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Scales for measuring SG

Legion

Staff member
In another thread we were talking about the trials of using regular kitchen scales when trying to get an accurate specific gravity measurement on hones.

The problem is, proper scientific scales with a reading range as broad as we need it are bloody expensive.

I've been looking at coffee scales as a possibly more accurate alternative. The ones I've been seeing have a range of 0.1g-3kg, which should be fine. And coffee beans are light, so you would think scales designed for that purpose are accurate, but are they? Would they be better than equivalently priced kitchen scales, which, at least on the ones I have at home, might vary 2g from one day to the next. I could live with that on a big stone, but 2g error when the stone is only 100g makes the result pretty useless.

Does anyone have a recommendation or ideas before I pull the trigger on something?
 
This is the most reasonable one that I could find. Seems like it would be useful for a range of things if you’re a bit of nerd like myself. It also has a calibration feature and levelling feet. Calibration masses are extra.

Not something you really need but it could be fun to play around with. Other models seem to have more elaborate features which you pay for and I doubt I would ever use. This is pretty much a straight up scale or “balance” as they are known in the field.

The 4200 model seems like the sweet spot. The ones with a lower max weight are more precise but are also more limited in what you can use them for.

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I have this one that measures to 0.001g but the max weight is 10g. It’s designed for weighing diamonds. Not much use for whetstones.

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Legion

Staff member
This is the most reasonable one that I could find. Seems like it would be useful for a range of things if you’re a bit of nerd like myself. It also has a calibration feature and levelling feet. Calibration masses are extra.

Not something you really need but it could be fun to play around with. Other models seem to have more elaborate features which you pay for and I doubt I would ever use. This is pretty much a straight up scale or “balance” as they are known in the field.

The 4200 model seems like the sweet spot. The ones with a lower max weight are more precise but are also more limited in what you can use them for.

View attachment 1607335

That looks pretty good, but a bit more than I want to pay, with several features I would never use.

I'm leaning more towards something like this.

 
That looks pretty good, but a bit more than I want to pay, with several features I would never use.

I'm leaning more towards something like this.

That’s a much better price point. This Kmart cheapy is alright for 5 bucks. It puts you in the ball park. You can roughly check the accuracy with a beaker and water. It seems to put you within +/- 2g. Plenty good for its intended purpose but not exactly a precision instrument.
 

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Legion

Staff member
That’s a much better price point. This Kmart cheapy is alright for 5 bucks. It puts you in the ball park. You can roughly check the accuracy with a beaker and water. It seems to put you within +/- 2g. Plenty good for its intended purpose but not exactly a precision instrument.
That's almost identical to the one I've been using. I need something that can be calibrated.

Plus something that is "just mine" means it will get looked after. I'll find the wife's one sitting in the kitchen with a bag of groceries on top, or stuffed into a full draw, and that probably explains why it gives a different reading every time.
 
In another thread we were talking about the trials of using regular kitchen scales when trying to get an accurate specific gravity measurement on hones.

The problem is, proper scientific scales with a reading range as broad as we need it are bloody expensive.

I've been looking at coffee scales as a possibly more accurate alternative. The ones I've been seeing have a range of 0.1g-3kg, which should be fine. And coffee beans are light, so you would think scales designed for that purpose are accurate, but are they? Would they be better than equivalently priced kitchen scales, which, at least on the ones I have at home, might vary 2g from one day to the next. I could live with that on a big stone, but 2g error when the stone is only 100g makes the result pretty useless.

Does anyone have a recommendation or ideas before I pull the trigger on something?


So I'm reasonably certain about this, on the kinds of normal kitchen scales we use - the accuracy decreases as they approach the limit of their weight range.

I've found that even on cheaper 0-3kg scales small stone readings are quite accurate, it's larger stones where you're trying to measure a kilo rock suspended in a litre of water where you start getting some error. And if you get kitchen scales with a 0-5kg range they seem pretty accurate for any stone.

YSMV.
 

Legion

Staff member
So I'm reasonably certain about this, on the kinds of normal kitchen scales we use - the accuracy decreases as they approach the limit of their weight range.

I've found that even on cheaper 0-3kg scales small stone readings are quite accurate, it's larger stones where you're trying to measure a kilo rock suspended in a litre of water where you start getting some error. And if you get kitchen scales with a 0-5kg range they seem pretty accurate for any stone.

YSMV.
This might be true. So you measure the rock, pretty accurate. Measure the container of water, Tare, add rock… getting pretty heavy and screwy. Now the relationship between the two (on which we do our math) is all skewed and bung.
 
I like the idea of having a nice balance in the kitchen that can measure down to 0.01g, but they do cost a lot.

Even good balances are subject to variarions. That's why measurements should be done in at least triplicate and the average used if you really need to be accurate.

I would prefer a balance accurate to an order of magnitude or two more than required. That should put your variations outside of the range that you are concerned with.

Check that video again, I am sure the balance with the measuring cylinder on it lost 0.2g from the reading after the stone was dropped into the water. I am not sure it that is a significant amount for your purposes though.

So in my opinion, if you can justify the expense then rather get a robust good quality balance for the kitchen and use that whenever you need to weigh whetstones.
It's a win-win situation; you may get accurately made fine baked goods out of the arrangement.

Get some quotes on reputable brands from local laborotory equipment suppliers if you can. Home brewing equipment suppliers may also carry this kind of thing, but with a bit of mark up added to the price.

I am trying the same approach myself for similar reasons....
 
This might be true. So you measure the rock, pretty accurate. Measure the container of water, Tare, add rock… getting pretty heavy and screwy. Now the relationship between the two (on which we do our math) is all skewed and bung.
If the accuracy of your balance is OK with just the rock, then you could also consider measuring the volume of the rock by displacement and use that to calculate the density of the rock.

For that you need to be able to measure a change in volume when the rock is submerged in a known volume of water.

First you need couple of small accurate measuring cylinders E.g. 100ml and 10ml.
You then painstakingly calibrate a glass container by pouring in some water from your measuring cylinder and marking off the graduations on a strip of paper or masking tape appropriately stuck to the side of your container.

It's like making your own very big measuring cylinder.
You can make something reasonably accurate that way.
 
This might be true. So you measure the rock, pretty accurate. Measure the container of water, Tare, add rock… getting pretty heavy and screwy. Now the relationship between the two (on which we do our math) is all skewed and bung.
That’s an interesting point about working in the middle of the working range of the scales. I have always weighed the rock separately to the water suspension tub.

It might be better to proceed as follows to ensure that all readings are taken in the middle of the working range of the scale.

1. Add tub with water to the scale
2. Tare
3. Add stone to tub and measure weight of stone (stone resting on bottom)
4. Suspend stone and take the displacement reading

This won’t make the scales more accurate but it will ensure that you are using them in the same working range for both measurements.
 

Legion

Staff member
That’s an interesting point about working in the middle of the working range of the scales. I have always weighed the rock separately to the water suspension tub.

It might be better to proceed as follows to ensure that all readings are taken in the middle of the working range of the scale.

1. Add tub with water to the scale
2. Tare
3. Add stone to tub and measure weight of stone (stone resting on bottom)
4. Suspend stone and take the displacement reading

This won’t make the scales more accurate but it will ensure that you are using them in the same working range for both measurements.
I just pulled the trigger on a set of analytical scales that range from .01g to 5kg.

I figure if the average rock I weigh seems to be around 700g, and I dunk it in about a litre of water, I'll almost always be working in the lower middle zone of the scales. Plus if I ever need to weigh something as heavy as 5kg that will come in handy.

Actually the main reason I went for the 5kg over the 3kg is the surface of the measuring part is bigger and rectangular, so hopefully centring longer items should be easier than on the smaller round plate.
 
I just pulled the trigger on a set of analytical scales that range from .01g to 5kg.

I figure if the average rock I weigh seems to be around 700g, and I dunk it in about a litre of water, I'll almost always be working in the lower middle zone of the scales. Plus if I ever need to weigh something as heavy as 5kg that will come in handy.

Actually the main reason I went for the 5kg over the 3kg is the surface of the measuring part is bigger and rectangular, so hopefully centring longer items should be easier than on the smaller round plate.
Now everyone can send their labelled stones to you in order to build up an accurate SG reference database.
 
This is the most reasonable one that I could find. Seems like it would be useful for a range of things if you’re a bit of nerd like myself. It also has a calibration feature and levelling feet. Calibration masses are extra.

Not something you really need but it could be fun to play around with. Other models seem to have more elaborate features which you pay for and I doubt I would ever use. This is pretty much a straight up scale or “balance” as they are known in the field.

The 4200 model seems like the sweet spot. The ones with a lower max weight are more precise but are also more limited in what you can use them for.

View attachment 1607335

Looks like my local coffee shop has the same model.
 

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Legion

Staff member
We are in business.

The first thing I noticed, @cotedupy is quite correct about cheap kitchen scales being accurate at lighter weights. Using a 100g calibration weight (the only size I have handy at the moment) both my old and new scales are within .5g of each other.

Going up to 8" hone weights, they start to differ more. And in fact the readings I was getting on the old scale today are two or three grams different from my notes when I last measured the same stones.

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