Angle grinder - 9 inch or 4 1/2 inch?

[Mark 5]

Thanks. Good info there.

A 5" would be more comfortable to use, less tiring then a 9" but a 5" with 10mm steel, that's big ask, it will do it, slow going and you will go through discs.

Like others my 115mm is my grinder of choice.

If you are going to be cutting through 4mm and up on a weekly basis, flat steel, a Plasma cutter would be a better choice.

 

[bourbon]

we really need to know what material you are cutting. !0mm bar, 4.5'' grinder. 10mm flat sheet, Plasma all day long.

 

[ELL]

we really need to know what material you are cutting. !0mm bar, 4.5'' grinder. 10mm flat sheet, Plasma all day long.

Flat sheet. Thanks.

 

[Bsmith]

Get both now because later you will find a job that needs the other size (it's sod's law).

 

[Craig-SM]

Get both now because later you will find a job that needs the other size (it's sod's law).

The correct answer. Don’t choose between the 2, just buy both

 

[Bsmith]

The correct answer. Don’t choose between the 2, just buy both

I think I have 3, 9" and 4, 115mm grinders now because I'm lazy when it comes to changing from cutting to grinding discs and wire brush etc

 

[Craig-SM]

Matebo do some nice grinders with plenty of power, noticeably better than my others including the old Bosch ones.
If you get a 9 inch make sure it has the rotating handle aa it makes a big difference of using it for long periods. You might find that you will need to change your circuit breaker with some of the bigger motors as the initial start up can trip them unless they have soft start.

 

[Craig-SM]

I think I have 3, 9" and 4, 115mm grinders now because I'm lazy when it comes to changing from cutting to grinding discs and wire brush etc

Similar but I have favourites that I don’t like to abuse and others that I’d be happy to kill.

 

[MetalMonkey]

5" Metabo would be a good choice. 5" discs are reasonably cost effective and it gives you slightly more depth, and you can still use 4.5" discs if you want.
I wouldn't use a 9 inch out of choice unless you absolutely need the capacity. 6" the consumables are not that common and can be quite expensive.

Metabo grinders are top class for reliability and safety and low vibration.

However, if you have large quantities to do, I'd agree with the suggestions that a plasma cutter would be a better way to go.

 

[Hood]

I never understand why people find 9" grinders so scary, I think they are as safe, if not more so than 4.5".
As for weight, 99% of the time you can have the weight sitting on the material and you are just moving the grinder along. You will also cut at least 20x faster with a 9" grinder.

 

[Arclikeharrypotter]

if your using a grinder daily then invest in something decent. I’ve used pretty much everything out there and my go to is my Bosch GWS 9-115. The Bosch 9 inch is a really nice grinder well balanced. More important imho is the quality of your consumables, best I’ve used are 3m cubitron

 

[Barking Mat]

I never understand why people find 9" grinders so scary, I think they are as safe, if not more so than 4.5".
As for weight, 99% of the time you can have the weight sitting on the material and you are just moving the grinder along. You will also cut at least 20x faster with a 9" grinder.

Because they can kick. And a 9" disk exploding will put you in A & E.

Been there done it, with gloves on.

 

[GRW]

I've used a 9" more for stone cutting or concrete chasing than metal cutting, as I've no real need to cut 10mm plus steel hardly ever. The 9" has a lot of centrifugal force and power that does mean its more tiring on arms as you have to hang onto it in case it kicks hard IMO.
My cheapie 5" Lidl 240v job is nice to use and cuts pretty well - I have a better quality 4.5" Makita, but I think 5" is a good compromise for size, weight, power and cut depth.

 

[Barking Mat]

A 9" on steel is hold on for your life.

if cutting RSJ's they're pretty much essential. A plasma or gas torch is ok, but won't give you a smooth edge to weld to.

 

[MetalMonkey]

Mainly I say I wouldn’t use one for the awkwardness of handling a 9" grinder over a smaller one when it’s not needed. You can easily one hand a 4.5" grinder (irrespective of if you should).

However, a 4.5" grinder is typically 500W/600W and you can stall out if things go south (I had one eat my shirt, and luckily wound it around the spindle and jammed up before it took off too much skin).
9" grinder, 2000 - 2500W, I've not tried stalling one of those out with clothing or appendages, but I suspect it wouldn't end so well....

 

[GRW]

A 9" on steel is hold on for your life.

if cutting RSJ's they're pretty much essential. A plasma or gas torch is ok, but won't give you a smooth edge to weld to.

Bandsaw it is then

 

[Hood]

Well all I can say is I use grinders daily and would never pick up a 4.5" if a 9" was there for doing any serious cutting. Small cuts then maybe but only if the 9" can't get in. I normally reserve the 4'.5" for flap discs.
I do use the 5" cordless for cutting but only if it is not too much and there is no mains lead already run out.
If I have a lot of grinding to do such as flushing welds on the outside of a shelter deck then I will often put a 7" flap disc on the 9" as it is way way faster than doing the same with a 4.5" with a flap disc.

I don't think I have never had a 9" disc explode, I have had them rip the centre out but not explode.

 

[Jelly_Sheffield]

I never understand why people find 9" grinders so scary, I think they are as safe, if not more so than 4.5".
As for weight, 99% of the time you can have the weight sitting on the material and you are just moving the grinder along. You will also cut at least 20x faster with a 9" grinder.

I you guess some combination of:

- Lack of familiarity,
- Differences in physical size and strength,
- Nature of the tasks they do.

I would always want to have at least one 9" in the workshop, because when you need to remove a lot of material it's far less tiring to spend a minute with big grinder than 15 with a small one.

That said the correct answer to OP's question is a plasma cutter, or a gas torch...

Flat sheet. Thanks.

Cutting 10mm plate even with a 9" grinder would be brutal!

If this is anything more that a couple of one-off cuts I would use a cutting torch of some type...

If it's a lot of cuts but a one off job, hire in a plasma or oxy-propane for the day from someone like Tedbar Tinker Hire

The correct answer. Don’t choose between the 2, just buy both

I wouldn't want to have less than 2 × 4½" and a 7" or 9" anywhere I was welding regularly, changing between disks is a huge time sink, as is heavy material removal with a 4½"

I'm now up to 8 angle grinders, (and 5 other grinders) and it doesn't feel excessive, as they all regularly get used.

Angle Grinders:
- 5 × Corded 4½" (Grinding Dusk, Cut Off Disk, Flap Wheel, Fibre Disk, Wire Cup)
- 1 × Cordless 4½" (they're worse in every way, but every so often it's useful to have that extra flexibility)
- 2 × Corded 9" (Grinding Disk and Flap Wheel)

Plus straight grinders:
- 3" Air Cut-Off Grinder
- 2 × Corded Die Grinders (Carbide Burr and Grinding Points)

And Abrasive Belt tools:
- Finger Sander
- Tube Belt Sander

 

[MetalMonkey]

For flushing welds, I use a fibre disc on a 3M backing pad. I found flap discs are too slow and don't last long enough to justify the high price.
Something like a cubitron disc will give a lovely flat surface and grind off the metal way faster than any stone. The only time I use a flap disc now is for getting into radiuses.

 

[Barking Mat]

Well all I can say is I use grinders daily and would never pick up a 4.5" if a 9" was there for doing any serious cutting. Small cuts then maybe but only if the 9" can't get in. I normally reserve the 4'.5" for flap discs.
I do use the 5" cordless for cutting but only if it is not too much and there is no mains lead already run out.
If I have a lot of grinding to do such as flushing welds on the outside of a shelter deck then I will often put a 7" flap disc on the 9" as it is way way faster than doing the same with a 4.5" with a flap disc.

I don't think I have never had a 9" disc explode, I have had them rip the centre out but not explode.

I had a 9" disk explode on me I was cutting pipe, and during the cut, the pipe crimped the disk, the fragments of the disk went though my gloves, nothing major, bet taught me a new level of respect for 9" grinders.