what causes this ?

[sawmiller]

heres a picture of a pcb that i am trying to etch with my router using a v bit designed for that .
i set the height using the aussie zero setter one time then cut each of these one at a time. it seems that if the gantry was off when i cut the second it would go deeper. the router went from one side to the other of the etching multiple times so it doesnt seem to be back lash
the pcb is stuck on a piece of 3/4 mdf and that is vac clamped.
obviously i havent noticed this before when cutting wood, dealing in the hundredths and thousandths of a inch
dan

[BobF]

Is the bed level with the axis? Did you use the machine to cut the bed so the bed is true to the machine.
What kind of machine is it?
When you say the router was off, does that mean the steppers were turned off? If so the restart could have moved one step and moved zero a thousandth or 2 depends on the gearing and motion system.

[sawmiller]

thanks for the reply bob.
yes , i leveled the bed with the router.
the steppers wernt turned off between jobs.
it seems that if the table was unlevel, one etch should be deeper than the other , they are side by side...

ths machine is a 3x6 mdf.... i probally shouldnt expect the quality to be a lil better, but i do, so now i am going to tweak the machine, once i figure out what is wrong.
dan

[epineh]

It does look like missed steps, I did a few boards early on with my router before I had ironed out the "bugs" and they turned out a little like that, the holes out of alignment on the right side board certainly look like that axis was out and the depth issue looks like missed steps on the Z.

You said it has been working fine for wood, was there anything you did different when doing the boards as to when you work with wood ?

Maybe something got jammed in the rails just at the right (wrong ) time.

Only other thing I can think of is that maybe the PCB moved while cutting.

Russell.

[epineh]

Just another thought, do you use the vacuum clamp setup when you machine wood ?

Maybe the vacuum itself is causing noise on the power supply line...you could try again and use a good quality double sided tape, just be careful, you don't need to use much, if you cover the PCB with it, it is possible to snap the PCB trying to get it off, ask me how I know . Small strips are better