This is a portion of my CNC motion control board assembly documentation.

CNC Controller Motion Board Fan Installation (Rev. D)

The fan is installed in the following steps:

The fan is placed on the corner of an ordinary piece of paper.
Using a pencil, the outline of the fan is traced on the paper.
Using ordinary scissors, the outline is cut out.
Using ordinary tape, the outline is taped to the fan on the side that does not have any struts holding the fan hub.
Using the side of an ordinary pencil lead, the edges of the fan cavity and the mounting holes are located. This is similar to placing a piece of paper over a leaf and getting the outline of the leaf. The result is kind of pretty.
Using an ordinary ruler, draw two lines that intersect in the center.
Using an ordinary drill bit that fits snuggly in the hole, drill out the four corner holes. The resulting holes are not very clean.
Using an ordinary sharp utility knife, clean of the tags of paper on the holes.
Using ordinary care, peel the paper template off of the fan. There is no need to try and remove the tape from the paper. Simply fold the tape back over to back side of the paper.
Again, using ordinary tape, place the template in the desired location of the fan on the box. I accidentally let the fan get too close to the transformer, so I had to carefully loosen the transformer screws, and slide it over just little so that the fan would fit, and then re-tighten the screws. I taped all four sides down.
Using an ordinary utility knife, I carefully cut the fan cavity outline out.
Using an ordinary sharp awl, I dimpled hole starts for all four fan mounting holes.
Using an ordinary drill press, I set up to to drill the four mounting holes.
The first ordinary hole is drilled.
And the remaining three ordinary holes are drilled.
Using a larger ordinary drill, a large starter hole was drilled in the center.
An ordinary nibbler tool is inserted into the starter hole and the fan cavity hole is nibbled out. The resulting edge is quite rough, but the fan will never know.
Using a rotary file in the drill press, the rough edges are smoothed out.
The resulting fan cavity hole is much closer to circular.
This is a somewhat clearer picture of the same hole in better lighting.
Using an ordinary round file, any left over burrs are removed.
The fan is attached using 1-1/4 inch #6-32 round head screw, a lock washer, and 6-32 nut. The grill should help keep fingers from touching the fan as it moves.
The screw goes through the grill first, then the box, then the fan, then the lock washer and finally the hex nut. The result looks quite reasonable.

	The fan is placed on the corner of an ordinary piece of paper.
	Using a pencil, the outline of the fan is traced on the paper.
	Using ordinary scissors, the outline is cut out.
	Using ordinary tape, the outline is taped to the fan on the side that does not have any struts holding the fan hub.
	Using the side of an ordinary pencil lead, the edges of the fan cavity and the mounting holes are located. This is similar to placing a piece of paper over a leaf and getting the outline of the leaf. The result is kind of pretty.
	Using an ordinary ruler, draw two lines that intersect in the center.
	Using an ordinary drill bit that fits snuggly in the hole, drill out the four corner holes. The resulting holes are not very clean.
	Using an ordinary sharp utility knife, clean of the tags of paper on the holes.
	Using ordinary care, peel the paper template off of the fan. There is no need to try and remove the tape from the paper. Simply fold the tape back over to back side of the paper.
	Again, using ordinary tape, place the template in the desired location of the fan on the box. I accidentally let the fan get too close to the transformer, so I had to carefully loosen the transformer screws, and slide it over just little so that the fan would fit, and then re-tighten the screws. I taped all four sides down.
	Using an ordinary utility knife, I carefully cut the fan cavity outline out.
	Using an ordinary sharp awl, I dimpled hole starts for all four fan mounting holes.
	Using an ordinary drill press, I set up to to drill the four mounting holes.
	The first ordinary hole is drilled.
	And the remaining three ordinary holes are drilled.
	Using a larger ordinary drill, a large starter hole was drilled in the center.
	An ordinary nibbler tool is inserted into the starter hole and the fan cavity hole is nibbled out. The resulting edge is quite rough, but the fan will never know.
	Using a rotary file in the drill press, the rough edges are smoothed out.
	The resulting fan cavity hole is much closer to circular.
	This is a somewhat clearer picture of the same hole in better lighting.
	Using an ordinary round file, any left over burrs are removed.
	The fan is attached using 1-1/4 inch #6-32 round head screw, a lock washer, and 6-32 nut. The grill should help keep fingers from touching the fan as it moves.
	The screw goes through the grill first, then the box, then the fan, then the lock washer and finally the hex nut. The result looks quite reasonable.