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Center drills, proper use

plastikdreams

Active member
So I've always used just the tip of center drill to spot a hole, the other day the old guy in the shop said I've been doing it wrong and that you need to go down to the tapered part of the center drill. So is there one correct way or would either work...it always worked for me.
 
I only use the tapered part if I’m using it for an actual centre.

If I’m spotting for a drilled hole I only use the pilot parallel section as trying to drill in to the tapered section causes chatter because of the change in angle. This chatter can also cause the drill to go off centre.
 

plastikdreams

Active member
I only use the tapered part if I’m using it for an actual centre.

If I’m spotting for a drilled hole I only use the pilot parallel section as trying to drill in to the tapered section causes chatter because of the change in angle. This chatter can also cause the drill to go off centre.

I typically use the tapered part as a quick chamfer after I've drilled or after tapping the hole.

I know on stuff like 304ss trying to go all the way in can destroy the center drill especially if they are a bit dull...
 

crossthread

Active member
That is correct. You should be using the tapered part of the center drill if you are actually using it with a center. It sounds like you may not be using a center and in that case you would only use the tip which is fine. Tell the "old guy" that it all depends.
 

plastikdreams

Active member
Yeah I know to go to the tapered part when using it as for a center, and I've always used just the tip (that's what she said) for drilling ops both on the Bridgeport and on a vmc. I'll usually go down like 50k.

You know how old guys are lol.
 

TeachMePlease

Active member
Proper use of center drills?

Drilling holes for centers, including the tapered section.

For spotting holes... Use a spotting drill.

Weird how the names are the same, right?
 

GregSY

Active member
It's fairly easy to snap off the centering drill if you plunge it in to the entire taper. At that point, you have a very hard bit of metal stuck where you had planned a hole to be. I only drill a beginning 'on center' point for the real drill bit to start. If I do need a full center I go slowly and carefully.
 

plastikdreams

Active member
It's fairly easy to snap off the centering drill if you plunge it in to the entire taper. At that point, you have a very hard bit of metal stuck where you had planned a hole to be. I only drill a beginning 'on center' point for the real drill bit to start. If I do need a full center I go slowly and carefully.

Yep...done that lol the dreaded thud sound and your tool is a few hundred k shorter lol.
 

Gordon Heaton

Active member
There are the 'purists' who will cringe (and preach to no end) when they hear someones using a center drill for spotting. When no-one's looking I bet they do it too! I have both spot drills and center drills and unless its hard to get to with a shorty center drill, I use that for spotting too.
 

plastikdreams

Active member
The guys I work with don't really have experience with exotics like 17-4 tool steels stainless steels and inconel...so they don't realize there are times you can't even dream of getting a center drill down that deep. I or us some carbide tools but even still I would dare anything more than 10 or 20 k down in some metals.
 
I use center drills to spot holes if I'm using a hand drill. On a machine I try to always use a spot drill.

When I was a kid, my dad taught me to never take a center drill deeper than half way up the tapered section. I tend to stick to that and it works well.
 

Cole2534

Active member
The real kicker is that a 1/4" single end spotting drill is abut 4x the price of a 1/4" double ended spotting drill.

Programmed via Mazatrol
 

crickets

Member
The way I look at it, it depends on the diameters. Problem with larger conventional drills is that they may have a pretty wide web. So if you just peck with the tip of the center drill, you don't really create a geometry a large drill can register against.
 

plastikdreams

Active member
I only use the tapered part if I’m using it for an actual centre.

If I’m spotting for a drilled hole I only use the pilot parallel section as trying to drill in to the tapered section causes chatter because of the change in angle. This chatter can also cause the drill to go off centre.

The way I look at it, it depends on the diameters. Problem with larger conventional drills is that they may have a pretty wide web. So if you just peck with the tip of the center drill, you don't really create a geometry a large drill can register against.

This is true, I have some large center drills...seems to work, but I don't do many large holes. I carry up to size 6.
 
So I've always used just the tip of center drill to spot a hole, the other day the old guy in the shop said I've been doing it wrong and that you need to go down to the tapered part of the center drill. So is there one correct way or would either work...it always worked for me.

My first thought is how much time the old guy wasted in his career drilling center drills that deep, probably weeks of time

Guhring has a good document explaining that it’s best to use a spot drill with an angle slightly larger than the drills included angle. This puts the very tip of the drill in contact of the material first where it will center the axis of rotation well.

I feel that the deep center drill idea comes from manual drilling on a Bridgeport, where the guy pulling the handle starts softly and doesn’t use a lot of pressure to start. Yes the drill will start a bit softer but is it closer to the correct spot?
It’s hard to tell a difference on location, I’ve checked by sweeping the holes, there is not a huge difference. I feel the advantage of a small spot drill is that you get a hole that is closer to the drill size and better finish.
 

plastikdreams

Active member
My first thought is how much time the old guy wasted in his career drilling center drills that deep, probably weeks of time

Guhring has a good document explaining that it’s best to use a spot drill with an angle slightly larger than the drills included angle. This puts the very tip of the drill in contact of the material first where it will center the axis of rotation well.

I feel that the deep center drill idea comes from manual drilling on a Bridgeport, where the guy pulling the handle starts softly and doesn’t use a lot of pressure to start. Yes the drill will start a bit softer but is it closer to the correct spot?
It’s hard to tell a difference on location, I’ve checked by sweeping the holes, there is not a huge difference. I feel the advantage of a small spot drill is that you get a hole that is closer to the drill size and better finish.

I think I'm gonna try and order some split point drills and not worry about center drills and spot drills.

I've also had good luck in 2024 with doing a quick spot with just the regular drill point.
 

Gordon Heaton

Active member
I think I'm gonna try and order some split point drills and not worry about center drills and spot drills. . .

Well, spot drills, especially solid carbide, are the cat's meow if you need to reach down past another feature to make the spot. Those solid shanks with just a bit of flute length keep the wobble and wander to a minimum.

Like you, if space permits I'll use a center drill to spot and chamfer a hole to be threaded. Saves a bunch of time.
 

juergenwt

Active member
A center drill is not for spotting a hole. If you are trying to pick up a center punch than use a very small spiral drill (1/16 or so)
and pick up the center punch to start. The small drill will pick up a center punch much better than a center drill since it will find the center
punch and bend slightly to stay on position. I am talking drill press or hand held drill or if the work piece is held by hand. If you use a center drill it will make it's own hole and act like a milling cutter. You will end up with a lot of holes out of position and also a lot of broken center drills. In a solid machine where the workpiece is held in position (clamped)use a spotting drill.
A center drill is for use on a lathe.
 








 
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