Measuring odd metric o-rings

[mr_v]

Howdy folks,

What's the best approach for measuring o-rings? I have a paper cutout with most common o-ring sizes. However, my equipment has some odd metric o-rings. Is there a service or a tool I can use? O-rings with cross sections that are a lot smaller than inner diameters, think 1:20 ratio, are a particular challenge.

Thank you!

 

[Still Kicking]

You can get calibrated cones for more precise measurements of orings but they are ridiculously expensive for what they are.

You might be able to find a template you can download and print on cardboard to make your own cone. A little less accurate but less expensive.

 

[rsingler]

Hang in there, we'll cover that in the Seminar!

Spoiler

Use digital calipers to measure cross section. That tells you which standard (AS568, BS1806, Metric, JIS, etc.).
For small o-rings, use a digital microscope to carefully measure OD, then calculate ID by subtracting 2x C/S.
The new tool Olypsys can get you VERY close with a cell phone camera.

LinkedIn

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For larger o-rings, like the 20:1 ratio you mentioned, make a paper tube and carefully stretch it to completely fill the ID of the o-ring. Mark the intersection of the paper edge with the rest of the tube with a pencil. Remove the tube, unroll the paper, and use calipers to exactly measure the circumference of the ID, between the unrolled edge and your mark. Divide by Pi (3.1415927) and that's your ID.

 

[admikar]

I use calipers and CAREEEEFFFUUUULLYYYYY measure OD. Calculate ID from CS.
Just repaired power inflator on my doubles wing that way.

 

[rmssetc]

You can get calibrated cones for more precise measurements of orings but they are ridiculously expensive for what they are.

You might be able to find a template you can download and print on cardboard to make your own cone. A little less accurate but less expensive.

If you've got a 3D printer:

Search Thingiverse - Thingiverse

Download files and build them with your 3D printer, laser cutter, or CNC. Thingiverse is a universe of things.

www.thingiverse.com

 

[rmssetc]

Howdy folks,

What's the best approach for measuring o-rings? I have a paper cutout with most common o-ring sizes. However, my equipment has some odd metric o-rings. Is there a service or a tool I can use? O-rings with cross sections that are a lot smaller than inner diameters, think 1:20 ratio, are a particular challenge.

Thank you!

I find that most of the time when I need to measure an o-ring, the old one is in terrible shape (dried out, stretched, compressed, etc) from long-term use, making the measurement difficult and different from the size of the replacement. This is particularly in non-SCUBA applications, such as inside an espresso machine, where the o-ring has been through a lot of high heat cycles.

Any suggestions?

 

[rsingler]

For espresso machines, most are static o-rings. Measure the land, subtract 2.5% for a little stretch and give it a try. For a static o-ring, if it seals, it's good. For a dynamic o-ring, a wrong size may give you lousy coffee and a leak.
For "life support" equipment, if it's a static o-ring, the logic still applies. If it seals, it's good. With the exception that if it's too soft, it may extrude. If it's too thin, it may extrude. Etc., etc. For a dynamic o-ring, especially lightweight parts where friction plays a role (second stage poppet seals to the balance chamber), substitute at your own risk!
For proof, look only at a port plug. The engineering specs require a 3-903 or 3-904 o-ring. Very few mfrs use anything but a 2-010, 2-011 or 2-012 for this static o-ring. For "life support equipment." Jes' sayin'.

 

[lowwall]

I'd suggest asking here. Someone will likely know or have the spec or manual at hand.

edit - Espresso machines? I was able to find a service manual for my old Saeco a lot more easily than my old Mares

 

[mr_v]

I will ask here for sure, but most of the time my OCD forces me to trust but verify.

 

[Larryjd1]

Hang in there, we'll cover that in the Seminar!

Hi Rob,

What a neat tool in the spoiler and an interesting alternative to the paper one you distributed with the class materials.! I already downloaded the app.

Are you referring to an upcoming regulator class or something different. I was planning on auditing the January class for a refresher.