Soapmaking Friend - Recipes Based on Mold Size

amd · Sep 27, 2020

As I said in my post... I think they do not have the x2 in the formula.

KimW · Sep 27, 2020

amd said:
As I said in my post... I think they do not have the x2 in the formula.

I did indeed see that. To find the volume for a cylinder it's pi times (r squared) times height, not pi times (r times 2) times height.

Of note, if you choose "Resize to fit mold size", then choose "By Total Size" and manually enter your mold volume the calculator works within what I'd call an acceptable range. In other words, it appears to correctly adjust the oil and lye amounts to fit the mold volume you've entered when variables such as water:lye ratio and superfat are altered. This appears to be true for both rectangular and cylindrical molds.

So, for example, a cylindrical mold with a radius of 3 inches and a height of 6 inches, would have a volume of 3.14 (9) (6) = 169.56 cubic inches. Multiply the cubic inches by .5541, to get volume in ounces: 169.56 (.5541) = 93.95 ounces. Giving the calculator this "Total Size" works pretty much a treat, and does save some figurin' when you want to tweak an old recipe. But, I'm weird and use a sharpie to write the volumes on my molds, so I always have these numbers.

Hopefully, someone in control of the calculator will see these posts and get it fixed up.

lshone · Sep 27, 2020

KimW said:
Agreed - this is exactly what I am seeing.

So, what I'm hearing is the "resize to mold" feature is working as designed in that it will not adjust the oils (and also therefore the lye) in a recipe if any variable - water:lye ratio, superfat, FO - are not at minimum levels. Meaning, it will only give accurate results if all variables are set to minimum/zero levels. Fair enough. I can work with anything if I understand how it's designed to work.

Yes and no. It's working as designed but the design has some flaws.

Volume x .4 = the weight of oils. if you use 32% lye concentration, 0% superfat the volume calc will work. Also 31% lye and 4% superfat or 30% lye concentration and 8% superfat.

Varying the lye concentration and/or the superfat concentration changes the volume. Soapmaking friend doesn't adjust the oil weight to maintain the mold volume. This is a design flaw IMHO.

lshone · Sep 27, 2020

KimW said:
For cylinders, I think they have figured the volume of a cylinder based on the formula for finding half the area of a circle. That is, "pi r squared divided by 2 times height", instead of "pi r squared times height". Or...they have the formula correct, but entered the value for 1/2 of π ...which would be even more weird.

I agree, the volume calc for the cyl. is hosed. I also think you are correct in your assumption of the fomula.

Using your example, Radius=3, Len=6. 3.14*3*3*.5*6 = 84.78 (half of what is should be).

Multiply this by .4 and you get 33.929, which matches the amount calculated by soapmakingfriend.

The cyl. calc doesn't calculate the volume correctly and has the same design flaw as the rect. calculation.

My guess is that the original design was to enter the diameter and calculate the radius (dia. *.5).