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Lidl bench grinder - induction motors usual in such tools ?

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baldpate

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I took myself to Lidl today and bought one of these:
http://www.lidl.co.uk/static_content/lidl_uk/images/UK/UK_69208_01_b.jpg
a 200W bench grinder for £20. Back home, I got it out to check that it ran OK.

I was pleasantly surprised at how quiet it was. Took about 4 seconds to get up to full speed, but even then it was pretty quiet. I have no previous experience with this type of tool, so I was expecting the shrill shriek of power hand tools (drill, router, angle grinder etc).

Reading the specs, I see it has an induction motor, which I presume is the reason for the quiet running. Can you please tell me if such a motor is usual for a bench grinder in the 'economy' price bracket (I had always associated this type of motor with more expensive tools)?

Thanks

Chris
 

gregmcateer

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Chris,
Don't know jack about induction / otherwise, but I do know that that sounds like a steal - with a thumping guarantee, to boot!
Nice one.
Do update us all about how well it works.
Cheers,
Greg
 

Webby

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i think i will checkout my local Lidl .................thanks for heads up :D
 

newt

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As far as I am aware all bench grinders use induction motors.
 

9fingers

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newt":onvrcli6 said:
As far as I am aware all bench grinders use induction motors.

Quite agree, universal motors run too fast for other than very smallest grinding wheels and you don't want to be anywhere near a bursting grinding wheel!

Bob
 

baldpate

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Thanks, newt & 9fingers - that answers my question. I had somehow got the idea that induction motors were a more expensive type of motor to produce, therefore only found in high-end machines. Obviously not!

9fingers: this motor spins the wheels at 2900 rpm, which I believe is much the same as a hand-held, mains-driven, electric drill. I believe such drills use what you call 'universal motors', don't they? So why aren't they suitable for bench grinders?
Not that I'm complaining, mind - I like quiet, and I certainly don't want grinding wheels bursting in my face! I ask in the spirit of enquiry since, even having a mathematical and scientific education, I seem to have a complete blank spot where electric motors are concerned :? .
 

chunkolini

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I have had a few of those type of grinders, screwfix and machine mart.
They do the job but if used a lot they do run very hot, like almost too hot to touch. ok I was wire brushing bike frames.
Eventually they die.
but they are only twenty quid.
How much are new wheels?
Q; how in hell does anybody make a bean out of them?
Ores are mined, metal is shipped to subcontractors, then to manufacturers. The thing is built, packed shipped to Rotterdam, then Britain, then by road to a distributors, then to the supplier. This always does my head in.
 

Mark A

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chunkolini":9osrrcb5 said:
Q; how in hell does anybody make a bean out of them?
Ores are mined, metal is shipped to subcontractors, then to manufacturers. The thing is built, packed shipped to Rotterdam, then Britain, then by road to a distributors, then to the supplier. This always does my head in.
A: Chinese and Taiwanese labour. Materials and shipping are cheap compared to the cost of wages, insurance, H&S, rent etc you would have to pay for a plant in Europe/Britain. They work harder for longer for less. It's crazy that manufacturing and shipping from half the word away would cost less than it would from, say, Bradford, but it evidently does.

Mark
 

RogerP

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A 40 foot container will hold 25 tons + and around 3000 sq feet and will cost around £3000 from China (with all the extras and commissions) to UK. How many grinders you could get in I couldn't guess but shipping per unit would not be very much.
 

9fingers

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baldpate":1gott6xw said:
Thanks, newt & 9fingers - that answers my question. I had somehow got the idea that induction motors were a more expensive type of motor to produce, therefore only found in high-end machines. Obviously not!

9fingers: this motor spins the wheels at 2900 rpm, which I believe is much the same as a hand-held, mains-driven, electric drill. I believe such drills use what you call 'universal motors', don't they? So why aren't they suitable for bench grinders?
Not that I'm complaining, mind - I like quiet, and I certainly don't want grinding wheels bursting in my face! I ask in the spirit of enquiry since, even having a mathematical and scientific education, I seem to have a complete blank spot where electric motors are concerned :? .
Electric drills and other similar mains powered tools with universal motors* are fitted with gear boxes to reduce the speed to manageable proportions. Adding such a feature to a double ended grinder would either need two such gear drives or a second shaft driven by gears.
* Universal Motor refers to the ability of these type of motors to run from either AC or DC power. They are also referred to as Brush Motors or Commutator motors. They produce a lot of power from a given volume but typically run at 20000 rpm but that speed is not controlled by fundamental design but instead by the load/losses imposed on it. They are noise both due to the spedd and the amount of cooling air that has to be forced through to stop them over heating.

hth

Bob
 

baldpate

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9fingers":3hbvvnpl said:
Electric drills and other similar mains powered tools with universal motors* are fitted with gear boxes to reduce the speed to manageable proportions. Adding such a feature to a double ended grinder would either need two such gear drives or a second shaft driven by gears.
* Universal Motor refers to the ability of these type of motors to run from either AC or DC power. They are also referred to as Brush Motors or Commutator motors. They produce a lot of power from a given volume but typically run at 20000 rpm but that speed is not controlled by fundamental design but instead by the load/losses imposed on it. They are noise both due to the spedd and the amount of cooling air that has to be forced through to stop them over heating.
Thanks for the tutorial Bob - it certainly does help : I didn't know any of that. This site is great for learning stuff!
 

cmwatt

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Hi, just wondering if anyone knows actually how well this thing works? Would it be fine for getting the primary bevel on chisels etc? My brother works at Lidl too, so I could probably get it for even less. :)
 

9fingers

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cmwatt":2pwtapot said:
Hi, just wondering if anyone knows actually how well this thing works? Would it be fine for getting the primary bevel on chisels etc? My brother works at Lidl too, so I could probably get it for even less. :)

There are loads of slightly different models in this class of grinder that will all do a basic job. To be sure of getting anything noticeably better, you would be looking at a significantly higher price tag.
I've got something similar bought many years ago and fitted different wheels for my metal working needs ( sharpening carbide etc) and it is fine.
The main thing is not to press too hard and slow the motor down - in any case pressing too hard will likely over heat your tools a draw the temper. The motor will possibly get hot running continuously buy not many people need more than a few minutes at a time.

hth

Bob
 

cmwatt

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Ok thanks for the info Bob. I asked my brother to get one for me when at work today (if there is any), so we'll see what it's like later. I've never used a bench grinder before, only oil stones, so any info is welcomed. (hammer)
 

hammer n nails

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well i went out and brought one today set it up and works great will be ok for light use chisels and things just the job but probably not good enough for heavy industrial use but for £19.99 a good buy for me
 

MACSWAG2

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cmwatt":hnk7myka said:
Hi, just wondering if anyone knows actually how well this thing works? Would it be fine for getting the primary bevel on chisels etc? My brother works at Lidl too, so I could probably get it for even less. :)
Hi friend,they work very well,but if you are sharpening turning tools or chisels invest in a PINK grinding wheel,you won't regret it,smoother and cooler using,saves your tools blueing and loosing temper, MAC.
 

AES

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@Baldpate:

Just a few words of caution if I may – I do NOT want to turn this into an ‘elf n safety” diatribe but as you say you know nothing about such machines here are a few simple words of caution for your own safety:

A) In industry nobody is allowed to mount a wheel on a grinder of any size or type unless he/she has been on a course. The reason is obvious (which makes a change for the “e n s elfs” these days) a grinding wheel is different to, say, a circular saw blade because it consists primarily of bits of grit of one sort or another glued together to form a disc (or cylinder). Normally speaking, unless it’s a cut-off disc (which is not for use in a bench grinder) there is no reinforcement – just grit and glue putting it very simply;

B) The basic reason for all this caution is that an exploding wheel is a truly frightening and potentially VERY dangerous thing. At the very least severe damage will be caused to any building or tools, benches, etc, that get in the way of fragments, and what it could do to the human (or animal) body just doesn’t bear thinking about;

C) Although I’ve never been on a “proper” industry course I was lucky enough to have a good bit of training in this area during my RAF apprenticeship. This included a film (no DVDs in those days!) showing a grinding wheel not much bigger than yours letting go. As said, horrendous in a big way;

D) OK, enough of the scare mongering, what’s to be careful of really?

First, do NOT exert too much pressure of the work piece/the tool being sharpened by pushing hard against the wheel. And this machine is NOT a substitute for a sanding disc or a belt or a file – at the very best, trying to remove lots of metal quickly with a bench grinder will result only in a wheel which is “glazed” and therefore useless until it’s been re-dressed;

Second, NEVER run the machine without the guards in place and ALWAYS use safety glasses;

Third, if as been suggested already, you decide to change at least one of the wheels for a better one (particularly the roughest grade wheel on most cheap bench grinders are pretty useless and will anyway wear out pretty quickly), DO - PLEASE – take a length of string to the shop with you! What? STRING? Yes, when choosing a wheel of any type it’s most important to check that it isn’t cracked. You just tie the string into a loop through the centre mounting hole then suspend the wheel in mid air. Tap it (gently) with a screwdriver or something and you’ll hear a sort of ring tone (a bit like a small bell). If you hear a dull “clunk” the wheel is cracked and you’re NOT taking it home with you, OK?

Fourth, when mounting the new wheel make sure that the printed paper discs on each side of the wheel stay there when you mount the wheel – as well as stating the manufacturer’s name, grit type and the max allowed rotation speed (which should NEVER be exceeded) these discs are there as safety compression washers. Note you do NOT need to over-tighten the wheel retaining nut/s (the grinder’s shaft rotates in a direction to automatically tighten the retaining nut/s). And you MUST use whatever distance pieces or collars which came with the new wheel to make sure that the new wheel sits snugly (but is neither sloppy nor a force fit) onto the shaft. It’s obvious that if you’ve had to remove the wheel safety guard to get the old wheel off/new wheel on, then the safety guard MUST go back on before you switch on again. PLEASE!

That’s about it really. Quite simple stuff when you know and not at all time-consuming.

A couple of words on usage if you like:

E) Keep an open tin of water by the grinder and use it REGULARLY when sharpening cutting tools – if the tip of the tool goes blue or even a bit yellow (never mind red) then you’ve lost that part of the tool (the overheating has softened the edge) so you’ll have to – GENTLY – grind all the discoloured metal away and start again. On small chisels, screwdrivers, etc, this will happen VERY quickly so it’s “a few seconds against the wheel then into the water then back to the wheel again" as a constant process – one of the reasons why getting the tool angles correct is a bit of a learning curve;

F) It may be a good idea to find a really old tool or piece of genuine scrap and practice a bit first;

G) Someone has already suggested a pink grit wheel for tool grinding. I’m certainly NOT an expert on grinding chisels, etc, but personally I’d prefer a brown grit (light-ish sandy colour) for that job;

H) Someone else has I think mentioned a green grit wheel but personally I only use that for sharpening brazed carbide (metal) lathe tools, and touching up (only) masonry drill bits, etc;

I) The little adjustable rest in front of the wheel that came with the machine will be of some help in getting the angles you want but you’ll likely find you’d like something a bit better after a few tries. You’ll find plenty of ideas on the internet (or send me a PM) but to start with do use the rest provided but as far as you’re able, using a protractor or something to set up the 30 degrees (or whatever angle you need) before starting to grind;

J) THEORETICALLY one is not supposed to use the flat side of the wheel for grinding. In practice we all do it (especially with some jobs it’s impossible not to) so just remember that the wheel was not constructed for this use (it’s stronger on the front edge facing you) so use even less tool pressure against the side of the wheel than you would on the front;

J) It is possible to re-dress a badly glazed or scored wheel. There are 2 possibilities, either a “star wheel” dressing tool (NOT expensive) or a big “block” of “black stoney stuff” which is even cheaper than the star wheel tool. Personally I prefer the star wheel. Both are easy to use – just GENTLY (that word again!) bring the dressing tool into contact with the edge of the wheel and keep it there until any irregularities, grooves, etc, are worn away. DO NOT – EVER - use these tools against the side face of the wheel.

Hope all this helps and is not overkill. It’s not designed to frighten you off either.

The machine you’ve got is perfectly OK if used with a little knowledge and a bit of respect. Like machine saws for example, once you’ve got beyond the basic stage of having a shaft which turns regularly, concentrically, and smoothly, it’s much more to do with the blade you fit (in this case the wheel) and how you use the tool that will determine your success.

And yes, induction motors which take a few seconds to wind up to speed (and back down again) are perfectly normal.

That little machine will last you a lifetime – as someone else said, I really CANNOT get my head around how “they” do it for the price.

Best of luck and enjoy mate.

AES
 

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