Dial in Your Angle

Added: 2026-05-05

[00:00:00]You ever wanted to dial in your angle beam calibration to the nearest tenth of a degree? Let me show you.

[00:00:08]It never ceases to amaze me that the more I do this NDT thing, the more I realize that there's more to learn. If there's anyone who spent a lifetime on the Dunning Krueger roller coaster, it's this guy. I was on the phone with my friend Chris Charte from NDT Group and he was telling me about this really cool trick to dial in your angle beam calibration for conventional UT to the nearest tenth of a degree. And I thought, man, that is really cool. And it's also kind of super obvious, but that's the neat thing with simple tricks. There's no trick to it. It's just a simple trick. Usually with conventional UT, you're working with 45, 60, or 70° wedges. And part of the calibration process is to double check that refracted angle. And you do that usually using something like an IW block, a DSC block, or a miniature angle beam or MAB block. On an IW block, you can usually calibrate the angle to within about a degree. Because the block is huge, there's lots of real estate to play with, lots of room to move the probe. But on a DSC or miniature angle beam block, it can be pretty coarse.

[00:01:09]There might be 2° marks if you're lucky, and they might even be 5° apart. And when you try to determine the wedge angle using one of these, you absolutely have to have the beam index point calibration already done, super dialed in, and you've marked that on the side of your wedge. But for this trick I'm going to show you, you don't need that.

[00:01:28]At this point in the calibration process, you've completely dialed in your velocity and your zero offset or wedge delay calibration. Now, close your eyes for a moment and really listen. To do this, you're going to use any calibration block with a small side drilled hole in it at a depth which puts the sound beam well into the far field.

[00:01:47]For this, I'm going to use my IW block with a 1 and 12 mm or 60 thou side drilled hole. On that note, you absolutely need to know the depth of that side drilled hole. On a metric block, it's 15 mm. On a US block, it's 600 thou. Now, I'd like to use millimeters today, but I can't because my block is in inches. So, I'm going to call a friend for some help.

[00:02:11]Hey Paul.

[00:02:12]>> Hey buddy. You guys don't use tens, right?

[00:02:14]>> No, we like to do things in fours.

[00:02:17]Four shrimp to an inch. Four crawfish eggs shrimp. Why? What you trying to do?

[00:02:22]You >> What's 600,000 poppy seeds?

[00:02:24]>> Oh, off the top of my head, I say 7.2.

[00:02:27]>> All right. Thanks, buddy.

[00:02:28]>> All right, D.

[00:02:35]The velocity and wedge delay are completely dialed in. Now you're going to temporarily set the part thickness to the depth of the hole minus a little bit. And that's because the sound beam doesn't strike the center of the hole.

[00:02:47]It strikes the edge of the hole. And even with a 1 and 12 mm hole, that little difference does make a difference. Let's do the mathy bits in metric just cuz it's easier for me. For a 1 and 12 mm hole at 45°, the impingement point is 0.53 mm less than the hole depth. At 60 degrees it's 38 and at 70 degrees it's 26 millimeters.

[00:03:09]Now unless you want to correct for the exact amount for each angle individually and I assume you don't I would just go ahead and use the one for 60° a because it's between 45 and 70 and two for 60° the math is really easy. The impingement point is always.5 time the radius or 25% of the diameter above the hole depth. So now you can quickly adjust for the size of that hole by just taking the diameter and dividing by four. And yes, using the 60° impingement point for a 45 and 70° will incur a little bit of error, but if your hole is really small, it should be minimal. So let's do this. My block is in inches, so we're going to take the design depth of the hole, which is 600 in. The whole diameter is 60 thou. 60 thou divided 4 is 15 thou. So you're going to take that 15 thou subtract it from 600 and you're going to get 0.585.

[00:04:04]Now on all modern flaw detectors that I've seen you can change the Xaxis mode to show you the ends of each leg. So on a sauna test wave it's like this. You can change it to band or line. I'm just going to set it like this. That blue line is the end of the first leg or as we've set our part thickness exactly where that signal should peak. Turn peakme on the machine. I'm going to zoom a little bit here and without any consideration to where the beam index point is on the side of the probe. I can see that I'm off slightly. So, I'm going to take this and just adjust the angle a little bit till that signal peaks right there. I kind of like that. So, the actual angle of that is about 70.6 or let's change it just a little bit, 70.7°.

[00:04:52]And that's it. We've just dialed in our angle beam calibration to the nearest tenth of a degree. And maybe this isn't novel. And maybe you've heard of it before. And maybe you're yelling at your phone, you dummy. How did you not know this before? And that's fair. You know, we've all got something to learn. I certainly learned something all the time. And if I make this video and some of you learned something, too, then it's a win. I hope you enjoyed it. If you did, please hit the like and subscribe buttons. And thanks for watching.

[00:05:19]>> Four quarters to an inch. 4/16 to a quarter. Four corns to an inch. Four poppy seeds to a corn. Four gator teeth to an inch. Four skater bites to a tooth. Why? What you trying to do? You all right?