View Full Version : How Do They Grind Small Drills/Mills

Paul Alciatore
07-16-2007, 09:23 AM
The factories must make small drills and milling cutters by the thousands. They can make split point drills as small as 1/8" or 2mm. I am curious about the grinding wheels they use for this process. For an 1/8" split point drill, they need a wheel with a sharp corner that will stay sharp for many drills - hundreds, even thousands. I would imagine that even a few thousanths of wear on that edge of the wheel would require changing it out as it would produce too large of a radius on the drill.

So I am prompted to ask what kind of wheels do they use? And how do they sharpen the drills? I mean, do they do the entire job with the same wheel or do they have a rough wheel and a finish wheel to minimize wear on the final one? And how often do they need to change wheels for redressing? Or do they incorporate dressing tools at the point of production?

This is mainly an academic question at this time, but sooner or later I may want to have/make a grinder for such work - but small quanties, not thousands.

07-16-2007, 11:42 AM

Diamond or Cintered Borazon Nitride would be my guess. The drill doctor has a diamond wheel and it will easily split the point on drills down to about 5/32". THe corners stay sharp and need no dressing. There are other drill grinding machines folks have mentioned here that do a nice job on drills down to the #60 or so range. End mills are not a problem either, although anything below 1/8" I usually just throw out and buy a new one due to the time/cost involved.

07-16-2007, 11:47 AM
Don't mean to be facetious Paul, but have a look at....
at the bottom of the page

07-16-2007, 12:16 PM
The CNC production Tool and Cutter Grinders generally use CBN, with an automatic wheel truing every so many parts.


07-16-2007, 10:42 PM
How about Mitsubishi - a .020" drill with coolant thru. Need a loop to see the 2 coolant holes.

Rich Carlstedt
07-16-2007, 11:46 PM
By hand !

recently, I had a real learning experience.
I had to drill over 1440 holes through 1/32 brass sheet manually
with a .022" drill (s).
No problem thought I, with my new (old) Dumore variable speed (upto 17 K r's) precision drill press and some new Cleveland drill bits!
Started and two holes later, I had a broken drill
Again I did two holes and "Snap' another bit went South.
Ahh, I need Lube......three holes and snap.
I looked at the holes..hmmm..lots of powder..and HEAT
I am too fast.. slow down to 5K and try it again,,this time with
a new Union drill and Lube... Five hole later..snap.
this is crasy.. 4 broken drills in under 5 minites.
Gee, I would need about 400 more drill bits at this rate.
I studied the other bits with a eye loope.....perfect, they looked magnificent
After 3 more failures, I was frazilled..what was going on.?
So I decided to try to sharpen the drills myself, using that $3 book I bought
about umteen years ago from Lindsay, that said 'Sharpen your own micro drills" or something like that.
So out came the India Stone (fine) and into a pinvise went a broken drill
First I flatened it, then found the "flats" with a magnifing glass, and marked the pin vise with a magic marker
since I could not "see" the flats when handling such a small drill.
Then 3 angle strokes, and flip and 3 angled strokes and it was done.
It looked good to me and I put it in the chuck, and WOW
the first hole had 2 beautiful little curly cue chips that were miniature
of what you see in a drill catalog..hot dog..and no powder
100 holes later..snap..no problem..get that stone over here.

So I learned that even factory drills may not handle the job at hand.
I believe the Brass sheet (hard) just needed a lot of rake on the
cutting edge as the new drills would heat up (on brass no less !)
and the slightly different cutting flutes gave just enough over size
to the hole to let the chips escape and not produce heat.
I got chips and not powder or heat !
it also drilled through in about 2 seconds versus 6 when I started
the rivets I used worked fine and when I measured the holes, a .025 drill would not go through, so it did work.

moral of the story.. when everything fails
try your hand in it..you may be surprised

Paul Alciatore
07-17-2007, 01:29 AM
Good replies. Thanks to all.

Yes, diamond and CBN I have heard of. A wheel that does not need dressing does not sould belieable, but perhaps so. Any brand names?

As for a $13,900 sharpening machine, if I spend that much I will have a CNC mill. Actually, I hope one day to have a CNC mill for a lot less. You would think for such a high price machine, they would post a better picture. Oh well!

Hand sharpening, yes I am a great believer. I can do a good job on a 1/4" or larger drill and have done some touchup on milling cutters. I needmore practice on smaller ones. One of my favorite tricks is to round the corners on a worn milling cutter to leave a nice fillet. At present, my question is mostly a search for knowledge.

I would still be curious about specific brands and model numbers for the wheels.

J. Randall
07-17-2007, 01:57 AM
Rich, I would have thought zero rake on brass. Are you maybe talking about a lot of relief?

07-17-2007, 02:24 AM

Shuswap Pat
07-17-2007, 09:01 AM
If you check out Guy Lautards 'Machinists Bedside Reader #1' there os a nice article on building a jig for honing small drills.


07-17-2007, 09:57 AM
On a less ambitious scale....

Rich Carlstedt
07-17-2007, 11:23 PM
" I would have thought zero rake on brass. "
Good Comment
You are right, and thats what I thought as well.
I have a set of drills (large) where I ground the cutting edge parallel
to the shank, presenting a 0 rake almost for brass work. it stops pulling and gouging.
Such a grind on a .022 drill means only touching about .012 on each lip..far beyond my ability
But the job I outlined before is just about as contrarian as can be for brass work.
The issue of powder(not chips) and heat when using brand new drills just threw me.
I even thought at one time they might be Left hand drills, because that is exactly
what you get when drills are used backwards....but they were normal jobber drills.
thats why I posted my experience...
its a head scratcher

J. Randall
07-18-2007, 01:59 AM
Rich, Thanks for the explanation, makes for another good tip to file away just in case.

07-19-2007, 01:20 AM
I have used my Dremel grinder and one of their slitting wheels and an eye loupe to split small drills.
Jim Sehr

Paul Alciatore
07-20-2007, 01:42 AM

Which Dremel wheel? Did you have to dress it?

07-20-2007, 10:38 PM
Wear glasses.


Jim Sehr

Weston Bye
07-21-2007, 06:53 AM
Another vote for the Dremel with the wheel pictured above. Back when I was making a lot of printed circuits, the glass-epoxy FR-4 board dulled a HSS drill pretty fast. I know, shoulda used carbide. Anyway, I got to where I could resharpen 1/32" drills almost casually, freehand with the Dremel.

07-21-2007, 07:54 AM
Yes, diamond and CBN I have heard of. A wheel that does not need dressing does not sould belieable, but perhaps so. Any brand names?
CBN wheels hold their shape extremely well. They can be trued but not by holding a wheel truing tool against them in handheld fashion. They can be dressed to restore cutting action by touching a piece of an aluminum oxide wheel to the CBN wheel. I have several CBN wheels and use them for grinding, among other items, custom made counterbores. CBN wheels hold a very sharp edge and keep it for a very long time grinding HSS. Note that diamond wheels aren't suitable for grinding high speed steel or any other iron containing alloy.

This is one type of CBN wheel that would be used:


This is a counterbore that I ground with a CBN wheel. The corner of the wheel is very sharp and stays that way as virtually no wear occurs to the wheel itself in use.


Paul, if you want brand names then contact me.