recently fixing my bench grinder, I lathed the shafts to fit the wheel holes tighter so that it helps keep it centered.
purchased a new fine grit wheel which really helped keep it centered & balanced.
and now it's just the coarse wheel which is out-of-round from previously using the hand-held wheel dresser.
first thing to resolve is to replace the flimsy rests with this rigid piece of L bar for a straight stable edge to rest & slide along.
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then I got this diamond tip dresser rod. obviously won't be accurate from holding the bare rod so I made this sliding jig to lock the rod length and slide across the L bar
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and it worked perfectly. both wheels are now concentric, flat and much more balanced with less vibrations 
