Needing advice about angle grinders...

Achingly ignorant question: I am putting together gear for a knifemaking shop, and I realize that it's best to get the angle grinder with the best combination of power and form factor (trigger type, etc.) you can afford, but I was wondering one more thing.

Is it best to stick with a 4.5" grinder, or if I can buy a larger grinder, will it run smaller discs? I realize a 7" disc will eventually grind down to 4.5" but before I make any other assumptions and stick myself with too much grinder, I figured I'd ask you all.

Should I get the best combo of bigger, better amperage, and more comfortable trigger, etc., or is it better to stick with the 4.5" grinder to start with? Most of my work will use 4.5" discs, but I was lucky enough to get a gift card, and I want to make a good decision on this.

(Right now I'm using a 4.5" grinder I got for ten bucks after coupon at Harbor Fright, and once it croaks, I want to be ready to move on my next one since I use it constantly.)

I should also ask, should I consider a cordless, or do they eat batteries?

I appreciate all the smarts that you folks are sharing here, and when I have something to show off I'll let you know. Right now I'm working steadily towards making that first thing I'm not ashamed of.

Many thanks,

TheElderBrother

Cordless is good if you need cordless, however a power cord in the wall never goes dead (unless you're in California).

The 7" will make you tired much faster

it really depends on much u will be using the grinder and how hard.. will u be taking a lot of metal off ??? if so step up to a 6 inch grinder ,bosch or metabo ,german made,,their 4.5 grinders are mostly chinese,, still good though, the german ones(metabo) have advanced features, like Safety clutch,RPM maintainer,Auto balance,and more,again if your doing a LOT of grinding,anti-vibe is a good thing,,if u have small hands, the paddle or sliding switch models may be too big around, u can get rat tail grinders with a smaller handle,,plenty of good angle grinders used on E-bay..for light use but long term dependability the Dewalt 4.5 inch 28402 is great,(this grinder helped put dewalt on the map, they have probally made a million of them).a little heavy, plenty of power (10 amps), will last f decades under lite or moderate use,,my hands are average size, and can use the paddle switch and hold grinder just fine,but i only use it f short periods..cordless ??? only if u REALLY need it, the circular saw, reciprocating saw, and angle grinders just suckup the battery power,,and thin out your wallet,,they work great but only if u really need one like working in a attic or on a roof,or under a house,,,

To my mind, the sweet spot is a 5" (125mm) corded grinder.

7" grinders really hog the metal and are more or less essential if you're doing heavy fabrication. On the downside they get heavy, can be hard to control and to my knowledge, no-one makes the ultra thin cut-off wheels to suit.
4.5" grinders are easy to control, but always seemed a little toy-like to me and it can be difficult getting the full range of products such as cup wheels, flap discs, wire wheels etc.
5" grinders have plenty of power, with care you can do fine work, and seem to have the best range of products, where I live at least. I've always considered them be best balance of weight and power.

Cordless vs corded? Personally, I'd take corded; it never needs recharging, minimal electronics, you will never have to buy replacement batteries and (perhaps the biggest thing), if you cable tie the spanner to the cord, if never ever gets lost and is always located within 6". I don't think there's much difference in performance between corded and battery.

If it was my money, I'd buy two 5" grinders, and fit one with a ultra thin cutting disk and the other with a flap disc. Swapping discs can become tedious and inefficient.

FWIW while I've used multiple sizes and different brands in industry, my sole personal grinder is a 25 year old Makita 125mm which has run flawlessly. I treated it to new bearings last year and it turns out the original ones were perfectly fine. By the time I knew this I had already bought the bearings and pulled the thing apart...
I've used it for every thing from wood working to light fabrication to bone carving, and the only time I've ever missed a 7" was when dressing an anvil. In all fairness my work is usually workshop based, and on the odd occasion I've worked offsite, I've still been within a 20m extension lead distance.

Your kilometrage may vary.

Cheer E

Quote:

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Originally Posted by Little Rabbit

To my mind, the sweet spot is a 5" (125mm) corded grinder.

7" grinders really hog the metal and are more or less essential if you're doing heavy fabrication. On the downside they get heavy, can be hard to control and to my knowledge, no-one makes the ultra thin cut-off wheels to suit.
4.5" grinders are easy to control, but always seemed a little toy-like to me and it can be difficult getting the full range of products such as cup wheels, flap discs, wire wheels etc.
5" grinders have plenty of power, with care you can do fine work, and seem to have the best range of products, where I live at least. I've always considered them be best balance of weight and power.

Cordless vs corded? Personally, I'd take corded; it never needs recharging, minimal electronics, you will never have to buy replacement batteries and (perhaps the biggest thing), if you cable tie the spanner to the cord, if never ever gets lost and is always located within 6". I don't think there's much difference in performance between corded and battery.

If it was my money, I'd buy two 5" grinders, and fit one with a ultra thin cutting disk and the other with a flap disc. Swapping discs can become tedious and inefficient.

FWIW while I've used multiple sizes and different brands in industry, my sole personal grinder is a 25 year old Makita 125mm which has run flawlessly. I treated it to new bearings last year and it turns out the original ones were perfectly fine. By the time I knew this I had already bought the bearings and pulled the thing apart...
I've used it for every thing from wood working to light fabrication to bone carving, and the only time I've ever missed a 7" was when dressing an anvil. In all fairness my work is usually workshop based, and on the odd occasion I've worked offsite, I've still been within a 20m extension lead distance.

Your kilometrage may vary.

Cheer E

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Never seen a 5" grinder, so can't speak to those. 7" are too heavy if you're not using them all the time, more-or-less professionally. I prefer the 4.5" grinders, personally, as you can get several of them fairly cheaply. One for a flap sander, one for a fine cutoff disk, also one for a coarse grinding disk, one for a finer grinding disk, and one with a polishing head, one with a cup brush, one more with coarse wire wheel, etc. If you're doing this stuff professionally, DeWalt, Metabo, Bosch, etc., are all at least decent. If you're an amateur, and doing stuff for fun, a $10-15 grinder will work fine and last a long time. Not having to change disks will make lots of things easy and fast, as you can select what you need and have it set up right there. Corded is the way to go for most folks. The grinders are cheaper and generally more powerful. Cordless is good when you're in an attic, on the top of a ladder, and other inaccessible places. They do eat batteries FAST! Batteries are NOT cheap, and you need several! Though if you're using an unpowered shed or garage, they may be the only way to go. Buy one, use it. When you can, buy another, and have two setups. Add one as time and necessity allow or require. I've got one cheap 4.5" grinder I bought cheap over 20 years ago, and a couple more I got shortly after that. I have two of the newer cheap Harbor Freight grinders. None of them like being used for a long time, and if you change out grinders fairly frequently you can keep grinding for a long time. I do need to check the bearings on that really old one. It's leaking a bit of grease now and then, when it gets hot. It won't hurt to get a larger, more powerful grinder for when you really need one. I've got an anvil here I'm trying to recondition a bit, every now and again, when I have time, and a 7" grinder would be helpful, but for most things you can do with one a little smaller. Also, check and see what size accessories are available in your area. If all you can get are 4" discs, you're probably not going to be happy with them on a larger grinder. And if you can readily get 5" wheels and such, by all means, go for it!

HTH!

Bill in OKC

Thanks Bill,

My bad! I have obviously forgotten how to get my head around imperial measurements. What I was referring to as 4.5" I was thinking of 4". The small dinky ones I've used have mostly been 4" but I've mentally lumped 4.5" into the same category as 4" in that they're not worth my time.

My grinder is actually a 5" jobbie, but it also takes 4.5' discs if I'm desperate. That said 5" consumables are pretty common here, but I tend to do my shopping at industrial supply places, not the big box stores.
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One thing to seriously look at when choosing an angle grinder regardless of size is the maximum amperage draw it can handle.
Most of the 4" 100 mm grinders will only have a 10 mm arbor their amp draw will range from 5.5 to 7 amps
the most popular small sized grinder being the 4 1/2" 115 MM will have the 5/8-11 arbor the body size is usually near the same as the 4" and the amp draw will range from 6 to 11 amps the switches on all 4 and 4 1/2 " grinders can be an issue since there are so many designs to choose from some are slide where you hold the switch by your thumb some are paddle where you hold the switch with the tips of your fingers some are flip that once on they stay on until you turn them off Rarely will a grinder in this size range have a handle and trigger like the much larger 7 & 9" grinders have.
5 inch grinders can be a mixed bag of mostly over rated 4 1/2" to mid sized grinders shaped more like the larger 7&9" I like the 5 " because mostly I can get them with trigger switches and I am gripping a handle instead of the motor body but they are heavier and you will most of the time want to use both hands to control one
their amp range can be from 7 to 12 amps.
now comes the oddball 6" grinder which is really just a 5 inch with a larger guard but often they will be low RPM less than 3000 making them ore of a polisher than a grinder. 8 to 12 amps
7 Inch grinders are more popular than the 9" their weight is usually slightly less and they can be less bulky their amps can be from 9 to 15 amps consumer grades will have smaller bodies usually
The Kings of the grinding world being the 9" monsters as some call them but not all are huge AEG used to make one though that had a 19 amp draw and weighed 25 lbs it turned 5,500 RPM and you could force your full weight on it and not bog it down but if the disk got hung up it would throw you across the room like a 3/4" drill motor would do with a 1" pipe handle
Bosh makes a 9" that is in my opinion actually a 7" with a 9" guard but it has a respectable 17 amp max draw and will last through years of abuse.
Some grinders have a handle that can be rotated 90° in either direction I have a 7" Ridgid with that feature quite handy at times and the grinder is a little better than middle of the road quality

While we are talking grinders, what kind and how much lube should be in the gearbox?
Thanks.

I need both a 4.5" for precise cutting and a 7" for more aggressive weld metal removal and surface prep. I've used the hell out of a Hitachi 4.5" grinder and it's still hanging in there well. I also am a fan of Makita super thin 4.5" cutoff wheels because they cut through steel quickly (though they wear down quickly too). A Makita 7" angle grinder is hard to beat for bulk material removal. I recommend for either that you buy a pair of kevlar lined cut resistant gloves and a face shield because it's better than any pair of glasses.

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Originally Posted by Karl_H

While we are talking grinders, what kind and how much lube should be in the gearbox?
Thanks.

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Most of the older grinders came with a lube that had a high paraffin content and were nearly packed full at the factory And would outlast 3 sets of carbon brushes and at least 1 complete motor rewind.
new grinders today have a much thinner grease in them and I've had some that would wear out before the first set of brushes
If you are filling the cavity with new grease try to choose one that has a high melting point and at the same time will readily yield to be drawn between moving parts,
I like a grease with either molybdenum disulfide or lithium hydroxide and paraffin as the thickener.
By the way addition to my previous post when it comes to the amperage draw those figures were for 120vac for 230/240 vac the numbers would be halved

It would be hard for me to choose one brand over another anymore I've owned about every brand you can imagine but for the past several years I have mostly hit the pawn shops and second hand tool shops for my grinders. Some times I can make a deal and buy half a dozen for $5.00 apiece some of them will last a couple of years while others may last only a few months. When I had my shop and several employees It really didn't matter what the brand was none of them would last much longer than the warrantee. Didn't seem to matter if the grinder cost $20.00 or $200.00. A $13.00 HF 4 1/2" might last me a years whereas a $100.00 Metablo or Hitathi Or Mikita might last a worker only a few months

Quote:

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Originally Posted by Crusty

I need both a 4.5" for precise cutting and a 7" for more aggressive weld metal removal and surface prep. I've used the hell out of a Hitachi 4.5" grinder and it's still hanging in there well. I also am a fan of Makita super thin 4.5" cutoff wheels because they cut through steel quickly (though they wear down quickly too). A Makita 7" angle grinder is hard to beat for bulk material removal. I recommend for either that you buy a pair of kevlar lined cut resistant gloves and a face shield because it's better than any pair of glasses.

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Hey Crusty,
I inherited a 9" Makita grinder over Christmas. Man oh Man! I used to think the superthin discs cut nicely, but a 9" disc through spring steel put a smile on my mug. and (ignoring obvious safety factors) when they wear down I can use them as grinding discs on my 5" :-)