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Shop Math: Measuring With Calipers



Chuck Girard: Hi, Kevin.

Kevin Caron: Hey, buddy.

Chuck Girard: What are you doing?

Kevin Caron: Trying to figure out how big that hole is, but this poor ruler is so screwed up; it's been so scarred up over the years, that I can't read all those old lines.

Chuck Girard: Yes, that's always hard to do, but I've got a tool that I brought with me that might help you out a little bit - a pair of calipers. Let me show you. Check this out, Kevin. Here we have a couple of different sizes of calipers: a 12-inch set, an 8-inch set, and then a digital set.

Kevin Caron: Cool.

Chuck Girard: For most of us that prefer not to spend a great deal of money on these, you can go and pick them up at Harbor Freight for about 30 bucks. Probably even less for a regular digital set.

It's a wonderful tool to have. You could measure an inside diameter, an outside diameter, a depth of something. You can even lay out with calipers. Very handy tool to have.

Kevin Caron: Wow.

Chuck Girard: Let's grab the middle size here. This is the 8-inch and this is the dial caliper. And if you just come in here and look at it a little bit. . .
The dial caliper isn't anything to be afraid of. It's set up at a hundred thousandths graduation, so if you kind of do a basic math with it, it's simple.

Kevin Caron: Wait, we've got to do math?

Chuck Girard: Ah, it's really simple. Come on. You break it down like a dollar bill; so basically, a quarter-inch is 250. A half-inch is 500, and so forth, every time the wheel goes around, that's a hundred thousandths. It's easy.

Let's put it to practical use here. For example, we've got this sprocket here that we're trying to get an idea of a diameter, right? On this side? Well, the scale's a pain in the butt. You know, you think you're right, but are you really right?

Kevin Caron: Not really.

Chuck Girard: OK. Calipers. All you have to do is just bring them in here. . .

Kevin Caron: Do you have to zero it first?

Chuck Girard: Well, yes, you do. My fault. You know more than you were leading on to. Anyway, you do zero them out.

Kevin Caron: How do you do that?

Chuck Girard: You simply bring them down here until they're touching and then they're zeroed. There are fine adjustments all over this and you can read the operator's manual so you can actually know how to do it.

Kevin Caron: How do you do that?

Chuck Girard: All we do is we drag them out; push them forward so that the teeth are touching, and make sure that the zero is on zero. The way to do that is you can adjust the dial up here, and you can also lock it.

Kevin Caron: Lock the dial?

Chuck Girard: You can lock the dial and you can also lock the calipers in the position that you want so that it doesn't move. And that's it.

So, let's go ahead and measure this bore right now. We're going to use an inside diameter portion of it, which is on the top of the caliper. We're going to stick it down here in the hole. It's not something that we want to pry on or add a lot of pressure. Just give a nice, gentle feel to it. Rock them up and down so that you know that you're where you're supposed to be. And this is actually 1 inch. Actually, it's 10 thousandths under one inch.

So, when you look at the caliper. . . Come in and check this out. This is pretty neat. There's a graduation scale that's down here and then there's also the dial. So we just add it together.

We look at the last number that was selected, which in this case is the 900 thousandths, add the other 90 thousandths on the dial, so we have 990 thousandths, which is 10 thousandths less than the actual 1-inch size.

Kevin Caron: Wow.

Chuck Girard: So, for this, we know if we put something over 1 inch, it's not going to fit. So, we'll probably have to take that shaft to a machine shop and have them turn it down so that it fits just like a glove.

But it's really great for anything around the shop, very handy. You can just use this side of the caliper to check and see what size this is. And it's kind of fun just to play with. This particular size is 1 and 7 16ths.

The Voice: Let's see that, Chuck. Hold that up for me.

Chuck Girard: OK. You have a sphere here. How do I measure a sphere? Well, a lot of people will just take their simple scale and say, "Yeah, it's 3 inches." But just to illustrate the purpose of the caliper, we can do the same thing, spreading it down here: 3 inches exactly!

But what happens to us quite commonly in the shop is that we get scraps lying around all the time. We've got this piece; what size is it? I thought I'd used 18-gauge. I thought I'd used 8th-inch. And when we start looking at it, we notice it's bent, it's manipulated. What are we really going to use? This is where it's really handy to have calipers.

All you have to do is bring them over here, snap it on there, that's 120 thousandths. That's 120 thousandths. Imagine that. I actually have two 8th-inch pieces.

What about this piece over here? I wasn't really sure, and sure enough: This is gauge and it's not 120 thousandths. So, if I actually tried to put all these pieces together, like the old Sesame Street, two will go in; one won't. Once again our handy tool saves the day.

Let's just do one other thing here real quick. Let's lay something out with our calipers. Let's say we that want a bolt pattern laid out for a caster. What we can do is set it for a certain size off of the edge of the part. We'll say a half an inch.

We'll go ahead and scribe a line. We'll come over and then make it 3 inches, so we'll go 3 and a half inches from the end. We'll lock that in. We'll go ahead and scribe again. And then we want to make our other thing the same way so that we have the exact same pattern, so we'll go a half inch from the edge again and then 3 and a half again for our simple bolt pattern.

The Voice: What are you scribing into there?

Chuck Girard: We just used a little bit of primer that we had on hand here in the studio. You can use Dyco. You can use a lot of other different things. But that's a really simple way to just lay out a simple pattern. Calipers: worth their weight in gold.

Kevin Caron: Well, what about one of these dividers?

Chuck Girard: These are utilized more for laying out circles and that kind of thing. You can use them as a measuring tool, but they're a little bit more antiquated.

Kevin Caron: Just like me.

Chuck Girard: Well, just like all of us.

Kevin Caron: Well, that's cool.

Chuck Girard: Check them out.

Kevin Caron: Excellent, buddy. I'll see you next time.

Chuck Girard: I'll see you next time.

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