27 March, 2015

Repairing an old Mitutoyo profilometer probe

Some time ago I repaired an old Mitutoyo profilometer 178-928D , which no longer has spares and which had broken the pin that transmits motion to the head holder; a calibrated shaft that moves left and right and which I hold in the following image (the pin / screw was in the center hole):

This probe has a very simple operation. The spindle that is coupled detects changes in a very similar way that is translated the marks in an old LP music disk, transmiting the movements caused by the roughness by a magnet and coil needle.
The shaft that moves the spindle is moved in a controlled manner with a step by step motor to an endless spindle, first the engine slowly forward in the measurement phase, and then quickly picking head to its starting position, all controlled from the profilometer which is connected with a cable with 6 wires (that is a seven or eight cable, but one or two are not used, as you can see in the following images after repairing the cable too):

Also had to repair the cable was completed using copper wires breaking
In the picture the already repaired and re-soldered wiring, just plug with the cover was filled with epoxy

To remove the shaft and remove the piece that had been embedded in the hole, you must first remove two polyethylene plastic "brakes", with the function of making it slide smoothly without rattles, located under two copper plates:

And so is the probe without shaft:

To fix it I screwed a small screw from the casing, that had just the right size for the function, after in position, adjust its width with a small rotatory tool (Dremel or similar) with a cutting disc for file it to enter into the slot that has the endless golden piece that moves, and after checking that there are no gaps and that it works correctly with this fix, you put a drop of epoxy so it does not come loose with the use:

Once the glue has dried put his head into the slot, and the tool is already fixed!.

Avoid forgetting to retire the polyethylene plastic pieces, like passed to me; I forgot one of them before getting out the shat and I found it preventing the rotation of the stepper motor which moves it:

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