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 Post subject: SG Machine
PostPosted: Tue Dec 20, 2016 12:24 am 
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I am wondering what the best way to set up your own home made SG machine is. I have access to a regular one but would like to have a small set up that I can easily take with me when I travel. The regular one is a calibrated scale and I leave it safe and sound in the lab. I have looked and seen different ways to set one up. What has been your experience. Thanks for any help. As a new member I don't seem to be able to do a search yet so am unable to quickly do a search on the subject. :)


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 Post subject: Re: SG Machine
PostPosted: Tue Dec 20, 2016 1:49 pm 
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There have been lots of design sketches here for homemade SG attachements. You can make them from the sketches very easily.

For it to be useful you should have a scale that reads to one milligram or 0.001gram. These are available fairly inexpensively these days. If you buy a cheapie which can be advisable for a field based unit make sure you check it's calibration using weights you have checked with your "good" balance.

Much to my surprise some really really cheapo scales were quite accurate. They are usually specified as plus or minus two or three digits in the miligrams place and several I have checked were more accurate than specified.


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 Post subject: Re: SG Machine
PostPosted: Thu Dec 22, 2016 12:11 am 
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Thanks for your reply G4Lab. I have browsed the internet and seen some set ups. I already have a suitable scale. Are you able to post some links to some set ups on this site and I am unable to perform a search. I'm interested in the different set ups and why people think they are best. I realise they are all the same in theory but there might be a handy hint or two that might come in useful. I normally use trade certified scales but that is one I don't want to move as it's set up and levelled etc. Just looking for something simple to use, just in case.


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 Post subject: Re: SG Machine
PostPosted: Thu Dec 22, 2016 3:12 pm 
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One does not need an accurate scale of any kind to measure SG. One can simply use a stick, a piece of thread, a couple of washers and istructions for making a Hanneman Relative Density Balance, which I will send to anyone who sends their name, address, and a self addressed stamped envelope to me at
264 Soledad Dr. Monterey, CA 93940.

Unlimited Range or Size * No Calibrated Weights Needed * Direct Reading

Hint: It is all based upon balancing momets. :D :D


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 Post subject: Re: SG Machine
PostPosted: Thu Dec 22, 2016 5:51 pm 
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One does not "need"anything except air water food shelter and maybe love.

However the methods I refer to are how everybody on the planet does it.
It is true it can be done with the Hannemann balance but very few people use that method because it is not as easy as using a properly designed balance and SG attachment which makes it a snap.

These also are the methods mentioned in most chemistry and mineralogy books although the latter sometimes will mention unconventional things like the jolly spring balance but that still is more closely related to the regular method than Dr. Bill's variation of the "steelyard" method. Every major gemological standards organization uses the methods I am talking about. Not just GIA but everyone else too.

With very accurate scales available for less than Mineralab charges for their knock off of Dr Bill's SG balance these alternatives are not really necessary anymore. If you are going out into the wild and don't think you will be back to buy batteries then maybe it's worthwhile to buy or build a Hannemann balance which is a nice way of avoiding getting a real balance. I note that Dr. Bill did used to have a mechanical balance at his house that could read to less than a milligram. It was a single pan Ainsworth Right A Weigh mechanical. Built in Denver Colorado. One of the few balances worthy to compete with Mettler and Sartorius.

The Hannemann balance is a VERY nice piece of design. I never bothered to build one because I snagged a 10 microgram reading two pan balance and a five diigit mechanical , both in the seventies. Both take SG readings very easily using weights and not having to rely on the accuracy of what amounts to a printed slide rule. Of course now with digital electronic balances even those are not loved anymore. I sold one to a guy in central america who wanted to weigh out quinine with it. (the single pan mechanical , almost exactly like the one dr. Bill has) I still have the double pan which I will sell to a collector pretty soon.


Last edited by G4Lab on Fri Dec 23, 2016 3:26 am, edited 2 times in total.

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 Post subject: Re: SG Machine
PostPosted: Thu Dec 22, 2016 10:15 pm 
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I was thinking about something along these lines. Simple to make and use. Any thoughts.


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 Post subject: Re: SG Machine
PostPosted: Fri Dec 23, 2016 3:22 am 
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That should work great. I was not familar with that layout until someone mentioned it years ago , here , and Dr. Brian the physicist said yes it works. In the meantime I have tried it and yes it works quite well and is a bit simpler to make. Adaptable to any balance.


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 Post subject: Re: SG Machine
PostPosted: Fri Dec 23, 2016 8:28 pm 
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Check out my sketches that WilsoninTexas was kind enough to post for me. They show how to make a really accurate S.G. balance. I also included a graph showing the variation of water density with temperature. Anyone reasonably handy should be able to make one in a couple of hours.


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 Post subject: Re: SG Machine
PostPosted: Fri Dec 23, 2016 9:19 pm 
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Thanks Alan F. Where would I find those sketches. Would you be able to post a link for me. Also thanks G4Lab for your feedback.


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 Post subject: Re: SG Machine
PostPosted: Sat Dec 24, 2016 8:04 am 
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Hi, look on the "Gem Equipment" thread under the title "Alan F's drawings for specific gravity". From the number of views it seems pretty popular and I haven't had many queries, but if there is anything unclear or a step you think I have missed, don't hesitate to ask.


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 Post subject: Re: SG Machine
PostPosted: Sat Dec 24, 2016 9:44 am 
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viewtopic.php?f=11&t=21479

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 Post subject: Re: SG Machine
PostPosted: Mon Dec 26, 2016 6:34 pm 
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So can someone explain how you use this one?
It looks like you put a cup of water directly on the balance and then you weigh the stone in the cap suspended in the cup of water.
Is that right?


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 Post subject: Re: SG Machine
PostPosted: Mon Dec 26, 2016 8:05 pm 
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You are correct and I didn't like it either the first time I saw it. Dr. Brian promised that it would work and it does.

You weigh the water including the specific gravity basket. which is supported from over head. Then you drop the stone in(onto the basket) and it displaces its equivalent volume of water which depends on its weight and SG. The reading will go DOWN by that amount because that amount of water is being supported by the overhead structure. That is you weight of an equivalent volume of water of water. (SG = 1)

You also have to get a weight for the stone in air. and calculate accordingly.

It saves you having to make a bridge for the beaker of water.


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 Post subject: Re: SG Machine
PostPosted: Tue Dec 27, 2016 7:46 pm 
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G4Lab wrote:
You also have to get a weight for the stone in air. and calculate accordingly.

It saves you having to make a bridge for the beaker of water.

Don't waste your time or money. It is easier, faster, cheaper, and not limited by size, if you don't have to weigh anything. Use Specific Density. :D :D


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 Post subject: Re: SG Machine
PostPosted: Tue Dec 27, 2016 9:27 pm 
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At the risk of pointing out the obvious, one of the four C's, that the entire gem trade is built on is Carat Weight. (0.01 ct=2mg)
Internationally accepted standards for weighing gem materials generally call for at least milligram sensitivity and sometimes more (millicarat= 0.2mg)
If for example, one would like to have ones appraisal service accredited by the American Gem Society or the Accredited Gemologists Association or meeting the standards of the International Committee on Harmonization of Gemological Labs or even if one just wants to take Gem ID from GIA or any of the other real schools,,one has not only to have an accurate balance for SG determination, but also for the actual weight of the stone and or the piece of jewelry.
This is standard practice for jewelry stores as well. If you are buying and selling diamonds and other stones by the carat at very high prices per carat you need a decent balance.

No one is arguing that the Hannemann steelyard doesn't work.(http://www.isasc.org/Tutorial/Scale-Typ ... #Steelyard) But if I came to an appraisers office and they had one and no real balance I would certainly turn right around. Weight/Mass and Density determinations are fundamental gemological measurements. Hobbyists can afford to use tinkertoys provide Gem ID data points. Professionals have to have real balances, sometimes ones that are legal for trade.


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