Buying a quality bench grinder is important. Newer ones sold in the big box stores tend to be either underpowered (and rated accurately) or overrated (and thus underpowered). Older machines tend to be way more powerful. For example, my 1/3 HP craftsman block (1974) grinder can handle more than some of the 3/4 HP big box store units can. Pretty impressive!
used baldor, craftsman block grinders (do a search to see what craftsman grinders fall under the category of block grinder), Queen City (usually only available in 10" + sizes, very heavy duty industrial units) are all goods brands to look for.
I have a 1/3 HP and a 1HP industrial rated craftsman block grinder. Both are wonderful units. The 1/3 hp cost me $30 and was only missing the eye shields (easy to solve, wear eye protection!), otherwise had the spark guards, tool guards, side wheel covers, the flex light, quench tray, etc. the 1 hp unit was $50 and was missing the tool guard, spark guard, and side wheel cover (and one flange) for the right side. Will cost me about another $50 to get all that. So for $100 I have a massively powerful 1HP industrial grinder with 8in wheels. That is way more than any homeowner will need (honestly, the 1/3 HP 6in wheel bench grinder has more than enough power for pretty much everything). Sometimes used units will need new bearings or other things, so you have to inspect them and know what to look for.
As far as angle grinders, the harbor freight units tend to get pretty good reviews. They all fail eventually, but for $15, quite a few members have gotten a few years out of them of heavy work. Sometimes even a few more years after replacing the brushes.
If you want a nice unit (less vibration, which is great for long periods using it, also more durable and more parts/support for if it does break, Milwaukee has a 5 year warranty vs harbor freights 90 day), Milwaukee and makita are great brands. Metabo is probably the best, but their basic German made unit (the Chinese metabos aren't a anything special) are $120 for a 6 amp grinder, where you can get a 11-13 amp Milwaukee or Makita for the same price. The Metabos are very smooth and durable however (almost no vibration for an angle grinder).
dewalt is good, but after seeing tear downs (on YouTube, forget who the person is) of the angle grinders, the Milwaukee and Makita are built better than the Dewalt (thicker copper windings, better bearings, grease, etc).
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