Center punch, center drill or spotting drill?

[tominboise]

I have to drill about 80 1/4" holes in 1/4" angle iron. I have a PM728 Mill and a Buffalo drill press. Basically 40 holes on 1" CTC spacing. I thought I would just use a center dill and the mill to spot the locations and then drill to final diameter. But I read that I should use a spotting drill to spot the locations and then drill. I have center drills but no spotting drills. Or should I just center punch and drill on the drill press? Or center punch and then drill on the mill?

 

[Jim in Wisconsin]

As long as you have a mill, you might as well use it - lay out the location for the first hole in the piece and keep dialing over 1".
I don't know what a spotting drill is, but a center drill and then the 1/4" sounds ok to me.
Maybe clamp the angle iron down on a piece of wood - (just don't drill through and hit the table!)

 

[ChazzC]

Use a Screw Machine/Stubby 1/4" drill and skip the spotting drill (used for "spotting" holes, as opposed to drilling holes for lathe centers, spotting drills typically have a cutting angle (120°) near that of the drill that will be used for the through hole (118°).

 

[tq60]

What he said!

Get a stubby 1/4 drill bit, get a few.

Put it deep in the chuck, 1/4 inch material, have it stick out no more than 1 inch.

Get the material as close to the spindle as possible so best rigidity.

Punch them out.

Sent from my SM-G781V using Tapatalk

 

[MrWhoopee]

Agree with the others, stub length drill without pre-spotting. I do it all the time, use more stub drills than jobbers length.

Here's a couple of spotting drills, they're essentially stub drills available in different point angles, designed for establishing an accurate hole location.
Center drills were always used for this purpose until the advent of the internet when we found out we'd been doing it wrong all along.

 

[SouthernChap]

Center drills were always used for this purpose until the advent of the internet when we found out we'd been doing it wrong all along.

That made me chuckle but its not entirely fair, really.

@tominboise

Spotting drills create a spot with a cone that has a steeper angle than a 118° drill, meaning that when the 118° drill encounters the spot, the cutting edges will hit the circumference of the spot before the tip of the dril hits the bottom of the spot. That's supposed to lead to less wander and more accurate drilling. Spotting drills are used a lot in CNC drilling.

I guess whether or not you need a spotting drill depends on the requirements of accuracy of the holes you're drilling. If you're drilling 80 holes, I hope for the sake of your sanity, you don't need them to micron accuracy.

Centre drills, strictly speaking, are designed for just what their name suggests, making the hole for a lathe's centre to go. That said, it'd be silly to shame someone for using a centre drill to spot on a mill or drill press; for most purposes a centre drill is fine. I do have spotting drills, which I now use in favour of centre drills on the drill press, but I did use centre drills before I got the spotting drills and that seemed fine; I guess I just like buying drills.

Stub drills (AKA screw machine drills) are brilliant things to have so you should buy them anyway, but what others have said about skipping the spotting step and using a 1/4" stub drill to pilot the holes is a great idea, given how many holes you're drilling.

 

[Ultradog MN]

Another fan of spotting drills here.
We've all broken off the tip of a center drill and then tried to figure out how to drill from the back side - if you can - to get the broken tip out.
Much less chance of breaking the tip off a spotting drill.

 

[cathead]

At times, I will use a center punch to establish where the holes are supposed to be and follow up with
a 1/8 inch diameter long bit that will gravitate into the punch mark, then drill the hole to final size. That's fairly
accurate but likely not as good as using a center drill along with a digital readout.

 

[RaisedByWolves]

Stub drill vs center drill in my opinion depends on the work being done.

If I’m drilling for a threaded hole I’ll use a properly sized center drill as it will leave a chamfer for the tapping operation after the tap size hole is drilled.

I’ll also use them for any job that requires better accuracy as this is what my company supplies and is standard practice for our shop.


For OPs job however a spotting or stubby drill sounds best.

 

[mmcmdl]

Just drill it thru with the spotting drill . No issues .