Drilling with very small drill bits (#80) - help?
The plan was to drill silver with #80 bits for piercing. I started
by practicing on a similarly sized copper piece. The metal is 2mm
thick, but I'm forced to use a 8/0 sawblade because of the
difficulty of the design to be pierced. Final score: Broken drill
bits, 20; Completedholes, 0; Frustrated artisan - 1. Fact of the
matter is, I didn't' comeclose to completing a hole.
Began with the Foredom handpiece then switched to Archimedes drill.
With both tools the moment I put enough pressure to cut metal the
drill bit would slip back into the holder or break. Switched to a
heavyish pin vise, hoping to use the weight to sink the drill bit,
same non-results. In each case, the drill was loaded correctlyin
whatever I was using (centered in the bit), and I manipulated the
drillby hand until it rotated without bowing. With the Foredom, I
started slowly, worked the drill until it spun straight and seemed
seated, and used different speeds to no success. Tried lubricated
I feel that if I had a good quality Archimedes drill I might have
luck with that, but I can't find a good quality model that would
(for instance) take watchmakers collets.
The drills are the "good" ones from Rio.
I hope to find the launched pin vise that is somewhere on the other
side of the shop tomorrow.
Any suggestions? Am I doing something obviously wrong, or is this
just a skill I need to develop? Any good tutorials online?
You're asking a drillbit that's about 0.35mm to drill about 6 times
its depth in copper. A very gummy material. That's asking a lot.
Couple of suggestions: Rio's 'good' bits are good, but probably not
good enough for this. If it's any hint, I went to my normal supplier
of industrial drills, and the smallest they had was #76. For $23
each. So, step one would be to look around for what are called
"screw machine" drills. They're shorter, and thus stiffer. And thus
less likely to deflect and shatter. Get high speed steel, not
carbide. HSS is more flexible. At this size, that matters a lot.
What kills drillbits, especially small ones, is if they bend. Hand
holding a bit that small is just about guaranteed to blow it up. You
need a drill press, and a good one, for holes like that. Start with
one of the foredom ones that holds a #30 handpiece, if you can find
one, or one of the other little "Precision" drill presses. What
you're looking for is absolutely minimal chuck runout, and what will
seem like insanely high speeds. You also need to make sure the
copper is clamped down solidly, so it can't move at all.
cutting edges that run across the "front" end. Everything else is
just there to either support those edges, or get the chips out of
the hole. How those edges cut is a function of how fast they
intersect the material they're cutting. That speed is a function of
diameter. For the same RPM, the outer edges of a 1/2" drill are
moving at 1/2X and so on. For copper, a good conservative speed
would be around 100 SFM (Surface feet/minute) At 1", that gives 382
At 1/2" you get 764 RPM. At the.0135" diameter of a #80 drill, you
need 28,294 RPM to get the drill running fast enough to cut
(RPM=((SFMx12)/(tool diameter x Pi)))
So, yeah, you need coolant. LOTS of coolant. And get the drill press
running as *FAST* as you possibly can. Then peck, very lightly at
it. You'll be under-turning the drill, no matter what you do, so
it'll want to jam with chips. The pecking brings the flutes out of
the hole so they can clear themselves before they jam and blow up
the drill. Also lets the drill cool before it fries. It doesn't help
that copper's as gummy and nasty as it gets. The silver final piece
will be easier, but not by a vast amount. Sterling's still pretty
Real, industrial drill presses that are actually intended for this
sort of thing can be had, but they're shockingly expensive. I ended
up at the right estate sale at the right time, and came home with
one, once upon a time. Its maximum diameter of drill is 1/4", and it
weighs 150+ pounds. Mostly in the spindle mount. When I put a new
chuck on it, I clocked the runout: 0.0002". And the max speed is
about 8K RPM. (Not nearly the 28K you need for that little drill, but
the best you're going to get for anything half way sane.) (google
"Hamilton Varimatic" or "Sigourney sensitive drill press" "Dumore
sensitive drill press") They're called "sensitive" drill presses,
because the spindles are designed to move *very* lightly, to give the
operator some hope of feeling what's going on with the bit. The big
thing about them is that they're fast, and the spindles are just
about as close to perfectly concentric as you can get. When you're
working with drill bits that are only about thirteen thousandths of
an inch thick, spinning at 10K RPM, a few thou of eccentricity in the
chuck suddenly becomes a very big deal.
Hope that helps,
Try putting the drill bit in the chuck with only 3mm exposed and see
if that helps. Take care, Paul Le May.
Fortunately youve mentioned the silver thickness.
so to drill through 2mm metal the drill needs to stick out of the
chuck a maximum of 3 mm. No more!
Think about it, if your using a drill that thin sticking out say 15
mm, the thickness to length ration is way too much for the drill
Try it as above and report back how you get on.
Use preferably your fordom, you will have better control than an
Drilling with small drills requires tools that will properly hold
the bits and run true. The main thing is to take very small bites
and use LOTS of lubewhich needs to be reapplied very frequently:
drill for a second, lube, repeat. One tip that I will pass on is to
rotate your work. This will compensatefor the slight angle that your
drill will be entering the piece and your hole will come out
centered. I have been at this for thirty plus years and I can come
very close to drilling straight centered holes holding the piece in
one position but by rotating I know it will come out centered.
Remember, slow and lots of lube. Best of luck.
than say 74 on the larger ones burr lube or bees wax or my favorite,
Make a divot with a centre punch first. You need to check the tip for
a drilling angle of at least 90 degrees, but better is an angle
around 115-150 so shallower to dig in without skating across the
metal. Make sure you are using a twist drill bit for metals- in fact
a diamond coated drills will work best. Don't put pressure on the
handpiece ; let the rotation at a slower speed than you are using do
the work since you say it keeps breaking. also HSS bits aren't as
strong as a tungsten or carbide drill, and titanium or cobalt
coatings over steel are acceptable as well. Keep the drill
lubricated. A number 80 is the finest bit - why not try a # 60?
#46-47 is closest to what is necessary for a 2mm sheet so using a
#80 bit is like using less than a 3rd the size that will go through
it most easily. even though you are using 8/0 saw blades to start the
piercing it doesn't matter what size the bit it- so use a reasonable
sized bit and make your life easier- 20 is too many to have gone
through already! Go larger. rer
The smaller the drill bit the faster it should be turned, therefore
get the speed up HIGH on this small of a bit. Use some form of bit
lube, bees wax, oil of peppermint, something. Make a "set mark" a
punch mark where you want to drill the hole to get the bit to stay in
place and not wonder off the mark. The first thing that went thru my
mind as I read your post was "the drill is being turned backwards"
and that is still "dining in my head" as the problem but you have
used different turning equipment so that is out. Are the drill bits
"reverse twist"? Reverse twist drills are not common but are they
ever handy to get a broken bolt/screw out of a hole!!!! Check the
twist direction of the drill bits to any of your other bits that work
Another thought, is the silver work hardened? A decent bit should
still have little trouble drilling hardened silver, just a thought.
Wish I could see what you were doing in person, this should not be
such a problem.
Best of luck,
Hi, Brian -
Thank you for all your excellent recommendations andthe math
reminder. For one brief minute I was back at HSM, with ForrestAddy
reminding me to "use your Handbook; if you can't put the problem
intonumbers it isn't fully defined"!
Not included in my original post was that I also tried my Servo
Drill. Better cutting at 20K rpm, but no control over drill breaks.
By that, I mean the tip of the drill would twist off in the hole
during rotation, essentially ruining the work because the broken
piece is flush and cannot be removed. I have a dim recollection of a
etchant used to remove steel bits from silver/copper, but I'm
thinking that any etchant that will help take out a drill bit would
probably ruinthe work.
I did, however, come up with a solution that works (sort of). By
that, I mean that drills still break, but won't break in a manner
that ruins the work or as often. Last night I got through 2mm of
copper for almost 20 holes before anything broke. To your point, I
am up to the#77 drill; anything less than that I can't get to cut.
My alleged 'solution':
-- Use a pin vise with *just* enough drill showing to fully
penetrate the work (minimizebending). -- The smaller the top part of
the pin vise, the better. (more twist = higher rpm)
-- Prick and center, being very careful to create the smoothest
"crater" possible without inverted mushroom sides, i. e. don't hit
it too hard. (my unproven theory is that they grab the drill) --
Anneal just in case the prick andcenter process hardened the work.
(why not remove that variable)
-- Use the thumb and forefinger to "twist" the pin vise while
lightly holding it upright and bracing the work with the other hand.
-- The key: Use a counter cutting motion to break chips. I twist
clockwise twice to cut, then spin back counterclockwise in the
non-cutting way at least once to break the chip.
-Clear the hole and relubricate often.
-Have a considerable amount of patience.
It's a pain, but it can be done.
I have found that I need to use a wax lub on my #80 bits. i first
mark whereI want to drill with a center punch then I use my flex
shaft and start out slow and work up the speed cutting a little at a
time with very light pressure then I stop and clean off the bit and
drill a little more. A slow process but works for me great very few
broken bits. if you are doing fine piercing work the work is going to
be slow anyway. I also only hold my saw with 3 fingers. reduced the
amount of pressure I can put on the saw blade and makes me slow down
and concentrate on the feel of the saw cutting. It is all about touch
and feel. Hope this helps.
Wow Brian, what a great explanation! It allowed us to see very small
things for the time necessary to comprehend the problem. Thanks
We used to make our own small diameter spade drills using a needle
which isalready hardened and tempered. The advantage is they don't
have a spiral cut in them which weakens the drill. The spade drill
sort of scrapes its way through.
One tip that I will pass on is to rotate your work.
Tim, How do you rotate the work without losing center
Janet in Jerusalem
You can dissolve broken steel bits from gold with alum powder, which
can be found in some old-fashioned drug stores as it was once used to
stop the bleeding from a shaving nick, or order it on-line. I haven't
tried it on silver, but it might be OK since it's probably attacking
the iron alloy & will not effect non-ferrous metals. It's been a
while since I did it, but if memory serves me, put a high
concentration of it in water, bring it to a boil, turn off heat, then
soak your piece over night. Use a pyrex pot, not a stainless steel
pot. What is a high concentration? I believe I used half of an 8 oz.
container in a small pyrex saucepan, but I can't be certain. But if
you have 77 broken bits you can try a few experiments.
You may need to treat it a few times to totally remove the bit.
Good luck, & if you do try it, I would be interested to know if a
particular ratio worked.
My experience, is the reverse, I drill as slow as possible, with
minimal pressure, use a lot of 'home made' lubricate rio grande blue
lubricant mixed with 3 in 1 oil and take every 10 seconds the drill
bit out to clean it, have not broken a drill bit in ages, touch wood
My experience, is the reverse, I drill as slow as possible, with
minimal pressure, use a lot of 'home made' lubricate rio grande
blue lubricant mixed with 3 in 1 oil and take every 10 seconds the
drill bit out to clean it, have not broken a drill bit in ages,
Your experience is correct. That is exactly how one should drill.
I can also add that drill should be as long as possible. Long drills
can absorb some misalignment which is unavoidable while drilling by
My experience is the same as that of Peter. I drill very slowly,
stoppingoften to lubricate the drill. If I am drilling through a
thick piece of metal--14gauge or more I slow the action way down.
This way the drill never grabs, binds, or develops that screeching
most people (particularly beginners) when they drill have the drill
come through the piece of metal in a location completely different
than where the hole was started on the front. This is due to the fact
that it is very difficult to drill 100% perpendicular. The rotation
of the piece compensates for this as well as slightly enlarging the
hole as you are drilling which is a good thing, this helps the drill
from binding in the hole as it goes deeper into the metal. Even if
you don't feel comfortable turning the piece, you should "wiggle" the
drill to accomplish the same thing, enlarge the hole slightly as the
drill passes into the metal. As far as rotating the piece, I am
speaking of turning the piece aprox. a 1/4 turn every time the drill
is removed for lubricating which should be every few seconds. The
smaller the bit, the more frequently it will need to be lubricated.
The piece is actually held stationary while the drill is being fed
into the metal. I'm sure you have seen a band ring with stones set in
it and looked inside to see the holes behind the stone all over the
place creating a very un pleasant and amateurish appearance. You
definitely want to make a punch mark in the piece to start your
drill, once it is started the rotation will have no affect on the
drill remaining centered only enlarge the hole slightly. I once won
$5 from a young and hard headed co worker by betting him that I could
have the drill come out centered on the inside of the ring while
holding the drill at an almost 45 degrees to the piece. Small bites
and lots of turning and his money was mine. Hope this helps, Tim
I agree Leonard. long bit and slow speed. Works best for me.