What's the purpose of a three flute drill bit ground to 78 deg.?

marka12161 · Aug 12, 2018

Now before anyone submits to the urge to reply "to drill holes", i get that part. But why three flutes and 78 deg. rather than the more common 60 deg.? Are they for a specific material? They are HSS.

I picked these up in a pile of other stuff i bought.

Sam Shublom · Aug 12, 2018

Probably a "core" bit for cleaning up cored holes in a casting. Not to be confused with core bits that cut out a cylindrical slug of what ever material they are drilling.

Gobo · Aug 12, 2018

One more cutting edge-higher feed rate.

PeteM · Aug 12, 2018

+1 to Sam.

L Vanice · Aug 12, 2018

Thee flutes (or four) are used on core drills because they will self-center in an existing pilot hole, where a standard two flute drill will tend to chatter and grab.

Larry

k3vyl · Aug 16, 2018

The 78 degree point is also less likely to grab and chatter.

mneuro · Aug 16, 2018

3 flute is great in aluminum. We use them all the time. self centering and high feed.

We also have custom drill points made regularly for customer specs.

cyanidekid · Aug 16, 2018

Sam Shublom said:
Probably a "core" bit for cleaning up cored holes in a casting. Not to be confused with core bits that cut out a cylindrical slug of what ever material they are drilling.

yea, there is a problem there, seems to me a drill that only enlarges a hole should be called an enlarging bit, and only called a core bit or drill if it produces a core

TDegenhart · Aug 16, 2018

cyanidekid said:
yea, there is a problem there, seems to me a drill that only enlarges a hole should be called an enlarging bit, and only called a core bit or drill if it produces a core

Drag yourself back from modern times to when casting were common. There were holes in the castings that needed to be machined. They were made by cores. Hence core bits or because they looked like drills, core drills.

Tom

Sam Shublom · Aug 16, 2018

Quote Originally Posted by cyanidekid
"yea, there is a problem there, seems to me a drill that only enlarges a hole should be called an enlarging bit, and only called a core bit or drill if it produces a core"

If there is a problem here, I think you are the only one having it. Yes, they were used to enlarge and dress up cored holes. Hence the name "core" bit or drill. I didn't invent the term. Please note this scan from a Cleveland catalog. They seemed OK with it so who am I to argue with them. I know if you asked any of the old time countermen at English Brothers in Kansas City MO, where I used to trade, for a core bit, this is what they would hand you. Buy the way, if you wanted a bit that would produce a cylindrical slug, they would more likely know what you were talking about if you asked for a "hollow" bit. Colloquial I suppose, but it got the point across.

cyanidekid · Aug 16, 2018

Sam Shublom said:
If there is a problem here, I think you are the only one having it. Yes, they were used to enlarge and dress up cored holes. Hence the name "core" bit or drill. I didn't invent the term. Please note this scan from a Cleveland catalog. They seemed OK with it. I am not going to argue with them. I know if you asked any of the old time countermen at English Brothers in Kansas City MO, where I used to trade, for a core bit, this is what they would hand you. Buy the way, if you wanted a bit that would produce a cylindrical slug, they would more likely know what you were talking about if you asked for a "hollow" bit. Colloquial I suppose, but it got the point across.

I'm well aware it is common usage, but that doesn't stop it from being irrational, confusing, and just plain stupid. :stirthepot:

Limy Sami · Aug 16, 2018

cyanidekid said:
I'm well aware it is common usage, but that doesn't stop it from being irrational, confusing, and just plain stupid.

You haven't quite got the hang of this life thing - have you

plastikdreams · Aug 16, 2018

Limy Sami said:
You haven't quite got the hang of this life thing - have you

Has anyone really?

k3vyl · Aug 16, 2018

Its possible that 100 years elapsed between the coining of the two usages of the term core drill.Im an electrician,they core drilled the reinforced concrete floors for our conduits back in the 70s.The cutting tools were hollow tubes with carbide inserts.Copious water was used.
Many years before that castings had to be drilled as a roughing step in the machining. The core holes were not round, so they needed drills that would center up in a "core" or cast hole.These drills were also called core drills.The english language has its limits.

Smoothbore · Aug 16, 2018

k3vyl said:
The english language has its limits.

As does the human mind.

.

Locodad · Aug 17, 2018

k3vyl said:
Its possible that 100 years elapsed between the coining of the two usages of the term core drill.Im an electrician,they core drilled the reinforced concrete floors for our conduits back in the 70s.The cutting tools were hollow tubes with carbide inserts.Copious water was used.
Many years before that castings had to be drilled as a roughing step in the machining. The core holes were not round, so they needed drills that would center up in a "core" or cast hole.These drills were also called core drills.The english language has its limits.

It gets even more complicated if you start “crossing crafts”. Every occupation has some of its own “terminology”. Let’s not mix apples and oranges.
[emoji4]

Sent from my iPhone using Tapatalk

DMF_TomB · Aug 17, 2018

long drill bits like 18" long do not like pilot holes .002" smaller than long drill bit. 2 flute drill bits sometimes start vibrating then break.
.
quite normal to drill 4 to 6" deep then switch to a longer drill bit to finish the hole. if 3 flute drill less sensitive to slightly under size pilot hole vibration then i can see using them.

Mike1974 · Aug 17, 2018

DMF_TomB said:
long drill bits like 18" long do not like pilot holes .002" smaller than long drill bit. 2 flute drill bits sometimes start vibrating then break.
.
quite normal to drill 4 to 6" deep then switch to a longer drill bit to finish the hole. if 3 flute drill less sensitive to slightly under size pilot hole vibration then i can see using them.

What does that have to do with anything? I'm dissapointed in you Tom

, there is a thread about a long endmill, and you posted another generic reply (like this one). I thought BIG tools and machines were your bread and butter? But I digress

When the OP said "ground to 78deg" I thought he meant like a taper dirll, but it seems it is the point? Could be done by hand.. dunno, just a guess. Don't know that 78deg would be better/worse than 82deg or 70deg, or xxdeg :willy_nilly:

DMF_TomB · Aug 17, 2018

Mike1974 said:
What does that have to do with anything? I'm dissapointed in you Tom , there is a thread about a long endmill, and you posted another generic reply (like this one). I thought BIG tools and machines were your bread and butter? But I digress

When the OP said "ground to 78deg" I thought he meant like a taper dirll, but it seems it is the point? Could be done by hand.. dunno, just a guess. Don't know that 78deg would be better/worse than 82deg or 70deg, or xxdeg

.
i quite plainly said vibration with undersize pilot holes with long drill with 2 flutes can be a problem and 3 flute drill probably have less of a vibration problem.
.
i run all different size machines. long drill vibration doesnt have much to do with size of parts. for reach purposes often you need long drills

What's the purpose of a three flute drill bit ground to 78 deg.?

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