Grinder Types 5,000 rpm vs 11,000rpm

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Why might one need the 11,000 rpm grinder over the 5,000 one?   one meant for zip-cuts? better grinding? a bit confused as why you'd use one over the other.
Reply:11,000 rpm gets more work done faster.
Reply:Higher rpm = "smoother" cutting.
Reply:NO NO NO RPM is based on the size and rated speed of the grinding wheel.  Smaller wheels generally need higher rpm to cut efficiently. Most 4", 4,1/2" and 5"  Wheels will run 10-11,000 rpm. But you need to check and see what is written on the wheel before running it.  Larger wheels need to run slower 7" wheels generally run 6-8,000 RPM and 9" wheels are around 5-6,000. Again, check what the wheel is rated for. Larger wheels have a larger circumference so the little bits of grit are moving faster on the edge of a 9 inch wheel than they are on the edge of a 5 inch wheel if they are both turning the same rpm. In the machining world its calculated as Surface Feet /Minute (SF/M)Lincolin Power Wave 450, Lincoln Powermig 255, Lincoln Pro Mig 140, Lincoln Squarewave Tig 275, Miller Big 40 G(with Hobart Hefty suitcase), Thermal Arc 95S and Esab PCM875 in an already full machine shop.
Reply:Originally Posted by propanehotrodNO NO NO RPM is based on the size and rated speed of the grinding wheel.  Smaller wheels generally need higher rpm to cut efficiently. Most 4", 4,1/2" and 5"  Wheels will run 10-11,000 rpm. But you need to check and see what is written on the wheel before running it.  Larger wheels need to run slower 7" wheels generally run 6-8,000 RPM and 9" wheels are around 5-6,000. Again, check what the wheel is rated for. Larger wheels have a larger circumference so the little bits of grit are moving faster on the edge of a 9 inch wheel than they are on the edge of a 5 inch wheel if they are both turning the same rpm. In the machining world its calculated as Surface Feet /Minute (SF/M)
Reply:There is a lot to be said about rpm and it applies to much not just angle grinders as I believe the thread is based upon. Not just for safety concern is it relevant to the task at hand.So everybody in this thread has posted relevant information to the question that was asked. Wheels decrease in size and do less work which would be the same for say chop and cutoff wheels but the wheel at the same time becomes more ridged thus more accurate and safer. It is hard to understand how a person could use multiple rpm and horsepower tools and not come up with their own answers from trials.
Reply:Originally Posted by blackbartExactly. It's extremely important to check RPM ratings. I have seen several victims of exploding wheels, they can kill you, or tear you up at the very least.
Reply:Just picked up a Mastercraft 11,000 rpm... Where have you been all my life! when I've seen welding symbols with ground flush On a side note kinda thought it was funny when typing Jus... and I forgot the "T" for JUST! It came up as Jews for auto-correct.Last edited by SHaW; 12-23-2015 at 07:35 PM.
Reply:Your disc or cutting wheel must always match or be rated for the rpm of the grinder itself.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:11,000 rpm all the way.......however........if I need to do some delicate grinding I will grab the 5,000 rpm grinder. Of course.....as was said......watching/using the appropriate wheels.