| Digital scale woes.. #143312 05/14/08 03:35 PM 05/14/08 03:35 PM |
Joined: May 2003 Posts: 4,451 West coast of Norway Rolf_Nilsen OP
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Posts: 4,451 West coast of Norway | Had a scary experience using digital scales for measuring out epoxy today. They are not always the most reliable, but fortunately we noticed before we began glassing the outside of the hull half we are working on: http://woodastic.blogspot.com/2008/05/dont-trust-digital-scales.htmlNow we are considering an old "manual" set of scales with counterweights. Would be nice if we could find a set instead of being unsecure about the digital scales. Our epoxy are metered by weight (100:32) so we need some good scales are a accurate weight, without breaking the bank. | | | Re: Digital scale woes..
[Re: Gato]
#143314 05/15/08 01:23 PM 05/15/08 01:23 PM |
Joined: Sep 2007 Posts: 531 Lake Murray SC FasterDamnit
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Posts: 531 Lake Murray SC | So-
Sounds like you have been using a scale for a couple of years without calibrating it? Either have it done professionally or buy some NIST standard weights to do it yourself. Do you make the some proclamation when your car breaks due to lack of maintenance? Stuff fails if it is not cared for... And sometimes it fails for no good reason.
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| | | Re: Digital scale woes..
[Re: Rolf_Nilsen]
#143316 05/15/08 05:46 PM 05/15/08 05:46 PM |
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Posts: 531 Lake Murray SC | Why the Whoa? Just giving my .02c. The correct use is to either have it calibrated regularly or use a set of calibrated weights before use. If the downside of inaccurate weighing is expensive in time and materials then maybe more money should be put into the balance or the weights to check it before use. Mettler/Toledo and Ohaus make nice balances and scales. and as a helpful hint, not a slam, use the term electronic balance or scale in your article in place of electronic weight. It will make more sense. No slings or arrows intended. Just info. from a former metrologist. http://www.northshorecare.com/lab-balances.html | | | Re: Digital scale woes..
[Re: Kevin Cook]
#143322 05/16/08 07:15 PM 05/16/08 07:15 PM |
Joined: Aug 2007 Posts: 190 lesburn1
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Posts: 190 | Rolf, I have been using inexpensive digital scales a long time. But I always keep 2 or 3 on hand so I will always have a back up. Same thing with vacuum pumps. Half way into a big lay up job is no time for either item to quit on you.
I mix batches anywhere from 100g to 3kg and find scales with a 1g accuracy (or is the word precision) do fine. The specification on a typical bulk epoxy resin (Dow Chemical DER 330) has the epoxide equivilent weight between 176 and 183. It is this property that determines the number of cross linking sites available for a given curing agent. Curing agents too have variability in their amine weight. So, even you have a super accurate scale, what you are mixing has some variability and that dosen't do much good. I have to agree! I was involved in a thread over at SA recently about vacuum pumps. And while I built my own vacuum pump and reservoir, I keep a vacuum generator (as a backup) plumbed into the system at all times!!
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