Re: [ATM] DC Motor for grinding machine question

[GARY FUCHS <gary@rcn.com>]

(First, thanks for the VFD info. That's on my Christmas list.)

Don, Mike, et al?,

I'm probably in over my head here, but why wouldn't the periodic error I think you're talking about actually be beneficial, making the machine's action just slightly irregular and more human-like? Don't typical machines have at least two places where periodic error would occur, but not at the same time?

Gary Fuchs


>
> Mike,
>
>
>
>We could test that theory.  Perhaps using technique mentioned by Texereau in
>"How to make a Telescope", the Lyot phase-contrast method. One could do a
>spatial spectrum analysis on the machine polished surface using the Lyot
>phase-contrast method to detect any periodic contribution due to the regular
>arraignment of balls in a ball bearing race. Since spindle rpm is known and
>the ball bearing race configuration is known, one would know what spatial
>frequencies to surface roughness to look for.
>
>
>
>
>
>Don Clement
>
>Running Springs, California
>
>
>> Don,
>>
>> Don Clement wrote:
>> > There is no contradiction.
>>
>> Yes, there was.  In one message you said there was no effect, then in
>> your next message you said there was.  Maybe it was a typo.  I was
>> just trying to follow your reasoning.
>>
>> > Using a FFT Dynamic Signal Analyzer
>> > (such as the Agilent 35670A) and the proper sensors one can see the
>> > effects of rotating equipment using ball bearing races. In fact,
>> > one can determine detailed information on the ball bearing race
>> > parameters (such as number of balls, etc) by examining the spectrum
>> > of rotating machinery. There is no doubt that regular spaced balls
>> > in ball bearing races add some periodic component to a rotating
>> > spindle of a polishing machine.
>>
>> I have no doubt you are correct in that statement - my day job is
>> signal processing and I play with FFTs all day.  I also have no doubt
>> that the vibrations affect the quality of finish in metal working, and
>> I found your post about 3-phase motors and speed controllers very
>> interesting and useful.
>>
>> However, I debate your assertion that the miniscule vibrations will
>> cause measurable effects on the surface of a mirror being polished on
>> a machine.  I certainly haven't detected any on my DC motor/variac
>> setup, or on a machine that uses a PWM controller.
>>
>> I guess you'll end up with a grinding machine that can double as a
>> decent turntable for playing vinyl, should your Marantz experience
>> problems.  :)
>>
>> (Yes, I know vinyl often sounds better.)
>>
>> Mike Lockwood
>>
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>>
>
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