About cheap grinders

[Sonic EscapeParticipant @sonicescape38234]

This is a review of two bench grinders I have. For some reason I regard the grinder as the most unimportant machine in my shop. Because of this the first one I bought was that 30 euro red thing. It has a 250W motor, a 150mm dubious quality grinding wheel on a 12mm axle and wet slow turning wheel that has almost 10mm left to right runout

The large wheel got glazed after grinding some mild steel. I tried to dress it with a flat diamond tool, like I read in Machining Fundamentals. But I glazed it even more. So now is useless.

Just check this glorious concentricity:

I traced the problem to this plastic nuts.

Another sad thing is the ridiculously small shoulder on its fast spinning axle, ~1.5mm. This is causing severe runout with some wheels.

Also, recently I purchased a bag of HSS blanks, and I started to make different lathe tools. The 150mm diameter wheel is too small and it created a visible radius on the workpiece. So, I decided to buy a new grinder with a 250mm wheel.

Since I am cheap when it comes to grinders, I searched again for a low cost one. And I found this no-name yellow grinder that is a good match with my workshop color. It weighs 35kg. Heavy is good. And at two hundred euro it is significantly below other more known brands. There was also the option to buy an old communist 3-phase grinder. The seller warned me that two people cannot lift it from the ground. This only increased my interest. But I had enough fun with restoration projects with my milling machine and I wanted an already working machine.

The first impression was good. The grinder feels solid and is very heavy. I spined the wheel by hand and I quickly noticed that the right wheel is quite oval. I measured the spindle runout but as you can see it is fine. I added the nut, and it is still not bad. This nut is a better system comparing with the old grinder. So, in the end I blamed the wheel.

But the horror came when I turned it on. The vibrations are severe. Now I have 35kg of metal jumping on the bench instead of some 8kg before.

I could try to dress the wheel. But with that dressing tool I was able to fix only a green wheel. That is more friable, and it turned round quite nicely. Or I just throw away the wheel. Anyway, I want to replace it with a white or pink one since I ground HSS most of the time.

But overall, the grinder is not bad. Whit good wheels it should be fine. The motor itself is quiet. The axle has 18mm instead of the more standard 20mm, but this is not a big deal.

[Mark RandParticipant @markrand96270]

Dress the wheels with a ‘Huntingdon pattern dresser‘. It will make a lot of mess but will make the wheels circular instead of oval. It will also be useful if you load the wheel up by grinding soft steel or brass etc. and just to keep the wheel ‘sharp’

The cluster diamonds are good for very fine dressing, but not very good if you want to ‘machine’ the wheel. 🙂

PS:- the link was just for an example. I am certain that you can find the same thing locally.

[not done it yetParticipant @notdoneityet]

Have you installed the wheels with “blotters” on each side?  If not, please do so before you have an accident.

[Mark Rand]

On Mark Rand Said:

Dress the wheels with a ‘Huntingdon pattern dresser‘. It will make a lot of mess but will make the wheels circular instead of oval. It will also be useful if you load the wheel up by grinding soft steel or brass etc. and just to keep the wheel ‘sharp’

The cluster diamonds are good for very fine dressing, but not very good if you want to ‘machine’ the wheel. 🙂

PS:- the link was just for an example. I am certain that you can find the same thing locally.

Good to know, I’ll look for one here.

On not done it yet Said:

Have you installed the wheels with “blotters” on each side?  If not, please do so before you have an accident.

Yes, the wheels have them on both sides. They are a little thin if you asked me, like an A4 sheet of paper. And are smaller in diameter than the large metal washer. So maybe I should replace them

[BazyleParticipant @bazyle]

You said the wheel was oval before you even switched it on. How did you determine that? It is common for the label to be non-concentric on low cost items. If hand rotated check the plastic bore adaptors for slapdash making of fitting.
The labels you have indicated are not ‘blotters’. Make new. Old fashioned cornflake box used to be good but a lot of modern packaging is way thinner and so hard milled that it has less give than aluminium. Select wisely.

To evaluate the wheel make a test arbor (not for motor spinning, just measurement) out of plastic or wood that is a good fit and does have a flange. Then you can hold it in a v-block, improvised as necessary, to confirm its shape.

The 1.5mm shoulder is enough if the washer flange is a correct close fit. If the holes in your supplied washers are punched with a vague or punch-chamfer make new as they won’t fit true.

[Nigel Graham 2Participant @nigelgraham2]

They should indeed be thicker and you are right: the raised rim of the washer should be fully supported on the paper.

I am though a bit puzzled by references to grinding soft metals like brass and mild steel – they choke the wheel.

A radius on the clearance part of a lathe tool does not normally matter as long as the clearance is still there. If you consider the geometry it is only a very shallow area that is close to the work even at large work diameter. So there is nothing wrong with using a 150mm diameter wheel; and that is quite a typical wheel size.

 

You pays your money and….

Those two grinders seem so poorly made they should not even be allowed to be sold. As made, they are not safe and many of their buyers are likely to lack your machine-tool knowledge, so would not recognise the hazards and try to correct the faults.

I see one is labelled Panzer – a German word. Like some router-bits I bought of “Erbauer” brand, but whose packing small-print states the truth, I suspect Chinese manufacture given a German name to allege traditionally high German engineering quality. The Chinese can make good stuff but they also know they can sell lots of poorly-made items at correspondingly low prices. Whether those bits, bought from a certain DIY supermarket, will flake out after the first few feet of routing, remains to be seen…..

[noel shelleyParticipant @noelshelley55608]

If you find a Huntington type wheel dresser with worn out wheels/discs that’s no problem as new wheels or discs are available and not very expensive. Or just buy the discs and make your own holder. Noel.

[Sonic EscapeParticipant @sonicescape38234]

You can see that the wheel is oval without turning the thing on. See the second video.

I ordered exactly that type of wheel dresser. I found it in a shop here in Romania.

Panzer is a very common brand here for low cost tools. Together with Stern. Many of their tools are not so bad. But I agreed that my Panzer grinder is bellow any expectation.

As for the yellow one, since the axle has no runout I think the other problems could be solved. I remember Blondihacks saying in one of her videos that when you buy a grinder you buy actually a motor, or something like this. The idea is that the original grinding wheels anyway have to be replaced. Maybe for more high end grinders is a different story. But with that dresser maybe I could save the oval wheel.

One more thing, this is important actually. I have a diamond wheel and I would like to use it with the yellow grinder since it has a 32mm bore. This is one reason why I bought this model. But I remember reading somewhere that some type of two wheel grinders need to be balanced? Is there an issue if I keep the left wheel and put the diamond one on the right? The diamond wheel weights nothing comparing with the other one. Or is it better to remove also the left one and keep only the diamond one?

 

 

[jimmy bParticipant @jimmyb]

I always dump the pressed steel washers, as they are complete waste of time.

 

The last time I had a cheap bench grinder, £12.50 from Argos, I’d have been better off just going ad buying a good quality one at 10 time the price (though where such a thing is sold, I have no idea).

 

I had to change the washers, pull the whole thing apart and put new bearings in and then put 2 good wheels on….

 

One of those cases of having a “bargain”??????

 

Jimb

[DiogenesParticipant @diogenes]

Making new flange washers can transform a cheap grinder; turn them up from mild steel using the pressed steel ones for a pattern.

It’s easiest if you have soft jaws for the chuck, if not try and complete the main features at one set-up and take some care to face the back dead-square if you can’t just part it off.

When you make the central holes, finish them with a boring tool so they are ‘best-possible-fit’ on the shafts.

It sometimes helps to mark the wheels and try turning them say quarter-turns when you first mount them, sometimes with a bit of patience you can find a ‘happy place’ where the (im)balance of each wheel helps cancel out the vibration of the other, worth spending a few minutes experimenting.

Won’t a bench-grinder run too fast for a diamond wheel?

 

 

 

 

[Diogenes]

On Diogenes Said:

 

Won’t a bench-grinder run too fast for a diamond wheel?

I have no idea. I don’t have the specs for my cup wheel. I saw similar models rated at 3500-4000 max RPM. Also another unknown is the actual rpm of the grinder if I remove the heavy wheels. I suppose it has a universal motor and for those the speed changes a lot with the load.

[BazyleParticipant @bazyle]

BTW mild steel and even brass has been mentioned. Rather than use a grinder use either the discs for an angle grinder or better a woodworkers belt grinder fitted with ‘linisher’ belts.

[Sonic Escape]

On Sonic Escape Said:
I have no idea. I don’t have the specs for my cup wheel. I saw similar models rated at 3500-4000 max RPM. Also another unknown is the actual rpm of the grinder if I remove the heavy wheels. <b>I suppose it has a universal motor and for those the speed changes a lot with the load.</b>

Doubtful.  I expect it is a two pole induction motor.

[noel shelleyParticipant @noelshelley55608]

As NDIY has said it is NOT going to be a brush or universal motor, it will be a 2 pole induction motor running at 2800 RPM. As to the diamond wheel it will be fine at this speed or even a bit faster. Noel.

[Sonic EscapeParticipant @sonicescape38234]

Yes, you are right. It is an induction motor. I removed the bottom cover and there is a large capacitor there.

I couldn’t wait for the dressing tool to arrive (up to 21 days shipping time!) and I tried to “machine” the wheel with the diamond tool. Also I tried different positions of the wheel and now there are significantly less vibrations. A cool thing about this grinder is the hole for the vacuum cleaner. The dressing tool created a lot of dust but the table remained clean. Very effective. This is a substantial improvement over the old grinder that was dirtying half the workshop.

The inertia of the wheels is huge. It stops exactly 10 minutes after I press the stop button. I hope the wheels are of good quality. They are very heavy and if somehow one breaks, I don’t think the safety glasses will be of any use. In fact, it would have been better if the opening in the wheel guard was smaller. Only 6-7cm would have been enough.

[noel shelleyParticipant @noelshelley55608]

When it comes to cheap grinders one of the first things to look at is the power or Wattage ! I was given a cheap grinder with a broken switch – the motor stated `150W ! I repaired the switch and tried using it. For drill sharpening or tool grinding it was OK but for removing much metal it was overloaded and would easily stall. I would say minimum of 250W or 1/3 Hp for normal work ! Noel.

[BazyleParticipant @bazyle]

If you stall a grinder you are pressing too hard perhaps because of the wrong wheel or it is glazed. It should only be lightly brushing the tool as it cuts. If you need to do serious shaping use an angle grinder first.

[Sonic EscapeParticipant @sonicescape38234]

Is not easy to measure the power for one grider. This one consumes less than a quarter of its oficial power. But this is when it is idle.

[Sonic Escape]

On Sonic Escape Said:

Is not easy to measure the power for one grider. This one consumes less than a quarter of its oficial power. But this is when it is idle.

Agreed!

Motors don’t deliver a constant power output.   Power depends the amount of work the motor is asked to do, which is determined by the load.

Starting a motor briefly consumes a lot of power because the rotor is accelerated hard to get up to speed for several seconds.  Then the motor idles.

An idling motor consumes relatively little power, basically only what’s needed to overcome bearing friction, to turn the impeller, and spin whatever else is connected to the shaft.

When the shaft is loaded, say by pressing an HSS blank into a grinding wheel, the motor has to do real work – cutting metal.   This causes the motor to draw much more power, and because a proportion of this, about 20%,  can’t be converted to work, the motor gets hot.

It’s how hot the motor can get before burning out that determines it’s maximum power output, which is much higher than the rating.  The rating is the sensible power the motor can sustain for some period of time, not necessarily continuously.  Many motors are only rated to operate in bursts 75%, 50%, or 25% of the time because they save money when the work is intermittent, with plenty of time between operations for the motor to cool down.

One difference between hobby and industrial equipment is industrial machines are far more likely to come with a generously rated continuous motor able to take a beating on a 3-shift factory floor.   The hobby equivalent is rated for intermittent use, because hobby workloads are expected to be more genteel.   The hobby motor produces the necessary power, but only in bursts, and the operator must allow it time to cool down.   Ditto the electronics.  Chaps used to industrial machines might burn out a hobby motor.

A naughty sales trick is quote motor input power rather than it’s output.  Due to inefficiencies, input power is about 20% higher than output, making a motor sound better  than it is.   Definitely misleading, especially when the salesman quotes peak input power, the maximum the motor can take for just a few seconds before something melts.

Short of owning a dynamometer, the most meaningful measurement is power input whilst the machine is working normally.   Power output is very roughly 80% of that.

Dave

 

 

[Trevor Drabble 1Participant @trevordrabble1]

<li style=”text-align: left;”>Jimmy , further to your post of 02/10 , my limited experience in the area of quality grinders is that many , many years ago when I was in the market for a grinder I enquired about an industrial Creusen  grinder . After a  constructive discussion with the sales lady she convinced me that their cheaper ( I THINK approx £160 at that time ) 7200 8″ grinder would more suit my needs. It came with a 5 year guarantee and I have to say she was exactly right.  It has done a fair amount of work , has always spooled up quickly , is vibration free and takes approximately 2 mins to spool down . It even still has it’s original quality wheels . I understand the company are still in business and that Gate Machinery supply their products. I subsequently purchased an extended Creusen polishing spindle but opted against using it for fear of damaging the bearings . It’s still in its box ! Instead I purchased a relatively cheaper ( by Creusen standards ) purpose made polisher of roughly comparable quality from Surtech , from whom I’ve had excellent service. (No connection other than as a satisfied customer ). I hope you find the above information of some use . Trevor.

[VicParticipant @vic]

I’ve got a grinder like the red one. It came from Wickes. The shaft was very poorly machined but it actually ran ok. More recently I’ve got this little one. Only £25 and very compact. I bought it for running up to 4”/100mm Diamond or CBN wheels. As per Harold Halls advice I remachined the shafts down from 1/2” to 12mm to true them up. It seems ok but I’ve not had chance to really use it yet.

[Vic]

On Vic Said:

I’ve got a grinder like the red one. It came from Wickes. The shaft was very poorly machined but it actually ran ok. More recently I’ve got this little one. Only £25 and very compact. I bought it for running up to 4”/100mm Diamond or CBN wheels. As per Harold Halls advice I remachined the shafts down from 1/2” to 12mm to true them up. It seems ok but I’ve not had chance to really use it yet.

It looks very nice. What grit are you using on the two diamond wheels?

[JezParticipant @jez]

I replaced a cheap (B&Q I think) grinder with a Creusen 6″ model which ISTR was quite expensive (for me at the time), having got fed up with not being able to turn the cheapo one into a decent machine by doing all the usual stuff – making new wheel cheeks, and dressing the wheels properly – I even replaced the wheels with quality ones to no avail.  I have never once regretted spending the money.  As you say – quiet, vibration free, and I’m absolutely sure will keep going more or less forever!

[Neil WyattModerator @neilwyatt]

I’ve been lucky with both of mine, in that the bearings ere good and the shafts true.

I’ve had to make better ‘wheel cheeks’ as Jez calls them. For the smal Clarke grinder I used for my T&C grinder, I fitted an aluminium mount for a diamond cup wheel and turned it true with the grinder between the centres already on the shaft. The result is the diamond wheel turns without any detectable vibration.

My bigger grinder is OK but not earth-shattering, I tend to use my belt linisher for lathe tools.

Neil

[Sonic Escape]

On Sonic Escape Said:

On Vic Said:

I’ve got a grinder like the red one. It came from Wickes. The shaft was very poorly machined but it actually ran ok. More recently I’ve got this little one. Only £25 and very compact. I bought it for running up to 4”/100mm Diamond or CBN wheels. As per Harold Halls advice I remachined the shafts down from 1/2” to 12mm to true them up. It seems ok but I’ve not had chance to really use it yet.

 

It looks very nice. What grit are you using on the two diamond wheels?

The one on the front is a 320g plated diamond wheel. The one “stored” on the back is a resin bonded wheel, I’m not sure of the grit now, it may also be 320? I plan to get another plated one at some point, probably 600g.

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