REALTIME CONTROL

Smooth the bottom end (the end with more thread) of the shaft using progressively finer grades of wet & dry abrasive paper. Spin the shaft in an electric drill while sanding. Polish the end and the other bearing surfaces with silver or brass polish. Wash off all traces of polish.  Clean the bore of the PTFE bearing.

Test the friction torque of your main bearing assembly as follows.

Cut out a 75 mm by 25 mm rectangle of 80 gsm paper (your printer paper is quite likely 80 gsm, check the label). Punch a 3 mm hole on the centreline of the rectangle and 12 mm from one end. Fit a nut to the shaft, then the paper, then another nut to secure the paper to the shaft. Fit the shaft into the bearing assembly.

Hold the bearing assembly with its axis horizontal and slowly rotate it. If the shaft turns in the bearings so the paper arm remains below horizontal  then consider the main bearing satisfactory.

If you need a 100 mm x 25 mm paper rectangle to pass this test, then speed and direction indication at less than about 4 knots will, at least initially, be inaccurate. Chances are the bearing will "run in" during the first good blow and be satisfactory thereafter.

If necessary check for the following

• Even tiny burrs left by the die at the inner ends of the shaft threads can increase friction. Remove any with a fine file or sharp knife.
• The top bearing housing nut clamps an olive which secures the PTFE bush in place. If this nut is overtightened, the olive compresses the bush radially, reducing its clearance on the shaft. If one is available, run a 3.3 mm drill through the bush. If only a 1/8 " (3.2 mm) drill bit is available, run that through the bush then use the bit as a file to open the bore out a little more.

The thrust bearing carries the weight of the rotor centrally on the shaft and so causes little friction torque. This contributes towards good performance in light winds.
It is important that the thrust bearing ball  is exactly in line with the shaft else friction torque is increased. The method described here allows you to accurately centre the ball and set its height despite any small errors in the placement of the holes in the housing.

Remove the shaft from the bearing. Fit two nuts to the end of the shaft with the longer thread. Set the nuts so that the end of the shaft is a little below the face of the outer nut, and tighten them fingertight against one another.

Hold the shaft vertical, nuts up. Place the ball in the open end of the outer nut. Adjust the nuts so the ball rests centrally in the nut and just clears the shaft end. Turn the shaft and check by eye whether the ball is running concentric to the shaft. If it's not, try one of the other nuts as the outer nut as some have burrs which stop the ball sitting centrally.

Place the ball in the centre of the sticky side of a 40 mm length of masking tape.

Fold the tape in half, sticky side in, onto the shaft so the edges of the tape end up parallel to the shaft and the ball is firmly held into the nut. Work the masking tape with the fingers to ensure it is well stuck to the ball, nuts and shaft. Trim off all but a millimeter or two of the "wings" of masking tape left by the folding operation.

Trim the masking tape from the half of the ball farthest from the shaft.

Again turn the shaft and check by eye that the ball and shaft are concentric. Correct any problem.

Fit the bearing housing to the top cap, using silicone to seal the joint. Tighten the nut. Don't remove the bearing housing again from the cap.

Fit the shaft to the main bearing and run a nut right down the exposed shorter shaft thread. Leave this nut finger tight. Fit the thrust bearing screw and nuts.  Assemble the housing. Adjust the thrust bearing screw position until there is about 1/4 mm clearance between the top of the PTFE bush and the adjacent nut.

Separate the two halves of the housing. Tighten the nuts on the thrust bearing screw without changing its position. Don't adjust the thrust bearing screw position again.

Coat the top of the head of the thrust bearing bolt with a milllimetre or two of epoxy adhesive. Reassemble the two housing halfs. Press down on the shaft to ensure the ball is impressed into the epoxy and in contact with the bolt head. With the housing in the sensor's normal operating orientation, allow the epoxy to cure.

Remove the nut from the exposed top of the shaft. Separate the two halfs of the housing, sliding the top half off the shaft. Cut the masking tape between the ball and the nuts, and separate the shaft from the ball and thrust screw.

Add epoxy if necessary around the ball to screw head joint to ensure that the ball is well secured.

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