Following the advice given by CNC Fusion from the previous article, where they had me loosen the side piece, tighten the motor mount, and then tighten the side piece as much as possible without causing any grinding. And it worked!
My Z-axis now has a measured backlash of 0.002 inches (2 mils). That is more than I'd like; I would have ideally liked to see under 0.001 inches (1 mil). Considering that the depth of cuts I am planning on making would be no less than 1/32 inches, or about 31 mils, that is plenty of room.
I also had to reduce the Z-axis microstepping set by jumpers in the motor driver from 1/8 (as set in the X and Y axes) to 1/2 because the motor seemed to have a hard time starting up from idle. This could have been due to the weight of the spindle. The motor ran well when active current was running through it, but when the driver reduced the current to idle levels, the motor would not start easily. Reducing the steps to 1/2 increased the power available to the motor in a single microstep, and that fixed the problem.
I am not worried about the reduced steps per revolution. The screw has five threads per inch, and the motor does 200 full steps per revolution, making 1 mil per full step. So any amount of microstepping, including 1/1 will work without sacrificing precision.
With the backlash of the X and Y axes under 1 mil, and the Z axis at 2 mils, I am very pleased with the way things turned out.
Some other related interesting things:
Cold monitors are no good
I keep the mill in my garage, which goes below freezing during the night. The cold temperatures have not seemed to affect the mill, the motors, or the electronics. However, I need to bring the monitor for the computer into the house when I'm done using the mill, because monitors cannot generally be stored in temperatures below freezing.
I learned this the hard way when the CRT monitor I had been keeping in the garage started taking longer and longer to display an image, until finally it wouldn't display an image any more. The CRT was too heavy to cart around, so I decided on using a small LCD monitor. It now lives inside the house until it is needed.
The X2 mill is noisy
When running, the X2 mill is incredibly noisy because it couples its motor to the shaft using plastic gears. I've also heard stories of the plastic gears sometimes failing because, well, they're plastic. Luckily, Little Machine Shop sells a belt-drive conversion kit for the X2 (US$129.95, plus $14.11 shipping), which not only made the mill much, much quieter, but also increased the spindle speed. The difference is phenomenal. The mill no longer sounds like it's about to come apart at any moment. The mill should have been belt-driven from the beginning.
Little Machine Shop also sells all sorts of sundries and essentials for mills, such as collets, edge and center finders, vises, test indicators, parallels, and so on.