Thread: 4' or 5' angle grinder

Bosch 4 1/2 Inch grinders are the best ive found - last for ages and use mine 6 hours a day

Originally Posted by rickybower

Bosch 4 1/2 Inch grinders are the best ive found - last for ages and use mine 6 hours a day

Except consumable are hard to find. Most stores stock 4 or 5 inch versions discs. Seriously the 1/2 inch isn't going to really cause anyone major issues. I've always been puzzled by the 4.5 inch grinder and why anyone bothers. You want it small (dremel/4 inch), you want longer lasting consumables with a little size boost then 5 inch. Need cutting depth go the 9.

I must admit that I'm glad I didn't buy a 9'' grinder first off.

gday I just updated to the protool 5 and 9 inch wow what a difference the 5 has a clutch and an inbuilt flywheel counterweight thingy which makes it the most balanced grinder I have ever used (gmc ozito bosch makita aeg hitachi to name a few)and the clutch in it stops the disc when it gets pinched the motor just stops you then free the disc and startup again . similiar story with the 9 inch although have so far only used that with concrete diamond blade cutting concrete this was quickest cut through I 've done other than using a demolition saw

Many of us do choose our first angle by its price .If its a 4"/100mm a/g then what you get is a clamshell barrel body.
This means the brushes are enclosed and the unit needs splitting to replace them. Also the bearings are a bush type and wear quicker than ball bearings. There's other bits and pieces like switches which are all designed with a price limit in mind.Also the cheapies have small wattage motors.

In short the cheaper units used in an apples compared to apples type situation can and do expire earlier than their more expensive brothers.

The 4.5"/115 diameter angle grinder is the nominal step up into a little higher quality sporting higher wattage motor, ball bearings ,better switch gear and wait for it, externally replaceable brushes.

That's not so say there were never high quality 4"/100mm units made ,but sadly people don't want to pay for them these days so most 4" jobbies are as described above.
I still yearn for my little Wolf Sapphire 4 inch angle grinder which had a slip clutch,ball bearings and external brush replacement.

So you see my brethren, oils ain,t oils and neither are angle grinder units,so in your never ceasing search for the true quality angle grinder you must be diligent and apply the question of quality about each and every feature.

Above the question is asked why bother with a 4.5 inch grinder.I believe that again it has been more of a price evolution that a quality or design question.

Look at your range of other power tools and the same design features apply to the price step ranges again and again.

Grahame

I have one of each... 4" with a grinding wheel for grinding because I find it small and easier to handle and 5" with 1mm cutoff discs for cutting because the cutting discs for the 5" cutoff wheels last a lot longer than the ones for the 4".

I have the same setup, and fully agree with gallegos' comment above

I have a 4.5" Ozito (that is 8 years old and has done a heap of work and still going strong) and a 5" Bosch that is about a year old. The Bosch is noisier than the Ozito.

Both use the same size centre boss and I buy everything in 125 mm and it's not long before flap sanders and cutting wheels are worn down to fit the 115 mm.

But my favorite metal cutting thingo is my 35 year old 1150W 8" table saw win which I run 125 mm thin kerf cut off wheels. It's slow but it is quiet and I can use it with water cooking and use the built in fence and mitre. That thing gets hammered and it's still working strong.

Originally Posted by quercus

Nobody has mentioned a 4 1/2" grinder, (115mm) which is my preference.

Has always been mine too, have a heavy duty Hitachi can't fault it.

5" grinder - aside of everything people have mentioned for power and reliability there is another bonus. If you have a 9 or 7" grinder, the worn out wheels from them can be used in the 5" - a worn down 9" wheel gives another use in a 5" because the spindle bores are the same 22.5mm - not the 16mm of the 4".

Originally Posted by desbromilow

5" grinder - aside of everything people have mentioned for power and reliability there is another bonus. If you have a 9 or 7" grinder, the worn out wheels from them can be used in the 5" - a worn down 9" wheel gives another use in a 5" because the spindle bores are the same 22.5mm - not the 16mm of the 4".

Perhaps a caution on that.
A 5"grinder will possible drive that 9" wheel faster than its rated for the 9" grinder. Because it fits does not necessarily mean its safe.

Grahame

Yeh.. I can see both sides of this 9" hand me down thing.

It is reasonable to expect that the limiting factor in the speed rating on 9inch and 7 inch disks is the periferal speed.

By the time they are worn down to 5 inch the perfieral speed will be proportionaly reduced.

The way I hear it the 5 inch grinder was very interntionaly bushed the same to allow this use of worn disks from larger grinders..... but realy is it so

There is a practicality that does not work for me..... if I was to mount up a worn disk from my hitachi 9 inch into my protool 5 inch......I would have to have worn the disk pretty well back to the clamping disks for it to be a fit.

reuse of a cutting disk is plausable...... but a gringing disk will be pretty much worn to the cup section before it will fit onto a 5 inch unit.

In a regulated industrial safety environment, I would not be reusing 9" wheels on small machines......in my home workshop... it simply does not stack up practicaly.

Now here is another common bushing to think on...... the standard stihl brushcutter bushing that takes a grass blade or a brush knife is the same as a 9 inch grinder or a 9 inch circular saw.

this does not then follow that the two are interchangable.

Running a masonary cutting blade on a straight shaft brish cutter might be marginaly appropriate for heavy edging........but a brush knife on an angle grinder or a 9" circular saw would just be electric powered death.

speaking of electric powered death......

Has anybody had a carefull look at a victa lawn edger...... ya have a petrol motor driving a piece of hardened flat bar sharpened at each end...... good thing they have long handles.... a scary thing.
But even worse....it was common at one time to take the blade from one of these and mount it in a circular saw and use it for cutting coldroom sheet.....even worse ya had to push down hard and pull the saw backward....Oh hell.

Realy there was a time we used to tolerate all sorts of things.....these days I think we are much better off using consumables specificany intended for the machine in question......grinder disks are not all that expensive are they.

cheers

Originally Posted by montiee

Except consumable are hard to find. . Seriously the 1/2 inch isn't going to really cause anyone major issues. I've always been puzzled by the 4.5 inch grinder and why anyone bothers. .

Have used 4.5" angle grinders for over 30 years, havn't found finding consumables an
issue.
They are stronger than a 4" , the extra 1/2" does make a difference and ease of
handling is retained.

I just got me an Hitachi 18V grinder, which happens, for some reason, to use 115mm disks. So added to my 4" Black and Decker and 5" Bosch I've now got all 3 sizes. As mentioned, it doesn't seem any harder to get 41/2" disks.

I supose that depends on where you shop.

If you buy from a metal trade supplier, you'll probaly have no problem.

But if you a stuck to finish a job on a weekend or publick holiday and onaly have access to a retail type hardware, it may be a different story..

cheers

comparing a 9" @ 6000rpm and 5" @ 12,000rpm gives the following tip accelerations:

a = r*w^2, where r is wheel radius and w is angular speed (radians/s) and a is acceleration in m/s^2. Actual units don't matter for comparison as long as the set is consistent.
http://theory.uwinnipeg.ca/physics/circ/node6.html
(edit: thanks BobL. I fail at (rw)^2/r)

9"
radius = 4.5" or 0.115m
a = 0.115 * (6000 *2PI/60)^2 = 45,400m/s2

5"
radius = 2.5" or 0.0635m
a = 0.0635 * (12000 *2PI/60)^2 = 100,275m/s2

A worn out 9" down to 5" disc sees significantly higher peak acceleration (leading to F=ma and disc stress being F/area) than when new because of the higher spin speed of the smaller grinder.

Mass per reinforcing fibre will reduce and so stress will fall with reducing radius, but this isn't readily evaluatable and you should still take note of the original disk performance limitations.

Spin up also adds a further acceleration vector, but may well be ignored for soft start grinders. For 'instant-on' versions, you'll get a significant overhead on the disc until you're up to speed.