Removing vibrations from a bench grinder

[Sonic EscapeParticipant @sonicescape38234]

I bought an Optimum GU18 bench grinder and I complained a lot about it here. I was thinking about buying another type. But how to find a good model? I was particular disappointed when I saw the stamped flanges from a Makita GB602. I almost ordered that model. At least my grinder has a more solid flange:

Next on my list was a more expensive Rikon. But I saw a video where a brand new one had significant vibrations before dressing the wheels. I started to believe that there is no grinder, at least not in my price range, which works fine out of the box. If you think otherwise, I would like to know your opinions about this.

So, I decided to try to fix mine. Here is what I did so far:

– I enlarged a little the bearings housing so there is an axial play. Now the wave washer can do its job.

– I measure the runout on the arbor. It is less than 16 microns. Runout on the side of the flange facing the wheel is < 0.1mm.

– Since the grinder vibrates even without wheels I tried to check if the rotor is balanced by placing it on two parallel blades. The test was inconclusive. Or it is perfectly balanced already. The rotor has some aluminium fingers on both ends and some of them were clipped. Maybe somebody tried to balance it? Later I saw that rotor balancing tests are done dynamically. Maybe my method was not sensitive enough.

– The bearings are CQQB. Never heard about that. Does it worth to replace them with a more known brand? I have the tool to remove them and a pair of SKF bearings are cheap.

– I removed the original wheels and mounted only one 150x10mm electroplated diamond wheel. It fits with no play on one flange. Since it is too narrow I mounted the second flange in reverse.

– there is an annoying vibration. I tried to grind a 10×10 HSS blank. It worked reasonably wheel, it didn’t jump when touching the wheel. But the vibrations are noisy.

Next I’m thinking to remove the side cover and to add a diamond cup wheel. On that wheel I could make some threaded holes and by trial and error maybe I can find the position where a screw will balance the whole assembly.

If this works then it means there is a cure. I’ll add two more diamond wheels on the other end and repeat the process.

Any suggestions are welcomed.

[bernard towersParticipant @bernardtowers37738]

you might get a better result by buying known quality wheels

[David George 1Participant @davidgeorge1]

I bought a Cruesen grinder and other than having to reinforcing the tool rest I have not had to do any work on it since I bought it four years ago. I have seen grinders with very poor wheel mounts which were either loose fit on the shaft with insufficient location as they were not wide enough to stop a grinding wheel from wobbling sideways as well as circular loose fit on the shaft and in the grinding wheel.

The wheel holding mounts should have a band on the grip face which is proportionate to the grinding wheel and there should be a card washer to even out any small deviations in the side of the wheel.

I would never use diamond grinding wheels for grinding any steel parts as steel reacts with diamond particles at speed and temperature and don’t work very well.  I always use white aloxite for steel and green grit for tungsten carbide. If the inner wheel supports do not run true it can cause the armature to oscillate side to side quite noisily. I also use a diamond dressing tool to dress the outside of the wheel which also stops bounce if not true.

David

 

 

 

 

[Andrew CrowParticipant @andrewcrow91475]

Many years ago I bought a Bosch 6 inch double end bench grinder and like yours had really bad vibration. I did what  Bernard suggested above and bought 2 new Norton wheels, problem cured.

Just one question, why are you using diamond wheels to grind HSS? Totally unnecessary, A46KV or A60KV grinding wheels are much better.

[noel shelleyParticipant @noelshelley55608]

If all you want to do is sharpen the axe then a cheap grinder might do, but for precision work you need to spend money – on both the grinder and the wheels. If the motor alone is unbalanced then give up on that one ! A good wheel will cost more than a cheap grinder. White wheel for HSS, green for carbide and diamond only for carbide. Good luck. Noel.

[Andrew Crow]

On Andrew Crow Said:

Just one question, why are you using diamond wheels to grind HSS? Totally unnecessary, A46KV or A60KV grinding wheels are much better.

The only reason is to avoid dust.

On David George 1 Said:

I bought a Cruesen grinder and other than having to reinforcing the tool rest I have not had to do any work on it since I bought it four years ago.

How are the flanges of that Creusen grinder?

On David George 1 Said:

I would never use diamond grinding wheels for grinding any steel parts as steel reacts with diamond particles at speed and temperature and don’t work very well.

I know that. But anyway I have this diamond wheel. It is electroplated so maybe it cools faster. I’ll give it a try. Anyway I don’t grind to much. I’m thinking also to put a coarse white wheel on the other side. To shape the HSS blanks. And the diamond one I’ll use it just for a few seconds for a final touch.

On noel shelley Said:

If the motor alone is unbalanced then give up on that one ! A good wheel will cost more than a cheap grinder. White wheel for HSS, green for carbide and diamond only for carbide. Good luck. Noel.

If you know a grinder that has machined flanges, 20 or 32mm arbor, cost bellow 300 euro and is guaranteed to run silent and have a balanced rotor I’ll order it now.

[John HaineParticipant @johnhaine32865]

I have 2 ELU grinders which run nearly silently.  C BN wheels are very good.

[Andrew TinsleyParticipant @andrewtinsley63637]

Many years ago, I purchased an 8″ Warco grinder which was made in Roumania. Absolutely silent and vibration free. When I needed new wheels, I purchased Norton ones. It wasn’t expensive and I have had over 35 years use from it. It still looks and performs like new.

Subsequent small Chinese grinders (modified for tool and cutter grinders) have been a nightmare to get working properly. Harold Hall must have been lucky with his prototype version.

Andrew.

[John MCParticipant @johnmc39344]

I have two bench grinders, both 200mm (8″).  The first is an “Alpine”, ran smoothly enough.  The second, a “Clarke”, vibrated rather badly from new.  To stop this I used two old lathe top slides bolted together with a diamond dresser in the “tool” position.  I used this setup to true the face and sides of the wheel, this improved matters considerably.

Over the years I’ve replaced worn out wheels on both machines a few times, they have all needed considerable truing, regardless of quality.

There is some vibration after truing, well within acceptable limits for a bench grinder, I think.

I’ve always assumed this to be variations within the wheels, inconsistent density?   I, again, assume this is why wheels on grinding machinery such as surface and cylindrical grinders need the wheels balancing before use?

 

 

[Sonic EscapeParticipant @sonicescape38234]

I made 6 holes in the diamond wheel to add some weights to try to balance the rotor.

A small weight (an M3 screw + a large washer + nut) on hole number 1 produce a slight improvement. Adding weights on any other position increases the vibrations.

I added a piezoelectric disc on the grinder to have some visual indication of the magnitude of the vibrations. In this was is easier to find the right spot. Fortunately such a buzzer output is few hundred millivolts and it is easy to spot on the scope without any amplification.

This is the sensor output without any weight:

There is an strong oscillation with a period of ~2.5s. I can hear it very well. Adding a weight on hole 1 cures a little this oscillation but the average vibrations are higher:

As I suspected I’m afraid is not possible to balance the rotor by adding weights 10cm away from it. I need to find a way to add a screw directly on the rotor.

[Pete RimmerParticipant @peterimmer30576]

Regarding the pressed steel side plates – I recently had to swap a wheel out on one of my bench grinders. When I fitted the new wheel, with the proper blotters it wobbled visibly. I put the cheek plates on my surface grinder and ground the centre a tiny bit until there was a flat land showingall around the hole, put it all back together and the wheel ran lovely and true.

[Andrew Tinsley]

On Andrew Tinsley Said:

Many years ago, I purchased an 8″ Warco grinder which was made in Roumania. Absolutely silent and vibration free. When I needed new wheels, I purchased Norton ones. It wasn’t expensive and I have had over 35 years use from it. It still looks and performs like new.

Subsequent small Chinese grinders (modified for tool and cutter grinders) have been a nightmare to get working properly. Harold Hall must have been lucky with his prototype version.

Andrew.

I have an old 6″ Warco “heavy duty” grinder, I bought second hand. It is virtually noiseless apart from a deep hum.

I suspect these old Warco grinders may have been Taiwanese.

[southernchapParticipant @southernchap]

Have you considered buying an old school second hand bench grinder.

Old bench grinders are pretty reasonably priced on eBay, and they’re likely to be better manufactured than the less expensive modern grinders.

 

[southernchap]

On southernchap Said:

Have you considered buying an old school second hand bench grinder.

Old bench grinders are pretty reasonably priced on eBay, and they’re likely to be better manufactured than the less expensive modern grinders.

 

I did. That is plan B. Actually I’m waiting to arrive an old Bosch PSM 125. I think they were made in GDR. I like it because it is small. I saw exactly the same model sold also by Flott. That is a good quality German brand. I have high expectations.

[Graham MeekParticipant @grahammeek88282]

Sonic,

You do not say if the Grinder is bolted down during your tests.

My Black & Decker Bench Grinder has plain bearings and is very smooth running without the wheels. Having the wheels on amplifies the Cyclic hum of the Single Phase motor. This is worse when the machine is not bolted down to something solid. The wheels do not only want to be balanced statically but they also need to be running true, ie not a wobble plate.

Regards

Gray,

[Graham Meek]

On Graham Meek Said:

Having the wheels on amplifies the Cyclic hum of the Single Phase motor.

In the quest for ultimate smoothness, is there any advantage in buying a three phase machine and VFD?

[Graham Meek]

On Graham Meek Said:

Sonic,

You do not say if the Grinder is bolted down during your tests.

My Black & Decker Bench Grinder has plain bearings and is very smooth running without the wheels. Having the wheels on amplifies the Cyclic hum of the Single Phase motor. This is worse when the machine is not bolted down to something solid. The wheels do not only want to be balanced statically but they also need to be running true, ie not a wobble plate.

Regards

Gray,

I can’t bolt it because I don’t have space for it. I put it on the desk only when I’m using it. What is cyclic hum on a single phase motor?

[Graham MeekParticipant @grahammeek88282]

Hi Sonic,

A single phase motor does not run smoothly due to its construction. There is an electrical term for this but due to old age this escapes me at the moment. The motor construction does not produce a constant field torque as does the 3 phase counter part. This then translates into a cyclic speed variation.

I have my bench grinder bolted to a board which I can hold in my Woodworking vice. When not in use I slide it out of the way.

Regards

Gray.

 

[PeteParticipant @pete41194]

100% agree with what Gray has said about 3 ph motors versus any single ph motor I have in my shop. Possibly one of the high end specialty motors used on single ph. tool post grinders might be one of the few exceptions? In my personal opinion, the old and really over built single ph motors were a lot smoother and vibration free than most modern motors today. So the mention of finding an old but good condition grinder might be another good option.

Although I did buy a 6″ single ph. grinder made or at least labeled as a General here in Canada about 20 years ago that’s unfortunately no longer available, and about $200 back then. Right out of the box it was very smooth with almost no vibration at all. For items like lathe tools and unless your grinding something like 25 mm sized tool blanks, a 6″ size grinder should be enough. And a lot cheaper when buying new wheels compared to the 8″ & 10″.

For high rpm and HSS, CBN wheels or aluminum oxide are what you probably want. Because of the almost instant high heat created at the tool edge, diamond starts to break down when reacting with that heat and carbon in the steel. Not instantly, but it will happen. Your wheel life is going to suffer. And all those stamped flanges are worthless, there no where flat or rigid enough. Machine new ones from bar stock. Just don’t make anything too tight and start adding any extra stress to the wheels.

George Thomas mentioned in one of his books that even a sharp but roughly ground tool will not produce a fine surface finish. That’s always stuck with me, so I also have a 600 grit bench block I use for the last final honing and touching up a tool. You can go a long time without any regrinding with one of them or something similar.

Want something even better for final lapping lathe tools to fairly precise angles? Google the term Goniostat and then search images. A once common tool for lapping compound angles on tools used on ornamental turning lathes. Fairly easy to replicate today with a bit of effort. They used oil stones, and moving the Goniostat holding the tool on a piece of plate glass, but today’s diamond laps might be even better.

 

 

 

 

[DC31k]

On DC31k Said:

On Graham Meek Said:

Having the wheels on amplifies the Cyclic hum of the Single Phase motor.

In the quest for ultimate smoothness, is there any advantage in buying a three phase machine and VFD?

Logic suggests that would be an admirable approach !

… my only caveat being:

Resist any temptation to over-speed the wheel.

MichaelG.

[Graham MeekParticipant @grahammeek88282]

In my experience a “Honed” edge will outlast a ground edge on a tool. It will also improve the finish on the work.

Below is something I made a few years back now. By swapping the stones the keenness of the edge can be changed. The stone can also be changed for a diamond faced one and carbide tools touched up.

 

Regards

Gray.

[PeteParticipant @pete41194]

WOW Graham, that’s simply beautiful work. 👍👍👍

[Graham Meek]

On Graham Meek Said:

In my experience a “Honed” edge will outlast a ground edge on a tool. It will also improve the finish on the work.

Below is something I made a few years back now. By swapping the stones the keenness of the edge can be changed. The stone can also be changed for a diamond faced one and carbide tools touched up.

 

Regards

Gray.

This looks super nice!

[derek hall 1Participant @derekhall1]

Many years ago I attended the disposal auction of the late great Tubal Cain aka Tom Walshaw.

Before the auction started I had chance to look at his Myford lathe and a nearby tin of his HSS lathe tools, all of the important ground faces on the lathe tools were finished like a mirror.

Tubal Cain knew that simply grinding the faces of HSS tool will not guarantee the best machined finish, the lathe tool needs further treatment such as honing.

[Sonic EscapeParticipant @sonicescape38234]

Today arrived the Bosch PSM 125. It is an old grinder made in DDR. It sounds like this:

Bad bearings. No problem, I replaced them with new ones. Now is more quiet, you can’t tell from the video. But vibrations are the same. It’s a pity because I like how small it is. Bad luck …

I start to seriously consider making an arbor for my diamond wheel and use it on the lathe. I can also use it at lower speed + I don’t waste the space in my tiny workshop with poor quality grinders.

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