View Full Version : How do i make my bench grinder run @ variable speeds?


Nealcrenshaw
04-04-2010, 05:00 PM
I'm thinking some kind of potentiometer or some kind of resistance that i can plug the grinder into,but i can seem to piece it together in my mind. :bounce:

Motofixxer
04-04-2010, 05:11 PM
I have seen variable speed devices for use on routers. I believe they just plug in and have a variable knob on it. Probably work for anything you can plug into it.

Nealcrenshaw
04-04-2010, 05:25 PM
where could one find such a device?

mikevango
04-04-2010, 06:05 PM
dimmer switch

Nealcrenshaw
04-04-2010, 06:12 PM
I found something but it doesn't work with Capacitor induction motors if i'm not mistaken thats the type of motor a bench grinder uses.


http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/speed_control.html

The dimmer switch may not be a bad idea

Big_John
04-04-2010, 06:17 PM
Find a Variac. Its a variable transformer made for stuff like this.

They've expensive new, but they've been around forever and with a little bit of looking, you can find a used one.

Do a search on Ebay.

J.A.F.E.
04-04-2010, 06:17 PM
I haven't looked but I would think Grainger has something. You need to check about the capacitor start and if it is designed to work with brush motors or inductive motors.

Zrexxer
04-04-2010, 06:34 PM
Dimmer switches, potientiometers, router speed controls, etc. will all work only with universal brush type motors. You will burn up an induction motor trying any of these on it. A variable frequency drive is the only way I know to control the speed of a motor like this.

nate379
04-04-2010, 06:41 PM
http://www.electroniccity.com/shopping/pricelist.asp?prid=1147

Something like that would work??

I am curious as my drill press only goes down to 500rpm and it would be nice to go down to 100-200 rpm at times.

gearbuilder
04-04-2010, 06:46 PM
Dimmer switches, potientiometers, router speed controls, etc. will all work only with universal brush type motors. You will burn up an induction motor trying any of these on it. A variable frequency drive is the only way I know to control the speed of a motor like this.

I agree with Zrexxer 100%

Jamie

Nealcrenshaw
04-04-2010, 06:49 PM
How does a variable frequency drive work??

Zrexxer
04-04-2010, 06:50 PM
http://en.wikipedia.org/wiki/Variable_frequency_drive

Nealcrenshaw
04-04-2010, 06:53 PM
Wow,this costs about 6x my grinder

nate379
04-04-2010, 07:58 PM
The one I listed cost $60. That doesn't seem bad.

Bolster
04-04-2010, 08:31 PM
Zrexxer's right. Very difficult to slow your grinder with any electrical add-on. Pillow blocks and pulleys will help you out but that's a lot of additional space needed.

Neal, I know it's frustrating when you ask a specific question, and you get answers that are hugely divergent...happens all the time here at GJ...forgive me for going off track, but here's an excellent alternative to a variable speed bench grinder. Actually, it IS a variable speed grinder...hugely versatile...I never use my 'round' bench grinder any more...and you can slow the sucker way down so you don't even get sparks at all, metal comes off like dust. Keeps your tool cool.

http://www.cootebeltgrinder.com/

Everyone who has played with mine wants one of his own, and for good reason! It's very well made.

crankshaftdan II
04-04-2010, 09:26 PM
Check out the local farm supply store, saw one for about $89.00 with variable speed control, 6" wheels, made in PRC?? Must have been a different type of motor with a reostat to regulate from 3450 down to what ever speed you require. Might be better than trying to control your regular grinder??

Moose-LandTran
04-04-2010, 09:32 PM
Just push harder on whatever you're grinding, that'll slow it down... :lol:

tatra
04-04-2010, 09:38 PM
beat me to it moose........:beer:

LoneGunman
04-04-2010, 09:45 PM
Everyone who has played with mine wants one of his own, and for good reason! It's very well made.
:wtf:

I agree with the freq drive people

cdent
04-04-2010, 10:12 PM
Look at the variable frequency drive carefully. Usually, they need to run a 3ph motor to get variable speeds. A regular stone wheel bench grinder isn't a very precise tool. It may not be worth putting much money into modifying it.

sanddrag
04-05-2010, 12:31 AM
1. Sell it
2. Buy this (http://www.lowes.com/pd_78808-46069-PCB525BG_0_?productId=3162491&Ntt=bench%20grinder&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=bench%20grinder$y=0$x= 0)

Bolster
04-05-2010, 11:19 AM
1. Sell it
2. Buy this (http://www.lowes.com/pd_78808-46069-PCB525BG_0_?productId=3162491&Ntt=bench%20grinder&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=bench%20grinder$y=0$x= 0)

Pfff!! It's "variable" is 2000-3450 RPM... meaning with a 6" wheel you're in the 3000+ SFPM range at slowest speed...that isn't going to slow a stone down enough to stop it from burning steel...you want to get into the 1000 SFPM range if you want to stop drawing the temper of the steel you grind.

Take 2/3 off the P-C grinder's slowest speed and now you're talkin'.

fordbroncodave
04-05-2010, 11:56 AM
use my method. proven and it works.

do not use a potentiometer, they are not designed to move large loads of electricity.

get a dimmer switch for a light in your house. get a square metal recepticle box for the switch. wire it in series in this order:

wall outlet, extension cord, dimmer switch, extension cord (female end). then you can use that for any tool you want.

works good with hand die grinders, routers, drills and more

shouldn't cost any more then $12 to make it. i make these for power supplies to regulate voltage output

mjozefow
04-05-2010, 12:42 PM
works good with hand die grinders, routers, drills and more



These are brush-type motors.

fordbroncodave
04-05-2010, 02:19 PM
These are brush-type motors.

whats your point? if you regulate the amount of voltage going in, it reduces the speed of the tool you are using. not going to hurt it at all

gorilla
04-05-2010, 02:24 PM
I converted my drill press to a 3/4 H.P. D.C. motor and a motor controller from Surplus Center. It has full torque at zero RPM and cost less than $150.00. This may be a good fix for your grinder problem. One thing to remember about VFD's is that they are designed to work with 3 phase motors that have enough iron in the core to run on lower frequencies if your motor is not so designed it will overheat.

Mickey O
04-05-2010, 02:25 PM
whats your point? if you regulate the amount of voltage going in, it reduces the speed of the tool you are using. not going to hurt it at all
Using a dimmer will destroy the motor, they make a kit (I have one, I'll post a pic when I find it) that you have to wire internally that will give you variable speed (wired similarly to how a drill switch is wired).

I have the router speed control, not sure how it works, I'll plug it in and post what I find.

Zrexxer
04-05-2010, 02:35 PM
whats your point? if you regulate the amount of voltage going in, it reduces the speed of the tool you are using. not going to hurt it at all
The point is, you have absolutely no idea what you're talking about and giving bad advice... If you reduce the amount of voltage going into a split-phase induction motor, it will overheat and burn up.

Mickey O
04-05-2010, 02:41 PM
Got some weird results, possibly because there is no load on it, but it appears to drop the voltage way down. 17 volts on low, 17.75 on high (not much of a range). I picked this up for an expensive router and decided not to try it because I was worried about smoking the motor, eventually I'll try this thing with something cheap, maybe a HF tool and see what it does.

http://i786.photobucket.com/albums/yy148/oldtoolads/vari-speed.jpg

Zrexxer
04-05-2010, 02:43 PM
I picked this up for an expensive router and decided not to try it because I was worried about smoking the motorRecall again that a router is a universal brush-type motor. Bench grinders do not use this type of motor.

lilredex
04-05-2010, 02:44 PM
whats your point? if you regulate the amount of voltage going in, it reduces the speed of the tool you are using. not going to hurt it at all

The point is, that your method only works on universal type motors ......the ones with brushes like routers, hand drills, die grinders, etc. Repulsion/induction type motors (no brushes) like bench grinders, drill presses, furnace fans, bench saws, etc. go up in smoke when you turn down the voltage, the current draw increases substantially because there is no repulsive magnetic field to limit the current draw as is the case of the higher voltage. Try it, it you want to see if your motor has "smoke" built in to it.

PS...if you ever experience a "brownout" it is important to yank the plug on your 'fridge or other appliances that may come on (with induction motors) so they don't go up in smoke because of the lower voltage present.

rockchucker
04-05-2010, 02:45 PM
The Motor MUST be able to be used as a Variable Speed Motor or it will fry your Motor. The amount of money you will spend on making the Variable Speed the correct way you can just buy a small Variable Speed Grinder. Like the one listed above from Lowes...Porter Cable. Or I have this one and it works great too...


http://www.sears.com/shc/s/p_10153_12605_00921154000P?vName=Tools&cName=Bench+%26+Stationary+Power+Tools&sName=Bench+Grinders

Damn! In the last few days it has gone up by $10.00!


More information...

http://en.wikipedia.org/wiki/Adjustable-speed_drive#Fixed_speeds_of_electric_motors


http://en.wikipedia.org/wiki/Electric_motors

LoneGunman
04-05-2010, 03:32 PM
Fordbroncodave, no offense I know you are just trying to help but using a dimmer on the motor Neal has WILL fry the motor, may not do it immediately but it will fry it the same. Everything you mentioned it working on has brushes. I work with motor controls almost daily as an electrician, believe me, I have tried it before I knew better.

alex71
04-05-2010, 03:38 PM
Look at the variable frequency drive carefully. Usually, they need to run a 3ph motor to get variable speeds. A regular stone wheel bench grinder isn't a very precise tool. It may not be worth putting much money into modifying it.

Correct, except for the usually part. No VFD that I know of is single phase.

Zrexxer
04-05-2010, 03:43 PM
Correct, except for the usually part. No VFD that I know of is single phase.Then here you go... http://www.anaconsystems.com/text/eagle1.html

alex71
04-05-2010, 04:33 PM
Then here you go... http://www.anaconsystems.com/text/eagle1.html

You learn something new every day...

"An industry-first, designed for use with Single-Phase AC Induction motors and is available in 115V or 230V at power levels up to 1.5 HP. "

This is the first and only unit like this that I have heard of. who knows how well it will work... and Damn expensive too, $500 for 1.5HP. you can get a single to 3 phase VFD in the same range for $100 all day long.

Nealcrenshaw
04-05-2010, 07:39 PM
Great info gentlemen!! I guess to be cost effective Moose's idea may work.^^^

Joe From NY
10-17-2010, 12:13 PM
Old thread, but how would a dimmer switch specifically made for a ceiling fan fit in here? I dont think that ceiling fans have carbon brushes.

http://www.brighthub.com/engineering/electrical/articles/63249.aspx

http://www.smarthome.com/solution29.html

hofferwood
10-17-2010, 12:37 PM
Old thread, but how would a dimmer switch specifically made for a ceiling fan fit in here? I dont think that ceiling fans have carbon brushes.

http://www.brighthub.com/engineering/electrical/articles/63249.aspx

http://www.smarthome.com/solution29.html

Shaded-pole motors have only one main winding and
no start winding. Starting is by means of a design that
rings a continuous copper loop around a small portion
of each of the motor poles. This “shades” that portion of
the pole, causing the magnetic field in the shaded area
to lag behind the field in the unshaded area. The
reaction of the two fields gets the shaft rotating.
Because the shaded-pole motor lacks a start winding,
starting switch or capacitor, it is electrically simple and
inexpensive. Also, the speed can be controlled merely
by varying voltage, or through a multi-tap winding.
Mechanically, the shaded-pole motor construction
allows high-volume production. In fact, these are usually
considered as “disposable” motors, meaning they
are much cheaper to replace than to repair.
The shaded-pole motor has many positive features but
it also has several disadvantages. It’s low starting
torque is typically 25% to 75% of the rated torque. It is
a high slip motor with a running speed 7% to 10%
below the synchronous speed. Generally, efficiency of
this motor type is very low (below 20%).
The low initial cost suits the shaded-pole motors to low
horsepower or light duty applications. Perhaps their largest
use is in multi-speed fans for household use. But the
low torque, low efficiency and less sturdy mechanical
features make shaded-pole motors impractical for most
industrial or commercial use, where higher cycle rates or
continuous duty are the norm.

I said that:shocking:
No copied from herehttp://ww1.microchip.com/downloads/en/AppNotes/00887a.pdf
Chuck

bsaint
10-17-2010, 01:37 PM
You need an inverter duty motor and a a VFD. 240v single phase in and 3 phase out. Don't want to mess around with electricity.