Angle Grinders Are Dangerous

Another thing to note if nobody has done it yet, is the smaller the wheel gets RPM goes up. if the wheel is severely worn, it may be operating out of its RPM limits.
 
v8r said:
Another thing to note if nobody has done it yet, is the smaller the wheel gets RPM goes up. if the wheel is severely worn, it may be operating out of its RPM limits.
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I having a little trouble wrapping my head around this comment. Assuming that we're dealing with a motor that runs only at one speed, then the rpm of the motor shaft is constant. This means the rpm of the disc is also constant regardless of the size. What does change however would be the surface speed at the edge of the wheel. The larger the diameter of the wheel, the faster that surface speed becomes. For a larger diameter, the edge of the wheel has to travel further around per revolution, hence the faster speed. Its just like a bicycle tire which I'm sure most everyone has noticed that the rubber part of the tire seems to go flying by much faster than the axle...which it is! So by this way of thinking, as the wheel gets smaller, the surface speed at the edge would become less, again because the rpm of the motor is constant. Am I missing something here?
 
v8r said:
Another thing to note if nobody has done it yet, is the smaller the wheel gets RPM goes up. if the wheel is severely worn, it may be operating out of its RPM limits.
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TonyRV2 said:
I having a little trouble wrapping my head around this comment.
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I think its a confusion of no-load speed.
Many grinders will increase RPM somewhat as rotation mass of its abrasive wheel decreases.
Anyway, machine speed is rated at no-load at its intended voltage & frequency.
One cant overspeed a wheel if those guidelines are followed.
 
Always check the rpm rating of the disc. Larger diameter discs are usually rated at slower rpm's to keep surface speed down. You don't want to overspeed a cut off wheel.


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TonyRV2 said:
I having a little trouble wrapping my head around this comment. Assuming that we're dealing with a motor that runs only at one speed, then the rpm of the motor shaft is constant. This means the rpm of the disc is also constant regardless of the size. What does change however would be the surface speed at the edge of the wheel. The larger the diameter of the wheel, the faster that surface speed becomes. For a larger diameter, the edge of the wheel has to travel further around per revolution, hence the faster speed. Its just like a bicycle tire which I'm sure most everyone has noticed that the rubber part of the tire seems to go flying by much faster than the axle...which it is! So by this way of thinking, as the wheel gets smaller, the surface speed at the edge would become less, again because the rpm of the motor is constant. Am I missing something here?
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No , you are 100 % right .It is very dangerous to use disc over its speed limit . Say my little Makita is going 11000 rpm and I use 115mm X 1.6mm 13300 RPM disc . It s insane to put larger disc there ...........
 
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AlaskanHunter said:
Always check the rpm rating of the disc. Larger diameter discs are usually rated at slower rpm's to keep surface speed down. You don't want to overspeed a cut off wheel.


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I do not think so , larger diametar discs is used on slower rpm's angle grinder BUT surface speed of disc is maybe the same as small disc on 11000 rpm ...
 
Natlek said:
No , you are 100 % right .It is very dangerous to use disc over its speed limit . Say my little Makita is going 11000 rpm and I use 115mm X 1.6mm 13300 RPM disc . It s insane to put larger disc there ...........
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You may find your little Makita hard pressed to spin a larger wheel anyway.
Not suggesting do this in actual use mind you...
But just putting a 7" wheel on angle grinder intended to run as 4 or 4.5" wheel.
It will barely run, maybe around 1000 RPM, I dunno...
Its surprising how much more energy is needed to spin the wheel whats basically 2x larger diameter.

On a similar topic.
For the guys with cheap & low power 2 wheel benchgrinder, ( you guys know who you are) I often suggest removing the wheel thats not being used at the moment. It helps performance some as the machine does not have to carry an unneeded load.
 
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Lieblad said:
........On a similar topic.
For the guys with cheap & low power 2 wheel benchgrinder, ( you guys know who you are) I often suggest removing the wheel thats not being used at the moment. It helps performance some as the machine does not have to carry an unneeded load.
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I need that extra wheel for the hamster. :D
 
I'll try and clear up how this gets confused:

The surface speed of a wheel ( edge sped) is a product of its diameter and the RPM of its shaft. The larger the wheel, the faster the SFM is. The larger the wheel, the slower is should need to be turned to get the desired effect.
As a wheel wears, the surface speed goes down and it cuts/grinds slower.

A wheels strength is rated at its recommended speed for its size. If the speed is increased, the wheel may be overstressed and explode.

As a wheel wears down, the chance f exploding from over-speed decreases, but the edge surface gets less round and may have small ( or not so small) divots in it. These create stress risers, and the wheel is thus less stable. Since the wheel is cutting slower, the tendency is to push harder, and the stress riser may cause the wheel to explode. Additionally, the wheel thickness ( especially near the edge ) will become thinner with use, and thus break easier. This is why a worn wheel is more likely to break in use.

People may put a larger wheel on a grinder to get faster cutting - bad idea unless the grinder and the wheel are both rated for the speed and the load. If the grinder is a 4.5" grinder ... it takes a maximum 4.5" wheel. To put a larger wheel on is inviting a disaster ( as well as a possibly burned out grinder).

Last info comment - There are wheels for different tasks. No wheel is universal. Use a cut off wheel for cutting and a grinding wheel for grinding. Using them for the opposite task will likely end with a broken or damaged wheel.
 
Stacy E. Apelt - Bladesmith said:
I'll try and clear up how this gets confused:

The surface speed of a wheel ( edge sped) is a product of its diameter and the RPM of its shaft. The larger the wheel, the faster the SFM is. The larger the wheel, the slower is should need to be turned to get the desired effect.
As a wheel wears, the surface speed goes down and it cuts/grinds slower.

A wheels strength is rated at its recommended speed for its size. If the speed is increased, the wheel may be overstressed and explode.

As a wheel wears down, the chance f exploding from over-speed decreases, but the edge surface gets less round and may have small ( or not so small) divots in it. These create stress risers, and the wheel is thus less stable. Since the wheel is cutting slower, the tendency is to push harder, and the stress riser may cause the wheel to explode. Additionally, the wheel thickness ( especially near the edge ) will become thinner with use, and thus break easier. This is why a worn wheel is more likely to break in use.

People may put a larger wheel on a grinder to get faster cutting - bad idea unless the grinder and the wheel are both rated for the speed and the load. If the grinder is a 4.5" grinder ... it takes a maximum 4.5" wheel. To put a larger wheel on is inviting a disaster ( as well as a possibly burned out grinder).

Last info comment - There are wheels for different tasks. No wheel is universal. Use a cut off wheel for cutting and a grinding wheel for grinding. Using them for the opposite task will likely end with a broken or damaged wheel.
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There are different discs for different materials too. I like the discs rated for stainless.
 
Lots of tools can be dangerous..I saw a guys foot get ran over with a 20 ton forklift,sideways..Trust me the steel toe and steel metatarsal plate did nothing to help. Sounded like a pop can getting crushed..Im sad to say it was completely his fault for trying to run and jump on a moving lift during winter no less.I know a guy who shoot 18" of .035 mig wire in his leg from hip to knee cap once too..Wasnt paying attention to his gun when he bent over. Two of my cousins lost 7 fingers between them working in a family saw mill, guess what..Wasnt paying attention. Inmate blowed out his scrotum(balls and all) while welding pipe in the rain,standing in water when he scratched his head with the stinger.Got many more stories just like these....See were Im going with this? Most of the timeif we pay attention and use tools right we don't get hurt..Trust me Im last one that should be preaching abut tool safety but Ive seen enough major injuries from tools over the years that Im pretty well versed in what they can do if you use them wrong..
 
Wow.. I'm definitely getting some new PPE equipment tomorrow after reading all these comments.. [emoji15]

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