant placement for the part cutting relative to the origin point from one running of the program to the next.
I have my work clamped to a fence fixing the lower left corner at x and y -0,0. I'm preceding the running of code by reffing all three axises, (making sure x and Y then read 0), jogging Z down to work surface, and then zeroing out the z. Problem has been in cutting path in the x and y . When I check the accuracy of my homing procedure by running it multiple times, it's within a couple thousandths, but I'm getting relatively huge errors when I run the g-code program, in the order of 1/16" or more. I"m making a batch of small jewelry box trays as my first project. It's to produce the tray shown here : http://www.alladd.com/moonrise_box.htm bottom of the page. The attached code below is to cut four of them from an 18" long x 2 5/8 " wide blank. I'm using the drawing to cut a profile with a .5 spiral bit on the drawings vectors, then planning to run a finish pass with a .25" bit on outer offset vectors. But I can't get it to cut consistant toolpaths, so no way I can get this two pass approach to work. Any suggestions? One should be able to cut a part , clamp a new one in, hit "program start" and get identical results and placement, over and over right? Thanks!

[Eurisko]

You're getting inconsistant cutting results (1/16 +), but are able to reference the axes within .002 each time.

It sounds like something is being pushed out of position during the cut.

That 'something' could be the workpiece, the cutting tool, the gantry, or the ballscrew.

Just to be sure, post the gcode, too. If there are any mistakes, some eagle-eyed CNCZoner will spot 'em.