Weiss VM32 Mill Conversion

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Slight project deviation today. Glass scales.
Are pretty much the best choice for these classes of small machines. They have excellent repeatability and do not drift with temperature or time. The snag is that you must order precut sizes, which is a problem because the delivery times from china are long. A simpler approach is to order the scales as long as possible and then shorten for your application. This also has the advantage that if one gets broken its easy to make up a spare. I have done this many times and evolved a good method for doing it..

Scale construction :-
The scales are enclosed in an aluminium extrusion with caps attached at either end by 4 crosshead screws, around PZ0 size. These can be removed to access the interior. The long strips of rubber/neoprene are dust seals. They are handed, the lower side having protruding lines of material to help the seal maintain the correct shape. The interior read head straddles the glass. One side is spring loaded to ride on the top and side of the glass scale with small bearings, the other side is automatically spaced on the opposite side, think inverted U. The bottom of the extrusion is asymmetrical and the scale itself is butted to it, and held in place by silicon rubber and nylon spacers placed at intervals. The end of the glass scale finishes approx 1 cm or so (min 4mm max 12mm) before the end of the extrusion. This is to give clearance for the end cap and is not critical.

To shorten you will need a tap and drill for the end screws, a BS1 centre drill and some general workshop tools, clamps battery drill, vice etc. . The end screws are generally m2 or m2.5. I will generally fit M2.5 as they feel more secure to me (we all have our foibles :-)). Firstly remove the end cap and read head. Place the read head and cable somewhere clean for later. Slide out the seals, or just remove the other end and pull them out of the way. Next cut the extrusion/glass to the travel length+80mm(read head)+ min 20mm overtravel. I have found the best way is to use my 6x4 bandsaw with the open end of the extrusion facing away from the motor so that the open edge gets cut last. The lower face of the extrusion should be the one that supports the glass. See pictures. Next take a pair of 1/2” pliers and break the end 4-6mm off of the glass. Its important to bend the glass away from its supporting edge or it will break longways. This glass is really soft and breaks very easily, you can even just crush the end. Remove the debris and place the extrusion in a mill to square up the end.

Next drill and tap the threads. Put a piece of square bar stock onto a bench vice and clamp the extrusion to it gap upwards, leaving 1 cm or so of protruding stock. Once secure the end piece can be fitted and clamped in position. Use a battery drill with a BS1 centre drill to a depth of a 1-2mm or so. Remove the end and proceed to carefully drill and tap as normal. Its only necessary to have a short length of thread, determined by the length of the screws protruding from the end cap. Small taps and drills are easy to break, so be gentle. Use lubrication on the tap, molybdenum grease or similar. Unclamp the extrusion and clean away all debris (I use an airline for best results). Refit the rubber seals making sure they are fully abutted to the other end cap and cut flush to the extrusion end using a razor blade. Refit the read head, and end cap. Job done.

Whilst we’re on scales a quick mention of wiring. There seem to be two standards of connections for the 9 pin D connectors. Seemingly designed to stop you using one read head with a different controller. I have only found two but there may be others. I have successfully altered the interior connections on one of my readouts to accept both types and they are electrically compatable. All my stuff is 5V so I don’t know how this would work for 3V stuff. See drawing.

More stuff soon

Best regards

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