View Full Version : Core Drills

09-02-2005, 08:26 PM
I have a few 3 and 4 flute core drills. I know they are used to rough cut through the cored holes in a casting. Is there an advantage to using these drills as opposed to using a regular 2 flute drill? Tips on the proper use of these in lathe or mill / drillpress would be appreciated.


09-03-2005, 07:15 AM
My understanding is that they have less tendency to follow the cored hole than a two-flute drill does, so they don't wander.

09-03-2005, 07:22 AM
Correct, and they are not as flexable.

If I remember right they must have a "pilot" hole wether a core or a drilled hole,they don't have a point.

The tame Wolf !

09-03-2005, 07:34 AM
Uhhh, Frank, there's nothing in this thread but machining. Aren't we supposed to insult or dis somebody too?

Gotta get with the program, man. http://bbs.homeshopmachinist.net//wink.gif

Sorry to have missed you at Iron Fever. Had car problems Fri. pm & the tow truck didn't show till 2am.


09-03-2005, 07:53 AM
Don't they have emails for personal conversations. http://bbs.homeshopmachinist.net//wink.gif

There's your negative remark for this thread,I hope it doesn't get any worse.

The tame Wolf !

Peter S
09-03-2005, 10:53 AM
Core drills work nicely for drilling out nylon bushes, they leave a better finish than a 'normal' drill.
We used them to resize plastic bushes after they were pressed into the end of tubes. A 2 flute drill is easy to feed too fast and leave a rough finish which is noisy.

09-04-2005, 07:16 PM
They don't have a point. A pilot would be a necessity if there isn't a core hole in the part. I didn't have time to look , but I wonder if there is a different cutting angle.

My appoligies to all for being on topic. http://bbs.homeshopmachinist.net//wink.gif

Bill, We were looking for you at the show. We figured something came up that you weren't there.

Thanks for all the input,

09-09-2005, 04:40 AM
........Core drills? So THAT'S what I bought at Reliable Tool http://bbs.homeshopmachinist.net//biggrin.gif. Drove over to pickup a 6" Kurt I was high bidder on, and went into their 'retail' store. They have skads of tooling of all types in there.

Most the edged cutting stuff like endmills, drill bits, reamers, etc are in bins and sold by the pound. I think it was $3.50/lb HSS and $4.50/lb for carbide.

In the one for drill bits there were 5 carboard tubes rubber banded together and when I pulled the tops they were odd looking drill bits to me. They were 3 flute, had lands on the back of the flutes and the front looked like a reamer.

At the front the lands have a sharp angle and no point. The center is recessed and has a hole for a center. I thought they were drill-reamers.

Or maybe that's what they are and they're NOT core drills? I haven't used any yet, but I would have more use for them as drill-reamers to enlarge holes then anything else. Not having a clue, but the fact that they were shiney and sharp and $3.50/lb I had to have them http://bbs.homeshopmachinist.net//cool.gif


09-09-2005, 08:38 AM
I don't remember the exact name for the shape, but if two flute drills tend to make a three "sided" hole, 4 flute drills tend to make a 5 sided hole.

I.e. The more flutes, the more round the hole, especially in very unpredictable conditions, (such as a cored hole).