Awl --
Some Qs came up some time ago regarding these drill sets, with most comments
being pretty favorable (including my own), esp considering the price:
$20-39, TiN coated, etc. 135 deg point (above 1/8, iirc), but with 3/8
shanks, above 3/8.
My main criteria was longevity, and they seem to last OK, overall
quality/case seemed decent.
Never thought to check them via measuring the holes they drilled.
Goodgawd.....
I was form tapping 5/16-18 holes, which requires an L drill (.290), and
after some peculiarities with the inserted set screws, I determined that the
drilled holes were coming out at .304 -- !!!! Holy shit......
WITH spotting!! In a Fadal!!!!!
AND, the drill actually does measure 290!!!
How does a .290 drill that actually measures .290 drill a .304 hole??????
With no ostensible wobble, or other defects.
And yet, some bit sizes drill close to their size, so you cain't even *predict* the error. The problem *seems* to be particularly bad on the
letter drills, judging from previous travails that I had not pegged to
regularly errant bits.
Just an fyi.
I guess the moral to the story is, You don't always get what you pay for,
but if you don't pay, the odds much much less..... like an effing accurate
hole, ferchrissakes.
And, of course, I have a *bunch* of these drill sets..... I guess I'll use
them to drill clearance holes for screws.
PV:
If the drill's lips aren't the same length (or angle), then drill may
drill oversize. You could try resharpening them, that should fix the
problem.
My uncle could hand grind a drill bit that would drill an oversize hole,
regrind it and drill an exact hole and regrind it and drill an undersize
hole. He told me to figure it out...I haven't.
Impossible to drill an undersize hole. As the drill will not go through the
hole. Sharpen the end offset as to the center point and you will get a
bigger hole.
A drill doesn't center itself with its point. It centers itself
wherever the forces from the cutting edges come into balance. If the
lip heights, or the lengths and angles of the cutting edges, aren't
identical, then the drill cuts off center, and effectively bores the
hole oversize. If you have a good grinder and like playing
trigonometry, you can do this on purpose with some remarkably reliable
results.
Making a drill cut undersize is more difficult. You have to fix it
so the different lengths or angles produce cutting edges that aren't the
same distance ahead of center.
Despite what JB might think, a Darex grinder is a really good way to
make drills that DON'T cut to size, precisely because it can't repeat
the lip heights. And regrinding your drills means you lose all that
nice gold coating you paid for. If you have any kind of cutter grinder,
you can touch them up yourself, albeit slowly and in low volume, and get
better results than the average Chinese manufacturer. Otherwise, since
the drills themselves are probably too cheap to justify the cost of
quality resharpening service, just use them for rough stuff and buy
better drills when you need to form tap a hole.
KG
Many years go knew an old guy who owned a drilling job shop. He could
hand grind small drills and be dead nuts on. If I hadn't seen him
regrind the drills myself I wouldn't believe it. For years his shop
ran parts for Cherry Textron on tolerances they couldn't hold in house
for the price he was charging them.
--
Tom
age
Ever try drilling, opening up, a hole in titanium, say a 1/32"? good
luck.
Whats the longest hole you have drilled? non critical, like mold water
lines? gun drill machines don't count.
Drill doctor? Darex? what about a Sterling drill sharper? Now thats a
drill sharpner.
For my home drill set, I ground hex's on the shanks on all drills
above 3/8" sweet no chuckey needed.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D
______
/_____/\ Best Regards,
/____ \\ \ Gil Pawl
/_____\ \\ / HOLDZEM=A9=AE
/_____/ \/ / /
/_____/ / \//\ West Chicago, IL
\_____\//\ / / USA
\_____/ / /\ /
\_____/ \\ \
\_____\ \\
\_____\/
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D
Oh, it IS wobbling, for sure. It is a well-known
fact that drill bits drill oversize.
How much oversize can be VERY variable! Feedrate
can make a big difference.
You will often see the entry start out triangular,
or sometimes pentagonal, and then smooth out
somewhat once the drill is half a diameter or so
deep. If you need a hole to be on size, you drill
undersize and ream. .014" oversize seems like a
greater amount of oversize than I'm used to, but I
see it all the time, and compensate if needed.
Jon
Sure, but then we would have thread after thread as to which natural,
biodegradable lube was better. Bear fat, because its long lasting, or
Chicken fat, because its cheap and a lot easier to get. ;-)
Errr Harold, will you explain that a tiny bit.
I measure the shank of a, say .500", drill. Stick in the machine and
drill a .450" diameter hole? In mild steel? 1 inch thick?
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
Errr Harold, will you explain that a tiny bit.
I measure the shank of a, say .500", drill. Stick in the machine and
drill a .450" diameter hole? In mild steel? 1 inch thick?
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
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