Grinder wattage

[Kent]

u said the higher the wattage the slower the disk wears out . no if u have a lower wattage grinder u will have to take lighter cuts in order to keep the surface speed up .a higher wattage one will not slow down when u put a bit more pressure on it and surface speed stops the same without reduction . that's what wears your stone quicker and grinder has to work harder

Yes I was only interested in does higher wattage have an effect. Obviously with this in mind it does In the fact its more able to keep the surface speed up

 

[daleyd]

If your putting enough pressure on that the extra torque is needed to keep the speed up then I’d say you would already be wearing your discs out pretty quickly.

From what I can see he is trying to justify the higher wattage tools using some fairly dubious “science”. I’m guessing higher wattage = higher price, he’s a salesman so of course he’ll want you to buy the more expensive option. (Did I mention that I don’t trust sales people?)

 

[rcx132]

This does sound like the "torque vs bhp" argument all over again ツ
Watts is "rate of work", so it's actually how quickly something can do something. A lower wattage tool could do the same work but it would take longer. In the case of grinding, a lower wattage grinder would need a smaller disc to create a smaller cutting surface so that it could maintain the speed for which the grinding disc was created. If that condition is met then grinding speed is maintained and the discs won't wear too quickly.

Personally I wouldn't trust the sales rep, the topic of grinder speed vs wear is a topic for the manufacturer, no offense to any sales reps, but I find they usually chat rubbish on things like this. I'd hope that the manufacturer has optimised the speed of their grinders so that it's correct under normal working load.

 

[normspanners]

I can see the logic behind it because if you run adisc slower it does not do the job effectively if you havnt got the power your speed will drop dramatically and the disc will wear quicker, so for the same pressure if the motor can keep its speed higher than the low wattage motor, it can save on discs but it is a very fine line a knife edge in fact. but once used to it I do think it would save discs, infact my makita cordless grinder hasnt got the power and uses discs but my milwaukee keeps going and the discs last longer, so I now use the makita for flap wheeling or wire brushing

 

[MalcolmX]

Reducing peripheral surface speed will make the abrasive wheel wear away quicker.

A machine with a lower power output, will under load, lose optimum surface speed easier and therefore your abrasive wheel will wear quicker and remove less material in a given time.

The peripheral surface speed also reduces as the wheel becomes smaller in diameter, therefore the rate at which the wheel wears away increases progressively.

Buy the higher powered tool.

 

[normspanners]

Try using a rotary grindstone in a drill at 4000 rpm and it is the stone that wears away, use it in a die grinder at 20.000 rpm and the stone does its job and cuts the metal sure the stone wears but at no wear (pun intended) near the same rate,
so if you can keep the disc spinning at its intended highest cutting speed, the disc (which works on the same principal as a stone IMO) will last longer, as long as it is not 'pushed' into the work too hard because you have more power available and then reduce its speed back to the speed of the lower wattage machine as said its YOU that that should be in control once you get used to it.
Again all, IMO
I love using 9" thin discs on my 9" makitas they seem to last forever, ok not as high a revs but its surface speed is what is critical, I use them until they get to 5" then they get used on my smaller grinders because the revs are then too slow and it eats the last few inches so pointless leaving them in.

 

[daleyd]

I think the theory behind it is mildly interesting, but would it justify me needing to buy a higher wattage machine? Nah - as I said above if your pushing a grinder enough that the speed is slowing down enough that wear becomes an issue then your doing something seriously wrong. I'm sorry but it still sounds to me like a salesman solving a problem that doesn't exist (At least for the majority of people, I'm sure there may be certain applications that would benefit) by selling you a more expensive machine.

 

[Kent]

This does sound like the "torque vs bhp" argument all over again ツ
Watts is "rate of work", so it's actually how quickly something can do something. A lower wattage tool could do the same work but it would take longer. In the case of grinding, a lower wattage grinder would need a smaller disc to create a smaller cutting surface so that it could maintain the speed for which the grinding disc was created. If that condition is met then grinding speed is maintained and the discs won't wear too quickly.

Personally I wouldn't trust the sales rep, the topic of grinder speed vs wear is a topic for the manufacturer, no offense to any sales reps, but I find they usually chat rubbish on things like this. I'd hope that the manufacturer has optimised the speed of their grinders so that it's correct under normal working load.

That's a bit unfair on reps. I used to train reps for a living and I can tell you the best know more than thier technical department before long - because they genuinely care and don't want to look a pratt phoning up every time they don't understand something..

 

[rcx132]

That's a bit unfair on reps. I used to train reps for a living and I can tell you the best know more than thier technical department before long - because they genuinely care and don't want to look a pratt phoning up every time they don't understand something..

Fair enough. I've seen the John Lewis reps tend to be good as well.

But at work I find they chat rubbish. Recently BT Business rep convinced me their free routers are suitable for business use despite my concerns I believed him. Darn thing wasn't even rack mountable, forget about having diagnostic tools or proper security functionality. I will still be careful before believing a rep.

 

[daleyd]

Fair enough. I've seen the John Lewis reps tend to be good as well.

But at work I find they chat rubbish. Recently BT Business rep convinced me their free routers are suitable for business use despite my concerns I believed him. Darn thing wasn't even rack mountable, forget about having diagnostic tools or proper security functionality. I will still be careful before believing a rep.

They always have an ulterior motive, it's in their interests to sell you something (The clues in their job title...), so while there are many decent ones I will always do my own research.

In my line of work the Reps will perhaps have an in depth knowledge of the features of the kit (They need this in order to sell stuff), but in no way would they ever know the ins an outs or the level of technical detail of the products to anywhere near the same level as the support staff - they just don't need to know that level of detail and don't work on it every day. Horses for courses, that's not a downer on sales people, just a fact of life.

 

[brightspark]

salesman sell products that there firm supply. the rep from city electrics is a mate and he knows better than try and sell me tools that they are pushing specially drills that are 2 sped electronic I only use geared ones . no loss of power on slow speed and more torque

 

[smashweld]

This thread is prime example of why I like to do my own research.
Wonder how many ‘reps’ would have the knowledge contained in this thread


Prob get whatever you’re after cheaper online anyway!

 

[MalcolmX]

FFS - the tool ‘rep’ is correct - let me explain how this works.

The lower powered tool slows down easier under load.

Therefore each abrasive grain is taking a larger chip of material/time, putting it under increased load and thereby pulling the grain out prematurely from the bond (phenolic resin)

Same applies as the abrasive wheel reduces in diameter (lower surface speed) Think of the reduced number of abrasive grains on the circumference doing the same work as a new full size wheel.

All this doesn’t really matter if you’re an occasional user, but if you’re buying premium abrasives with Zr or ceramic grain, you’ll get more value from them with the higher powered tool and get the job done quicker too.

Your money - your choice.

 

[Gareth0123]

I think the rep is getting the disc diameter mixed up with grinder wattage.
230mm grinders are normally rated at about 6000rpm and are normally between 1500-and 200 watts.
125mm grinders are normally rated between 7000 and 12500 rpm and are between 900 and 1700 watt.
115mm grinders are normally rated 13500-14000 rpm and anywhere between 500 and 1200 watts.

A couple of years ago I had an incident with a Ryobi 850watt 13000 rpm grinder: the 115mm backing disc I purchased from Machinemart was rated to only 8000 RPM (I didn't check the rating on the backing disc) and it came apart during use on me. The sanding disc backing for my 115mm angle grinder exploded, the piece flew off and hit the side of my bench vice about 18" away and the broken off bit bounced back and hit me across the fingers of my right hand, which was still holding the grinder at the time.

I got lucky because I was still holding the grinder which was spinning down and shaking about unbalanced due to the lump missing from the backing disc. The weight of the grinder and the unbalanced centrifugal force no doubt absorbed the energy as the backing disc hit my fingers and because the grinder is a solid object it took the brunt and I walked away with all my fingers intact

After this incident I started checking the ratings on discs I was purchasing in bulk from a couple of very reputable websites and found the (blue) Zirconia 115 discs were rated to 9000rpm and the (red) ceramic discs were rated to 10000rpm both of which are well below the 13000 rpm rating of my grinder.

To make matters worse a lot of 125mm metal cutting discs and wire brushes are rated at only 7500rpm and are sold alongside the variable speed Aldi/Lidl grinders. Local builders will rush into the stores and buy out these piles of cheap 125mm discs, flap wheels and wire brushes because they will fit under the guards of 115mm DeWalt, Makita and Milwaukee Angle grinders (but not under the guards of Clarke and Ryobi 115mm grinders).

 

[daleyd]

I think the problem is a mistrust of sales reps (at least on my part, I’m not speaking for anyone else here..), plus the fact that it’s not put into any context.

For example, how much extra would the higher wattage machine cost over and above a “standard” version? What would be the payback time for this extra cost to manifest itself?

If, say a 600w grinder slows down x amount during use, comparatively how much would the higher wattage machine slow? And how would that translate into extra wear? I would guess it wouldn’t be a linear relationship so say a 10% speed reduction might result in perhaps 1% increased wear. Because the machine slows down less you would perhaps then have the operators forcing the machine through more, negating any supposed savings.

Ok, the larger machines might (almost certainly would) speed up stock removal, but then you’ve got the heavier nature of the machine, operator fatigue, the ability of a smaller grinder to get into more places so making them more handy.

It’s not a downer on a high(er) power grinder (I have one, they have their place, but 90% of the time I reach for my smaller ones because they are much more wieldy) , but to make a blanket statement like “higher power machines wear discs less” just glosses over everything else.

It just seems (in the context of the op original post) to justify upselling something to fix a problem that doesn’t really exist. (For most people)

 

[MalcolmX]

OK guys n gals
Just speaking to my tool rep about some more angle grinders. He says the higher the wattage the slower the discs wear out as regards stones and slitting discs.
Now I currently run 600watt for sanding mainly coz they are slimmer and lighter and 1000 watt for stones and cutting..

Looking at up to 1700 Watts on the matabo range and wondering I know they will be capable of faster working but disc use being extended ?

Q. Better disc life - as per the original question?

A. Yes, all other things being equal.

No mention of machine being heavier, more unwieldy, accessibility.

Can you get sandals on with socks, yes.........but you’ll look a right c@nt.

 

[brightspark]

god it doesn't matter what size wattage of machine u buy just keep the surface speed up . light passes with a smaller grinder and use your ears and u can tell if your pulling it down

 

[8ob]

god it doesn't matter what size wattage of machine u buy just keep the surface speed up . light passes with a smaller grinder and use your ears and u can tell if your pulling it down

+1 and keep your mits away from the motor vents, my lads have cooked quite a few grinders by blocking the vents with their hands. Easy done when using smaller grinders without the handle fitted.

Bob