Mounting the Motor & VFD
VFD Conversion Project Start page | Home

The mill VFD conversion continues here with some mechanical work rather than wiring - yay! As this mini-project progresses, I am ending up with a mill displaying a variety of colors. It looks odd at times, but the mill is too old to warrant painting to match. Accurate and solid function is the goal. Don't let this stop you from making your conversion as pretty as you'd like! The original mill color was pure ENCO, kind of a weird aqua or turquoise color. Grizzly has their mills painted green, and the NEMA 56 motor mount plate was of this color. Of course, the VFD unit is bright sky blue, and the enclosure box is gray.

Why, oh why can't manufacturers use a proper gray paint, as a machine tool is made to be?

With the contactor box mounted on the right side of the mill column, I turned my attention to the area of the mill which will mount the VFD itself. The original switch was carefully dismounted, and packed away as a mill spare.

On the unpainted gray iron of the head was mounted the original mechanical 2-speed switch. Like most Taiwan mills, this mill was painted in its entirety after components like switches were mounted. There was some filler buildup and ridges which were filed down so as to present a nice, flat surface for the VFD mount.

The location of the three 5mm tapped holes was noted and measured so that I would not have to drill and tap additional holes in the head.

After determining where I wanted the VFD (parallel with, and left of, the ENCO nameplate), I engineered a simple bracket of fairly heavy aluminum plate. The backplate is 1/2" thick, and the side-plate is 3/8" thick. I wanted the VFD to be firm, not moving at all as I access the speed pot and the buttons. The backplate was intentionally tall, as the lower portion is needed to secure the power input and 3P output wiring. There is also room below the VFD to mount a small box, which can contain electronics for external control of the VFD beyond the standard START, STOP, and SPEED controls and buttons.

Another benefit of an aluminum mount such as this is the excellent heat absorption; contact between the plate mount and the native VFD heat sink wil help dump any excess heat.

This VFD has a cooling fan as well, below the VFD heat sink. The air is directed upwards through the fins.

I was tempted to make this mount fancy, with beveled edges - something to break up the boxy outline, but ultimately, after 2 contactor circuits and the drill-press VFD conversion, I just wanted function... just get it mounted and running! Besides, most of the mount is hidden from view as it is.

Note that the original mill power switch is still mounted in this photo.

The original Chinese motor was very heavy compared to the new Leeson motor. A small hoist would have been handy, because the angle one must assume to lift the motor free of the head is quite awkward and potentially dangerous. Still, it went OK, and the motor soon was stored with the original switch and cable for restoration later, if needed.
On a sheet of newspaper on the mill table, the Leeson motor was placed shaft up, and the Grizzly NEMA 56C mount was secured with 4 ea 3/8" X 16 SHCS plus lock washers. These were torqued fairly heavily, and the plate was mounted. Much easier than machining a new plate from iron or similar. Worth twice the price (in convenience) than its $60 U.S.

One of the three new cast-iron sheaves was mounted - the smallest. This will deliver maximum torque but with a lower top RPM. I was (and still am) a bit concerned about the amount of overhang required, as the output shaft is a bit short. Ideally, you'd want to load the motor radially as close to the motor bearing as possible. I could have made a sleeved adapter or similar, but decided to try it this way first. As pictured, this motor sheave will engage with the uppermost (smallest) spindle sheave.

Before mounting, I coated the shaft and sheave boring liberally with a rust preventative. I hate it when systems like this are installed dry. Ultimately, the shaft/boring interface corrodes, sometimes due to galvanic action, and the sheave ultimately becomes fixed so solidly that it may as well be welded in place.

I had no fear of the sheave slipping, as the motor/sheave is equipped with a stout 3/16" square key. A nice touch, the set screw bears upon the key rather than the motor shaft. It's certainly easier to replace a key rather than try and repair a marred motor shaft.

The motor installed, but no wiring or v-belt as yet. The lever middle-right is the brake for the spindle. I needed to take its location into account when designing the bracket.

At the bottom of the bracket, you can see a pair of 1/2" NPT threaded holes for the armored cable fittings which will help route the power. There is also a 10-32 tapped hole for grounding connections.

One more web installment, and the VFD conversion will be complete!