grinder wheel question!

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okay so your not suppose to use a worn down 7inch wheel on a 4.5 inch but can you use a 4.5 inch on a 7inch grinder. im asking because the rating speed for the smaller wheels are higher than the big grinders so...
Reply:Not really sure what your question is.It depends on the type of disk. They have different max RPMs sometimes.Last edited by Canadian Welding; 12-11-2014 at 03:31 PM.
Reply:Originally Posted by farmwelderokay so your not suppose to use a worn down 7inch wheel on a 4.5 inch but can you use a 4.5 inch on a 7inch grinder. im asking because the rating speed for the smaller wheels are higher than the big grinders so...
Reply:as long as the max RPM of the wheel is higher than the RPM on a grinder you are safe
Reply:I am barely able to put my 4.5" grinding wheels on my 4" due to rpm ratings. MY 7" runs around 7000 rpm where the 4" is around 12000 rpm. I can't see running a 7" disc down to fit on a 4.5 on 7" grinder. Step it down a grinder size and throw it away or re purpose.
Reply:Bigger wheels have lower RPM ratings because the radial stresses increase the further you get from the center.  If the wheel is worn down to 4.5", it will have the same stresses as a 4.5" wheel.That said, the construction may differ (though I doubt it), and the wearing-down process may have induced other damage to the wheel that would make it unsafe (which I don't doubt), but it is theoretically possible to use a worn-down wheel in a smaller, faster grinder.Hobart cutting/welding torch.MM252, and nothing else.  My first welder.  Buy once, cry once....but I really would like a nice 50/60A circuit to run it at full strength.A bunch of ideas, and not enough time and money to bring them to life.
Reply:Originally Posted by OkieDaveBigger wheels have lower RPM ratings because the radial stresses increase the further you get from the center.  If the wheel is worn down to 4.5", it will have the same stresses as a 4.5" wheel.That said, the construction may differ (though I doubt it), and the wearing-down process may have induced other damage to the wheel that would make it unsafe (which I don't doubt), but it is theoretically possible to use a worn-down wheel in a smaller, faster grinder.
Reply:Originally Posted by OkieDaveBigger wheels have lower RPM ratings because the radial stresses increase the further you get from the center.  If the wheel is worn down to 4.5", it will have the same stresses as a 4.5" wheel.That said, the construction may differ (though I doubt it), and the wearing-down process may have induced other damage to the wheel that would make it unsafe (which I don't doubt), but it is theoretically possible to use a worn-down wheel in a smaller, faster grinder.
Reply:the question is why would you put a 4.5"wheel on a 7' grinder you can't cut $hit . Of course I only used a 9" grinder to face pipe and put the land on it. and when they were down to 6" or less they were no good for that. Some times I think some of you guys are just cheap! weld better grind less.
Reply:Originally Posted by gxbxcthe question is why would you put a 4.5"wheel on a 7' grinder you can't cut $hit . Of course I only used a 9" grinder to face pipe and put the land on it. and when they were down to 6" or less they were no good for that. Some times I think some of you guys are just cheap! weld better grind less.
Reply:Originally Posted by mikecwikI am barely able to put my 4.5" grinding wheels on my 4" due to rpm ratings. MY 7" runs around 7000 rpm where the 4" is around 12000 rpm. I can't see running a 7" disc down to fit on a 4.5 on 7" grinder. Step it down a grinder size and throw it away or re purpose.
Reply:Start 9 and go to 4.5 all the time down to the hub.Use it up .
Reply:Originally Posted by farmersamm... maybe someone else can do the math.
Reply:The closer we get to the disk center the more fibres and glue there is and less abrasive ...we end up with a disk that last forever, glaze big time removes almost no material...grinding forever no thank's.  As for rpm it's better to calculate in inches per minutes (diameter x 3.1416 x rpm = ipm) same applies to the chopcut saw then make different test with different brands. You will get different results.  As farmersam says 7 in. by 3.(roughly) = 21 x 7krpm =   147k. inches per minutes....4 in x 3 = 12 x 12 krpm = 144 kipm. so they work best in a similar range.Cheap disks are usually worth what you're paying for and less.