0:14 [Music]
0:16 I'd like to talk a little bit about
0:19 center drills and center drilling. Uh
0:20 it's pretty pretty simple. Seems like a
0:22 pretty simple thing to do and it is as
0:25 long as you you do it correctly. But
0:26 like anything else, if you do it
0:28 incorrectly, and there are a few ways to
0:32 uh drill a center hole wrong, it uh can
0:34 come back and bite you later on and and
0:35 cause you problems with a with a part
0:37 because your part basically revolves in
0:39 the lathe. Anyway, your part revolves
0:41 around the center hole. So, if it's not
0:44 put in right, it can transfer into
0:46 problems later on. Uh first, let's talk
0:48 a little bit about different types of
0:52 center drills. Um these are plain plain
0:53 center drills, they call them. They're
0:55 they're 60° angle on them and they have
0:57 a little pilot.
0:58 Uh this is a they come in different
1:00 sizes. This is a number one. This is a
1:02 number four. Those are the the two most
1:04 common sizes I have. There are bigger
1:07 ones like this. There are bigger ones
1:09 yet, but for for this lathe and type of
1:11 work I do. A number one and a number
1:13 four pretty much does everything I need
1:16 to do. Uh you can also get plain center
1:18 drills in long long versions like this.
1:20 They're good in for use in the milling
1:21 machine for reaching down inside of a
1:24 pocket to spot a drilled hole or
1:27 something like that. These work great.
1:29 Um, besides the plain center drills,
1:31 there's there are different type couple
1:33 other different types. This one's called
1:35 a bell center center drill. It has, you
1:38 can see it has a little extra angle out
1:41 here about a 15° angle out on the very
1:43 outside. So when you drill down in here,
1:45 this this seats the the 60° part
1:48 slightly before below the surface of the
1:51 part. That's that's for if you have a a
1:52 part that you want to do multiple
1:54 operations on and you want your your
1:56 center hole protected a little bit, this
1:59 is a good one to use for that. Um or if
2:00 you can use a plain one and just be a
2:02 little bit careful and try not to mess
2:06 up the center hole. Um another one is uh
2:09 it's called a radius center drill. that
2:12 one instead of having a 60deree cone
2:14 shape on it, the sides of the of the
2:16 tapered part are radiused a little bit.
2:19 They're kind of kind of curved. And
2:22 those are used mostly for for like
2:24 grinding. If you want to do external
2:26 grinding on the part, they use those
2:28 because they're a little more accurate
2:30 because they only bear on a on a a line
2:32 around the center instead of on the
2:34 whole face of the center. But we don't
2:35 we don't need to worry about that here.
2:36 Just a plain center drill is all you
2:39 need. I'd get, you know, a handful of
2:40 ones and handful of fours. That should
2:44 should do you pretty well. Um, okay.
2:45 Let's talk about about center drilling.
2:48 What do we How do we do it? Well,
2:50 first thing we need to do before we
2:54 center drill is face off our stock. Get
2:56 rid of the sawed surface.
2:57 Let's go ahead and do that. We already
2:59 covered that in the video, so we don't
3:01 have to talk much about it. Let's just
3:04 face this off and
3:24 [Music]
3:33 [Music]
3:35 Okay. Okay. Hopefully that's hopefully
3:37 that's close enough that you can see. Um
3:40 Um
3:42 well, there are couple things you can do
3:43 that will cause you problems when you're
3:46 center drilling. Uh one of them is to
3:49 center drill too shallow.
3:51 That uh results in a a center that's not
3:54 really big enough to support the part.
4:02 when you if you just start drilling in
4:04 on the uh the tapered part, just put a
4:07 little bit of a center in
4:09 that. Uh well, in this case, it's
4:10 probably fine. But if it's a bigger
4:12 part, that may not be enough to to
4:14 support it and support the part and the
4:16 machining on it. And the part may the
4:17 center may fail about halfway through
4:19 your machining operation, which tends to
4:22 ruin your day because you end up with a
4:25 part that's off center.
4:27 Um, another problem that a lot of people
4:30 have or some people have is
4:33 going too deep.
4:35 Show you what that looks like. You
4:36 should use whenever you're center
4:38 drilling, you should use uh oil. It's
4:40 not it's not that important on aluminum,
4:42 but on steel, if you don't use oil, it
4:44 can very easily break the the pilot off
4:46 the center.
4:54 you can see that we ended up with a little
4:56 little
4:58 cylindrical bore before it starts
5:00 tapering in. So, when you put your
5:02 center in that, it only bears on the
5:04 very outside, just a line rather than
5:07 all along the the tapered surface. And
5:10 again, your your center will fail. You
5:11 know, partway through your machining operation.
5:13 operation.
5:14 you'll loosen up and the part will start
5:16 wobbling and your your center won't be
5:19 doing its job anymore. So, that's that's
5:22 too deep.
5:25 Let me face this off and we'll
5:33 All right,
5:35 your center hole should go about 2/3 of
5:38 the way in the conical part of the of
5:41 the drill. Right about there.
5:42 no farther. If you need a smaller
5:46 center, then use a smaller center drill.
5:48 You need a bigger one, use a bigger one.
5:50 But, you know, every center center drill
5:53 should go about 2/3 deep on the tapered
5:54 section. That's that's a good a good
6:01 Um, okay. So, if we're turning a part
6:03 between centers, we we'd center drill
6:06 each end just like this.
6:09 Flip it around and do the other end same
6:10 way. Then we'd mount it between centers
6:14 and do our turning. Uh sometimes it's tempting
6:15 tempting
6:18 to uh support the end of the work with a
6:21 chuck like this and center drill the the
6:23 out the outboard side or the outboard
6:26 end and do your turning that way. Well,
6:28 that's fine as long as you rem as long
6:31 as you uh plan ahead a little bit and
6:33 don't center drill your part with the
6:35 part all the way in the chuck like this.
6:37 If you do that, your life will end up
6:39 with a surprise later. Now, let me show
6:41 you show you why.
6:44 Let me go ahead and center drill this part
6:50 like we normally would, like we did on
7:10 like that. Two/ird of the way in.
7:11 Okay, there we got a a part that's
7:13 centered on both ends. Now, let's say I
7:15 want to stick this out and support one
7:18 end of it with a chuck.
7:20 So, I can do my turning.
7:22 Let me back the camera out here a little bit.
7:33 get a center in the tailtock. I'll show
7:40 All right. So, we want to support this
7:42 end with a center. That's fine. But look
7:44 what happens here. If your if your
7:48 stock's not uh round or if it's bent or
7:50 you know, if it's got scale on it, you
7:52 can end up with something like this. See
7:54 how much the center's wobbling?
7:56 So, if you think ahead a little bit, if
7:57 you want to extend a part out of a chuck
7:59 and hold it in a chuck, then do your
8:01 center drilling with the part already
8:04 extended. Okay? Put it in a chuck first,
8:05 sticking out as far as you need, and
8:08 then center drill it. Then your center
8:10 will be on the rotational center of the
8:12 part. Right now, if I go ahead and run
8:15 my center in like this, it doesn't care.
8:17 It'll straighten the part out. See, the
8:19 part will run nice and true. And you can
8:20 go ahead and do all your turning on it.
8:22 But as soon as you take that center out,
8:24 guess what? You're going to end up with
8:27 a a bent part again. So all that nice
8:31 machining is all for not. So if you're
8:33 you're planning on machining a part
8:35 sticking out of a chuck like this,
8:37 center drill it with the part sticking
8:39 out. Don't center drill it all up close
8:41 to the chuck like I like I demonstrated here.
8:44 here.
8:47 Um that's about all there is to center
8:50 drilling. Uh maybe next time we'll uh
8:53 we'll cover turning to a diameter.
