Hi All!

Firstly I love how much information can be found here and how helpful the members are.

I am new to the MIlling world and would like to ask you guys for your ideas or best practises on a particular scenario.

I have a Chinese 3020 CNC mill and only machine wood with it. It works well and produces nice results.
My problem is that I don't really know how to machine 2 sided parts accurately.
I can machine the top and the bottom part very accurately separately but when I try to machine it on the same stock, I can't alight the stock perfectly enough so the top and bottom operations are perfectly aligned ans I end up with drifted dimensions due to me not placing placing the stock back on the machine perfectly after turning it upside down or not zero-ing the machine perfectly.

Here is some info that might help:
- Stock is always 50mm(x) x 50mm(Y) by 7mm(z)
- I always set the Gcode to start from the centre of the Stock on the X,Y axis
- I find the centre of the stock with a caliper, mark it on the stock
- I place the stock on the machine and fix it in place with a flat vise
- I manually move the machine to the marked centre on the stock and visually check that it is on the mark, then zero the machine and regenerate the G-code so the machine knows where it is positioned compared to the stock
- I then machine the top out of the stock

When its done machining the top part from the stock I turn the stock upside down and mark the centre again as I did before on the top side then place it back on the machine top facing up this time
- then I again find the centre of the stock manually by moving the machine spindle over the mark and zero the machine and regenerate the gcode
- I machine the bottom part

the problem is that the above method does not give me perfect precision and I end up with a part that has the top part perfectly centred while the bottom part is misaligned compared to the top operation.

How can I get around this?

I thought about fixing a 90 degree corer onto the machine that would always stay in the same place. This would ensure that the stock is always in the same place on the machine
then I was thinking of somehow defining a zero point on mach 3 relative to the stationary corner placed on the machine. Since my stock is always the same size, in theory this could work.

Do you guys have any suggestions that does not involve me spending a lot of money?

Thank you