I was going through my Machinery Handbook, and trying to figure out the
optimum drilling RPM. I ended up having to look at one table to get
recommended FPM for the material, and then another table to convert FPM
to RPM. The RPMs seem high to me, so I wanted to run them by you guys
as a sanity check.

For HSS drills in low carbon steel, I read 100 FPM, and maybe half that
for harder steel.

Converting that to RPM, I will list a range of RPMs for a given drill
diameter.

1/4 inch - 1500 to 750 RPM
1/2 inch - 750 to 400 RPM
1 inch - 400 to 200 RPM

Is this anywhere near right? If so, I need to change the pulleys on my
drill press, as I drill a lot of holes in the range of 1/4 inch to 1/2
inch, maybe set it to 750 RPM or so. It is a pain to change, so I want
to pick a compromise value.

The other question relates to pilot drills. I did not find anything in
my Machinery handbook on pilot drills. Does it make any sense to use a
pilot drill for finished hole sizes of 1/4 inch or less? If so, what is
the rule of thumb for pilot drill sizes? Do I need to change RPM
between the pilot hole and the final drill size?

Assume that most of my drilling is in low carbon steel of 1/4 inch to
5/8 inch thickness.

Thanks in advance.

Richard

Richard Ferguson wrote:

I was going through my Machinery Handbook, and trying to figure out the
optimum drilling RPM. I ended up having to look at one table to get
recommended FPM for the material, and then another table to convert FPM
to RPM. The RPMs seem high to me, so I wanted to run them by you guys
as a sanity check.

For HSS drills in low carbon steel, I read 100 FPM, and maybe half that
for harder steel.

Converting that to RPM, I will list a range of RPMs for a given drill
diameter.

1/4 inch - 1500 to 750 RPM
1/2 inch - 750 to 400 RPM
1 inch - 400 to 200 RPM

Is this anywhere near right? If so, I need to change the pulleys on my
drill press, as I drill a lot of holes in the range of 1/4 inch to 1/2
inch, maybe set it to 750 RPM or so. It is a pain to change, so I want
to pick a compromise value.

The other question relates to pilot drills. I did not find anything in
my Machinery handbook on pilot drills. Does it make any sense to use a
pilot drill for finished hole sizes of 1/4 inch or less? If so, what is
the rule of thumb for pilot drill sizes? Do I need to change RPM
between the pilot hole and the final drill size?

Assume that most of my drilling is in low carbon steel of 1/4 inch to
5/8 inch thickness.

You're in the right ballpark. Running HSS a bit slower won't hurt much.
Remember MH is written for guys for whom time is money, and big $$ at that.
Use some cutting oil and take it easy on feed.

For HSS on mild steel, remember "300 divided by your drill bit size."

For example, 300 / ¼ = 1200 rpm, or 300 / ½ = 600 rpm.

And if you ever see blue chips coming off a HSS drill bit, STOP and slow
it down. Running really small drill bits often leads to breakage. If your
drill press table is really rigid (unlikely) then drill 1/8" right through
and then drill your final hole in one go. Else take it in a few steps. - GWE

Those numbers look about right. The only things I would add a

1. Use cutting fluid. Even motor oil helps quite a bit if you don't have
access to the "real stuff". Just avoid the fumes if possible as it smokes.

2. If you start to get chips iin any color other than silver, slow down
either the feed rate or RPM. The chips will discolor before the tool is
ruined because the chips are actually colling the tool end as they go by...
Hard to imagine, but they are... But eventually, that tool tip will
overheat and stop working.

If you ever need RPM guidelines, you can cound on the MHandbook. Although I
suually suggest RPMs that are around 10% less than what they do for
customers as people tend to mess a perfect environment up every time.

Regards,
Joe Agro, Jr.
http://www.autodrill.com
http://www.multi-spindle-heads.com
..

In article ,
Richard Ferguson wrote:
I was going through my Machinery Handbook, and trying to figure out the
optimum drilling RPM. I ended up having to look at one table to get
recommended FPM for the material, and then another table to convert FPM
to RPM. The RPMs seem high to me, so I wanted to run them by you guys
as a sanity check.

For HSS drills in low carbon steel, I read 100 FPM, and maybe half that
for harder steel.

Converting that to RPM, I will list a range of RPMs for a given drill
diameter.

1/4 inch - 1500 to 750 RPM
1/2 inch - 750 to 400 RPM
1 inch - 400 to 200 RPM

Is this anywhere near right?

Pretty close. If you want to convert SFM to RPM precisely, what
you do is:

1) Multiply diameter in inches by Pi (3.14149.....) to get
circumference in inches.

2) Divide circumference in inches by 12 to get circumference in
feet.

3) Divide that figure into the desired SFM to get the needed RPM.

Note that it is common to simplify that a bit by converting
12/Pi (3.8197) into 4 as an approximation, so you divide the
diameter by 4 to get an approximate circumference, and divide
that into the SFM to get an approximate RPM (close enough).

As I keep a good pocket calculator handy -- one which includes
Pi built in, I do the more precise way, as it is almost as
quick.

If so, I need to change the pulleys on my
drill press, as I drill a lot of holes in the range of 1/4 inch to 1/2
inch, maybe set it to 750 RPM or so. It is a pain to change, so I want
to pick a compromise value.

Note that these SFM values (and the resulting RPM ones) are
considered maximum speeds for a good tradeoff between tool life and
number of parts machined per hour. You *can* run much slower, and the
hole will just take that much longer to drill.

The other question relates to pilot drills. I did not find anything in
my Machinery handbook on pilot drills. Does it make any sense to use a
pilot drill for finished hole sizes of 1/4 inch or less?

Not normally -- and even less if you have a set of split-point
drill bits. The primary purpose of the pilot drill is to eliminate
having to force the chisel tip of the drill bit (the blunt line at the
center) into the workpiece. When running a 1" drill bit into a
workpiece on a lathe or drill press, that chisel tip takes a lot of
force (and thus is more likely to bow the drill sideways and enlarge the
hole). If you make a pilot hole with a much smaller bit (just a little
smaller than the length of the chisel tip) the force needed goes way
down, and the job gets easier.

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)

If so, what is
the rule of thumb for pilot drill sizes?

As above -- just a little smaller than the length of the chisel
tip.

Do I need to change RPM
between the pilot hole and the final drill size?

It would make the drilling faster -- but might take you longer
to change the speed than to drill at the slower speed. Mine is pretty
quick to change, so I tend to change when it feels right. (I probably
drill too slow most of the time, anyway. :-) Some of these days, I will
pull the single-phase motor from that drill press, and pop in a
three-phase with a VFD to allow me to change speeds more easily (just a
twist of a knob, unless I need a really big change, as when going from
drilling a 1/16" hole to a 1" hole), so it will be done more often.
Obviously, with the really big changes, I will still need to change
belt settings.

Assume that most of my drilling is in low carbon steel of 1/4 inch to
5/8 inch thickness.

With other materials, of course, the SFM changes (and the
resulting RPM), but nothing else does.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Not normally -- and even less if you have a set of split-point
drill bits. The primary purpose of the pilot drill is to eliminate
having to force the chisel tip of the drill bit (the blunt line at the
center) into the workpiece. When running a 1" drill bit into a
workpiece on a lathe or drill press, that chisel tip takes a lot of
force (and thus is more likely to bow the drill sideways and enlarge the
hole). If you make a pilot hole with a much smaller bit (just a little
smaller than the length of the chisel tip) the force needed goes way
down, and the job gets easier.

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)



Not insane at all. Pilot drills are usually fat and stubby so the point
won't wander. I've used a carbide pilot drill with a 1/8 shank and 1/32
tip to set up a close tolerance pattern of 3/32 holes. If we drilled the
holes directly with a 3/32 bit (even a split point), there would be
differences of several thousandths when compared to the same pattern
that was pilot drilled first.

In article ,
Tim Killian wrote:

Not normally -- and even less if you have a set of split-point
drill bits. The primary purpose of the pilot drill is to eliminate
having to force the chisel tip of the drill bit (the blunt line at the
center) into the workpiece. When running a 1" drill bit into a
workpiece on a lathe or drill press, that chisel tip takes a lot of
force (and thus is more likely to bow the drill sideways and enlarge the
hole). If you make a pilot hole with a much smaller bit (just a little
smaller than the length of the chisel tip) the force needed goes way
down, and the job gets easier.

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)



Not insane at all. Pilot drills are usually fat and stubby so the point
won't wander. I've used a carbide pilot drill with a 1/8 shank and 1/32
tip to set up a close tolerance pattern of 3/32 holes.

We seem to have a confusion of terminology here. What you
appear to be talking about is the combined drill and countersink
intended to be used for making center holes for lathe turning between
centers. (And it is normally double-ended as well.)

If we drilled the
holes directly with a 3/32 bit (even a split point), there would be
differences of several thousandths when compared to the same pattern
that was pilot drilled first.

Hmm ... I would consider that application a "spotting" drill,
not a pilot drill. And there are spotting drills purpose made, which
have a center-cutting single-flute design with nothing much beyond the
single flute -- sort of like a single-flute countersink.

A pilot drill -- as I was using the term --and as I think the
original poster was using the term -- is a smaller drill bit used to
drill full depth clearance for the web to reduce the forces needed for
pushing the chisel point of the larger drill through the workpiece.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"Richard Ferguson" wrote in message
news
I was going through my Machinery Handbook, and trying to figure out the
optimum drilling RPM. I ended up having to look at one table to get
recommended FPM for the material, and then another table to convert FPM
to RPM. The RPMs seem high to me, so I wanted to run them by you guys
as a sanity check.

For HSS drills in low carbon steel, I read 100 FPM, and maybe half that
for harder steel.

Converting that to RPM, I will list a range of RPMs for a given drill
diameter.

1/4 inch - 1500 to 750 RPM
1/2 inch - 750 to 400 RPM
1 inch - 400 to 200 RPM

Is this anywhere near right?

Yes, in fact, quite accurate. You'll get good performance within those
speeds for mild steel. Do keep an eye on the sharpness of your drills,
however. Dull ones will cut quite hot, whereas sharp ones will cut cool.

One tip-----the color of chips coming off your drill are a great indicator
of a desirable speed. If you chips come off steel colored, you're likely
running too slow. Look for chips to come off ever so slightly yellow when
you drill dry. Anything more than that, you're going too fast. By the
time chips are coming off blue, you've likely already damaged the cutting
edge from speed and heat.. When your chips come off pale yellow when
drilled dry, the drill should do quite well when you lubricate it with
cutting oil.

Pilot drilling:

If you expect a ¼" drill to cut size, it's good shop practice to open the
hole using a smaller drill first. Generally one chooses the next size down
when using fractional drills, so use the same rule of thumb for number or
letter drills, meaning you'd choose a drill approximately .015" smaller.
Not only will the finish drill cut size that way, but the hole will
generally be a much nicer one with fewer irregularities. Needless to say,
lubricate the drill when you're drilling. Even an acid brush dipped and
wiped will be quite beneficial as opposed to nothing. Flood cooling works
even better, but it's messy and not many home shops have a drill press so
equipped.

Harold






If so, I need to change the pulleys on my
drill press, as I drill a lot of holes in the range of 1/4 inch to 1/2
inch, maybe set it to 750 RPM or so. It is a pain to change, so I want
to pick a compromise value.

The other question relates to pilot drills. I did not find anything in
my Machinery handbook on pilot drills. Does it make any sense to use a
pilot drill for finished hole sizes of 1/4 inch or less? If so, what is
the rule of thumb for pilot drill sizes? Do I need to change RPM
between the pilot hole and the final drill size?

Assume that most of my drilling is in low carbon steel of 1/4 inch to
5/8 inch thickness.

Thanks in advance.

Richard

"DoN. Nichols" wrote in message
...
snip----

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)


Not to be confused with the concept of double drilling holes to insure hole
size. It's poor practice to drill holes in one step when the diameter is
critical. Even when not stated, holes have a standard tolerance which is
easy to miss with a twist drill. By double drilling, starting roughly .015"
undersized, you have a much better chance of ending up with a hole of the
desired size. It usually take three steps to drill a proper hole. Center
drill (or spot drill), drill undersized, drill desired size. .

Harold

"Harold & Susan Vordos" wrote in message
...
Even when not stated, holes have a standard tolerance

Gak.

Regards,

Robin

"Robin S." wrote in message
news

"Harold & Susan Vordos" wrote in message
...
Even when not stated, holes have a standard tolerance

Gak.

Regards,

Robin

Gak?


??

H

In article , DoN. Nichols says...

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)

Not at all DoN - I do this all the time when making small printed
circuit shield enclosures. I want the connectors to wind up in
the right spot, within a few thousanths - so I lay out with
dial calipers used as a scratch gage, under a microscope, and
then centerpunch with a scribe.

For the larger holes I centerdrill with a carbide 3/64 drill
to keep the larger (0.10 inch or so) holes from wandering.
This sort of layout technique will get everthing in within
about five thou and is a lot faster for prototyping than
trying to drag everthing down to a milling machine and sticking
it down with double-stick tape.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

In article ,
jim rozen wrote:
In article , DoN. Nichols says...

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)

Not at all DoN - I do this all the time when making small printed
circuit shield enclosures. I want the connectors to wind up in
the right spot, within a few thousanths - so I lay out with
dial calipers used as a scratch gage, under a microscope, and
then centerpunch with a scribe.

For the larger holes I centerdrill with a carbide 3/64 drill
to keep the larger (0.10 inch or so) holes from wandering.
This sort of layout technique will get everthing in within
about five thou and is a lot faster for prototyping than
trying to drag everthing down to a milling machine and sticking
it down with double-stick tape.

Again -- we have a difference in terminology. You are
discussing "spotting" -- to locate a hole.

I was discussing pilot drilling -- drilling a smaller hole
(about the thickness of the web of the larger drill) full depth, to
reduce the force needed to push the chisel point of the larger drill
through the workpiece. For *that* function, there is little point to a
pilot drill for a drill as small as 0.100.

There is still adequate reason for spotting for accuracy of hole
location.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"Harold & Susan Vordos" wrote in message
...

Gak?

Yeah. What's a "standard" tolerance for a hole?

At work, we do DIN, ISO, Canadian, American and automotive OEM standards.
I've never heard of a standard hole tolerance (when not stated).

Regards,

Robin

In article , DoN. Nichols says...

Again -- we have a difference in terminology. You are
discussing "spotting" -- to locate a hole.

For me, if the hole goes all the way through the material,
I think of that as pilot drilling. In this case of course,
0.030 G10 board would be tough to *not* drill all the way
through, but there you are.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

"Robin S." wrote in message
...

"Harold & Susan Vordos" wrote in message
...

Gak?

Yeah. What's a "standard" tolerance for a hole?

At work, we do DIN, ISO, Canadian, American and automotive OEM standards.
I've never heard of a standard hole tolerance (when not stated).

Regards,

Robin


Gotcha!

That's what I meant, sort of round about. My experience in the missile
industry taught me that one was not free to stab a hole in any part and call
it good. While holes often had a specific tolerance, there were times when
they did not. In that case, QC reverted to specific standards, in my case
to MIL specs. My point in posting what I did was that it's a good idea to
double drill holes *because* one is likely not free to end up with holes,
size be damned. You just told me the same thing, only supplying the
references to which you must work. Do you wonder how many have ever
considered that holes must be held to a specification?

Harold

"Harold & Susan Vordos" wrote in message
...

That's what I meant, sort of round about. My experience in the missile
industry taught me that one was not free to stab a hole in any part and
call
it good.

Who has that luxury?

While holes often had a specific tolerance, there were times when
they did not. In that case, QC reverted to specific standards, in my case
to MIL specs.

It is rare that I see a drawing without a general tolerance guide in the
title block.

My point in posting what I did was that it's a good idea to
double drill holes *because* one is likely not free to end up with holes,
size be damned.

Well, application is important. I drill a lot of clearance holes for screws
in the dies at work. Sometimes the holes are greater than 400mm deep,
perhaps Ø16mm+. In this instance, the diameter is pretty loose and the holes
are too long and numerous to double drill.

Of course, the panels produced using our dies require very specifically
sized holes.

You just told me the same thing, only supplying the
references to which you must work. Do you wonder how many have ever
considered that holes must be held to a specification?

That doesn't even register. There is always a specification/tolerance.

Regards,

Robin

"Tim Williams" wrote in message
...
"Harold & Susan Vordos" wrote in message
...
My experience in the missile industry

Out of curiosity, what's your opinion of beryllium? (Yes it's poisonous,
I
know; I'm just fishing for metalworking thoughts here.)

Tim

My opinion is it's a wonderful metal for proper applications. Easily heat
treated, even at home. I've worked it all through my machining career,
although never in quantity. I've turned it on a lathe, which is less than
fun, especially drilling or reaming. It's not uncommon to have a reamer
seize in a bore and have to be machined out to recover the reamer. I've
made (flat) springs from it on many occasions, some of which I still have in
my spares box. They were for use in tooling in the aero-space industry.

The toxicity is such that at one of my customer's facility, where they made
various tooling components from it (the source of the tools I built), the
company policy was for machinists to machine it for a maximum of 90 days,
then never work it again. Apparently it accumulates in the body.

If you have a specific question in mind, ask away. If you're looking for
someone to tell you that you should start casting it, and machining it in
the future, I'd suggest you forget it at your young age unless you have a
specific need. No sense risking your health for no good reason.

Harold

It seems probably quite a few have considered the question. Back in the
'good
old days', holes were spec'd as ... 1/4 drill thru..... Nowadays, it is
more likely to be
spec'd as .... .25 thru... with a corresponding part of the drawing labeled
"tolerances"
specifying how much deviation (tolerance) is allowed as to two, three, four
place decimal
numbers. The same tolerance block would perhaps carry the notation "unless
otherwise
specified, tolerances must meet xxxxxx, whether it be mil spec's, or the
company's own spec's.

I once had the occasion to check on "parts out of tolerance". The drill
press operator
showed me in black & white, "drill #30 thru". And of course he had correct
drill, but it was
so badly worn, it was drilling way undersize.... But, according to print,
he was not at fault.

As you well know, the first place any machinist looks on a drawing is the
tolerance block,
or for any other applicable spec's. A lot of drawings even carry notation
of "generally
accepted good machine shop practice".

Good luck!
"Harold & Susan Vordos" wrote in message
...

"Robin S." wrote in message
...

"Harold & Susan Vordos" wrote in message
...

Gak?

Yeah. What's a "standard" tolerance for a hole?

At work, we do DIN, ISO, Canadian, American and automotive OEM standards.
I've never heard of a standard hole tolerance (when not stated).

Regards,

Robin


Gotcha!

That's what I meant, sort of round about. My experience in the missile
industry taught me that one was not free to stab a hole in any part and
call
it good. While holes often had a specific tolerance, there were times
when
they did not. In that case, QC reverted to specific standards, in my case
to MIL specs. My point in posting what I did was that it's a good idea
to
double drill holes *because* one is likely not free to end up with holes,
size be damned. You just told me the same thing, only supplying the
references to which you must work. Do you wonder how many have ever
considered that holes must be held to a specification?

Harold

"Ace" wrote in message
news snip----

I once had the occasion to check on "parts out of tolerance". The drill
press operator
showed me in black & white, "drill #30 thru". And of course he had
correct
drill, but it was
so badly worn, it was drilling way undersize.... But, according to print,
he was not at fault.

Where I was trained, he would have been. That's the point. Unless
otherwise specified, there were standards to which we had to drill holes..
QC made sure we did. Do keep in mind we worked to MIL specs, however. We
were engaged in building a missile. The tolerance block on the print did
not apply to drilled holes aside from location. Hole size was dictated by
a standard with an ever increasing tolerance, according to hole size, and it
was far more restrictive than the block tolerance. It made sure that a
hole could not vary by going much undersized, and was relatively tight for
oversized. To me, it made sense. In today's throw away society, with a
bar that has been lowered below ground level, perhaps it no longer does.

Harold

Ace wrote:
Years ago before "ma bell" was forced to break up, I had the opportunity to
examine a print
for "tooling" required for one of their components. EACH & EVERY HOLE for
dowels, bolts, etc.
were completely toleranced as to size and location.

You have to remmeber, AT&T was famous for documenting every aspect of
the business so that two workers on opposite ends of the continent would
do things the same way, even if they were each doing it for the first
time and without supervison. I remember a 20 foot wall with 7 foot tall
bookcases filled with Bell Standard Practices. That was not all of them.

It was actually possible for a tech with general training to grab a book
and fix just about any of the hardware at the company (given enough time).


Daniel

wrote:

Ace wrote:

Years ago before "ma bell" was forced to break up, I had the opportunity to
examine a print
for "tooling" required for one of their components. EACH & EVERY HOLE for
dowels, bolts, etc.
were completely toleranced as to size and location.


You have to remmeber, AT&T was famous for documenting every aspect of
the business so that two workers on opposite ends of the continent would
do things the same way, even if they were each doing it for the first
time and without supervison. I remember a 20 foot wall with 7 foot tall
bookcases filled with Bell Standard Practices. That was not all of them.

It was actually possible for a tech with general training to grab a book
and fix just about any of the hardware at the company (given enough time).


Daniel
I agree! - My dad was tasked to write one manual - a mere 250,000 page monster
that described to the device a Radar system that involved three parallel processing
computers, 2 floors of disk drives, one of tapes, and then the special and custom
hardware. It cost him 2 years of putting off his planned retirement.

Martin

--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder