Zahn Cups

Quick and dirty effluent times. Not exactly adherent to ASTM D. The hole sizes for #1 and #2 are not to the standard. The sizes are +.05-.15 based on my calibration tests. The gemoetry has been changed from a true hemisphere into a cone/hemisphere to mitigate the effect layer lines will have on time. Changes have also been made so no supports are needed to print.

The handles are tapered so they don't have to be glued in place. One could only print 1 handle for the whole set. There are overhangs on the taper which may give a warnning during slicing. These overhangs are designed to bite into the cup and should not be supported.

Cups #1 and #2 were “calibrated” using water. I am aware water dose not have a visocsity in the range of the Zahn Cups. I used water because it was the only liquid I had access to which had a relatively known viscosity. Honey, maple syrup, joint compound, olive oil, … They all vary by brand, type, and temperature making them poor cailbration medium. I tried 4 different geometries and orifiice diameters to get cups #1 and #2 to give water a viscosity around 1 centistokes at room temperature.

Cups #3-5 orifice were sized to ASTM D. The volume of all the cups is 44mL as per ASTM.

The equations to convert time to kinematic viscosity can be found at: https://en.wikipedia.org/wiki/Zahn_cup For those who don't want all the information and just want the equations:

• Zahn Cup #1: ν = 1.1(t − 29)
• Zahn Cup #2: ν = 3.5(t − 14)
• Zahn Cup #3: ν = 11.7(t − 7.5)
• Zahn Cup #4: ν = 14.8(t − 5)
• Zahn Cup #5: ν = 23t

If you test water using the #1 or #2 cups, the resulting kinematic viscosity should be around 1cSt. Cups #3-5 will yeild negative values when using water as the calibration medium.

NOT FOR SCIENTIFIC USE. These are for hobbiest who dont want to spend $300 on a set and just need a ballpark viscosity.