Angle grinder recommendations

Discussion in 'Tools' started by Quattro, Mar 11, 2010.

  1. Mar 11, 2010 #1

    Quattro

    Quattro

    Quattro

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    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.
     
  2. Mar 11, 2010 #2

    Wuzzat?

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    You need torque [T] or speed 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
     
    Last edited: Mar 12, 2010
  3. Mar 11, 2010 #3

    kok328

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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.
     
  4. Mar 11, 2010 #4

    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.:)
     
  5. Mar 11, 2010 #5

    Nestor_Kelebay

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    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:

    [​IMG]

    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.
     
    Last edited: Mar 12, 2010
  6. Mar 12, 2010 #6

    Wuzzat?

    Wuzzat?

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    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.
     
    Last edited: Mar 12, 2010
  7. Mar 12, 2010 #7

    Nestor_Kelebay

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    [​IMG]

    Yep, women's sumo wrestling makes my pants get up and dance too.
     
    Last edited: Mar 12, 2010
  8. Mar 12, 2010 #8

    Quattro

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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. ;)
     
  9. Mar 12, 2010 #9

    Nestor_Kelebay

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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.

    [​IMG]

    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:

    [​IMG]
    [​IMG]

    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.
     
    Last edited: Mar 12, 2010
  10. Mar 12, 2010 #10

    Wuzzat?

    Wuzzat?

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    Yes. I've already notified the authorities! :D

    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.
     
    Last edited: Mar 12, 2010
  11. Mar 12, 2010 #11

    Quattro

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    OK, I'll post up some options I'm looking at. BTW - what's the difference between an angle grinder and a hand grinder? The photo of the Bosch is what I'm referring to.
     
  12. Mar 12, 2010 #12

    Wuzzat?

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    The operator has to oppose the torque generated by the grinder in operation. The angle gives him/her a lever arm to make this easy.
    With no angle gear drive, the operator would have to grip the body of the grinder very tightly to constantly oppose the torque. Arm and body muscles are stronger than the forearm muscles that control the hand grip.

    Not to set off another nerd alert, but:
    For 32 lb-in of torque and a handle 8 inches long, the operator has to use 32/8 = 4 pounds of force at the end of the handle to control the tool.
    Stall torque is higher, and the operator has to then cancel out this sudden, higher, force or he/she will lose control of the grinder.

    If you're expecting a lot of stalling I'd use large hose clamps to fasten a 24" pipe or stick to the grinder body. The force is then 32/24 = 4/3 rds pounds.
     
    Last edited: Mar 12, 2010
  13. Mar 12, 2010 #13

    Quattro

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    Dude, I get it, you're smart. But, you don't answer questions very well, honestly.

    I asked: What is the difference between a hand grinder and an angle grinder?
     
  14. Mar 12, 2010 #14

    kok328

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    An angle grinder has a 90 degree mesh gear configuration.
    A hand grinder is simply a straight rotary grinder without the 90 degree angle to it. These are most commonly air driven whereas an angle grinder is electrial. However a hand grinder can come in the 90 degree variety also.

    image_8808.jpg

    image_8809.jpg
     
  15. Mar 12, 2010 #15

    Wuzzat?

    Wuzzat?

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    Dunno'. :confused: The only grinder pics I could find were of angle grinders. Sorry.
     
    Last edited: Mar 12, 2010
  16. Mar 12, 2010 #16

    Nestor_Kelebay

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    Sorry, it was me that caused the confusion. The original post in this thread said that Quattro was looking for a 4 1/2 inch ANGLE grinder. The angle grinder stuck, but the 4 1/2 inch didn't, so I was thinking the guy was looking for a 7 or 9 inch grinder.

    Basically, an angle grinder is a portable grinder that has the arbor at a 90 degree angle to the tool. A "hand grinder" is one that's small enough to be held in one hand. So, a "hand grinder" is simply a small angle grinder, and so a 4 1/2 inch angle grinder IS a hand grinder.

    [​IMG]
    A DeWalt 9 inch angle grinder.

    [​IMG]
    A DeWalt 4 1/2 inch angle grinder (aka: 4 1/2 inch "hand grinder")
     
  17. Mar 12, 2010 #17

    Nestor_Kelebay

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    I've had both a Bosch 4 1/2 inch hand grinder and a DeWalt 4 1/2 inch hand grinder, and:

    What I liked about the Bosch was that it seemed to be smoother, and didn't vibrate as much when using it. Also, I found the paddle switch on it to be very convenient. What I didn't like about the Bosch was that it required a special tool to tighten and loosen the nut holding the grinding wheel in place. Also, I didn't like the fact that the paddle switch made it easy for the grinder to go one whenever it was plugged in, even when you didn't intend it to. So, if you buy the Bosch, ALWAYS unplug it when it's not in use or when you're replacing blades or whatever.

    What I like about my DW400 4 1/2 inch DeWalt hand grinder is that it seemed to have more power than the Bosch. Also, it has a little arrow molded right onto the housing showing the direction of rotation of the arbor, and that can be convenient. And, I can use an ordinary wrench to replace a grinding wheel in it. What I don't like about the DeWalt is that it seems to vibrate more than the Bosch. Also, the on/off switch is close enough to the business end of the tool that if you're using without the safety guard, it's possible to have your finger hit the grinding wheel on the other side of the tool.

    (Normally, on the DeWalt, the guard around the blade prevents your fingers from coming close to the blade. However, when I'm using a handgrinder fitted with a thin masonary blade to cut Wonderboard, I actually like to take the safety guard off so I can see better from both sides. And, no I don't recommend other people do that, but I have noticed that when I've done it, the on/off switch is a little too close for total comfort to that spinning blade. The paddle switch on the Bosch allowed me to turn the grinder on and off with my hand well away from the blade at all times. But, when you're using a masonary blade, it doesn't have sharp teeth that will tear flesh off you like a great white shark, and you're just more likely to skin your finger rather than lose big hunks of it. Still, no one recommends people use any equipment without all it's safety features in place. I just mention it because it's something I did notice that I didn't like.)

    I liked the Bosch better. It simply struck me as a better built tool. In my case, I only bought the DeWalt because it was on sale. Price isn't normally that much of a consideration for me because tools are tax deductable in my case, so I'm buying them with before tax dollars, not after tax dollars. But, before I'd buy any grinder, I'd check that the arbor on it is 5/8 inch diameter and has 11 threads per inch. Some tools, notably Makita, have a metric size arbor, and so you might have difficulty finding grinding wheels, rotary brushes and accessories that'll fit, which can be a pain. Everyone in North America makes grinding wheels and rotary brushes to fit a 5/8 inch 11 thread per inch arbor. At 12,000 rpm, "close" doesn't count. It has to fit properly.
     
    Last edited: Mar 13, 2010
  18. Mar 13, 2010 #18

    Quattro

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    Thanks for sharing your experiences...that's exactly what I'm looking for.

    I do appreciate the knowledge here (Wuzzat?, Nestor, others), sorry if I came off sounding otherwise.
     
  19. Mar 13, 2010 #19

    Wuzzat?

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    Here's several brands from Grainger

    4.5" angle grinders
    price amps price/amps
    $69 7 9.9
    $95 8 11.9
    $95 10 9.5 best ratio [DeWalt]
    $99 10 9.9
    $99 5.5 18.0 worse ratio [Milwaukee]
    $105 10 10.5
    $139 12 11.6
    $159 12 13.3
    $159 13 12.2
    $159 13 12.2
    $159 13 12.2
    $159 12 13.3
    $105 8.5 12.4

    You pay about $12 more for each additional amp.
     
    Last edited: Mar 13, 2010
  20. Mar 13, 2010 #20

    Nestor_Kelebay

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    Quattro:

    Also, I'd spend a bit more and see if you can get a grinder with variable speed.

    I did some pretty scary things with my Bosch hand grinder, and having it variable speed would have been a lot safer. I bought a Makita 4 1/2 inch diameter wood cutting blade meant for their mini-circular saw and used it at 12,000 rpm to cut wood in some very tight spots. The blade was rated for that speed, but that little blade had big sharp teeth, and if I ever lost control of the grinder, I expect I woulda lost a sizeable chunk of flesh somewhere. Also, I used a really worn down masonary blade (that was rated at 5500 rpm) from my 7 1/2 inch circular saw and used it at 12,000 rpm in my hand grinder. It was worn down to about 5 inches in diameter so it would just fit in my hand grinder and I figured the smaller the diameter of the blade the higher the rpm it could take. It was purely good luck that it stayed in one piece.

    I look back on those things, and I figure I'm lucky I didn't hurt myself. But I also realize that both stunts woulda been a lot safer if I could have operated the grinder at a lower speed. So, spend a few dollars more, and get one with variable speed if possible. That way, if you do end up doing something stupid with your grinder, like lots of us do, at least you can control the speed of the grinder and thereby have some control over the danger you're exposing yourself to.

    The 5/8-11 tpi arbor and variable speed would be the trump cards if I was in the market for another hand grinder. I'd look for those features more than the name of any particular manufacturer in making your purchase decision.
     
    Last edited: Mar 13, 2010

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