My Mill

I purchased my mill used in 2012. As purchased, the mill had DROs (digital read-outs) already installed for the X,Y, and Z axes, as well as a spindle stop. The photo to the left shows the mill (with way covers in place) in my small basement workshop. The purchase also included a sturdy metal stand on casters, a small mill vise, a set of collets, the tools that come with the mill when purchased new, and a LED lamp (which I have since replaced with two LED lamps).Below are two more views of the mill.

The photos below show the nameplate for the mill, with model number and specifications. In the middle photo below you can see the spindle stop (blue rectangle at the bottom of the mill head); the spindle stop is a handy addition and I'm glad to have it. The bottom right photo shows the on/off switch for the mill (green and red buttons), as well as a reversing switch which was installed by the previous owner.

Specifications

Mill Modifications and Enhancements

As noted, I purchased my mill used; the following modifications were already installed:

• DROs for all thee axes
• Tachometer

Some time later, I had the unfortunate experience of burning out the mill's brush-less motor (ouch!). So:

• Replaced mill motor (April 17, 2013)
• Added temporary temperature monitor (see below)

Installing the motor

The replacement mill motor did not come with any installation instructions, but it really didn't need any as installation is just the reverse of removal, as follows:

1. Feed wires thru side of controller box (use the plastic nut from the old motor, as one was not provided with the new motor!)
2. Connect the ground wire
3. Loop the other three wires thru the toroid (this is a plastic covered metal doughnut which you will had to remove from the old motor wiring to disconnect the motor); connect the three wires following the labels on the wires and the circuit board
4. Plug connector into circuit board
5. Screw the circuit board to the case
6. Replace the controller box cover
7. TEST the motor - turn the speed control to zero, switch on the mill, and slowly turn up the speed control (hold the motor so it doesn't fall). The motor should start and increase speed. Turn off the mill and unplug.
8. Replace the motor gear (from the old motor).
9. Screw the motor to the mounting plate (make sure the wiring harness is oriented to the left).
10. Screw the plate to the mill, first making sure that the gear is engaging the belt; push the plate backward to put some tension on the belt.
11. Check all screws for tightness.
12. TEST the motor - turn the speed control to zero, switch on the mill, and slowly turn up the speed control. The spindle should rotate normally and smoothly, without vibration.

Digital Read-Outs (DROs) and Tachometer

The photos below show the three DROs. The DROs are a very valuable addition which make adjustment of the axis settings much easier, and essentially eliminate the issue of backlash. Unfortunately, the Z-axis mounting somewhat restricts the top and bottom travel of the mill head. This may be fixable with a modified mounting - a future project perhaps.

Here are the readouts for the X and Y axes, as well as a spindle speed readout. The mounting for these is serviceable, but does not hold the readouts at an ideal angle - something I need to fix in the future.Below is a diagram showing the measurements of the mill base. Note that these measurements should be considered approximate, though they are reasonably accurate. Click on the drawing to get a larger view.

Mill Motor Heat Damage

Unfortunately, while working a project I overstressed my mill motor and burned it out. I thought I might as well get something out of the experience (besides a bill for a new motor!) so I dismantled the old motor and took pictures to document what it looks like, both outside and inside. As can be seen from the slideshow below, the motor has not ventilation - it is cooled entirely by using the aluminum case as a heat sink.

I also note that there are no manufacturer marking on the motor.

Mill Motor Temperature Monitor

As noted above, I had the unfortunate (and expensive) experience of burning out my mill motor, and having to replace it. In retrospect, I realize that it burned out because it overheated and melted some internal components; I did not become aware of the overheating until it was too late, and the only external signs of overheating was that the motor housing became hot to the touch, and on very close inspection gave off a "burnt" smell.

In the spirit both of locking the barn door after the horses got out (but also of avoiding another motor burn-out), I decided to see if monitoring the motor temperature was worthwhile. As a temporary measure (and using what I already had on hand), I attached the temperature probe of a digital oven thermometer to the motor housing using a "spring clip" made from aluminum cut from a soft drink can (see picture below). The clip simply holds the temperature probe into a corner of the motor housing.

To test whether the probe would actually measure any change, I ran the motor for five minutes at 1,500 rpm (half speed). As can be seen from the pictures below, this results in a 8°F increase in temperature. For the time being, I will keep the probe in place and see what kind of temperature readings I get in actual use. I note that the digital readout has a nice feature in that one can set an alert that goes off when the probe reaches a preset temperature; this can be used to set a warning temperature if the probe (motor) gets too hot. This leaves these questions:

• What temperature qualifies as "too hot?"
• Will the temperature alert be audible when the mill is running?

I will update this page when I think I have answers to these questions.

Note: In the pictures below, the temperature shown on the left is the probe temperature; the temperature shown on the right is the "alert" temperature.