Costco/"Worksmith" 115 drill bit sets saga

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.
Reply to
Proctologically Violated©®
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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.
Reply to
BottleBob
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.
Reply to
Buerste
Did he also walk up-hill to AND from school?
Reply to
Proctologically Violated©®
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.
Reply to
Calif Bill
Well, I've seen it done too. The trick is a rounded corner at the edge of the cutting edge going to the flute. Like a Racon sharpening
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Karl
Reply to
Karl Townsend
With barb wire for snowshoes?
Reply to
Garlicdude
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
Reply to
Kirk Gordon
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
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Reply to
brewertr
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
Reply to
cncmillgil
Come on, Tom. He was using rubber drill bits. ;-)
Reply to
Michael A. Terrell
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
Reply to
Jon Elson
But that is like a step drill and the drill is made smaller part way up the shank.
Reply to
Calif Bill
Take a fairly good drill and measure it at the tip and every 1/2" down.
Reply to
Buerste
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. ;-)
Reply to
Michael A. Terrell
Human fat. It could be extracted from between the ears of democrats.
Reply to
Buerste
That stuff in rancid, and you have to strain out all the maggots. :(
Reply to
Michael A. Terrell
snip---
No, it isn't. It's not all that uncommon.
Harold
Reply to
Harold and Susan Vordos
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)
Reply to
Bruce In Bangkok
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)
Reply to
Robert Swinney

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