Large Right Angle Grinders

[Wamsutta]

This is going to be kind of a dumb question, but do you think a 9 inch grinding disc spinning at 6600 rpm would remove more material at a faster rate than a 5 inch grinding disc spinning at 11,000 rpm? Let's say the material being removed is a steel weld bead that's approximately 8"L x 3/4"W x 1/2"T.

 

[The Cobbler]

I think to answer that you need to figure out the surface feet per minute and see which one is faster .
as a rule, I think the larger the diameter, the faster the removal is , runs cooler and slower wear as there's more surface contacting the work

 

[Wamsutta]

^
That's what I was thinking. A larger disc to surface contact area would overcome the lower rpm.

 

[Dave455]

A quick crunch of the numbers suggests that the circumference of the 5 inch is moving at 172,000 inches / min, the 9 inch at 186,000, so the 9 inch just wins it.

But in practice that’s not a lot of real difference, and of course the designers are trying to get comparable rates, being the max that a disc can sensibly take.

Depending on what you are doing, you of course have a greater radius of the disc in use with the 9 inch, and experience says the 9 inch will do the job a lot faster.

Having said that, I find the big grinders quite cumbersome, and not always great to use. I have a 9 inch Makita that I hardly ever use. Last time was cutting a paving slab. I find the 7 inch to be much nicer to use, although it’s a less common size.

Ergonomics play a part too, and if I’m cleaning weld I usualy favour my 5 inch Fein, with the extended handle. The handle makes a difference.

 

[mitusa]

If the weld is out in the open and laying flat, I would definitely go with the larger set-up. Just the weight of the bigger grinder will be a benefit.

 

[cannuck]

The rate of material removal is a function of how much power the drive motor has. So, no question the big grinder is going to remove a lot more material per unit of time than the little one.

 

[Packard V8]

I can still swing and control the big dog and from experience, it will eat weld slag many times faster than the 5" and 7" toys. Concentration, however; it will also eat your kneecaps if you get tired or lazy.

jack vines

 

[Wamsutta]

I can still swing and control the big dog and from experience, it will eat weld slag many times faster than the 5" and 7" toys. Concentration, however; it will also eat your kneecaps if you get tired or lazy.

jack vines

I actually had that happen to me one day about 30 years ago. I was running a 7 inch pneumatic sander with a sanding disc mounted to it while working aboard the U.S.S. Tripoli. I was positioned on my knees grinding the steel deck. I looked up at something momentarily while the disc was still spinning. Centrifugal force brought the sanding disc into my knee. No major damage but left a permanent scar. Nice show of blood.

 

[danielbuck]

larger heavier grinders seem to remove more material easier, especially if you're grinding on a horizontal piece, because of their weight. You don't have to press down as hard.

 

[driftpin]

larger heavier grinders seem to remove more material easier, especially if you're grinding on a horizontal piece, because of their weight. You don't have to press down as hard.

I agree w/that, as expressed by others too.

Let the machine do the work. If you find yourself getting tired from how you need to hold the tool, i.e., vertically, stop, rest, and come-back to the job when you have your strength and stamina refreshed.

Small jobs, I'll probably use something like a 4 to 4-1/2" side grinder, but if there's a lot to do, the Big Dog gets to bark. I have two corded Milwaukee side grinders in the 9" size/the 'Big Dogs.' No commercial use, just a maintenance/hobbyist use.

I also keep at least two full face shields ANSI rated, handy for use, so I am not tempted to work without one. One is on the workbench where I do most of my side-grinder work. One is by my toolbags if I need to do something at a property away from the residence.

 

[Sumboodie]

That RPM is no load too. Usually the 9" had a bigger motor so doesn't bog down as much.

I have a 9" Milwaukee i bust out once in a while for the big jobs. The old Iron plow . Thing weighs as much as a small dog.

 

[Mr.N]

This is going to be kind of a dumb question, but do you think a 9 inch grinding disc spinning at 6600 rpm would remove more material at a faster rate than a 5 inch grinding disc spinning at 11,000 rpm?

Not sure... I've an old school B&D 9" that is works awesome... however I find myself using a 5" disk on a 12 or 11 amp cordless Milwaukee 98% of the time. It's just quick, easy and I think actually similar speed except for the very big stuff.

 

[cat-mechanic]

I bought a 9" Ingersol Rand air grinder at an auction a few years ago. I don't have a compressor that can keep it running. I keep grabbing my milwaukee battery grinder now a days. But I don't do a lot of metal work.