Not moving correct distance - 424 and Mach 4

[kberta]

Not sure where to ask this so hopefully someone can help.  I have the following setup;

5 TPI
1.8 degree per step (200 steps per rotation)
10 micro steps using Gecko 203V

My calculation yields 10000 steps per inch.  After milling my first part, my dimensions were off (part was tool small).  So I went to the negative 9 inch position on my mill and zero'd Mach 4 X axis.  I then moved 18.00 inches on my table, but Mach 4 says that I moved 18.337 inches.

Any ideas how to fix this and what could be the problem? I have this problem on every axis!

Thanks.

[kberta]

Solved my issue! 

[12strings]

Solved my issue!

And the answer was????  This may help someone else.

[kberta]

I bought the conversion kit and it had metric screws that I was not aware of.  It was 5.08 turns per inch and not 5 as I originally believed.