Slowing down my grinder?

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Forum topic by Babieca posted 11-15-2015 01:26 AM 1036 views 0 times favorited 29 replies Add to Favorites Watch
View Babieca's profile


120 posts in 1079 days

11-15-2015 01:26 AM

I inherited this old grinder and have been using it to sharpen my turning tools, but I know if would be better if it were running at a slower speed.

Does anyone know if I can use the rheostat that HF sells as a router speed controller to slow it down?

29 replies so far

View 489tad's profile


3149 posts in 2586 days

#1 posted 11-15-2015 01:41 AM

I would try it. Seems like it would work.

-- Dan, Naperville IL, I.G.N.

View TheDane's profile


5068 posts in 3238 days

#2 posted 11-15-2015 01:59 AM

Won’t work. The router speed controllers are designed for use with universal motors. Your grinder probably has an induction motor.

Without going into technical details, induction motors (motors without brushes) are not the same as universal motors (motors with brushes). Speed controls for induction motors work by varying the frequency of the power with devices known as VFD’s, which are a lot more than the cheap router speed controllers.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View Jim Finn's profile

Jim Finn

2475 posts in 2497 days

#3 posted 11-15-2015 02:23 AM

what the Dane said!

-- "You may have your PHD but I have my GED and my DD 214"

View Dark_Lightning's profile


2689 posts in 2684 days

#4 posted 11-15-2015 02:30 AM

If you can find stones that are half the diameter, the machining speed (surface feet per minute) will be half that of the 6” wheels. Same rotation speed, but half the cutting rate…and half the heat.

-- Random Orbital Nailer

View tomd's profile


2038 posts in 3345 days

#5 posted 11-15-2015 03:15 AM

#2 what Dane said.

-- Tom D

View klassenl's profile


173 posts in 2234 days

#6 posted 11-15-2015 04:57 AM

The other thing you can try is a ceiling fan speed controller. Just make sure it’s rated for the current of the grinder

-- When questioned about using glue on a garbage bin I responded, "Wood working is about good technique and lots of glue........I have the glue part down."

View ForestGrl's profile


450 posts in 661 days

#7 posted 11-15-2015 05:07 AM

The other thing you can try is a ceiling fan speed controller. Just make sure it s rated for the current of the grinder

- klassenl

Ooooo, interesting idea! Sometimes, I wish even my 8” slow-speed grinder could go slower. Best I can do is turn it on briefly, off—sharpen a bit, then repeat.

-- My mother said that anyone learning to cook needed a large dog to eat the mistakes. As a sculptor of wood I have always tried to keep a fireplace. (Norman Ridenour)

View Fred Hargis's profile

Fred Hargis

4261 posts in 2068 days

#8 posted 11-15-2015 12:54 PM

I think I would read what Dane said one more time…for induction motors (split phase is an induction motor) it takes a frequency controller. Those normally won’t work for 120V motors. Trying one of the universal motor speed controllers may have some bad consequences.

-- Our village hasn't lost it's idiot, he was elected to congress.

View dhazelton's profile


2464 posts in 1871 days

#9 posted 11-15-2015 01:14 PM

Only way to change the speed without killing the poor thing is to use the arbor to belt drive another arbor with the appropriately sized pulleys. If you have issues building up heat you just need to quench your work frequently as you go. Or it’s a good excuse to get a Tormek or the Grizzley knockoff for yourself. Or use a small belt sander, the kind knife makers use to put an edge on their steel.

View Tennessee's profile


2481 posts in 2089 days

#10 posted 11-15-2015 01:27 PM

Most of the ceiling fan controllers are rated around 1.5 amps max. Ceiling fans draw very little current. I don’t think I would try that with your grinder which is rated at 4.9 amps.

-- Paul, Tennessee,

View TheDane's profile


5068 posts in 3238 days

#11 posted 11-15-2015 01:31 PM

Let me be more succinct … a rheostat (whether it be for a router speed control, ceiling fan, etc.) WILL NOT WORK on an induction motor.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View Wildwood's profile


1959 posts in 1709 days

#12 posted 11-15-2015 01:55 PM

I learned to sharpen on a Sears 1/3 HP, 3,400 RPN bench grinder and still have it. My Wolverine system with optional Vari-grind jig gave me repeatability at the grinder. Only drawback is grinder body too big & ¾” wide wheels. Gouges use a jig, chisels & scrappers free hand. My grinder over 20 years old & still going strong.

Have used, 8” & 10” bench grinders and like them lot more, have no idea of no-load RPM rating of those grinders buy enjoyed the wider wheel.

Going to stop responding to slow speed (1725, 1800, 2000 rpm’s) verus high speed (3,000+) bench grinders. If bluing tools while sharpening you are pressing to hard. Need only a light touch, if dressing the bevel you are taking care of tip of tool too!

Point trying make once gain confidence sharpening your tools; size & RPM’s of a bench grinder makes no difference.

Unless find an adjustable speed belt sander, those also have high rpm’s too!

-- Bill

View Tennessee's profile


2481 posts in 2089 days

#13 posted 11-15-2015 01:55 PM

Gerry – correct you are. The ceiling fan controllers they market now are little pulse AC induction controllers, for the most part. That is why the low amps. I think the HF units are rheostats, basically controlling only the voltage, and again only good for universal motors.

-- Paul, Tennessee,

View lndfilwiz's profile


92 posts in 1175 days

#14 posted 11-15-2015 02:33 PM

I did what dhazelton described. I was able to find an old arbor and then bought a 825 RPM motor to turn the arbor. I then added a pulley on the motor half the diameter of the pulley on the arbor. Slowed the arbor rotation to ~412 RPM. I also added a wire wheel to one side of the arbor. Makes cleaning metal part so much easier because theey are not ripped out of your hands.

-- Smile, it makes people wander what you are up to.

View Babieca's profile


120 posts in 1079 days

#15 posted 11-15-2015 06:04 PM

Thanks for all the replies. That’s what I was afraid of.

The results I’m getting now are good enough that I’m not about to spend $100 + on a new grinder or rig up some pulleys. It would have been worth $15 bucks though.

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