I remember reading a lot of technical books back in the early '50's - I wanted to 'get into' engineering etc activities.
In those days small electrically powered tools were less common and geared, hand-driven, bench grinders were the norm for home mechanics: the writers stressed the need, before finally tightening the locking nut(s), to turn the wheel on its spindle until the least dis-balance could be detected.
Perhaps we should do something similar today - or are even the cheapest bench grinders of today near enough balanced already?
Eric Lougheed
________________________________
From: Rick Sparber <rgsparber@aol.com>
To: "gingery_machines@yahoogroups.com" <gingery_machines@yahoogroups.com>
Sent: Wednesday, 20 July 2011, 14:16
Subject: Re: [gingery_machines] new article available: An Experimental Way toStatically Balance a Bench Grinder
Chuck,
I believe you are describing a means of dynamically balancing the wheel. IMHO, it is easy to statically balance it but to get rid of those damn resonances, it has to be dynamically balanced. I'm still looking for a low tech way to do that.
Dynamic balance involves both the position of the weight relative to the center of rotation and the distance along the center of rotation from some arbitrary point. This is why I say that wobble is more about dynamic imbalance and should be minimized. But there must be other sources.
I'm sure you are right about the paper. It only has to be thick enough to prevent the individual grains on the surface of the wheel from directly touching the washers. As you point out, that would cause a point contact and concentrate the force which could crack the wheel.
Rick
Rick.Sparber.org
On Jul 19, 2011, at 9:09 PM, Chuck Kuecker <ckuecker@ckent.org> wrote:
> Out of lurk for a bit...
>
> When I worked at NTN America a few years ago, I had to set up and
> maintain several CNC grinders. The machine that ground the outside
> surfaces of the housings for the bearings we made had a wheel about two
> feet in diameter when new, and up to four inches wide, belt driven by a
> big three-phase motor. They were keeping sub-micron tolerances.
>
> The wheel was dressed in the machine with a diamond coated form dresser
> driven by a separate spindle, and the balance of the wheel was actively
> controlled by a computer driving a motorized balance weight attachment
> on the end of the wheel spindle. This was both powered by and
> communicated to via an induction coil in the frame of the machine.
>
> When a new wheel was brought up, the unbalanced wheel's vibration was
> easily felt with a hand on the machine frame. The computer used inputs
> from an accelerometer on the spindle housing to adjust the weights to
> minimize the vibration. The balance cycle took less than a minute. We
> never dressed a wheel until the balance cycle ended.
>
> There were paper gaskets between the wheels and the clamping surfaces.
> We kept a few spares in case one got ripped. The wheels were attached
> with a number of big Allen screws to hold the outer clamping disk to the
> end of the spindle. The balance gadget bolted to that outer disk.
>
> My take on the paper was to eliminate point contacts which would create
> large stresses in the wheel.
>
> Chuck Kuecker
>
> On 7/19/2011 10:17 PM, David Frantz wrote:
>> Hi Rick;
>>
>> That reply took a long time to show up in the forums! Must of got lost.
>>
>> When I wrote that I was a busy guy, now I'm on my back with a broken leg. So that means few excuses for not reading your article. So I hope to get to it real soon.
>>
>> In any event I think you are missing a few points here. First it doesn't matter if the steel washers compress or not, they are there to spread out the load created by the nuts. However the steel washers should never be used alone, there should always be a paper or fiber washer between the wheel surface and the steel washer.
>>
>> In tool rooms it is common to see a toolroom grinder with a bunch of grinding wheels hung near buy. With those wheels there is usually a collection of washers hanging. It has been considered good practice to use such paper or fiber washers for as long as I've been around.
>>
>> I don't want to dismiss the importance of balancing the wheels as it can have a huge impact on usability. I'm more concerned about safety.
>>
>> Now we are about to digress and rely on my failing memory On really large grinders they had a device that would attach to the grinders spindle to balance the wheel. I never got the low down on what the specifics of the device was but I was left with the impression it was filled with shot. This will require some research but it would be nice to have a solution that was more or less automatic.
>>
>>
>>
>> Sent from my iPad
>>
>> On Jul 19, 2011, at 8:18 PM, RG Sparber<rgsparber@aol.com> wrote:
>>
>>> David,
>>>
>>> Andy's washers are very different from the ones I have so it is not an
>>> issue. My washers are twice as thick and do not compress. The ones I made
>>> have the same contact area on the wheel but are a much closer fit to the
>>> shaft. The backing washer is part of the insert and greatly reduces wobble.
>>>
>>> I hope you get a chance to read the article so you can see the bigger
>>> picture.
>>>
>>> Rick
>>>
>>> -----Original Message-----
>>> From: gingery_machines@yahoogroups.com
>>> [mailto:gingery_machines@yahoogroups.com] On Behalf Of David Frantz
>>> Sent: Saturday, July 16, 2011 5:22 PM
>>> To: gingery_machines@yahoogroups.com
>>> Cc: gingery_machines@yahoogroups.com
>>> Subject: Re: [gingery_machines] new article available: An Experimental Way
>>> toStatically Balance a Bench Grinder
>>>
>>> Hi Rick;
>>>
>>> I haven't had a chance to read your new piece yet so I don't know exactly
>>> what is being described there. However I totally agree with Andy those
>>> washer have a purpose, you really want to avoid interfering with or removing
>>> those washers.
>>>
>
>
>
> ------------------------------------
>
>
>
>
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