7 inch Vs. 9 inch Angle Grinder

[Wamsutta]

Is the 9 inch too big and scary? I'd be using it as a cut off wheel for disassembling fillet welds to be specific. Two cuts 90 degrees from each other. I'm finding out that with my little 4.5'' grinder, the threaded collet in the center starts to contact the work when the disc gets too warn down. I just frickin hate that. I need a bigger disc for a deeper cut without hitting the collet.

 

[Jim greengo]

Sounds like a death trap to me! Hahaha
Do you have a picture of what you're doing?

 

[tncatadjuster]

How strong are you, that much weight tends to influence decisions on tools.

 

[Wamsutta]

Sounds like a death trap to me! Hahaha
Do you have a picture of what you're doing?

You just take two pieces of steel that are 2'' X 8'' strips. Weld those into a T configuration by running a pass on each side. Now disassemble with a grinder. It's quicker to run a full length cut beneath the welds than it is to grind the weld out.

 

[jayemm]

With a 9" grinder, it'd be a ***** to lose control or have a wheel explode.

 

[Wamsutta]

With a 9" grinder, it'd be a ***** to lose control or have a wheel explode.

That's what I need to hear so I don't buy the wrong machine. I've used a 9 inch grinder for grinding flat, but I've never used one for a cut off wheel.

 

[GeoBruin]

Portaband?

 

[finn]

I haven’t used my 7” grinder in 15 years, ever since I decided it was out to kill me.

4 1/2 or 5” are ok.

 

[jayemm]

I know it's not relevant to the OP's situation, and there's probably enough experiences on here to start a grinder thread (I didn't look) but this reminds me of a conversation I had years ago with a service manager of a construction equipment dealer shop. He was glad he didn't lose a mechanic who was on a creeper grinding the underside of a piece of equipment using a 9" grinder. The grinder caught and kicked and the disc came within a few inches of the guys throat. That still gives me the creeps just thinking about it.

 

[Wamsutta]

I know it's not relevant to the OP's situation, and there's probably enough experiences on here to start a grinder thread (I didn't look) but this reminds me of a conversation I had years ago with a service manager of a construction equipment dealer shop. He was glad he didn't lose a mechanic who was on a creeper grinding the underside of a piece of equipment using a 9" grinder. The grinder caught and kicked and the disc came within a few inches of the guys throat. That still gives me the creeps just thinking about it.

I'd be using it in the horizontal position. The work piece clamped to the table. A 9 inch disc might be wide enough to slice underneath an 8 inch weld all at once, but I don't need it to slice through all at once. It's just that a 9 inch would give me more time before the disc wears down enough before the collet contacts the work piece. I thought I'd ask a few guys here what they think about a 9 inch grinder being used as a cut off wheel.

 

[RivennHewn]

You’re thinking too small.

Go big, 14 inch!

 

[jayemm]

I'd be using it in the horizontal position. The work piece clamped to the table. A 9 inch disc might be wide enough to slice underneath an 8 inch weld all at once, but I don't need it to slice through all at once. It's just that a 9 inch would give me more time before the disc wears down enough before the collet contacts the work piece. I thought I'd ask a few guys here what they think about a 9 inch grinder being used as a cut off wheel.

Yes, I understand, that's why I said my post wasn't relevant to what your application is. The subject just reminded me of that mechanic's scary experience. That's all.

 

[humber2]

The best options in those big grinders have an electronic soft start.

Without it the grind usually starts at some other place to where you have aimed.

Wearing shorts and flip flops is not advised.

YMMV

 

[Wamsutta]

Yes, I understand, that's why I said my post wasn't relevant to what your application is. The subject just reminded me of that mechanic's scary experience. That's all.

No I appreciate the comment. It may be that a 9 inch is too hard to control, I don't know.

 

[1982fxr]

Control issues aside, those Fuckers get heavy. Fatigue is a serious enemy anyway, but especially with a tool like that.

 

[dutchgray]

7" and 9" grinders are usually the same size and weight, the only differences is a different speed rating to suit the disc size and the blade guard.

I have found very little use for 7" grinders but plenty for a 9".
Though the 7" can be good for a heavy 5" wire cup wheel.

 

[Wamsutta]

Control issues aside, those Fuckers get heavy. Fatigue is a serious enemy anyway, but especially with a tool like that.

Yes and I'm finding out that a 6 inch grinder is 1/2 the weight of a 7 inch grinder.

 

[2oolhound]

If you're only cutting a few welds at a time fatigue shouldn't even enter the picture. If you've got 10 minutes of work lined up then it does.

What is the thinnest cut off disc that's available for 9"?

 

[FlaGman]

Have you tried one of the diamond cutting wheels for your existing grinder? They don’t wear down like the other ones so it may work for your application.

 

[Wamsutta]

If you're only cutting a few welds at a time fatigue shouldn't even enter the picture. If you've got 10 minutes of work lined up then it does.

What is the thinnest cut off disc that's available for 9"?

The thinnest available is a Weiler and it's 0.0625''.

 

[strutaeng]

I have a 7" Makita that I only use for heavy material removal. It is heavy, but the weight helps on grinding. I've never used it for cutting that I can remember. The manual does list the same motor for their 7" and 9" models now that I remember.

After getting a 6" DeWalt grinder, my 4.5" grinders almost seem like toys. 6" is so darn versatile yet light enough to use it extended periods of time. I always sprint for the DeWalt first.

I'm a DIYer, but have done some larger sized metal working projects.

 

[Hohn]

I have the beastly 15s Hitachi that moves more air than my shop vac. It's 12# of hate and respect.
You'll find that most 7" and 9" grinders are essentially the same. They are geared a bit differently to optimize their respective wheel speeds, but they'll have the same motors, fans, and basic chassis.

The weight savings of dropping from 9" to 7" is almost basically just the smaller guard and wheel and nothing else.
Which means that if you get a variable speed 7", you can swap the 9" guard and wheel on, slow the speed down and basically have a slightly less torquey 9" from your 7".

You can do the same with a 9" converting to 7", but instead of stepping down in torque, you'll step down in speed relative to a true 7".

Real world, there's precious little that needs the extra RPM of a 7" compared to 9".
My recommendation is get the 9, convert to 7" if you need a bit less weight. The only downside to the 9" is a tiny bit less speed with 7" wheels. And if you need speed, put the 9" wheel on.

 

[driftpin]

I have a 9" Milwaukee model 6065, 5500 rpm, 15 amps, 120V. It says it can do 7" duty for grinding, just use a smaller guard.

It uses type G grease (Milwaukee) #49 08-4140 which is back-ordered everywhere I've looked on the 'net, and at local service/repair shops.

 

[Hohn]

It's worth considering that much of the safety hazard of angle grinders relates to the high speed of the wheel. Using a lower RPM 9" grinder at 6500rpm or so with a 7" wheel is going to be a good bit less dangerous (in terms of stored energy in the wheel" then using that wheel on a 7" grinder at 8500rpm.

 

[bcradio]

Have you tried one of the diamond cutting wheels for your existing grinder? They don’t wear down like the other ones so it may work for your application.

This is what you want here

 

[Hohn]

This is what you want here

Be sure that you aren't grinding anything where you have to preserve the steel properties. Diamond wheels will dissolve carbon from the surface when hot.

This is why top end knife and tool grinders use CBN wheels and not diamond.

 

[scooby074]

Bandsaw Or 4.5, 5 or 6" from a quality manufacturer like Walter or some Makita models. Makitas 9005 Made in Canada model is a beast if you can still find one.

7's and 9's are too much imho.

Edit: Be sure to use a Zip Cut wheel with any grinder

 

[1982fxr]

If you're only cutting a few welds at a time fatigue shouldn't even enter the picture. If you've got 10 minutes of work lined up then it does.

What is the thinnest cut off disc that's available for 9"?

Sure if that's the only task you do that day. Life gets in the way of that though.

 

[Walkers]

You can still use 4.5" or 5" grinders, just purchase the type 29, depressed center cut off wheels. Also, be sure that your back side support disk is thick enough to put the nut at the end of the threads when tight.

 

[msharley]

The thinnest available is a Weiler and it's 0.0625''.

A 1/16th inch wheel on a 9" grinder is a problem (I have two Power Cats, one with wire/bead brush the other with a 9" x 1/8" bead wheel..) The bead wheel will thin down your "filet" welds in a hurry...

Can then easily finish them off with a 1/16" zip wheel on your heavy duty METABO....(don't waste your money on the "light duty" model...a zip wheel takes a whole lot more to run than does a 1/4" wheel on the "surface")...

With a Power Cat, one needs to keep one's wits about them during use...

 

[GaryM909]

I used a 9" Makita for quite a few years and I still have one just in case. I find that they are fairly easy to control with both cutting discs and grinding discs but they DO get heavy.
I worked in a shop that supplied us with 2 - 9" Makita grinders. One for cutting or grinding discs and one with a wire wheel. Also a 5" Makita with only grinding discs. People were going through 5 - 10 discs a day.

 

[MJD1]

Get yourself a good quality 6" grinder, such as metabo. With good quality cutoff discs a quality 6" grinder will outlet the larger ones.

 

[Packard V8]

I have two 9" B&D Wildcats and a Makita. They take a man to operate them and the man better stay focused, else they'll eat him up and spit out the bones. I wouldn't think of using them as a freehand cutoff.

jack vines

 

[rsanter]

You need an actual portable cut off.
They use the 9" grinder but has a bolt on guard and base plate.
It's heavy and hard to use. Hard to use in the order of hard work that will tire you.

Trying to cut with those thick grinding wheels will take forever and cutting with the thin cut off wheels with no guard is asking for trouble.
In fact I don't use the composit cut off wheels anymore unless I have very very hard material. The rest of the time I use a diamond blade. It has saved me hundreds of dollars and does not explode

 

[Gutman]

Since a regular 4.5" cutoff wheel works, to a point, then a 4.5" diamond cutoff wheel should work for you, as it'll maintain constant diameter. I had to do something similar, and I got this wheel off the net at the beginning of the year:





Once I used it for my specific application, I've just been continuing to use it, and have not had to burn up the stack of cutoff wheels I had on hand. I think they're like $18 bucks now, much cheaper than a new grinder.

That said, I never want to be accused of suppressing a desire for a new tool.

 

[Steve_P]

I haven’t used my 7” grinder in 15 years, ever since I decided it was out to kill me.

4 1/2 or 5” are ok.

I have an ancient 7" B&D from my dad, and I can't even remember the last time I used it, but it was 20+ years ago. And for sure, there is a need for something so massive in certain scenarios, like maybe working on a grader or bulldozer, but not for me.

I have a couple of variable speed Metabo 5" grinders that I've bought in the last 5 years, and they've absolutely ruined me from using anything else. I bought a few of the Lenox diamond wheels and while they are not the fastest, they don't blow up and they last a long time.

 

[Wamsutta]

I have a couple of variable speed Metabo 5" grinders that I've bought in the last 5 years, and they've absolutely ruined me from using anything else.

OK, you gotta tell us why you like the Metabo's so much.

 

[Hohn]

Better yet, don't tell us why you love Metabos so much, I can't afford to indulge.

 

[DerekV]

OK, you gotta tell us why you like the Metabo's so much.

The variable speed feature is excellent, maintains RPMs under load extremely well, too. Once you use it, you realize a lot of your grinder work doesn’t need to be at full blast. These grinders also have soft start as well as a physical clutch in the event of a bind. They’re very smooth, very little vibrations, great for those dealing with carpal tunnel. Last but absolutely not least, the power seems endless, literally endless. Amazing grinders.

The only downside is that the speed control knob is delicate. Don’t go full gorilla changing speeds or else it’ll snap off eventually, requiring the whole speed control board to be replaced. It’s a part that’s not always in stock, which is the cherry on top.

I have a WEV-125 that I’ve set up to 6” use, FYI. I’ll be getting more of them for sure

 

[jsaw]

After using a 9" grinder, anything smaller seems slow and not powerful enough to Me.

Biggest thing to remember is to always hold it so that it will pull away from You if it binds or catches.