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Old 03-11-2010, 12:29 PM  
Quattro
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Default Angle grinder recommendations

I'm in the market for a new 4.5" angle grinder. I've had cheapies, and I'm tired of them burning up.

I'm considering a 10A DeWalt on Amazon for $90.

Anyone have opinions on angle grinders?

Thanks.



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Old 03-11-2010, 01:03 PM  
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Quote:
Originally Posted by Quattro View Post
I've had cheapies, and I'm tired of them burning up.
Anyone have opinions on angle grinders?
You need torque [T] or speed [S] or power [=TxS]?
http://www.vbmfans.net/p3.jpg

10A at 120v = 1200 VA in, so probably 600 VA out, almost 1 hp, at some specified RPM. The no load RPM means of course there is zero power being delivered.
You want light weight? Quiet operation?

For reliability, there is generally a zero correlation between price & quality.
Motors that run cooler will last longer. You need to use an extension cord that is capable of supplying enough current to the motor.

Post specs on some that you burned up and
some that you may want.

What Grainger & MSC Direct sells is a good database for comparison purposes and they actually publish specs that you can use, actual numbers [rather than saying light weight, reliable and powerful]. Volts and current in will give a relative indication of power.
I'd also throw in Harbor Freight so you know the high and low limits for what you can expect.

Angle grinder - Wikipedia, the free encyclopedia


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Old 03-11-2010, 03:19 PM  
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The last work in angle grinders is "Metabo". So much so that tradesman often call out for a Metabo when they want an angle grinder like it's the name of the tool instead of the brand.

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Old 03-11-2010, 03:33 PM  
Bud Cline
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All of my grinders are used in a highly distructive environment cutting and grinding ceramic tile and stone and concrete. I own six or seven working grinders at the moment and have had my best luck with DeWalt and Bosch. They are all probably less than ten years old with the exception of one Bosch that I have worked for more than seventeen years and the damned thing is still going strong. I have know idea what's wrong with that sucker.

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Old 03-11-2010, 04:51 PM  
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Quote:
Originally Posted by Wuzzat? View Post
10A at 120v = 1200w in, so probably 600w out, almost 1 hp, at some specified RPM.
I just thought I should mention that the equation:

Watts = Volts X Amps

Only holds true for purely resistive loads, like a toaster or a light bulb.

Once you get into reactive loads, like capacitors or electric motors, then you have to take into account the impedance of the capacitor or motor. In that case:

Watts = Volts X Amps X Power Factor.

Think of a man pulling a tire, like you see below:



There is tension in the rope he's pulling the tire with, so the force applied to the tire has a horizontal component and a vertical component. ONLY the horizontal component of that force serves to "pull" the tire. The vertical component of the applied force doesn't do anything except to try to lift the tire. But, since the tire doesn't actually rise, there's no work done by that vertical component of the force. That is, Work = Force X Distance, but since Distance is 0, Work done in the vertical direction is also zero.

In a reactive load, like an electric motor (or in this case, a grinder), multiplying the volts times the amperage gives the volt-amperes delivered to the grinder motor.

However, just as only part of the pulling force applied by the man goes into "pulling" the tire, only a fraction of the VA delivered to the grinder motor serves to actually turn the motor. The rest goes into overcoming the magnetic fields inside the motor that are opposing the flow of current through the motor's windings.

So, only a fraction of the volt amperes that are delivered to the motor is available to actually turn the motor. That fraction is called the "power factor".

And, depending on the mechanical friction inside the grinder, only a fraction of the mechanical power generated by the motor goes into turning the grind wheel.
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Old 03-11-2010, 08:22 PM  
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Quote:
Originally Posted by Nestor View Post
Watts = Volts X Amps
reactive loads
Watts going on?
man pulling on something
There is tension
women are watching
he's still pulling on that thing
women are laughing
Couldn't you have illustrated the difference between vectors and scalars, volts, amps, vars, va, PF, inductive reactance, motor core losses, magnetization current, flux linkages, hysteresis, permeability, back emf, etc., by using a photo of women mud wrestling, or something?
Not that I ever watch such trashy stuff as that.
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Old 03-11-2010, 10:48 PM  
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Yep, women's sumo wrestling makes my pants get up and dance too.
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Old 03-12-2010, 07:41 AM  
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Nerd alert!

OK, thanks for the science lesson, but really I'm looking for brand/model suggestions.

I don't know the specs of the ones that have failed me, but I do know they were very cheap tools from places like HF. They were both gifted to me, so I just used them with abandon. Whichever tool I buy will be treated marginally better.

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Old 03-12-2010, 11:21 AM  
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I had a Bosch Model 1375A hand grinder for years before it finally bit the bullet and I replaced it with a DeWalt. Unless you're doing a lot of heavy grinding of steel, I'm thinking that a hand grinder would be a better choice than an angle grinder. It's smaller and lighter, and that means you can hold it in one hand, and that makes it more convenient to use where you want to grind or cut something small enough to hold in the other hand.



Here are some things I found important:

1. Try to get a hand grinder with a 5/8" X 11 tpi arbor. The reason why is that many rotary brushes will require this thread to mount on a hand grinder:




2. The place to find masonary or metal cutting blades or rotary brushes rated at 12,000 rpm (which is typical of what a hand grinder will spin at) is at welding supply stores.

Generally you'll find that cutting wheels meant for metal will be made of aluminum oxide, whereas those meant for cutting masonary will be made of silicon carbide. The reason for this is that the two abrasives work differently, and that results in each one being better suited for cutting a different kind of material.

Masonary is softer than steel, so the harder and more expensive abrasive (silicon carbide) will last longer cutting a softer material (masonary) than cutting a harder material (steel). You CAN cut metal with a silicon carbide blade, but the abrasive grains will just get dull faster, resulting in poorer performance.

Aluminum oxide is a softer and less expensive abrasive, but when aluminum oxide crystals break, they break to form sharp edges, and that continuous renewal of the cutting surface results in better cutting performance in hard materials like steel. That's because it takes a hard material to break the softer aluminum oxide grains.
Again, you CAN cut a softer material with aluminum oxide, but unless the aluminum grains actually break to form new sharp edges, then grains will just dull and cutting performance will decline.

So, silicone carbide works better and lasts longer when used to cut soft materials cuz it's harder, and aluminum oxide works better and lasts longer when used to cut hard materials because it breaks, forming new sharp cutting edges.

3. Whenever using a wire brush for cleaning, ALWAYS wear eye protection (even if it's your prescription eye glasses) and also wear heavier clothing. That's cuz the brush can let go of wires, and at 12,000 rpm those wires will fly right into your skin. I've had to pull steel wires out of the skin on my shins even when wearing blue jeans. If they'll go through blue jean denim and stick into my skin, then they'll go into an unprotected eye no problem at all. This isn't just one of these "cover my a$$ warnings" to protect the manufacturer. Whenever you use a rotary brush on a hand grinder, keep your face and especially your eyes out of the trajectory of a flying wire.

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Old 03-12-2010, 11:27 AM  
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Quote:
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Nerd alert!
Yes. I've already notified the authorities!

OK, so how many days, weeks, months or years, for how many bucks [check for current prices], did you get out of good 'ol HF? This is one extreme.

We'll have to depend on forum member's memories for how well and how long the better stuff performed.

Probably the most fragile part of the grinder is the electronic speed control, if it has one.

BTW:
Vacuum cleaner motors have a resettable overtemp switch to protect the motor from overheating due to inadequate airflow due to a clogged bag.

It would be good if you found a grinder with an overtemp switch that trips when the motor is overheating because it's being overloaded, but I don't know if any manuf. would spring for the additional 50 cents or so for this part, in return for a large increase in motor reliability.
It depends on what the paying customer seems to want and is willing to pay for.

Probably a lot of people abuse these grinders; they're in a hurry and they have a lot of material to remove.
So, the grinder should be designed to resist abuse that is reasonably foreseeable by the manufacturer.

Post some candidate grinders; with what specs are available we should be able to at least say what are poor values for the money spent.
Companies who charge way outside of the mainstream are either trading on their reputation or there really is some good reason people pay that much. It might just good advertising.

Since their money is riding on the outcome, you can bet the CEOs of these manufacturers are looking at similar charts each week to see how they doing, relative to the value of what their competitors are giving to the consumer.


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