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+--- Thread: O-ring size... (/showthread.php?tid=8234)
O-ring size... - jimxms - 28-06-2019
I've got an o-ring that has split and is no longer a 'ring' as such.
The total length of it laid in a flat line is 440mm and the thickness of the rubber is 2mm.
Its been a long time since I did math, but would the 440mm count as the circumference and therefore the diameter would be 140mm?
And if I take into consideration that the thickness of the o-ring is 2mm, the OD should be 441mm and ID should be 339mm? Although the 1mm either ways is probably negligible as I'd imagine it can be stretched a tad if needed?
O-ring size... - Stoney - 28-06-2019
Pretty close to that mate, yeah. Long time since I did maths too!
EDIT: Actually... thinking about it.... you are wrong!
440 / 3.1415926 = 140.05635 (Central diameter)
140.05635 + 1 = 141.05635 * 3.1415926 = 443.14158 (Outer circumference)
140.05635 - 1 = 139.05635 * 3.1415926 = 436.8584 (Inner circumference)
Check:
Difference of 2mm * 3.1415926 = 6.28318
443.14158 - 436.8584 = 6.28318
The difference between inside and outside diameter is not 2mm. But 2mm * Pi.
Many decimal points not rounded, to retain accuracy of calculations.
O-ring size... - Stoney - 28-06-2019
Sorry, it's early in the morning still. Where I wrote Outer Diameter and Inner Diameter, I mean CIRCUMFERENCE not Diameter! And "The difference between inside and outside diameter is not 2mm. But 2mm * Pi." Should read Circumference also! Jim confused me, as I think he may have made the same error with his OD and ID? Surely OC and IC?
Mods... edit... help?
O-ring size... - Sparkystav - 28-06-2019
Edit, but sure OD is Outside diameter so 141 and 139 are the figures you want
O-ring size... - Stoney - 28-06-2019
Sparkystav Edit, but sure OD is Outside diameter so 141 and 139 are the figures you want
Thanks.
Sure. I calculated 141.05635 and 139.05635 for the diameters. (OD is Outside Diameter, but Jim put it at 441, which is a circumference measurement (though not the right one?)
As Jim was multiplying back up to get the circumference, I did also, and my figures for it should be correct? Though you are right, I'm not sure circumference measurements are actually required!
O-ring size... - jimxms - 28-06-2019
Stoney Thanks.
Sure. I calculated 141.05635 and 139.05635 for the diameters.
As Jim was multiplying back up to get the circumference, I did also, and my figures for it should be correct? Though you are right, I'm not sure circumference measurements are actually required!
Hahah I'm so confused.
My train of thought was that the length (circumference) was 440mm which when converted to diameter equalled something in the region of 140mm.
As this was the 'diameter' and not the internal or external diameter, it was effectively measuring across the middle of the o-ring (if it were still a ring) to the middle of the rubber on either side. As the rubber was 2mm thick, this would mean that there would be 1mm of rubber either side of where I was measuring.
But thinking about it now, that would be 1mm either side of the rubber for each 'side' of the circle, wouldn't it? So shouldn't the OD be 142mm and ID be 138mm?
O-ring size... - Stoney - 28-06-2019
jimxms Hahah I'm so confused.
Yeah, me too!!! :lol:
Maybe I'll ask my mate on facebook.... he is a high school Maths Teacher!
Na, got with 138 and 142. That should do the trick. There will be a 4mm difference between the diameters (2mm difference in the radius!)