Grinding wheel ..balancing hole?

[John PParticipant @johnp77052]

From Ian Parkin's description of the holes in this grinding
wheel .

"But theres another hole on the other side these are nice clearly
made holes 8mm dia perfectly round and flat bottomed 5mm deep
ones at 12 o clock and the others at 4 o clock on the other side
these are put in during manufacture"

This would seem to suggest that in fact that this wheel has been
very well balanced during manufacture ,the displacement of these
two holes would suggest that it has been done on a dual plane
balancing device.

The obvious thing to do is to use a containment structure around
any new wheel when first running up to speed ,this is something
that i do not only to protect me but also the machine.

If you have viewed the Don Bailey video you will have seen
the large amount removed from the wheel to balance it ,he also
makes the point on the importance of having the wheel balanced.

The chances are Ian that had you not seen these holes the wheel
would have been fitted and used without a thought ,how many
other people peel off the blotters and have a look underneath.

John

[HopperParticipant @hopper]

Pretty sure those are balance holes.

See 9:00 onwards on this video

[David ColwillParticipant @davidcolwill19261]

I must admit that I have found this post quite alarming, so much so that I decided to find out more.

I contacted Saint Gobain and spoke to a chap in their technical department. He said that this is probably part of the testing process.

Basically they sand blast the hole near the centre for a given period of time to give them an accurate indication of the hardness of the wheel. This is not done on all wheels but on one or two in a batch.

He also said that putting the dimple near the centre did not affect the wheel in any adverse way.

I told him that there were two holes in this wheel and he did not seem to think that there was anything to worry about.

I should also point out that I did make it clear that this was not one of their wheels.

Regards.

David

[Ian S CParticipant @iansc]

The biggest concern I have had here in NZ is with one big retailer (Where Every One Gets A Bargain), sells wheels without the blotter discs.

Ian S C

[mechman48Participant @mechman48]

Watched Hopper's video link… well my flabber was well & truly gasted… am now retired & after all my years in the engineering business that's the first time I have seen balancing done this way, including my 18 mo. in the tool room, so as they say 'the proof of the pudding… 'you learn something new every day'… even at my age. Hasn't altered my view though ….'nuff said on the matter from me.

George

[Ian ParkinParticipant @ianparkin39383]

Those holes in the video are very much like mine BUT i'm fairly sure that my holes are not put in after manufacture but as part of a pressing /moulding operation

[Enough!Participant @enough]

Posted by Russell Eberhardt on 24/03/2016 09:20:02:

Why are they there? We can only speculate. They must be intentional. Could it perhaps be to suit some specific machine which has driving pegs on the flanges?

 

I was speculating along the same lines. One thing that would mean is that, if you installed the wheel and then trued/balanced it, you could remove the wheel and later replace it in the same orientation so it shouldn't need re-balancing.

Pure speculation though.

Edited By Bandersnatch on 24/03/2016 15:52:12

[Martin WParticipant @martinw]

Hi

Perhaps they are intentionally there so that the wheel will not be balanced but by adding mass in these holes the wheel can be brought into balance. The benefit of this approach is that the wheel itself doesn't have to have material removed and remains as manufactured. Where the mass is added will be subject to minimum centrifugal/centripetal force and is well below the useable limit if the wheel.

Might be grabbing at straws but an alternative idea.

Martin

[David ColwillParticipant @davidcolwill19261]

See my earlier post. There is no doubt that these holes are not for balancing but to test the wheel. They are put in post manufacture and do not affect the integrity of the wheel. At least this is what I heard in a telephone conversation with a chap called Simon Peel who works for Saint Gobain / Norton. This has put this matter to bed as far as I'm concerned.

Regards.

David.

[David ColwillParticipant @davidcolwill19261]

The process is called erosion testing. There are mentions of it on google but not many.

David.

[John Stevenson 1Participant @johnstevenson1]

Two Pages ago someone said why don't we ask an expert.

So eventually David Colwil rang St Gobain up and a guy called Simon Peel who explained what the holes are for.

Now as one of the largest grinding wheel producers in the west, also incorporating Norton, they should know but David had to repost this again and probably will have to repost it Yet again as 'our' ex-spurts don't agree.

And they you wonder why anyone asks for advise when they know they are going to get 15,837 different answers.

[Steven VineParticipant @stevenvine79904]

Posted by David Colwill on 24/03/2016 18:21:05:

See my earlier post. There is no doubt that these holes are not for balancing but to test the wheel. They are put in post manufacture and do not affect the integrity of the wheel. At least this is what I heard in a telephone conversation with a chap called Simon Peel who works for Saint Gobain / Norton. This has put this matter to bed as far as I'm concerned.

Regards.

David.

Hi David

That was good of you to go to that trouble. I visited the Saint Gobian site (amongst others) and read the literature in my efforts to deduce what the holes were for. That expert verbal opinion you obtained works for me, and allays any of my fears.

Steve

[David ColwillParticipant @davidcolwill19261]

I was bothered by the wider issues.

The general opinion seemed to be that this wheel was unsafe (which I was inclined to agree with) but how many others would have bought and used them and how many of them would have seen this discussion?

I think we can all agree that nobody should be on the receiving end of a dodgy grinding wheel.

Regards.

David.

[Roger HeadParticipant @rogerhead16992]

Perhaps not many people have viewed the video posted by Hopper, but I'm surprised that there hasn't been any comment on the quantity of balancing holes drilled into the wheel used for the demonstration, and which is subsequently mounted and spun up. Have a look at 10:33 in the video – it's only properly visible for about 2 seconds, roughly from 10:32 to 10:34. I was running at full-screen, it may not be so obvious at the normal 'embedded' size. Anyway, I was suitably astonished.

Roger

[mechman48Participant @mechman48]

Posted by Roger Head on 25/03/2016 00:14:24:

Perhaps not many people have viewed the video posted by Hopper, but I'm surprised that there hasn't been any comment on the quantity of balancing holes drilled into the wheel used for the demonstration, and which is subsequently mounted and spun up. Have a look at 10:33 in the video – it's only properly visible for about 2 seconds, roughly from 10:32 to 10:34. I was running at full-screen, it may not be so obvious at the normal 'embedded' size. Anyway, I was suitably astonished.

Roger

Had another look… Flippin Heck! …to put it mildly, I counted 6 in all, I must disagree with the video, there's no way I would put that on a machine… experts or not!

George.

[KWILParticipant @kwil]

Around 8.50mins he take the wheel to the drill press and DRILLS holes to remove material to balance the wheel.

I note that this is only a single plane balance, if it is unbalanced across the wheel, a "couple" will exist which would require balancing on the other face ( think vehicle wheel with balance weights inside and out)

Edited By KWIL on 25/03/2016 10:39:35

[Roger HeadParticipant @rogerhead16992]

Posted by KWIL on 25/03/2016 10:39:06:

I note that this is only a single plane balance …

Yes, but I would expect that most general engineering (and home/hobby) shops only have a simple static balance rig for grinding wheels. For a thin wheel the assumption is made that the density is essentially constant through the thickness of the wheel, and that that any couple resulting from either an original density variation or a variation induced by removing material from only one side, is very much less than the unbalance due to the original static condition.

Of course, once you get to the straight/flared cup style where it becomes a much more important consideration, you are at the mercy of the manufacturer, for who among us has a dynamic balancing machine? Certainly not me.

Roger

[John PParticipant @johnp77052]

Posting by Roger Head @ 11:51

"Of course, once you get to the straight/flared cup style where it becomes a much more important consideration, you are at the mercy of the manufacturer, for who among us has a dynamic balancing machine? Certainly not me."
Roger

Well Roger
If you want one of these you could just make it, these simple
dynamic balancers are commonplace among the model
gas turbine community.

If you log on to the Gas Turbine builders association website
in the public section you will see some examples of these
machines.

One photo in album Balancer of my own balancing machine,
uses sensors from Maplins at 2 for a £1 ,can be used for
turbine rotor balancing or as here a pulley for a machine
or just as easily a grinding wheel.

John

[Roger HeadParticipant @rogerhead16992]

Thanks for the reminder John. I remember one such machine being described maybe 15 – 20 years ago, although what I saw was incomplete. Given that the compressor and turbine in model turbojets are basically thin disks, albeit spinning at very high speed, do these balance machines determine the true compensation points through the 'thickness' of the balance object, or do they simply indicate a 'one side or the other' adjustment?

Anyway, I'll have a look at the GTBA site, I'm sure things have advanced significantly.

Roger

[mark costello 1Participant @markcostello1]

An article or two would be nice but I am across the pond and the exchange rate makes the cost of a subscription horrendous.

[John PParticipant @johnp77052]

Hi Roger

I don't think that development of these hobby balance machines
has advanced by any great amount over this time.

These simple machines only provide a location for adjustment
on both sides as opposed to a true geometric position within
an object.As can be seen from some additional photo's in
the album in the case of these compressor wheels material
is removed from the disc at the rear and the protruding hub
at the front and is shown by the red marks.

These compressor wheels would be considered
as a drum rather than a disc for balancing purposes and
should be balanced in two planes .
These locations may not be the true positions where weight
should be removed but are the only safe places that can
be done .

A similar condition would exist in the example of the cup grinding
wheel as there would be little scope in being able to remove
material to achieve a balanced condition.
An article by Keith Johnson in MEW 180 " Balancing grinding
wheels" shows some method of attaching adjustment weights to
a cup grinding wheel and i would think this would be the best way
forward.
In the next photo on the left is a silicon carbide cup wheel for use on the
Quorn grinder ,it was always out of balance from day one as can be seen
a blob of plasticene placed by trial and error long before i had a
balance machine effected a cure.
The wheel on the right is a 125mm taper cup wheel and has a
balance adjustment visible here at the rear ,this wheel is for the
Universal grinding machine and as such the hub was made
deliberately heavy and as such shifts the centre of gravity of the
whole assembly.
I have only used the cradle in the next photo to balance this.

The one occasion where the balance machine came to the rescue
was with my bench grinder ,it had a secondary function in that it
could be used to settle concrete the vibration was so bad.
This was an internal rotor imbalance problem ,a couple of extra
steel disks were fitted inside on the rotor and the rotor balanced
on the machine ,the result was no more vibrations and round wheels
after dressing.

These simple hobby type of machines will never be able to compete
with the computational type of machines that seem to be available
in the real world and i would think they would be beyond most
people's pockets.

John

[WatfordParticipant @watford]

I still think there is evidence of a former life and that this makes this wheel a very suspect object. See 32 – 12 and some other characters less distinct on a lower label.

Could it be that Chronos are selling New Old stock I wonder?

In passing – I could not find any reference to this type of wheel on their site but this may be that I looked in the wrong place.

Mike

[Ian ParkinParticipant @ianparkin39383]

http://www.chronos.ltd.uk/acatalog/info_C60JV125.html

[WatfordParticipant @watford]

Thanks Ian

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