What level G??
What level G??
(OP)
Folks, if a 14" diameter body, rotating at 1000 - 1500 RPM, weighing about 40 pounds is balanced down into the 0.1 g - cm. range, what grade of G is that?? (Is there one?)
BK
BK
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RE: What level G??
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Eng-tips forums: The best place on the web for engineering discussions.
RE: What level G??
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Eng-tips forums: The best place on the web for engineering discussions.
RE: What level G??
ISO G1.0 corresponds to unbalance roughly 6*W/N. i.e.
U/(inch-ounce) = 6 * (W/lbm) / (N/rpm)
= 6 * 40 / 1250
= 0.192
0.192 inch ounce would correspond to ISO G1.0
You have (0.1*gram*cm)* ounce/(29*gram) * inch/(2.54*cm) = 0.00136 inch-ounce.
0.00136 inch-ounce / 0.192 inch ounce =0.007 which means you are 0.007 times the limit for G1.0 which places you around G0.007
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Eng-tips forums: The best place on the web for engineering discussions.
RE: What level G??
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Eng-tips forums: The best place on the web for engineering discussions.
RE: What level G??
On the other hand, that is about the sort of precision we measure driveshafts to, at 5000 rpm. But we'd never claim to hit 1 g cm residual unbalance repeatedly. more like 10.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: What level G??
The spec was something we were handed; we were not involved in deciding if it is req'd. From what I can see, they appear to need it.
BK
RE: What level G??
>>REALLY<< Attaining G1.0 is much more than a few calibration runs in a balance machine, and I think claiming those low numbers should be done only after some serious soul searching, and tolerance analysis. I often look at Table 1A on page 4 and compare the mechanical centering repeatablity of the balance arbors, parts at assembly, etc, etc, etc. Over 1000 rpm ISO G 2.5 simply does not grow on trees. I would submit that other ISO documents recognize what a problem low G balancing is by the suggested adoption "inspection tolerance" of +15% for G-16 - G2.5, +20% of ISO G1 and +30% for G 0.4
RE: What level G??
Now they tell us they never have made one that meets these specs. Well golly, imagine that.
BK
RE: What level G??
The data seems pretty clean in the 1X area, but there is quite a bit of signal, with minimal pattern (no clear ___ X's) in the 80 - 160 Hz range.
Does it make sense to look at this broad a spectrum, in order to merely achieve balancing? Is it not normal that balancing looks exclusively or chiefly at the 1X data?
BK
RE: What level G??
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: What level G??
Regards to all, and I tip my hat again to eng-tips.
BK