Sonic Vs Mechanical Wall Thickness Gauge

[10 bore]

Originally Posted by Dave Suponski

Mechanical....Sorry I'm just too "Old School"

or just "Old"

[edgarspencer]

Ultrasonic thickness gauges can be as accurate as most measuring techniques, but the transducer surface, and frequency need to be tailored to the specific piece being measured. In most applications, the sending element and receiving element of the transducer are housed in the same package. It is critical that the transducer be positioned exactly perpendicular to the surface being tested. any angle that deviates will give exaggerated, higher readings. Picture a circle, within a circle. A point at 6:00 on each circle will be the actual thickness, but if the transducer is not facing straight on, you might be at 6:00 on the outside, and the beam will strike the 9:00position on the inside. This can be cured with a transducer having an exact radius machined on it's shoe, not practical for any but the diameter it was machined to fit.
Mechanical wall thickness gauges are POINT-TO-POINT devices, like a large mouthed caliper, which measure from an exact point on the OD, to an EXACT point on the ID, Not the inside surface in general. The barrel can only be touching these two points.
Ultrasonics, both in flaw detection, and thickness measurement, have their place, and are the best way to measure when the opposite side of the wall is difficult to reach, such as the hull of a ship, wall of a tank, or inside cavity of a complex shape.

[Autumn Daze]

Yup what Egger said...

[Drew Hause]

I appreciate Edgar's insight. Some of you are likely following this thread
http://www.doublegunshop.com/forums/...=357105&page=1

I believe we're going to end up with a cascade of options for non-destructive (duh ) testing of vintage barrels; fluid steel or pattern welded, starting with external and internal (via a digital bore scope) visual examination.

The problem with pin and micrometer wall thickness gauges is when pits are present. It is very difficult to position the pin exactly in the bottom of visually identified pits, and impossible if the pits are on the medial wall.
I hope to have the results of radiography on a second barrel tomorrow. This is a negative x-ray image of the first, which enhances the defects in the barrel wall, and may also be useful for measuring wall thickness



Stay tuned.

[Eldon Goddard]

I should have given more information in my original post. If you look at precision ultra sonic wall thinkness gauges. you will see they can measure in the range we need. For example the TI-007 Precision ultra sonic wall thinkness gauge has a measurable range from .006'' to 1'' with a resolution of .001''. However if you read the manual you will see that the minimum radius for convex surfaces measured is .5'' or a little larger than a 4 bore. or 2.5'' for a concave surface. So even a 1900 dollar wall thickness gauge can not measure a barrel smaller than 4 bore.