"Dave Baker" wrote in message
...

No one suggested predrilling with a smaller diameter drill.

Probably because it's usually a very bad idea.

That's an aggressive posture.

Rarely (never?) in machining are things black and white.


Something like a
1/16" drill would be good.

The thinner the drill the more it flexes and wanders around. Once you have
a
hole that's on the **** the larger drill tends to follow it and the job is
****ed. If you seriously think you can drill an accurate 2 inch deep hole
with
a 1/16" drill then I have to suggest you've never tried it.

Again, posturing. What's with the attitude?

The 1/16" hole doesn't need to go all the way through, although if it does
it probably won't hurt. Once the drill has entered the material and is going
reasonably straight, it should hold its course. Mind you, all of this is up
in the air anyway. If he wants to put a 13/64" hardened shaft through the
hole, it almost certainly won't work as there will be some wander anyway.
But we've only estabilished that he's looking for *less* wander than he had
before.


There is one good reason for double drilling and that's to get good
tolerance
on hole size.

Perhaps in a pinch. I'd be inclined to order the reamer, if you really want
to get technical. But in this instance, we're not getting that technical.

In fact, lets reafirm our objectives he "Home shop machinist" Bill
Chernoff doesn't appriciate that his 13/64" drill wanders .020" through a
piece of 2" thick 6061 aluminum. He hasn't stated his feeds, speeds, machine
he's using, amount of experience he has, other situations that would lead
him to make assumptions, etc.

The above will help us later.


Putting a very small starting hole in a job is a no no.

I work by 15-30% (for a new drill the web is typically about 15% of the
diameter).


My solution basically mirrors a previous suggestion. Start by aligning the
machine as accurately as possible.

How accurately? Do you see notes on drawings saying "as accurately as
possible"?

Yes, I'm being a jackass. As you can see it's about posturing.

Ensure your drill chuck has no runout.

It certainly sounds like we have a profesisonal journeyman machinist here. I
should like to see this drill chuck, and I should like to pay very little
for it because Bill Chernoff probably doesn't want to spend $400+ on such a
chuck.

Remember our reafirmation of objectives above?

Jackass? Yes. It's all about posturing.

Make
a countersink to just over the finished hole size with a centre drill.

A countersink with a center drill? You have to choose.

Go as
deep as you can with a 2 flute slot drill (milling cutter) in a collet
that's a
tad under finished size. You'll get almost zero wander with a slot drill.
Then
either single or double drill to final size at a slow speed and feed.

100RPM, .0003/rev? That's slow.


Peck lightly and don't press the drill hard enough to bend it.

Do you frequently feel your drills bend?

Use a brand new
drill.

Most HSM's have unlimited budgets and time to buy new tooling whenever
required.

I find you never achieve such evenness of flute width and accuracy of
cut on a resharpened drill as you do with a new high quality one.

Perhaps you need to resharpen more drills.

I can see the necessity for new tooling in a production setting but for the
HSM and frequently in tool shops, one drill could be sharpened ten times
before it shatters and another one is used.


A carbide drill has a higher modulus of elasticity than a steel one i.e.
it
bends less.

Ha! That's certainly something Bill Chernoff should go and buy tomorrow
morning. A carbide drill!

Dave, here's the news. Chances are (not absolutly though) that most HSM's
here bought the drill press on special at Harbour Freight and picked up a
set of drills to go with. Total cost was maybe $200.

HSM chucks bit of desired hole diameter and switches drill "ON" at factory
preset RPM. Could be 2500, could be 60. HSM proceeds to lower drill to
piece. Drill bounces around a bit and finally bites. Drill is perhaps
already bent and the bouncing didn't help. HSM crams drill through material
as the bit spins in the $10 chuck with one stick jaw and a bag of grinding
dust in the bearings. Drill miraculasly gets through the material and of
course the hole is in the wrong place.

I'm not attacking the "HSM" but I remember using a micrometer as a c-clamp
once too.

Carbide drills and new tooling for tomorrow's production run on the
receiving bay's floor tomorrow at 9am is best left to the professionals like
you. As for those who like to fiddle around in the basement (and probably
have more fun than anyone getting paid to do it), they just want to know why
the drill made a hole the shape of a "c".

BTW, it's all about posturing. Your posture got me in a bad mood and sent me
off on this rant. If we could all be a bit nicer, this wouldn't happen so
often. I'm a bit squirly today because I had a practical midterm today. The
German Chamber of Commerce has calculated that 7.5hrs is required to make
the assembly you have to make, given a qualified apprentice. They give us
8hrs (precisely no more). Under the gun for 8hrs straight (minus two breaks)
causes people to get a bit frazzled.

Regards,

Robin