Spunjin

Bench grinder on a variable speed switch?

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I would say probably you could. But when run slower the motor will not develop as much torque so you will probably find that when on load it struggles a bit.

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Terry has it. 

 

to do variable speed properly you need one of 2 things, either a 3 phase motor & a vfd, or a dc motor and a dc speed controller.

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You CAN find variable frequency drives for single phase, but they aren't common. Nor are they inexpensive. Entirely different from the 'router speed controller' devices that work with universal motors.

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McQ...that's some WAY back in the day machines!  Spunjin, on most modern motors, you'll burn something up if you slow it down.  Use it like it is for shaping and rough sharpening and save the nickels and buy a slow speed grinder.  I bought the Grizzly slow speed grinder at about 1/4 the price of the Tormek and it works great.  Capt Eddie Castelin (YouTube wood turner) uses the high speed grinder (with a fine wheel) to sharpen everything.  He just has a good set up and just works fast with a light touch.

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I heard that the Grizzly slow speed wet grinder was had some bad wobble in the wheel due to out of balance drive shaft. That may have been one persons experience but I have 2 Grizzly machines and couldn't be happier with their performance.

Did you have to do any significant truing of the grinding wheel when you got it?

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No...no wobble 'cept me and no truing needed.  Now I won't say it's 100% true as it spins- there may be a very slight side to side movement but no eccentricity problems with the stone.  It's moving so slow anyway, it really wouldn't matter.

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Overheating a tool on a grinder is more in the hands of the person doing the grinding than in the speed of the grinder.

Yep.....light touch and quick work.  On my slow speed I still only make a couple of passes across an edge because I'm just freshening it up.  If I were shaping something heat sensitive like tool steel with the high speed grinder, it would be a light pass and a dip in the water.  Still the answer Spunjin is "DON'T DO IT!!!" :o But see......MY mind then asks all sorts of questions I can't answer...

"Why can you slow down a router, a ceiling fan, and a blender?" Maybe it's like Don said, they're all motors with brushes. ?????? Someone with more electrical knowledge will have to take a hand off.

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Thanks, Tim. This was just out of curiosity. I bought a router table with lift and it came with a free PC 690 router. I noticed it wasn't a soft start and I had a variable speed control in hand so I installed it into my router cabinet so I could control the speed from the outside. It just had me wondering if it would work on a grinder (which I don't currently have).

I am itching to turn some stuff buy my gouges are super dull (takes dust not shavings) and I don't like the grind on my bowl gouge. I'll just have to save up a bit and buy a quality slow speed grinder with all the jigs.

While on the topic, should I just get a 8" or 10" wet grinder instead so I can sharpen my planer/jointer blades?

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If I didn't already have the crank grinders I would build a variable speed grinder with the spare DC motor I have laying around, would be easy to do; or a treadle grinder. Not sure what your budget will be like but I've heard good things about the Porter Cable variable speed.

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While on the topic, should I just get a 8" or 10" wet grinder instead so I can sharpen my planer/jointer blades?

 

 

You should also think about a scale if you plan on doing your own knives. All multi knife cutter heads need balanced knives and if you have to grind much on one the you take the head off balance. An imbalanced head is a dangerous head.

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Wow I never even thought of that. I may just send out for my blades to be done. Have two sets. One in the cutter head and one out for sharpening/waiting.

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Check your knives even if you send them out. The scale will pay for itself many times over. An archery scale cost very little and is all you need. You should be within 1/10 of a gram.

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