[How do I?] Variable speed grinder

C-Bag said:
My router speed control lives with my Foredom grinder because the little angle head grinder shouldn’t be run at full rpm. Works good and has eliminated the foot pedal that came with the Foredom. I’ve also used the SC on my HF die grinder to slow it down and it worked flawlessly.

Are you wanting to slow your grinder down David for like honing lathe bits? Many times faster is not better for me as it’s easier to control finishes at a slower rpm.
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Yes, that’s exactly why I want to slow it down. At 3450 rpm the sfm of the belt is very fast and metal disappears in a heartbeat. Sharpening drill bits is also a bit nerve racking!


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Stop and listen...

Many have start winding and switch that cuts out as rpm comes up.

Turn unit on then after at speed turn off and listen for a click as it slows down.

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tq60 said:
Stop and listen...

Many have start winding and switch that cuts out as rpm comes up.

Turn unit on then after at speed turn off and listen for a click as it slows down.

Sent from my SAMSUNG-SM-G930A using Tapatalk
Click to expand...
Ok. Does that mean you can’t use the speed control with the machine, or that you can? Or that you can start at full speed then back off the speed as long as that centrifugal start doesn’t kick out?
 
Yes...

Motor will try to run at full speed regardless of voltage or frequency.


Best bet for vari speed is 3 phase with vfd

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Curious why would you want to control the speed of the grinder? As you slow it down I think you'll loose a lot of torque.
What's the application?
 
AC motors as are in a bench grinder have the rpm set by the frequency of the power and the number of poles in the motor. Reducing the voltage will cause slip in the fields, the same as when you apply load to the motor. With slip you get heat. Ceiling fan motors I believe are whats called a Shady Pole motor. They will tolerate the heat of reduced rpm, same as the small motor in a zone valve will sit on stall all the while the valve is open.

Greg
 
DavidR8 said:
Yes, that’s exactly why I want to slow it down. At 3450 rpm the sfm of the belt is very fast and metal disappears in a heartbeat. Sharpening drill bits is also a bit nerve racking!


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Click to expand...

I sharpen drill bits on my belt sander & it's also 3450 rpm. If it's cutting too fast for your liking try a finer grit belt.
 
darkzero said:
I sharpen drill bits on my belt sander & it's also 3450 rpm. If it's cutting too fast for your liking try a finer grit belt.
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Good point. I'm using 80 gr ceramic belts at the moment. I'll pick up some 100 and 120's
 
That is coarse IMO for drill bits. The very first one I tried was with a 100 grit ceramic belt cause that's what I keep on there most of the time for general purpose (180 grit for the disc) & felt it was a bit too coarse. I've since been using 120 grit. I do have finer but haven't tried them yet with drill bits. Maybe 180 might be ok for me for touch ups. I only sharpen drills larger than 1/2" on it.
 
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