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.

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