It was all going so well.....I decided yesterday arvo to do a job I'd been wanting to get to for ages- properly bedding in the mag chuck on my surface grinder. I took the chuck off, had to remove a few other bits as well to enable the spindle to come down a lot lower than usual and grind the surface that the chuck mounts on. It was quite bowed and I probably had to grind about a couple of thou off the ends before the wheel touched the middle; took a while but I finally got a nice flat surface to mount the chuck to.

The next stage was to mount the chuck upside down, clamp it down lightly with the magnet off and proceed to grind the bottom of the mag chuck. It's a 150 x 450mm chuck. Again took quite a few passes before I was contacting over the whole surface, finished up with a couple of .002mm passes then a 'spring' pass and congratulated myself that I had a decent starting point and called it a night.

Got back to it this afternoon. Turned the chuck over and clamped it down lightly, dialed in the back edge, tightened it down, turned on the magnet and dressed the top surface of the mag chuck to the flattest, smoothest most perfectest ever. Very very happy with the finish and confident that it was flatter than a dunny man's hat. With the final spring pass I think I was splitting the molecules in the coolant.

I decided it was time to try it out on a couple of 100 x 25 x 14mm parallels that were looking a little worse for wear. I mounted the pair on the mag chuck and took a few light passes on one side. The cross-feed wheel started to develop a tight spot that puzzled me a bit; checked that nothing was fouling anywhere and pressed on with the job. Flipped the parallels over and got half-way through one pass when the cross-feed handwheel started freewheeling without moving the table. Removed the feed screw assembly and discovered that the thread is stripped across a goodly section of the middle of the screw. Completely cactus. It appears to be a 3mm trapezoidal thread (didn't measure the diameter, probably 25mm). Obviously the nut will also be stuffed but the thing that hurts is that to get the nut out, I'll have to remove the chuck AND the table or whatever the side-to-side moving part is called. So all my good work of the last 2 afternoons will have to be done again.

The other fun thing is that I don't have the change gears to cut metric threads on my lathe. And I don't have all the necessary change gears for my universal dividing head to make the 127-tooth gear for the lathe. So, I can either finally get around to making the 20dp gears for the dividing head so I can finally get around to making the 12dp 127 and 60 tooth gears for the lathe so I can make the 3mm thread for he SG....or I can just make a 8tpi ACME feedscrew and nut for the surface grinder.


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