offsets to X Axis

Hi all. I am not a complete newby but new to useing a silver steel scriber on my marlin printer to scribe the tracks on a PCB board, I am confident to scribe the first side and have learned how to create an offset equal to the size of the board but I have not yet found the way to assign the offset value to 0 (home position) so that the gcode for the second side generated by Eagle and useing negative X positions will work. I will try to explain, the first side prints from the natural home position front left corner of the bed being the front left corner of the board and works fine the board being 68mm long I set the X axis offset to 68mm with a veiw to homeing to X0.00 at the offset and scribing the back side of the board useing X- measurements generated to alighn tracks and holes with the front. After I set the offset and home the X axis it defaults to the natural home position and not the offset, is this due to the firmware settings,

not sure I understand entirely

but home is always physical home, ie move until it hits a limit switch and then your at the home location as defined in firmware.

If you want to go to a certain location, just G1 to it, if you need that to be 0, then eg G1 X68 G92 X0, now X0 is physically at X68 and all further G1 X0 will go to it (till its reset)

Got any pictures of the results? Sounds interesting way of etching or similar things
Are you correcting for differences in Z height due to non perfect surface?

Edited 2 time(s). Last edit at 03/28/2016 01:06AM by Dust.

Thanks Dust, I saw this youtube clip which started me off www.youtube.com/watch?v=sNh0ubRcTYU I made the elastic band tensioner on the scriber and it apears to compensate for the board thickness and scribes the tracks with great precision, much finer than I can cut with my cnc due to tool sizes, my problem is when I turn the board over to scribe the second side the gcode produced by Eagle software starts at the offset and asigns negative X start points from the offset i.e.X68 Y0.00 useing X68.00 as 0

Hi Dust,
did you follow the youtube link.
I tried your suggestion i,e, G1 X68 G92 X 0 which as no errors were generated I assumed was fine, but when I entered G1 X-10 the printer went straight th the X home position, "limit switch" and not as I expected X58 from the limit switch position. Do I need to set X68 as an offset prior to the G92 ect

do a "G1 X68 G92 X0" (no space between X and 0)
Then a M114 (http://reprap.org/wiki/G-code#M114:_Get_Current_Position)
to verify its really thinks its at X0

And try again

Hi now that I have tried I find that bothe th G commands work though not when they are on the same line so I have created a command button in pronterface with G92 X0.00 and when I jog X to 68mm I click the button and bingo X0.00 is set to actual position. This works great because I can jog to any X position and click the button to set its position to 0.00. Thanks again for all the help