9" Grinder comparison

[Monte]

8,500RPM with a 7" disk vs 6,600RPM with a 9" disk

Which is better for 1/2" mild steel?

i don´t know The best is to have both i guess
If i have to cut thicker sheet metal i use the plasma cutter or torch, if i have to cut tubing/beams i use a band saw (stationary) or a 5" angle grinder or a recip saw. I use my 7" grinder very seldom. If then with a large cup brush, flap wheel etc. For these metal working task various discs etc. are available. For the 9" grinder there are only cutting/grinding/diamond wheels. You can run 7" acessoires but not at optimum speeds. What i think is the 7" grinders are more used in the metalworking sector and the 9" on construction sites where you also need to cut stones etc. with diamond discs hence you need the larger cutting depth. I think in metalworking other tools are used if you need that large cutting depth. But for chamfering steel i probably would use a high amp 5" grinder (Fein 15-125, Metabo WE14-125, Flex L 3410, Bosch AG50-125PD) and a good 40 grit flap disc and then you´ll have a nice clean and shiny bevel.

 

[Miarka]

Are the rated RPMs on a grinding disk referring to the no load speed or speed under load?

for example if a grinder has a no load speed of 6,600RPM and a load speed of 4,600RPM then can I use a grinding disk with a max speed of 5,000 RPM?

 

[Miarka]

the 7" Metabo runs at higher RPM but has less torque.
its No Load speed of 8,500RPM drops to a Load speed of 5,800RPM

The 9" Metabo runs at a No load speed of 6,600 which drops to a Load speed of 4,500RPM

 

[bcradio]

the 7" Metabo runs at higher RPM but has less torque.
its No Load speed of 8,500RPM drops to a Load speed of 5,800RPM

The 9" Metabo runs at a No load speed of 6,600 which drops to a Load speed of 4,500RPM

Load speed will vary based on the load... Can't just say it has X load speed. That may be an average though.

 

[Miarka]

Load speed will vary based on the load... Can't just say it has X load speed. That may be an average though.

I believe that more specifically it states Minimum Load SpeedWhatever that means...

But I agree with you in that the speed varies depending on the amount of resistance you put against the spin, probably up to the point of stopping the spin completely...

I am just trying to figure out what my options will be in terms of disks/wheels etc with the machines i'm looking at.

From what I understand, the max RPM on the wheel/disk refers to the working speed.

the Norzon flaring cups in the data sheet below are what I am very interested in using. I am trying to figure out if I'll be able to "safely" use the 6,000RPM ones with the grinders I referenced earlier.
http://www.nortonindustrial.com/upl...s/NortonCatalog-Snagging-WheelsConesPlugs.pdf

 

[neophyte]

Are the rated RPMs on a grinding disk referring to the no load speed or speed under load?

for example if a grinder has a no load speed of 6,600RPM and a load speed of 4,600RPM then can I use a grinding disk with a max speed of 5,000 RPM?

I believe that more specifically it states Minimum Load SpeedWhatever that means...

But I agree with you in that the speed varies depending on the amount of resistance you put against the spin, probably up to the point of stopping the spin completely...

I am just trying to figure out what my options will be in terms of disks/wheels etc with the machines i'm looking at.

From what I understand, the max RPM on the wheel/disk refers to the working speed.

the Norzon flaring cups in the data sheet below are what I am very interested in using. I am trying to figure out if I'll be able to "safely" use the 6,000RPM ones with the grinders I referenced earlier.
http://www.nortonindustrial.com/upl...s/NortonCatalog-Snagging-WheelsConesPlugs.pdf

I'm fairly certain the maximum RPM listed for abrasives is the no load speed.

Variable speed grinders are not even supposed to be used with abrasives or other accessories, if the top speed is higher than the maximum rated speed of the accessory, even if the speed can be varied below the accessories maximum RPM.

There is almost certainly a bit of leeway built into the maximum RPM of the accessory, but that difference should be a minor amount like the 6,600 and 6,500 numbers since this likely falls within power supply variances.

If in doubt call the manufacturer and ask.

 

[Miarka]

Does anyone know how much horsepower or torque the Makita GA9020 has?

 

[Monte]

Does anyone know how much horsepower or torque the Makita GA9020 has?

The GA9020 is a entry level grinder without any anti-vibration features. The GA9040 would be more comparable to the Bosch + Metabo you mentioned.
The GA9020 has 2200 Watt input power and 6000rpm. Unfortunately they don´t advertise the torque nor the important output power. The output power usually is about 30% less than the input power that would mean about 1600 Watt output power. (Metabo W 26-230: 2600 Watt input/1800 Watt output, 6600rpm)

 

[Miarka]

The GA9020 is a entry level grinder without any anti-vibration features. The GA9040 would be more comparable to the Bosch + Metabo you mentioned.
The GA9020 has 2200 Watt input power and 6000rpm. Unfortunately they don´t advertise the torque nor the important output power. The output power usually is about 30% less than the input power that would mean about 1600 Watt output power. (Metabo W 26-230: 2600 Watt input/1800 Watt output, 6600rpm)

Yeah I called Makita(as well as Metabo and Norton) this morning. The Makita tech said that they don't rate their grinders by Horsepower or torque.

discovered the Makita GA9040S a moment ago just before checking this thread lol

How does the Makita GA9040S compare to the Metabo W24-230 and W26-230?
What is its Watt input?
seems that with a 6,000RPM no load speed it can be used with all of the "Norton Type 11 Flaring cups"

However,I noticed that one of the 9" Milwaukee's has a 6,000RPM no load speed but then has a disclaimer saying "Use Wheels with Max RPM Above 6600 RPM"
http://www.milwaukeetool.com/power-tools/corded/6088-30

what's up with that?

 

[MJD1]

From what I have seen wheels are rated at a higher rpm than a grinder will develop provided you are not exceeding the size it was made for. For example if you took the guard off of a 4.5" grinder and put on a 7" wheel you would have an issue. I have about a dozen grinders and honestly have never checked the ratings on wheels or the speed of a grinder. The biggest issue I have come across is some wheels will vibrate like hell when they get worn down quite a bit.

 

[Miarka]

Are most handles for 9" grinders interchangeable between brands?
can I for example take the handle from a Metabo W26-230 and use it on a Makita 9020S?

I've noticed that with smaller grinders the bolt threads do vary. for example my Makita and Bosch handles are not interchangeable.

 

[Miarka]

Where is the Makita 9020S made? How many Watts?

 

[Miarka]

called Makita again, they could not give me the handle thread size...voids warranty...

The Makita GA9040S actually looks more comparable to the Metabo W26-230.
The input watts on the GA9040S are 1,800 and the output watts are 2,600.

I kind of like the W26-230 a bit more because of the great reviews and more effective looking anti-vibration handle as well as overall efficiency of design.

But since the Makita runs at 6,000 no load RPM, it is compatible with many more Flaring Cup wheels(specifically Type 11), hopefully making it much more useful to me...

Also the GA9040S is made in the USA!

 

[barnbarn2k]

Ive used almost every kind of 9" grinder. I currently use the metabo w26-230. I use that with a sait silica carbide masonry 9" type27 wheel to grind cemented tungsten carbide for 3 hours at a time once a week. There really isn't much of a noticeable difference between the higher amp 115v grinders. The best disk for structural steel is nortons norzon plus.

While you can in some cases put a 9" wheel on a 7.7k or 8.5k grinder you shouldn't. There is a chance they can explode and maim. Get a leather apron, a face shield, and a 100p respirator if you are going to be doing a lot of grinding. Vacuum yourself off when done before you remove safety gear. Set up so you use it belly button height and hold it in such a fashion that your thumbs don't do much work. Do not use an air wand to blow yourself off it will impregnate metal slivers into your clothing. And do not remove the guard.