Good Powerful Bench Grinder

[Greebe]

Hey guys,

I am in the need for a new bench grinder. I had a Delta 8" single speed that I sold recently. It seemed well built but for heavy use it was very underpowered. It was still fairly new with less than an hours use on it.

I was wanting to upgrade to something that I can grind heavy plate or bar stock with out having to back off every second to let it spool back up. The Delta, I literally had to grind for a second or two and then let it spool back up for a few second. So time at the grinder was twice what it should have been.

Any suggestions? Looking for a 6-10 in wheel size. I typically grind 1/2 plate and up to 3/4 bar stock.

How are the Dayton grinders? We had one at one of our state maintenance shops in Nome but I never used it.

Thanks
Greebe

Edited August 28, 2009 by Greebe

[David Einhorn]

It is not the brand name that provides the power rating but the horse power rating (HP). A bunch of years ago the manufacturers started putting the motor's *max* horsepower ratings (burnout rating) on the motors rather than the normal running speed HP. To find out the motor's true horsepower you look at the amperage on the label of the motor and use that amperage to find out the actual normal running rating. I use the chart in the little green book from the hardware store called, "Wiring Simplified".

Also, people can correct me if I am wrong, but Black and Decker, Delta, Dewalt and Rockwell are all the same company. The same factory also made the bunch of Sears power tools that I purchased when we bought our first house. Needless to say it all started falling apart as soon as they were removed from the boxes. Since then I have tended to avoid purchasing anything with moving parts or a motor from Sears, and try to avoid equipment made by Black And Decker in general. Yes both Sears and B&D claim to have improved their equipment, but I spent a lot of money on the junk that fell apart. As the saying goes, "Fool me once, shame on you. Fool me twice, shame on me."

If you want a powerful grinder, then you will likely need to check out machinery dealers that cater to "professional" heavy-duty equipment. Your local hardware store, or farm store will only carry homeowner type equipment rated for casual/periodic light use.

[Greebe]

How bout this one. It looks good. It runs $230 and can run on 230V which is nice. Plus I get a hefty discount on their products as I am a member of a certain association here in WV.

Some specs:
Wheel Dia 8 In, Max RPM 3450, 3/4 HP, Voltage 115/230, 7/3.5 Amps AC, 1 Phase, 60 Hz, Arbor Hole 5/8 In, Face Wheel Dimensions 1 In, Wheels Center-Center 16 1/2 In, Length 21 In, Height 13 In, Dust Collection, Exhaust Port 2 1/2 In, Includes Adjustable, Ratcheting Tool Rests, Adjustable Eye Shields With Hurricane Bolts, Spark Arrestors, 36 And 60 Grit Grinding Wheels, Single Point Dust Collection, 6 Ft Cord

Greebe Edited August 28, 2009 by Greebe

[John B]

Does it have to be a bench grinder?

For rapid metal removal heavy duty belt grinders work great.

[David Einhorn]

I went downstairs and brought up the book, "Wiring Simplified" by Richter and Schwan. Here is their chart:

Motor.........120 volts........240 volt
------------------------------------
1/4 hp.........6 amp...........3 amp
1/3 hp.........7 amp...........3 1/2 amp
1/2 hp.........10 amp.........5 amp
3/4 hp.........14 amp.........7 amp
1 hp............16 amp..........9 amp
1 1/2 hp......20 amp..........10 amp
2 hp...........24 amp...........12 amp
3 hp...........34 amp...........17 amp
5 hp...........56 amp...........28 amp

How bout this one. ............ 3/4 HP, Voltage 115/230, 7/3.5 Amps AC, 1 Phase, 60 Hz, Arbor Hole 5/8 In,.....Greebe

So when we look at the chart we see that 7/3.5 amp is 1/3 horsepower[HP] and *not* 3/4 HP. So the rating is, in my humble opinion, a bit deceptive.

1/3 HP is not enough for your purposes. 1/3 hp is not much more than a toy. I purchase little hand tools that have 6 or 7 amp ratings.

I can remember a time when I could go to the hardware store and know the thickness of lumber or the horsepower of a motor without converting it to its real number from its "nominal" number (nominal defined as "in name only", a big word that means that the store thinks its customers are idiots). :( Edited August 28, 2009 by UnicornForge

[Ken Ra]

Complete bench grinders have an integral housing, if part goes it all goes. A motor arbor and belt hooked up to a motor on a hinge plate works well and the horsepower is what you want it to be. It also can be hooked up to a flap sander. disk sander or a lap! mine is 3/4 hp 7.5 amp 120V

[keithgartner]

Beaumont Metal Works, Manufacturer of Industrial belt grinders and finishing equipment

[HWooldridge]

Dayton's grinders are pretty good - I have a 6" and it's pretty tough to bog down. However, I use my belt grinder for almost everything so the bench unit has been relegated to sharpening my tungsten electrodes.

[Greebe]

OK. So it sounds like I would be better off with a good belt grinder such as the KMG and then a smaller bench grinder for sharping my tungsten for TIG on one side and sharping my carbide tools for machining on the other.

I was planing on building a KMG style belt grinder this Sept. when I get moved into my new house.

Any suggestions then for a decent smaller 6" bench grinder to serve the above usage?

Thanks again
Greebe

[Greebe]

I went downstairs and brought up the book, "Wiring Simplified" by Richter and Schwan. Here is their chart:

Motor.........120 volts........240 volt
------------------------------------
1/4 hp.........6 amp...........3 amp
1/3 hp.........7 amp...........3 1/2 amp
1/2 hp.........10 amp.........5 amp
3/4 hp.........14 amp.........7 amp
1 hp............16 amp..........9 amp
1 1/2 hp......20 amp..........10 amp
2 hp...........24 amp...........12 amp
3 hp...........34 amp...........17 amp
5 hp...........56 amp...........28 amp

I have a question concerning this chart. Doesn't amperage also vary with efficiency? So could an electric motor produce more power ( in the form of HP) with less amps if the motor is more efficient since amperage is how much the motor is drawing?

When shopping for anything that uses a motor should you base how strong the motor is based off of amp's? For instance I know that 230 is more efficient than 115, but uses half the amperage.

Any electricians feel free to answer as well.

Thanks
Greebe

[Frosty]

Unfortunately a belt isn't good for sharpening lathe cutters, a wheel works better.

I've used the grinder in the DOT shop in Nome, it's a good one. If you're talking about the pedestal grinder that is.

Frosty

[bluemountainforge]

I use an older Sears 8" grinder which looks similar to some Baldor grinders I have seen. This thing is a 60+ lb monster but was made decades ago! Baldor grinders and motors are good, but you pay for what you get.

[welder19]

At one shop I go to they have a 10" Dayton, it works good and has plenty of power. It all depends on what your grinding, there isn't really one machine that will do it all, in my shop I have 3 bench grinders, a 6" and two 8", a 4"belt/6"disc combo and a 20" disc. By far the best for fast heavy stock removal is the 20" disc with 24 or 36 grit discs, it will eat through 1" plate faster than any bench grinder, they arn't cheap machines, even used, but worth every penny, to me any how.
If you want a top of the line bench grinder then go with a Baldor.

welder19

[BIGGUNDOCTOR]

Fast stock removal--I agree with the disc sander. I have a JET 20" disc that I got off of Craigslist for $500. It also has a reverse switch which comes in handy. These will remove stock like nobody's business. One of the guys in the shop found out how fast they can remove 90% of a thumbnail one night. Thin stock and a wide table to disc gap don't mix.

For a bench grinder I would look around at auctions. My Dad bought a 14" pedestal grinder for $50 at a high school machine shop auction. Even if you find a a large industrial grinder that has a burned out motor you can still use it. Remove the rotor assembly, and open a window in the the housing after gutting the stator windings. Turn a pulley groove(s) into the shot rotor, and reassemble. Now just run a vee belt(s) over the rotor to a single phase motor. Basically just use the housing for the bearings, and arbor. Don't shy away from 3 phase equipment. A phase converter may seem expensive, but you can save a lot of money buying industrial tools. At the high school auctions I went to the 3 phase stuff went dirt cheap, because it was 3 phase. The single phase lathes, etc went high because the home shop guys fight over them. My home lathe is an 18.5" x 54" Monarch lathe that weighs 5,200# I use a jack motor arrangement to run the 3 phase motor off of single phase 220. I haven't gotten around to getting my Arco Roto-Phase phase converter wired up yet since the jack motor works so well. The main item I need the phase converter for is my 3 phase 650 amp MIG.

I got an old heavy cast iron Stanley 7" bench grinder for $5 at an estate sale. When you hit the switch it only hummed. Looked under the base and saw a capacitor. I wrapped a cord around the wheel nut, and gave it a yank to spin the motor up then switched it on--ran fine. Bought the grinder figuring I just needed to find a capacitor, then I found one at the same estate sale, and they tossed it in. Knowledge can be a key factor in purchasing.

[thingmaker3]

I have a question concerning this chart. Doesn't amperage also vary with efficiency? So could an electric motor produce more power ( in the form of HP) with less amps if the motor is more efficient since amperage is how much the motor is drawing?

"Horsepower" and "watts" are both measures of "power." "Power" is the rate at which energy is converted from one form to another. Electric motors will be anywhere from 20% efficient to 60% efficient, so 746 watts of electricity might get converted to a fifth hp or more than a half hp. (746 watts = 1 hp). Any electrical energy which does not get converted into mechanical energy gets converted into waste heat, waste noise, waste electromagnetism, and such.

The chart from Richter and Schwan's book is a good rule of thumb.

When shopping for anything that uses a motor should you base how strong the motor is based off of amp's? For instance I know that 230 is more efficient than 115, but uses half the amperage.

Power (in watts) is equal to voltage (in volts) multiplied by current (in amperes). 230 V is not actually "more efficient" than 115 V, but it does let us use smaller wires because we use half the current for the same power. Smaler wires means less weight and less cost.

And just to remind us how complicated life can get, any electric motor will draw more current when it bogs down. The "stall current" is the high current drawn by the motor when the shaft is unable to turn - this is used to calculate the artificially inflated "max hp" rating.

-Lee Cordochorea, IBEW Local 48