ProfessorBernardo
New member
- Joined
- Aug 13, 2021
- Messages
- 4
Today at 11:00 AM
Since I make shave soap and use a 3" PVC Sch40 pipe for a mold, I needed to adapt my recipes to fit that mold size volume-wise.
Here's the interesting part:
1. Use the calculator for a cylinder dimension of: 1.5" radius and 23" height. NET RESULT IS: Total Batch Weight 1884.47 grams
That number is shy of the true amount by about 786 grams! Whoa Nellie! I kept looking at the number given me and in my mind I just knew that the 1884 number was off by quite a bit... actually by about 42% !! Time for the webmasters to "git 'er done" and correct this anomaly.
2. Correct way to compute is: Radius of 3" cylinder is 1.5", this number needs to be squared: 1.5 x 1.5= 2.25
Since the classic formula is Pi x r/2 for area, for a cylinder it is: V=πr2h Volume = pi x r/2 x h (height)
So the 3" x 23" cylinder's volume works out to: 1.5 x 1.5 = 2.25 x pi (3.14) = 7.07 sq. inches x 23" height = 162.61 cubic inches.
(Now we go to Google to convert cu. inches to cubic centimeters (equivalent... more or less to grams of oil).
We'll round this off to 163 cu. inches for simplicity's sake.
163 cu. inches converted to cubic centimeters is: 2671.09 cu. cm. this is "roughly" equivalent to the amount of oils, etc. used to fill the cylinder with soap mixture.
Actually my recipes are set to 2670 grams on the "By Total Size" adjustment and they completely fill up the PVC pipe which is actually 23-3/4" in height with a 1/2 thick thick internal plug for the bottom of the mold.
Thoughts? Suggestions? Comments? I know there will be some MENSA scholar or M.I.T. grad out there who will take me to task on my above though processes, but hey it's not the first time I've been around the "proverbial block". At my age, Rhino Hide Skin is a blessing. I'm no Einstein that's for sure!
So... I wanted to point this out in the hope of getting that part of the calculator recipe resizer tweaked and corrected. I'm someone resized a batch and was a little baffled about the net result.
Some replies from the Soap Making Forum Website:
From SoapDaddy70:
I do think there is something wrong with the cylinder conversion on Soap Making Friend but what you have listed is incorrect. In your first bullet point where you say the TOTAL BATCH WEIGHT is 1884.47g. That is actually not the total batch weight but the total amount of oils/fats that should be used for a cylinder of that size. Someone can correct me if I am wrong but from what I have learned - to find out the amount of OILS/FATS to use in a recipe for a cylinder mold - the calculation you have is correct as pi x r/2 x h (height). After that you take that number and multiply by .4 and that gives you total ounces and then you multiply by 28.35 to get total amount of oils in Grams. I actually came up with 1842 grams of oils for a 3 x 23inch cylinder. I plugged these numbers into Soap Making Friend and it actually gave me exactly half the number it should be.
From ResolvableOwl:
Not an Ivy League graduate, but I confirm that you've really hit something strange there.
First, the volume formula itself:
Good news: soapmakingfriend does respect these dependencies. Doubling the radius will quadruple the volume/weight, and doubling the height will double it.
BUT the absolute values of these numbers are indeed utterly off. Shortly switching over to the rectangular mould, the calculator recommends for a mould of 10×10×10 cm³ = 1 L volume a “Total Batch Weight” of 986.87 g (recipe: 100% almond oil, 2:1 lye, but we'll come to this later). A cylindrical mould with the same 1 L volume has at r = 10 cm a height of h = V/(π r²) = 1 L/(π × 100 cm²) = 3.183 cm. But when we enter these values, the batch weight shrinks down to 493.42 g. That's exactly half of the actual batch size. No other explanation than a stupid formula error.
Next, another issue that isn't just a mathematical copy-paste mistake: Batch size does not depend on lye concentration. SMFriend is just assuming some average recipe. Then it computes the amount of oils for it, and scales the recipe (amount of lye/water/…) so that it fits this number. You can change the lye concentration/ratio/water amount, the “total batch size” varies accordingly, but not the amount of oils!
To be fair, estimating the density (specific gravity) of a soap batter is a nontrivial thing to do, and depends heavily on a lot of factors I wouldn't be fond of maintaining in an intermediate-level hobbyist soap calculator either. But AT LEAST the amount of water is easy to track. I mean, the script knows about X grams of oil and Y grams of water, which, roughly at the same density, need roughly the same volume for some weight. So I'd expect that the amount of oils goes down when I lower lye concentration – but it just doesn't. They have the numbers, the math doesn't need to be complicated, not even particularly precise, but it should better be considered at all. There is indeed some advanced logic behind the calculation, since the amount of oils (hence, batch size) does depend on the saponification value of the oils.
Another (unrelated) bug in the SMFriend GUI that just now popped into my eye is that the value of the Saturated:Unsaturated ratio is given in the wrong order (unsaturated first, saturated second).
From Professor Bernardo:
Thanks to both of you - @SoapDaddy70 & @ResolvableOwl !
I figured I missed something or wrong digits or whatever. Having ADD can be little frustrating sometimes. Used to drive my Algebra and Geometry teachers nuts because they knew that I knew the formulas; it was the mathematics aka simple arithmetic that I would FUBAR. LOL!
@ResolvableOwl Your reasoning about the batch size, etc., is one of the reasons I went to Google to figure out the cu. inches to cubic centimeters to oil to blah blah blah. My shave soaps turn out excellent using the "By Total Size" computation, after conversions are made to grams from cubic inches to cubic centimeters etc.
Hopefully, this will encourage the folks at the top of the food chain here to rectify this error.
Since I make shave soap and use a 3" PVC Sch40 pipe for a mold, I needed to adapt my recipes to fit that mold size volume-wise.
Here's the interesting part:
1. Use the calculator for a cylinder dimension of: 1.5" radius and 23" height. NET RESULT IS: Total Batch Weight 1884.47 grams
That number is shy of the true amount by about 786 grams! Whoa Nellie! I kept looking at the number given me and in my mind I just knew that the 1884 number was off by quite a bit... actually by about 42% !! Time for the webmasters to "git 'er done" and correct this anomaly.
2. Correct way to compute is: Radius of 3" cylinder is 1.5", this number needs to be squared: 1.5 x 1.5= 2.25
Since the classic formula is Pi x r/2 for area, for a cylinder it is: V=πr2h Volume = pi x r/2 x h (height)
So the 3" x 23" cylinder's volume works out to: 1.5 x 1.5 = 2.25 x pi (3.14) = 7.07 sq. inches x 23" height = 162.61 cubic inches.
(Now we go to Google to convert cu. inches to cubic centimeters (equivalent... more or less to grams of oil).
We'll round this off to 163 cu. inches for simplicity's sake.
163 cu. inches converted to cubic centimeters is: 2671.09 cu. cm. this is "roughly" equivalent to the amount of oils, etc. used to fill the cylinder with soap mixture.
Actually my recipes are set to 2670 grams on the "By Total Size" adjustment and they completely fill up the PVC pipe which is actually 23-3/4" in height with a 1/2 thick thick internal plug for the bottom of the mold.
Thoughts? Suggestions? Comments? I know there will be some MENSA scholar or M.I.T. grad out there who will take me to task on my above though processes, but hey it's not the first time I've been around the "proverbial block". At my age, Rhino Hide Skin is a blessing. I'm no Einstein that's for sure!
So... I wanted to point this out in the hope of getting that part of the calculator recipe resizer tweaked and corrected. I'm someone resized a batch and was a little baffled about the net result.
Some replies from the Soap Making Forum Website:
From SoapDaddy70:
I do think there is something wrong with the cylinder conversion on Soap Making Friend but what you have listed is incorrect. In your first bullet point where you say the TOTAL BATCH WEIGHT is 1884.47g. That is actually not the total batch weight but the total amount of oils/fats that should be used for a cylinder of that size. Someone can correct me if I am wrong but from what I have learned - to find out the amount of OILS/FATS to use in a recipe for a cylinder mold - the calculation you have is correct as pi x r/2 x h (height). After that you take that number and multiply by .4 and that gives you total ounces and then you multiply by 28.35 to get total amount of oils in Grams. I actually came up with 1842 grams of oils for a 3 x 23inch cylinder. I plugged these numbers into Soap Making Friend and it actually gave me exactly half the number it should be.
From ResolvableOwl:
Not an Ivy League graduate, but I confirm that you've really hit something strange there.
First, the volume formula itself:
You somehow pasted this wrong, but went on working correctly with it. It's A = πr² = π×r×r = π/4×d×d for the area of a circle with radius r (or diameter d), and V = πr²h = π×r×r×h = π/4×d×d×h for a cylinder with height h. Mind the square power (not “divide by two”).
Good news: soapmakingfriend does respect these dependencies. Doubling the radius will quadruple the volume/weight, and doubling the height will double it.
BUT the absolute values of these numbers are indeed utterly off. Shortly switching over to the rectangular mould, the calculator recommends for a mould of 10×10×10 cm³ = 1 L volume a “Total Batch Weight” of 986.87 g (recipe: 100% almond oil, 2:1 lye, but we'll come to this later). A cylindrical mould with the same 1 L volume has at r = 10 cm a height of h = V/(π r²) = 1 L/(π × 100 cm²) = 3.183 cm. But when we enter these values, the batch weight shrinks down to 493.42 g. That's exactly half of the actual batch size. No other explanation than a stupid formula error.
Next, another issue that isn't just a mathematical copy-paste mistake: Batch size does not depend on lye concentration. SMFriend is just assuming some average recipe. Then it computes the amount of oils for it, and scales the recipe (amount of lye/water/…) so that it fits this number. You can change the lye concentration/ratio/water amount, the “total batch size” varies accordingly, but not the amount of oils!
To be fair, estimating the density (specific gravity) of a soap batter is a nontrivial thing to do, and depends heavily on a lot of factors I wouldn't be fond of maintaining in an intermediate-level hobbyist soap calculator either. But AT LEAST the amount of water is easy to track. I mean, the script knows about X grams of oil and Y grams of water, which, roughly at the same density, need roughly the same volume for some weight. So I'd expect that the amount of oils goes down when I lower lye concentration – but it just doesn't. They have the numbers, the math doesn't need to be complicated, not even particularly precise, but it should better be considered at all. There is indeed some advanced logic behind the calculation, since the amount of oils (hence, batch size) does depend on the saponification value of the oils.
Another (unrelated) bug in the SMFriend GUI that just now popped into my eye is that the value of the Saturated:Unsaturated ratio is given in the wrong order (unsaturated first, saturated second).
From Professor Bernardo:
Thanks to both of you - @SoapDaddy70 & @ResolvableOwl !
I figured I missed something or wrong digits or whatever. Having ADD can be little frustrating sometimes. Used to drive my Algebra and Geometry teachers nuts because they knew that I knew the formulas; it was the mathematics aka simple arithmetic that I would FUBAR. LOL!
@ResolvableOwl Your reasoning about the batch size, etc., is one of the reasons I went to Google to figure out the cu. inches to cubic centimeters to oil to blah blah blah. My shave soaps turn out excellent using the "By Total Size" computation, after conversions are made to grams from cubic inches to cubic centimeters etc.
Hopefully, this will encourage the folks at the top of the food chain here to rectify this error.
