Upgrading the CNC mill -3. Moving a threaded hole in steel plate.

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this is the new Y axis servo motor, sitting on its mounting plate, after the old servo has been removed

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Unfortunately the existing M8 threaded holes in the mounting plate are just in the wrong position for the new motor’s 8mm mounting holes.

So, do I 1. make a new mounting plate and assembly?   2. machine or file the new motor’s holes to fit the old plate?   Or 3. Fill the old mounting plate hole, then drill and tap new holes in the correct position  ??

  1.  seemed a lot of work   2. would have looked ugly and probably voided the motor’s warranty      3.  Seemed tricky, but I decided to give it a go.   If unsuccessful I could always revert to 1.

Filling the old holes.  Could have used steel thread and silver soldered it into place.  In retrospect, would probably have been the best option.   Could have used steel thread and Loctited it into place…. decided against, in case subsequent machining  softened the Loctite.   Could have filled the old holes with bronze, and drilled and tapped new threaded holes….   well, for better or worse, that’s what I decided to do.

The new holes impinged about 25-33% on the old holes.

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The old holes were bronzed.   I improved my technique as I moved around the holes.

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After cleaning up on the mill, the new holes were center drilled 

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Then drilled to size, and tapped.  revealed that the bronze did not entirely fill the voids. 

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I wondered if the bronze would accept a suitable degree of tightening of the M8 cap screws, but all seemed fine.   Note the jacking bolts, to prevent distortion of the weldment in the milling vice.

The bronze-steel sandwich did cause the tapping drill to wander slightly, but not enough to cause concern.  Next time I will try silver soldering in a steel filler piece.

Meanwhile, I have been removing parts and wires from the electrical enclosure.

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The servo controllers are removed.  Bit of a rats’ nest hey!  About 90% to go…