I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

I'm not convinced that there are any standards, Dan. When this topic was
aired some time ago, Bill D sent me some pictures in which he had
outstanding success in drilling deep holes in stainless. In essence,
there's always the possibility that the drill will go straight, but also the
possibility that it won't, which is why I always say that twist drills do
not drill straight holes, which, in general, they don't. Than again, what
does "straight" mean?

I'm of the opinion that one can expect anything from dead on to enough
runout for the drill to bind in the hole. I've seen it both ways in my
years in the shop. Lots of things cause variations, right down to personal
application. It's a good policy to always assume it won't go straight, so
if it's important that it does, you take precautions that will prevent
making scrap. By suggesting that twist drills don't drill straight holes,
it more or less keeps the idea fresh in your mind.

Harold

"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

Sorry. I meant to ask if the far end is expected to be on the bottom.

Bob Swinney
"Bob Swinney" wrote in message news:...

"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?
---snip---

I depends on how the hole is started. If you are dead-on into a punched
mark, and you retract frequently at the start, you should end up within
..001" when finished. If you are starting to drill with a perfect drill, you
may get the same result. Most drills will wobble before penetrating that
first thousandth and that is where you get your error. Your best practice is
to locate the part under the chuck exactly where you want it, then start the
hole with a centerdrill and change to the finish drill after breaking the
surface.

Wayne

"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Your design process in backwards. How accurate does it HAVE TO be?

If the exit location is .0023" from where the nominal location is, what
happens? What about if it's .0079"? Will the part not function correctly?

Do you have the capability to measure the location, size, profile and
possibly the roundness of the hole? Would you know if it was straight or
not? What if it has a bellmouth profile or bends as opposed to going
straight (but not necessarily concentric with the axis of the spindle)?

Perhaps these are obnoxious questions, but the tolerance gods don't work in
..0002, .001 and .005 increments...

BTW, you may want to go for parabolic drills. They are made for deep hole
drilling (generally beyond diameter:depth ratio of 1:4 or great, IIRC).
They're more expensive, however, than standard twist drills.

Regards,

Robin

"Robin S." wrote:

"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Your design process in backwards. How accurate does it HAVE TO be?

If the exit location is .0023" from where the nominal location is, what
happens? What about if it's .0079"? Will the part not function correctly?

Do you have the capability to measure the location, size, profile and
possibly the roundness of the hole? Would you know if it was straight or
not? What if it has a bellmouth profile or bends as opposed to going
straight (but not necessarily concentric with the axis of the spindle)?

Perhaps these are obnoxious questions, but the tolerance gods don't work in
.0002, .001 and .005 increments...

BTW, you may want to go for parabolic drills. They are made for deep hole
drilling (generally beyond diameter:depth ratio of 1:4 or great, IIRC).
They're more expensive, however, than standard twist drills.

Regards,

Robin

Maybe get some plug gages to check the results. They will give you a real good
idea how your holes come out, inexpensively. Have you tried drilling something
yet? Do you have measuring instruments to check the results? Theory is great,
but how about taking a cut and checking it? You'll find out if something is
amiss and have some procedure to either do again or modify if need be. Make
some chips!

mj

"Robin S." wrote in message
...

BTW, you may want to go for parabolic drills. They are made for deep hole
drilling (generally beyond diameter:depth ratio of 1:4 or great, IIRC).
They're more expensive, however, than standard twist drills.


Robin,

Parabolic drills arent particularily accurate as far as maintaining a target
location at depth in my experience.

In fact, I have found exactly the opposite to be true--however, chip
evacuation with parabolic flute drills is indeed superior to any other
design to my knowledge.

As to the original question and in the situation described, I would think
+/- .005 inches location should be easily obtainable under general
conditions, unless someone is a real "KluTz" G as to drilling or
sharpening of a std jobber drill. For a bolt clearance, simply use a drill
that is a 1/16 or 1/32 in. oversized.........

Better yet probably would be to use a stub, or "screw machine"
drill...........I maintain an inventory of these in the common sizes so as
to eliminate the need for center drilling whenever the job/ tolerance will
allow.

Else, as you say--if greater accuracy is needed, a more reliable process
would be to first drill the hole undersize, then bore with single point for
size and location--in a production environment, more economical control of
size can often be had by first pre drilling, then boring for location,
followed by a final reaming operation for size control.

Cheers,

--

SVL

It isn't the design process that I am thinking about. Say you have a
blueprint that calls for a 1 inch deep hole .138 diameter +/- .003 (
just so you don't worry too much about the diameter ) but true to the
axis within .004. Can you reasonably expect to drill it with a twist
drill? Since that requires that the angle be within about .25 degree,
my guess it might be possible with a rigid machine. But has anyone
here know if one could do it with one operation or is it something
that requires two operations and a lot more cost?

I agree that measuring is part of the problem.

Dan


"Robin S." wrote in message news:aAqJb.18138
Your design process in backwards. How accurate does it HAVE TO be?

If the exit location is .0023" from where the nominal location is, what
happens? What about if it's .0079"? Will the part not function correctly?

Do you have the capability to measure the location, size, profile and
possibly the roundness of the hole? Would you know if it was straight or
not? What if it has a bellmouth profile or bends as opposed to going
straight (but not necessarily concentric with the axis of the spindle)?

Perhaps these are obnoxious questions, but the tolerance gods don't work in
.0002, .001 and .005 increments...

BTW, you may want to go for parabolic drills. They are made for deep hole
drilling (generally beyond diameter:depth ratio of 1:4 or great, IIRC).
They're more expensive, however, than standard twist drills.

Regards,

Robin

"Dan Caster" wrote in message
...
It isn't the design process that I am thinking about. Say you have a
blueprint that calls for a 1 inch deep hole .138 diameter +/- .003 (
just so you don't worry too much about the diameter ) but true to the
axis within .004. Can you reasonably expect to drill it with a twist
drill? Since that requires that the angle be within about .25 degree,
my guess it might be possible with a rigid machine. But has anyone
here know if one could do it with one operation or is it something
that requires two operations and a lot more cost?

I agree that measuring is part of the problem.

Dan

Yes, it is within reason to drill such a hole with a twist drill. What
you might discover is the odd hole would not be within the acceptable
limits, but in general it is possible to achieve.

Harold

On 3 Jan 2004 11:07:31 -0800, (Dan Caster) wrote:

It isn't the design process that I am thinking about. Say you have a
blueprint that calls for a 1 inch deep hole .138 diameter +/- .003 (
just so you don't worry too much about the diameter ) but true to the
axis within .004. Can you reasonably expect to drill it with a twist
drill? Since that requires that the angle be within about .25 degree,
my guess it might be possible with a rigid machine. But has anyone
here know if one could do it with one operation or is it something
that requires two operations and a lot more cost?

I agree that measuring is part of the problem.

Dan

Greetings Dan,
One thing to consider is the average axis of the hole. If you are
using a pin to measure location the pin that fits without bending will
average out the center if the hole is curved. And that's what counts
if the complete depth is being used as a locator. EG, a pin pushed in
the full depth of the hole and used as a locator. Drawings dimensioned
in true position will sometimes give a dimension in the Z direction
that says that a hole center must fall within a circle of a certain
size a certain distance above or below the X,Y plane. Some times the
centerline tolerance is expressd as an angle. And a 1" deep .138" hole
straight within .004 can be done by center drilling first and then
drilling with a split point drill. Even using just the split point
drill it could be done but the drill needs to be started very
carefully. In fact, with proper technique, I'd be surprised if the
hole wasn't within .004" This assumes the work is being done a good
machine. Not many drill presses would qualify. If I needed to get the
hole right the first time with no opportunity to drill a test part
then drilling, boring and reaming would be the method I'd use. I am
looking at a boring bar right now that will bore .060" min dia. with
,500 D.O.C.. This bar would be usd to bore the hole undersize and then
it would be reamed the full depth. Using a carbide D reamer that fits
the bored hole would work for sure. Of course, that hardly ever
happens. And I've got an Interapid indicator with a .094" dia. needle
that's 2.625" long. It reads to .0005" directly and can be
interpolated easily to .0002". So a .138" hole could be checked
directly for straightness and location.
Cheers,
Eric

Thanks for your reply and that of PrecisionMachinest. It is nice to
hear from people with some experience and the equipment to measure
what they did. And really nice to have some numbers on which to base
what I do. Not that I need to drill extremely accurate holes very
often, but I would rather not buy a boring bar for extremely small
holes if I don't have to. The discussions that say you can drill
straight holes or that say that twist drills don't drill straight
holes aren't much use without some numbers on what is straight. I
mean that I could say you can't get a straight hole even if you drill
then bore and ream. Just depends on what you mean by straight.

But certainly a hole can be drilled that is more than adequate for
guiding a hand drill and or tap. On some occasions where I had to use
a hand drill, I have just drilled a hole thru a piece of two by four
with the drill press before going to where ever I needed to drill and
tap a hole. That is better than trying to drill and tap with no guide
and has always proved to be good enough.

Dan


Eric R Snow wrote in message
Greetings Dan,
And a 1" deep .138" hole
straight within .004 can be done by center drilling first and then
drilling with a split point drill. Even using just the split point
drill it could be done but the drill needs to be started very
carefully. In fact, with proper technique, I'd be surprised if the
hole wasn't within .004"
Cheers,
Eric

On 2 Jan 2004 10:31:04 -0800, (Dan Caster) wrote:
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Even with perfect alignment and entry, twist drills won't reliably produce
a straight hole to depths much greater than about 2 drill diameters. Any
deviation from perfect tip symmetry, variation in the drilled material's
uniformity, or recutting of chips will cause the drilled hole to drift out of
line. The limit case is where the bit binds and breaks in the crooked hole.

For best results in deep hole drilling (ie holes deeper than about 2 drill
diameters), you need to use a different tool than a twist drill. Gun drills
use a supported single point cutter (and high pressure oil down the stem
to clear the chips). This solves the problem of tip asymmetry, and the
problem of recutting chips, but there's still the problem of non-uniformity
of the material being drilled. Any hard or soft spots in the material being
drilled will still deflect the cutter and give you a crooked hole.

Now all this begs the question of what "straight" is. How much deviation
from a straight line the hole can have is a function of the particular purpose
of the particular hole. Most of us would agree that a deviation of half a
hole diameter would be "crooked", but might suffice for a drain passage.
A 10% deviation might be acceptable in some cases. Other cases might
require 1%, or even less.

AFAIK there are no standard or guaranteed numbers for the deviations
from perfectly straight a given twist drill bit will produce in a given material.
I've drilled deep holes in wood for alarm wiring where you couldn't see the
exit when looking down the entry hole. In other words, the drilled hole's
wander exceeded one drill diameter. That was Ok for feeding wires through
a wall, but wouldn't be at all acceptable if a rotating shaft had to pass
down the hole.

I'm afraid your question is in the form of "how high is up?" There really
isn't any single hard and fast number that will answer your question.

Gary

"Dan Caster" wrote in message
m...
And really nice to have some numbers on which to base
what I do.

I appriciate your situation, but I truely think you're going about this
situation backwards. Any number quoted here may or may not apply to you when
you drill your hole.

Coming from the perspective of someone who has both designed/built/hacked
mechanical systems together with very little knowedge as well as produced
parts to a print at work, your question is somewhat agrevating.

I think the bottom line is that a) you don't need to use anything beyond a
center drill and a drill for your hole and, b) you don't really need a hole
of that depth to achieve accuratetly threaded holes with a tap.

Not that I need to drill extremely accurate holes very
often, but I would rather not buy a boring bar for extremely small
holes if I don't have to. The discussions that say you can drill
straight holes or that say that twist drills don't drill straight
holes aren't much use without some numbers on what is straight.

But those numbers are supposed to come from you, the designer. Perhaps I'm
bitter from selling drill bits to people who want a "precision slide fit"
and reamers to others who want bolt clearance holes.....

I
mean that I could say you can't get a straight hole even if you drill
then bore and ream. Just depends on what you mean by straight.

Indeed, this is very important. I think Eric touched on the idea that the
effective diameter (such that it clears a nominally-sized shaft) is not the
same as the diameter at any given point in the hole, necessarily. Geometric
dimensioning and tolerancing addresses these issues. Simply having an X and
Y positional tolerance as well as a diameter tolerance will not suffice when
one is designing very precise holes. A tolerance zone must be defined that
extends at least throughout the entire length of the hole, and perhaps
beyond its physical boundaries.


But certainly a hole can be drilled that is more than adequate for
guiding a hand drill and or tap. On some occasions where I had to use
a hand drill, I have just drilled a hole thru a piece of two by four
with the drill press before going to where ever I needed to drill and
tap a hole. That is better than trying to drill and tap with no guide
and has always proved to be good enough.

Well, it's good we got this all (you guessed it) straightened out...

Regards,

Robin

In article , Robin S. says...

Indeed, this is very important. I think Eric touched on the idea that the
effective diameter (such that it clears a nominally-sized shaft) is not the
same as the diameter at any given point in the hole, necessarily. Geometric
dimensioning and tolerancing addresses these issues. Simply having an X and
Y positional tolerance as well as a diameter tolerance will not suffice when
one is designing very precise holes. A tolerance zone must be defined that
extends at least throughout the entire length of the hole, and perhaps
beyond its physical boundaries.

Cylindricity of a bore is actually a pretty tough
issue.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

My question was a lot more specific than how high is up. From the
various answers others have given it looks as if somewhere about .004
or .005 is reasonable for a drilled hole. Straighter than that and
one should plan on some other method of making the hole.

Dan



Gary Coffman wrote in message
On 2 Jan 2004 10:31:04 -0800, (Dan Caster) wrote:
So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?


I'm afraid your question is in the form of "how high is up?" There really
isn't any single hard and fast number that will answer your question.

Gary

Robin,

In previous discussions of whether twist drills drill straight holes,
I never wound up with any idea of when I should just use a drill and
when I really needed to drill undersize and bore. So this time when
the question came up, I tried to get some numerical answers from
people with a lot more experience than I have. And I was looking for
answers from the machinists point of view, not the designers point of
view. True any number quoted here can be wrong, but at least now I
have a better idea. And maybe others have a better idea too.

Years ago I took a course in "Vacuum Tube Technology". It turned out
to be a course in the technology of how to build vacuum tubes, and not
the usual receiving tubes, but traveling wave tubes, backward wave
oscillators, klystrons, etc. It was taught by the troubleshooter for
Varian, Renee Rogers.
And one of the better things I learned from the course was his thought
process in troubleshooting production problems. He would put numbers
on things and do calculations to see if things were reasonable. An
example of the types of problems we did was to calculate the diameter
of the wire in a 10 ma fuse. The way the fuses are made is to put a
small platinum wire is a copper tube and swage the copper around the
platinum. Then draw the copper tube into a thin wire. Attach the
copper wire to the supports for it, protect the ends, and then etch
the copper off the platinum. So knowing the resistance and melting
point of platinum, the heat loss from radiation, you can calculate
the diameter that would melt at 10 ma of current. Anyway after that
class I always like to have some sort of number to base things on,
even if the number is only accurate to plus or minus 100%. It keeps
me from buying reamers for bolt clearance holes.

Dan






"Robin S." wrote in message m...

I appriciate your situation, but I truely think you're going about this
situation backwards. Any number quoted here may or may not apply to you when
you drill your hole.

Coming from the perspective of someone who has both designed/built/hacked
mechanical systems together with very little knowedge as well as produced
parts to a print at work, your question is somewhat agrevating.


Not that I need to drill extremely accurate holes very
often, but I would rather not buy a boring bar for extremely small
holes if I don't have to. The discussions that say you can drill
straight holes or that say that twist drills don't drill straight
holes aren't much use without some numbers on what is straight.

But those numbers are supposed to come from you, the designer. Perhaps I'm
bitter from selling drill bits to people who want a "precision slide fit"
and reamers to others who want bolt clearance holes.....



Well, it's good we got this all (you guessed it) straightened out...

Regards,

Robin

Dan Caster wrote:

My question was a lot more specific than how high is up. From the
various answers others have given it looks as if somewhere about .004
or .005 is reasonable for a drilled hole. Straighter than that and
one should plan on some other method of making the hole.

Dan

Gary Coffman wrote in message
On 2 Jan 2004 10:31:04 -0800, (Dan Caster) wrote:
So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?


I'm afraid your question is in the form of "how high is up?" There really
isn't any single hard and fast number that will answer your question.

Gary

Using a proper machine and setup, your hole should easily and routinely be
within +/- .002 on the farside. Closer to +/- .001 is what I personally would
expect, spotting and drilling. Proper machine is not a drill press, and proper
setup is not a prickpunch. Have you taken a cut yet?

mj

On 4 Jan 2004 14:44:26 -0800, (Dan Caster) wrote:
My question was a lot more specific than how high is up. From the
various answers others have given it looks as if somewhere about .004
or .005 is reasonable for a drilled hole. Straighter than that and
one should plan on some other method of making the hole.

It appeared to me that most of the answers were really addressing
the question of how closely you could *locate* a twist drilled hole
rather than how straight a many drill diameter long bore would be.

The key factors for that are drill bit symmetry, material uniformity,
and whether you're recutting chips or not. Assuming a high quality
bit and a very uniform material with no inclusions or voids, the only
remaining issue is how to avoid recutting chips. For deep holes with
a twist drill, that requires a pecking technique, and the results of
that are highly variable from worker to worker.

I wouldn't be comfortable claiming a 0.004 to 0.005 variance for
*any* worker with *any* bit in *any* material, though a particular
worker might achieve it fairly routinely with a particular bit geometry
in a particular material.

There have been too many times when I've hit a hard spot in CRS,
or a void in cast iron, or a knot in a wooden plank, to issue a blanket
statement about how straight a deeply drilled hole will wind up being,
no matter how skilled the worker.

Gary

(Dan Caster) wrote in message om...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

Hello Dan,
There is a military standard for drill hole size tolerances. It is
AND10387. See http://www.bjg-design.com/designbook/holest.htm
Also look at http://www.bjg-design.com/designbook/drilld.htm for drift
tolerance for drill holes. Also look up
http://www.bjg-design.com/designbook/formhsiz.htm for positional
tolerances.
Sy

Thanks Sy,

This is exactly what I was looking for and I have now bookmarked the
starting page for the design book. Lots of data there. From what
others have said it looks as if one can be within about half or one
third of these tolerances if one is very careful and has some good
luck.

This should be very helpful to a lot of us recreational metalworkers.

Mil specs and handbooks often have a lot of valuable information.
Finding the mil spec can be a problem.

Thanks again,
Dan



(Sy) wrote in message

Hello Dan,
There is a military standard for drill hole size tolerances. It is
AND10387. See http://www.bjg-design.com/designbook/holest.htm
Also look at http://www.bjg-design.com/designbook/drilld.htm for drift
tolerance for drill holes. Also look up
http://www.bjg-design.com/designbook/formhsiz.htm for positional
tolerances.
Sy

Sy wrote:


So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

Hello Dan,
There is a military standard for drill hole size tolerances. It is
AND10387. See http://www.bjg-design.com/designbook/holest.htm
Also look at http://www.bjg-design.com/designbook/drilld.htm for drift
tolerance for drill holes. Also look up
http://www.bjg-design.com/designbook/formhsiz.htm for positional
tolerances.
Sy

Hi Sy

I to appreciate having these tables as a guide. What I do wonder about though, is if there are any
qualifiers on these values. IE are they applicable to a drill press, a mill or a lathe and in any
particular material? (or just drilled holes of any kind any place with any kit)

The reason I ask is that on a lathe I routinely drill 3 to 5" deep holes in Al with accuracy that this
data would achieve at only an inch or two. IE this is a letter I wrote detailing what happened when I
tried drilling a deep hole with an intentionally off center ground drill tip.

The letter***************

I just wanted to say that even the tip geometry is not to important in maintaining a
straight hole. (At least not in Al as per this illustration.) I did the hole in the
picture with one flute purposely sharpened to be twice the length of the other. That's a
5.125" long 1/2" Al rod and the exit hole was .005" off of center and the entrance hole
was about .002 off of center. (going by memory)

It's not a pretty hole as the tip of the drill found the center of rotation and the long
flute swung wide for the entire 5 inches and acted like a boring bar, using the point at
the center of rotation to pivot about. The drill was about .145" and the hole it drilled
was about .190. That math is just about right when you consider that the long flute was
about 2/3 of .145 is .097" so it should cut a .194" hole if it acted as a boring bar. It
did!,,,, so it must have been acting like a boring bar centered by the tip on the center of the axis.

Actually the exit hole was about .145" but I could see that the entire length of the hole
was much larger, so I turned a few thou off of the end to expose the actual size of the
hole.

As far as I can see, was that once the tip reached the end and had no more metal to stay
centered in, it reverted to acting like a drill and just cut a normal sized hole through
what material was left.

My thoughts anyway.

Bill D
*******************

I do understand what standards are but at the same time I would expect that anyone could achieve similar
numbers in similar conditions and I know that the chuck I was using was a couple of thou out of whack to
start with.

Bill D

(I know that I should not post this) (0:

"Dan Caster" wrote in message
m...
Thanks Sy,

This is exactly what I was looking for and I have now bookmarked the
starting page for the design book. Lots of data there. From what
others have said it looks as if one can be within about half or one
third of these tolerances if one is very careful and has some good
luck.

This should be very helpful to a lot of us recreational metalworkers.

Mil specs and handbooks often have a lot of valuable information.
Finding the mil spec can be a problem.

Thanks again,
Dan
(Sy) wrote in message

Hello Dan,
There is a military standard for drill hole size tolerances. It is
AND10387. See http://www.bjg-design.com/designbook/holest.htm
Also look at http://www.bjg-design.com/designbook/drilld.htm for drift
tolerance for drill holes. Also look up
http://www.bjg-design.com/designbook/formhsiz.htm for positional
tolerances.
Sy

Of all the territory covered here I didnt' notice anyone mention to use a
new drill bit from a reputable manufacturer (save the resharps for rough
work) and use a screw-machine length if possible. Maybe it goes without
saying.

Also I didn't see mentioned classic drill jigs with precisely located
hardened guide bushings. That's got to count for a lot when using skinny
bits or when using a drill press instead of a mill.

I vaguely recall a Teenut thread on the topic of sharpening drill bits, and
spent a minute Googl'ing without success. Gist was, sharpening is fine
(though its economics are questionable for small bits), but even with skill
and a good quality grinder it's impossible to get drills to drill to new
spec with regard either to diameter or straightness.

Bob

Bill Darby wrote in message ...
Sy wrote:


So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?

Dan

Hello Dan,
There is a military standard for drill hole size tolerances. It is
AND10387. See http://www.bjg-design.com/designbook/holest.htm
Also look at http://www.bjg-design.com/designbook/drilld.htm for drift
tolerance for drill holes. Also look up
http://www.bjg-design.com/designbook/formhsiz.htm for positional
tolerances.
Sy

Hi Sy

I to appreciate having these tables as a guide. What I do wonder about though, is if there are any
qualifiers on these values. IE are they applicable to a drill press, a mill or a lathe and in any
particular material? (or just drilled holes of any kind any place with any kit)

Hello Bill,
Before retirement,I was a machine parts & tooling inspector at the
aircraft companies. I did not drill holes, just checked them.
Sorry,I can't answer your question(s). Good luck,
Sy

The reason I ask is that on a lathe I routinely drill 3 to 5" deep holes in Al with accuracy that this
data would achieve at only an inch or two. IE this is a letter I wrote detailing what happened when I
tried drilling a deep hole with an intentionally off center ground drill tip.

The letter***************

I just wanted to say that even the tip geometry is not to important in maintaining a
straight hole. (At least not in Al as per this illustration.) I did the hole in the
picture with one flute purposely sharpened to be twice the length of the other. That's a
5.125" long 1/2" Al rod and the exit hole was .005" off of center and the entrance hole
was about .002 off of center. (going by memory)

It's not a pretty hole as the tip of the drill found the center of rotation and the long
flute swung wide for the entire 5 inches and acted like a boring bar, using the point at
the center of rotation to pivot about. The drill was about .145" and the hole it drilled
was about .190. That math is just about right when you consider that the long flute was
about 2/3 of .145 is .097" so it should cut a .194" hole if it acted as a boring bar. It
did!,,,, so it must have been acting like a boring bar centered by the tip on the center of the axis.

Actually the exit hole was about .145" but I could see that the entire length of the hole
was much larger, so I turned a few thou off of the end to expose the actual size of the
hole.

As far as I can see, was that once the tip reached the end and had no more metal to stay
centered in, it reverted to acting like a drill and just cut a normal sized hole through
what material was left.

My thoughts anyway.

Bill D
*******************

I do understand what standards are but at the same time I would expect that anyone could achieve similar
numbers in similar conditions and I know that the chuck I was using was a couple of thou out of whack to
start with.

Bill D

(I know that I should not post this) (0:

"Sy" wrote in message
om...
Hello Bill,
Before retirement,I was a machine parts & tooling inspector at the
aircraft companies. I did not drill holes, just checked them.
Sorry,I can't answer your question(s). Good luck,
Sy

Thanks Sy

You just told me a lot.

Thanks much
Bill

On Mon, 05 Jan 2004 21:00:23 GMT, "Toolbert" wrote:

I vaguely recall a Teenut thread on the topic of sharpening drill bits, and
spent a minute Googl'ing without success.

Hummmm Anyone have the Collected Wisdom of Teenut saved? That might
make a very nice zip file for the drop box.

Gunner



"Aren't cats Libertarian? They just want to be left alone.
I think our dog is a Democrat, as he is always looking for a handout"
Unknown Usnet Poster

Heh, heh, I'm pretty sure my dog is a liberal - he has no balls.
Keyton

I vaguely recall a Teenut thread on the topic of sharpening drill
bits, and spent a minute Googl'ing without success.

Hummmm Anyone have the Collected Wisdom of Teenut saved? That might
make a very nice zip file for the drop box.

http://yarchive.net/metal/drill_grinding.html

He has a bunch of RCM stuff archived there...
--Glenn Lyford

On Thu, 08 Jan 2004 00:25:29 GMT, Glenn Lyford
wrote:

I vaguely recall a Teenut thread on the topic of sharpening drill
bits, and spent a minute Googl'ing without success.

Hummmm Anyone have the Collected Wisdom of Teenut saved? That might
make a very nice zip file for the drop box.

http://yarchive.net/metal/drill_grinding.html

He has a bunch of RCM stuff archived there...
--Glenn Lyford

Cool! Bookmarked and saved to disk.

Gunner




"Aren't cats Libertarian? They just want to be left alone.
I think our dog is a Democrat, as he is always looking for a handout"
Unknown Usnet Poster

Heh, heh, I'm pretty sure my dog is a liberal - he has no balls.
Keyton