I have an Ajax DM45nc CNC mill with a Centroid control. It is the last version of the Linux software (upgraded from version 1.01 to I believe it is 2.72 - have to look to be sure).I know that I have some Z axis backlash - maybe as much as .005" - I need to look into that to see if I can reduce it by adjusting the bearings, but that is a separate issue. This machine uses manual homing, and the procedure I'm using for startup is this - power on and let the machine boot up. Hit Cycle start to home the machine - no errors - it homes just fine. I use a Fowler Electronic Edge Finder for all setup. I set my reference (tool 0) by lowering the Z axis to a 123 block on the table - sliding the block under the tip of the tool until it just lights the led. I make three or four parts on this machine right now (just hobby work). All my tooling is in tool holders and the tool numbers are loaded into the machine. I have set the tool lengths on all tools using the same 123 block on the table as I use to set the reference tool. After homing I set the part 0 using the Fowler Edge finder. In my mind - I should be ready to make parts. Saturday I went through and reset the reference tool height - it was a few thou different. I reset the tools I was using on that part and everything was fine all day. Sunday I set my home and my part 0 - same tools as the day before. The Z axis was now off by about .020". I've been using this machine for a couple years and the Z axis has always been a bit touchy - I'm wondering if the encoder is starting to miss counts once in a while. This machine uses Brush type DC servos. Should I be doing a complete reference tool set up and reset all tools I am using every time I start the machine up? I would think that once the reference tool is set and all tooling is set up, all I should have to do is home machine and reset the actual part 0 and go. Thanks - Dan