This weekend I did some testing with my sonic tester. First I calibrated it on the 5mm steel plate that comes with it.
I then tested a brass cylinder, 130 wall 2 1/2 " inside dia. I checked thickness with a Harbor Freight digital caliper. After setting the instrument for brass I checked the thickness on the outside. It measured about .005 thicker than the caliper.
But the inside measurement was considerably higher. About .070 on the 2 1/2" circle.
I also measured a 3 1/2" inside dia steel cylinder, .210 thick after changing the setting to steel. It was like the brass test effort. A tiny bit thicker measuring on the outside but a larger number than actual thickness when testing on the inside.
I could try putting some emery cloth on the inside of a cylinder and sanding it to fit. That idea came from a comment on Amazon. The only thing you would risk is buying a new probe, seems reasonable.
Or finding out what the space is between the probe and a given dia of a circle you are trying to measure. The probe is .431 wide. Then subtract it like Charlie said and see how close it is.
Any math/geometry experts out there who know that formula ?
It would be easier than actually sticking something in there and measuring it. It would take a little doing but it could be done.
Also will try some different oils, some might be better than others. I just used some Fluid Film for this test.
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