What factors drive the selection of the drill bit angle? I need to
restock on bits and I've always just bought jobber TiN bits. Now, I'm
doing some research and am wondering about the angle. The jobber bits
have always worked just fine for me.
Second related question: are cobalt bits worth the additional cost
over TiN for drilling mild steel and occasional tempered steel? I am
not dealing with "ordnance"/extremely hard steels - mostly raw stock
and various automotive-related parts.
All suggestions are appreciated.
From the Darex M3/M4 drill sharpener manual:
135 degree Angle Point
This point is frequently preferred for hard and tough materials such as high
alloy steels. Increasing the point angle increases the effective rake angle
of the cutting edge (lip) and reduces the length of the lip. The result is
a reduction of the driving torque required to drill these materials. The
feed pressures are increased. Reducing the lip relief angel strengthens the
lip. To produce this point, simply set point angle at 135 degrees and align
chuck arrow with 135 degree mark on chuck grip band of relief setting
90 degree Angle Point
Many soft and low-strength materials, such as some cast irons, aluminum,
plastic, and wood can be drilled more efficiently with a reduced point
angle. Although this change reduces the effective rake angle of the cutting
edge (lip) and the length of the lip is increased, the driving torque
required to drill these materials usually remains with acceptable limits.
The reduced feed pressures and the increased lip relief angle frequently
permit higher feed rates. To produce this point, simply set point angle at
90 degrees and align chuck arrow with 90 degree mark on chuck grip band of
relief setting fixture.
The Cobalt bits are Much better than HSS in both wear and heat resistance.
Often a requirement for stainless steel. Tin bits are simply coated like
Titanium bits. In both cases the coating allows the chips to leave the drill
bit without creating as much friction and thereby allowing the bit to remain
cooler and last longer.
Thank you Robert. I'm going to assume that the 118 degree bits must
be a compromise between the two angles you mentioned. I notice the
118 bits seem to be cheaper and will likely move with those. I've
only had a couple of occasions where I wished I could cut hardened
steels - one was a jammed stop nut that just laughed at all my bits.
No. No compronise - 118 deg. bits are, by far the most common. Darex only
mentioned 135 deg. because their equipment can sharpen that angle which is a
little better for harder material. IMO, you can probably do just as good a
job in harder material with 118 deg. bits, if you are extra careful -- and
if the bits are quality; which is more important than the point angle.
Personally, I never use anything other than 118 deg.even though I have the
equipment to grind 135 deg. points.
Aside from what has already been discussed, another factor is
"split points". These offer some significant advantages.
1) They take less force to drill through a given material, because
you are not having to force the "chisel edge" in the center of
the point into the workpiece. (This is more of a problem with
larger sizes, but can be a benefit for any size.
2) It is a lot easier to *start* a drill bit where you want it
with a split point. Normally, you can use a center punch to
produce a guide for the drill bit -- but in some materials
(Titanium, and some stainless steels) the work hardening caused
by the center punch can make it more difficult to start cutting,
as the drill bit is having to deal with a hardened material.
As an example of how much of a help a split pont can be, I had
to drill some pins *in place* on my garage door. One end of the
pins held the rollers which traveled in the track, and the other
end tended to sometimes move too far and drop out of one side of
the stamped metal "bearing". With a 1/16" split point, I was
able to start the hole, and drill through using a hand-held
electric drill, no center punch, and no fixturing. The diameter
of the shaft was 5/16" IIRC -- enough of a curve to make
starting a normal drill bit more difficult.
Also -- another thing to consider is drill bit length. There
are some times when you need a jobber length, and even some times when
you need the aircraft drills (6" or 12" long), but for most things, you
can use the "screw machine" length, which is shorter than the jobber
length, and thus stiffer.
I have several sets of standard HSS drill bits, but my favorite
is an index of screw machine length cobalt drills with split points in
the number (0-60) size range. Some of these days, I hope to get the
same in fractional, letter size, and even metric.
Of course, they are more expensive. This set I got when MSC was
offering the set on sale -- in a HUOT index which was modified to hold
the shorter bits properly.
Gotcha. I'm going to check out Enco's HotDeals catalog and order in
either some cobalt or TiN 118 bits. I saw the 135s and wasn't sure
whether to bother or not - if I've ever used them, I honestly don't
know. Thank you again Robert.
O.K. Though remember that a split point is not the same thing
as a 135 degree bit -- you can have 118 degree bits in split point
format as well.
Be aware that while the Drill Dr. claims to be able to produce
split points, it seems to work only on larger drill bits -- while I
often want them on smaller bits.
I use the Drill Dr. on larger bits (greater than 1/4"), but I
also have a drill bit sharpener for bits from 1/4" down to #70. This
one was made by DuMore (the maker of toolpost grinders), but it is no
longer made. All in all, it is a really neat design, and works quite
well -- once you have all of the collets -- one per bit size. A pity
that they were discontinued. (Though it, also, does not produce split
points, it does do a much nicer job of sharpening the smaller bits.
When you discover that it is time to replace a given drill bit
which you use frequently, I suggest that you order a 10-pack (the normal
minimum quantity) from MSC or somewhere else, in cobalt, and with a
split point, and you will be amazed how much nicer it is.
Don, I've always wanted to sharpen my old bits because I feel guilty
and pitching otherwise good bits. I'm basically a do-it-yourselfer
who enjoys metalworking, fixing cars, etc. Thus, I tend to be a
fairly basic drill bit user.
I've heard others say the Drill Doctor 750 did fine by them & am going
off that - I've never used one. Would you recommend it to a basic
user such as myself?
It does fine as long as you don't want split points on smaller
drill bits. (And I'm not sure how it does on the tiny bits (e.g. 1/16"
or perhaps a #33), but it does fine on larger bits, and I use it for
anything above 1/4". (Sometimes the ponts look a little strange, but
they work well, which is what matters.
However -- one thing that I have read can be a problem. It will
*not* work (using the fixture which sets the angle of the bit on initial
clamping into the collet) if you have a drill bit with an unusual spiral
(either high-spiral or lo-spiral), because the fixture is setting things
based on a point some distance back from the actual tip. There are ways
to fake it, but the proper setting points are nor marked.
For the typical drill bits, it will work fine. It is just those
with unusual twists which are a problem. (Also -- if you have any
left-hand bits, they also will not work at all. And left-hand drill
bits are particularly good for drilling out broken off screws, so I
have a few.)
So -- you opted to try both the new material and the new point
angle at the same time. You should have a pretty near indestructible
set of drill bits, especially for drilling in tough steels, with that
I would have considered it more interesting to try just the new
material first. Then the new point angle -- and perhaps not a full
fractional set for the first try. But you should get years of service
out of that set.
Are you using them in a hand drill, or a drill press, lathe, or
other stationary power tool? I would have opted for the standard 118
degree point for hand held electric drills (drill motors) -- or even
better split points, simply because the 135 degree takes a bit more
force applied by the tool, and is easier to control in something like a
drill press than with a hand-held drill motor.
I probably would not have asked this if you had gotten a number
size set or a letter size set, but fractional are more often used in the
I do both handheld and drill press. I didn't mention it, but I bought
one of their cheap 135 degree HSS import sets for $14.95 for
situations where I'm pretty sure the bit will be at risk due to the
angle or situation in general. It was $9.95 for the 118 degree so I
spent the extra money. There sure have been times I wishes the bits
would enter the work easier.
Yeah, I took the plunge. I've been itching to try the cobalt drills
but thought a set would be well over $100. As things dull, I
definitely have a dollar incentive now to sharpen them. I looked at a
Lisle sharpener for $995 and it sure made the Drill Doctor seem
attractive at $125 plus the posts over the past year seemed generally
favorable. I do very little drilling under 1/8" but do a fair number
of 1/8", 3/16" and 1/4" sheet metal holes for rivets, welding, etc.
I have packages of drill bits in those sizes plus step drills and a
Roper Whitney Jr. punch. I tell you, I sure like the step drills &
punch for sheet metal vs. twist bits.
Don, can you clarify what a split point bit is? At first I thought it
was related to the angle and since this thread started I've inferred
from some of the posts that it is not.