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