Made some good progress today. Got the base put together with the ballast, and even got it painted. I did shorten the post by an inch and had to install the supports again. I don't think I posted how I kept that plumb and square. I used a my Workmate, of course. If you didn't want one before, you should want one now
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And, no I'm not smuggling a couple of kilos.

This is the ballast. I used those little bags full of air that some car parts were packaged in. I then filled them with paver sand and duct taped them closed. I probably got about 30lbs in and it made a big difference with the the stability.
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Here it is all buttoned up:
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A close up of the locking mechanism. Just a carriage bolt with a "t-slot" lock down handle. The center of gravity stuff that I worried about makes it so the grinder wants to stay where it is - either vertical or horizontal. In other words, it does not want to "flop over" when it is loosened up.
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It's kind of overcast day, so the pictures are a little dark. I'll take a few more when the sun comes out.
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Next are some holders for the cord, belts, and accessories. I'm hoping that being able to roll this outside will keep the garage a little cleaner.