O Ring sizer

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Martin3528

Martin3528

Member
Sep 23, 2017
357
453
Flagstaff. AZ, United States
I ordered some O-rings from the O Ring Store and saw they had this grid paper that you can use to determine the size of O rings. For $10, I thought I'd give it a shot.
I will insert some pictures and hope they make sense. It works pretty well. What you do is lay your O-ring on the grid, open the app and take a screen shot. It computes all the data and gives you a dimension of the O-ring.

Here is the grid
Grid.jpg


Set your O-ring in the middle and screen shot in the app. It processes the picture and:

View1.jpg
View2.jpg


Then it gives you a screen of the dimensions and a possible part number. The first O-ring I shot was a 8mm x 1.5mm.
pretty close dimensions. 0.02mm difference.

View3.jpg


This is one of a 20.5 x 2mm. ID is a little farther off, but probably my picture taking.
FWIW, it may be useful to someone. I would use it to order the best size that makes sense. For instance, on this one, I would look for a 20.5 x 2 mm

View4.jpg
View5.jpg
 
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I trust my digital caliper more, but I may be an old fashioned mechanical engineer :)
The other thing is, I always download the (airgun) Manuals from websites, re type the entire o-ring BOM (bill of material) into my spreadsheet.
When I need to order anything for my own stock - I buy in little bags of 25 or 50 = that volume is for lifetime.
If I can recall correctly I have about 78-80 sizes - from the books - in my o-rings safe.
I like oringsandmore, the online selection is well organized and ordering I find very friendly.
 
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I tried that picture taking app a few times and it was pretty accurate. Good lighting, and good picture taking is the key, but it worked well. I would have to do it a few times and get the same size to feel comfortable ordering. BUT, I have sworn off any airgun that does not publish sizes. I think it's absolutely ludicrous to keep it a secret. I still use Huma regs even though they won't help with sizing, but I have measured all I need or found the reference online and made notes. Here again, it's stupid to keep it a secret, so we have to order overseas for $5 worth of orings that can easily be ordered in country or even in town. Ok, I'm done with my rant.

I use calipers most of the time and if I have any reference, I can get er done.
 
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O rings will change in dimension, particularly the diameter, if you put pressure on them so using a caliper takes a little finese but it is still my preferred method. I do it more than once until I am comfortable with the measurement. The thickness is easier. There is some give but not nearly what there is on the diameter. If the app works better for you, go for it. I also look for a parts list for the gun but in my experience they have not shown every O-ring.

I also like to keep my list of O-rings showing the OD, thickness and ID. I measure the OD but the O-ring lists from the supplier shows the ID. I've been known to order the wrong size. I wish more suppliers listed the OD. It seems it is the industry standard to list the dimension that is the hardest to measure.
 
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Uhh ya I kinda thought that could go without saying... :) My friend Dwight (RIP) did his valve engineering using the valve stem sealing on the ID, most guys use the OD. He reasoned that A our flow requirement was very low, and B dimensions are more tightly held on the ID. He was very much a genius valve designer, Dwight's been in the ground for 30 years, his designs are being manufactured today.
 
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