Weiss VM32 Mill Conversion

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Continuing with the saddle Y axis and some electrical work.
Limit switches, soft limits and home (zero return, grid 0, origin, etc.) position. These systems are designed to prevent the machine trying to go to areas outside the set envelope. Hard limits are set with switches that are triggered when the axis exceeds its normal working range and are used to set home coordinates. Soft limits are often set to confine the work area to a subset of the total area. With stepper motors if the mechanical limit is exceeded all that happens is the motor stalls with few other consequences. If there is a reduction drive it will be subjected to the maximum force the motor can supply. Forunately no smoke or fires occur. However, if this occurs it means that things have gone seriously awry, and the work may or may not be recoverable. There is little to be done to prevent the Z axis hitting the bed during an error as the tooling used is of indeterminate length, so no mechanical switch can be used. When a CNC controller starts, usually the first thing it does is to go to the axis home and detect the position with the limit switches. From that point on all coordinates are calculated relative to these positions.

As this conversion will use glass scales I have used the Y scale bracket to trigger the microswitches. The rear of the saddle has the X limit microswitches, and the left of the saddle the Y. I will upgrade these at a later date to improve the homing accuracy using a latching optical disc sensor I read about here :-
https://www.cnczone.com/forums/uncat...mit-works.html. The switches will be wired normally closed to ensure that any break will stop the machine.

Sketch with dimensions is really just my crib sheet so take it with a pinch of salt. Also check dimensions of your machine before assuming my drawing is correct. Initial test install of the ballscrew showed an issue with the hole in the front base of the machine. This was approx 1mm too small for the thrust bearing I was going to use. This was opened out using a 33mm hole saw. The position of hole saws is tricky to maintain without a pilot hole to guide. Positioning was achieved by use of a metal plate turned to the outside diameter of the saw cup. This was a simple and successful way of enlarging and centering the hole. The table and saddle were then marked out using a scriber and engineers blue, then drilled and tapped. As shown on one of the pictures its easy to use a metal piece with a right angle cut out to align the drill/tap perpendicularly. The base was similarly treated. To get good right angle holes and threads tapped into the base the drill needs to be held horizontally. This can be simply achieved with a few books or magazines under the drill body, piled to the correct height. I have used std V5 microswitches, the Y ones are mounted on a carrier plates for simple adjustment. Last pictures show the current state of play.
Best Regards
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