I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3 & 5mm I
think. But at 7mm the bit just refused to bite. I tried another similar
sized bit from a different set, still no good. It was as if either the
bits were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey

"Frank Stacey" wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be particularly
hard.
I tried to drill a small diameter hole and gradually increase the diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3 & 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from a
different set, still no good. It was as if either the bits were blunt or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


how did you sharpen the 7mm drill bit? although HSS drills are not difficult
to sharpen there is a knack and if not just right the cutting edge does not
touch

You are using HSS drills I assume

Try the 7 mm drill in a scrap bit of mild steel and see if that works you
will soon know if it is properly sharp

alos be aware that the drilling speed are much lower for 7 mm than 3 or 5 mm
typically 2000rpm for 3mm and 900 for 7 mm

If you have overheated the bit you may have ruined it

some info here

http://www.ultimatehandyman.co.uk/DI..._technique.htm

On 29 Sep, 16:56, Frank Stacey wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. *I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. *It worked for the first 2 diameters, 3 & 5mm I
think. *But at 7mm the bit just refused to bite. I tried another similar
sized bit from a different set, still no good. *It was as if either the
bits were blunt or the metal suddenly much harder.
I *have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey

You can buy a "drill" that is conical and enlarges holes in thin metal
really well
Picture here.
http://www.lawson-his.co.uk/scripts/...20Drill%20Bits

You are on a hiding to nothing trying to drill thin meatal with a
twist drill.

In message , TMC
writes

"Frank Stacey" wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be particularly
hard.
I tried to drill a small diameter hole and gradually increase the diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3 & 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from a
different set, still no good. It was as if either the bits were blunt or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


how did you sharpen the 7mm drill bit? although HSS drills are not difficult
to sharpen there is a knack and if not just right the cutting edge does not
touch

You are using HSS drills I assume

Try the 7 mm drill in a scrap bit of mild steel and see if that works you
will soon know if it is properly sharp

alos be aware that the drilling speed are much lower for 7 mm than 3 or 5 mm
typically 2000rpm for 3mm and 900 for 7 mm

If you have overheated the bit you may have ruined it

some info here

http://www.ultimatehandyman.co.uk/DI..._technique.htm

You may have *work hardened* the blade.

I would expect mower blades to be made from a hardenable steel, hardened
and then tempered back to a compromise between retaining a sharp edge
and too brittle/subject to fracture.

When I had a proper job, odd bar ends of bearing steel (SKF3) used to
find their way to my home workshop. I quickly found unlubricated turning
swarf self hardens to little springs.

Red heat and slow cooling would solve your problem but may spoil the
blade for the purpose you intend.

An expert will be along shortly:-)

regards


--
Tim Lamb

Tim Lamb wrote:

You may have *work hardened* the blade.

Steel doesnt 'work harden', it has to be heat treated.
Something like a rotary mower blade would not be hardened all over, as a
little bit of flex would be good in such a situation. Case hardening of
the blade edges would be possible, though unlikely for the usual
back-garden mower.

I would expect mower blades to be made from a hardenable steel, hardened
and then tempered back to a compromise between retaining a sharp edge
and too brittle/subject to fracture.

I'm not so sure. My Hayter rotary blade is pretty soft, and has to be
changed/sharpened once a year.
If hardened, I'd expect it to last a lot longer.

Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

On 29 Sep, 18:58, (A.Lee) wrote:
Tim Lamb wrote:
You may have *work hardened* the blade.

Steel doesnt 'work harden', it has to be heat treated.

Sorry. Try http://www.azom.com/details.asp?ArticleID=295
or http://www.engineersedge.com/materia..._hardening.htm

and many others.

"Frank Stacey" wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be particularly
hard.
I tried to drill a small diameter hole and gradually increase the diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3 & 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from a
different set, still no good. It was as if either the bits were blunt or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


Next time drill first then cut, and the metal won't get so hot, and is
easier to hold. Drilling with the work immersed in water or oil may help
too. Once it gets hard: it's time to anneal or start again if you wanted to
preserve the original qualities of the metal. At a pinch you can try a
glass drill, but the tungsten tips of those get very hot and soon fall out
or snap. Then you could try enlarging your pilot holes with diamond burrs.
Better to think of the proper approach in advance.

S

"TMC" wrote in message
...

"Frank Stacey" wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be
particularly
hard.
I tried to drill a small diameter hole and gradually increase the
diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3 & 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from
a
different set, still no good. It was as if either the bits were blunt or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


how did you sharpen the 7mm drill bit? although HSS drills are not
difficult
to sharpen there is a knack and if not just right the cutting edge does
not
touch

You are using HSS drills I assume

Try the 7 mm drill in a scrap bit of mild steel and see if that works you
will soon know if it is properly sharp

alos be aware that the drilling speed are much lower for 7 mm than 3 or 5
mm
typically 2000rpm for 3mm and 900 for 7 mm

If you have overheated the bit you may have ruined it

some info here

http://www.ultimatehandyman.co.uk/DI..._technique.htm


Generally agreed but for relatively thin metal the tendency is for big
drills to get half way through then rip things to bits. At faster speeds
this tendency is less likely, but you harden the metal and blunt the drill
more quickly. All a bit trial and error. Possibly best get as far as you
can, then sharpen, and turn piece over and try and cut through quick at
speed from the other side, before the metal guesses what you are up to ;-)
And see my other note.

S

In article , Frank Stacey
writes
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3 & 5mm I
think. But at 7mm the bit just refused to bite. I tried another similar
sized bit from a different set, still no good. It was as if either the
bits were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

Metal cutting drill bits just aren't meant to cut that way, they are
meant to start a cut near the (centre) point then propagate and maintain
that cut to remove material. By all means drill a pilot but then let the
correct size bit start and maintain the cut.

I can see why you went that way but a drill bit is not the tool for
gradually increasing a hole. Arguably, 8mm in a 3mm depth is probably
enough for the bit to be self centring and avoid it counting as 'sheet'.
In a borderline case, I'd be inclined drill the largest hole that could
be maintained as self centring then enlarge it with a conecut or tapered
reamer.

I don't do a lot of this kind of thing but the above was recounted to me
by one who did.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

Try some Bosch or Dormer HSS-G drill bits, you can pick them up cheap
on fleabay.

Managed to get a Bosch white holesaw "bi-metal" to throw yellow metal
today on a backbox. So old it was undecided until the last moment
whether to friction weld, eject its teeth or actually achieve some
cutting before the universe goes cold.

Quality bits and jobber bits can vary quite considerably, and plenty
of bent half-blunt stuff kicking about. I binned a lot of old bits and
just bought HSS-G, whilst tired a few nights ago I found I had drilled
quite hard brick with one quicker than the Bosch Multi-Construction
bit. I have found even those branded drill bits to vary a little more
than I would like.

On Sep 30, 3:56 am, Frank Stacey
wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick.

I've just drilled 19mm holes in boxes made from 2mm mild steel.
http://i51.tinypic.com/i1bl3b.jpg

I'm no expert but it seemed to work. My theory is to drill a small
hole a bit wider than the central non-cutting part of the big drill,
i.e. about 6mm in my case.
Then I used the 19mm drill with a very slow speed, about 240 rpm using
cutting fluid.
The work has to be held very firmly.
I don't think it pays to try to widen a hole a mm at a time with a
twist drill.
A reamer would be better, but might be wrecked on hardened steel.

Frank Stacey wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3 & 5mm I think.
But at 7mm the bit just refused to bite. I tried another similar sized
bit from a different set, still no good. It was as if either the bits
were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey



It is possible to get tungsten carbide metal cutting drills (solid or
inserts)for difficult steels .

"F Murtz" wrote in message
...
Frank Stacey wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3 & 5mm I think.
But at 7mm the bit just refused to bite. I tried another similar sized
bit from a different set, still no good. It was as if either the bits
were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey



It is possible to get tungsten carbide metal cutting drills (solid or
inserts)for difficult steels .


There is a drill grinding technique that involves reducing the cutting angle
on the lips of the drill. It avoids the drill getting pulled into the metal.
In effect you are giving it a negative rake

"1501" wrote in message
...
On 29 Sep, 18:58, (A.Lee) wrote:
Tim Lamb wrote:
You may have *work hardened* the blade.

Steel doesnt 'work harden', it has to be heat treated.

Sorry. Try http://www.azom.com/details.asp?ArticleID=295
or http://www.engineersedge.com/materia..._hardening.htm

and many others.

When drilling, the steel will inherently be in the plastic limit, where as
you correctly point out, Young's Modulus will be increased. But unless the
steel is of type which can be heat treated, the steel will be pretty
uniform, and so drilling one area shouldn't be very different to drilling in
another.

I suspect it's more down to the drill geometry, though could be wrong.

My experience of lawnmower blades if that they're pretty soft where I've
been able to file the blade to an edge. The last thing a manufacturer wants
is a shattered blade. Plus mulching grass isn't such a bad thing!!

"F Murtz" wrote in message
...
Frank Stacey wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3 & 5mm I think.
But at 7mm the bit just refused to bite. I tried another similar sized
bit from a different set, still no good. It was as if either the bits
were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey



It is possible to get tungsten carbide metal cutting drills (solid or
inserts)for difficult steels .

I have used tungsten carbide masonry bits with steel since it's also easier
to grind them to a sharp edge which cuts. However they are very unforgiving
if the work pieces moves or get stuck, resulting in a chipped tungsten
carbide bit.

In message , Fredxx
writes

"1501" wrote in message
...
On 29 Sep, 18:58, (A.Lee) wrote:
Tim Lamb wrote:
You may have *work hardened* the blade.

Steel doesnt 'work harden', it has to be heat treated.

Sorry. Try http://www.azom.com/details.asp?ArticleID=295
or http://www.engineersedge.com/materia..._hardening.htm

and many others.

When drilling, the steel will inherently be in the plastic limit, where as
you correctly point out, Young's Modulus will be increased. But unless the
steel is of type which can be heat treated, the steel will be pretty
uniform, and so drilling one area shouldn't be very different to drilling in
another.

Place isn't the issue. Quality of the steel is. If the blade were made
of mild steel the OP should not have had a problem if using properly
sharpened bits.

I think he has locally hardened the steel surrounding the initial hole.
Annealing the work by taking up to red heat and then allowing to cool
slowly should solve the problem. It is a very long time since I was an
apprentice but quenching from red heat in water should produce brittle
hardness and quenching in oil an intermediate level.

I suspect it's more down to the drill geometry, though could be wrong.

A pilot hole larger than the core diameter of the finishing drill should
do the job. Low speed and ample coolant avoid localised work hardening.

My experience of lawnmower blades if that they're pretty soft where I've
been able to file the blade to an edge. The last thing a manufacturer wants
is a shattered blade. Plus mulching grass isn't such a bad thing!!

Combine harvesters have serrated blade edges which self sharpen in work
although impact with mole hills can have shattering effects:-)

regards



--
Tim Lamb

The steel you're drilling has work hardened and no HHS bit will touch
it.
I don't know what you're using the steel for but heating it to red and
cooling slowly (preferably under sand) will soften the steel and allow
you to drill it. Alternatively, use one of the TCT wonder drills that
you see advertised. I've seen them drill files, hacksaws and bearings
and the do work. They look like masonry drill but take higher
temperatures. The technique is to use max speed, max pressure and no
coolant/lubricant. It sounds cruel but friction heats the steel to the
point that it softens, then the drill cuts it. The swarf comes off red
hot, sometimes incandescent. I've drilled out broken cap heads with
these when no HSS drill would touch them. I now keep at least one set
for getting out of trouble.

John

A.Lee wrote:

Tim Lamb wrote:

You may have *work hardened* the blade.

Steel doesnt 'work harden', it has to be heat treated.
Something like a rotary mower blade would not be hardened all over, as a
little bit of flex would be good in such a situation. Case hardening of
the blade edges would be possible, though unlikely for the usual
back-garden mower.
http://en.wikipedia.org/wiki/Work_hardening
--
---
zaax
Frustration casues accidents: allow faster traffic to overtake.

On 29/09/2010 16:56, Frank Stacey wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3 & 5mm I think.
But at 7mm the bit just refused to bite. I tried another similar sized
bit from a different set, still no good. It was as if either the bits
were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

Speaking as someone who has drilled many thousands of holes in all sorts
of soft and hard metals...

1 The drill was not ground to the correct angles. I'll try and post some
photos about this.

2 It was spun too fast and polished the metal, rather than work hardened it.

3 The twist drill was allowed to spin without pressure on the metal and
it couldn't bite.

4 The twist drills were of very poor quality and couldn't keep an edge.
It happens.

Dave

On 29/09/2010 22:18, Spamlet wrote:
"Frank wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be particularly
hard.
I tried to drill a small diameter hole and gradually increase the diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3& 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from a
different set, still no good. It was as if either the bits were blunt or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


Next time drill first then cut, and the metal won't get so hot,

The metal should not be even warm when drilling. If it is, the twist
drill is not sharp.


Drilling with the work immersed in water or oil may help
too.

If the twist drill is a good one, then you won't need a coolant.

Once it gets hard: it's time to anneal or start again if you wanted to
preserve the original qualities of the metal.

For the metal to change state to hard, it would have to get to a very
high temperature. I think you are confusing this with the bit polishing
the metal because it can't bite and cut.

At a pinch you can try a
glass drill, but the tungsten tips of those get very hot and soon fall out
or snap. Then you could try enlarging your pilot holes with diamond burrs.
Better to think of the proper approach in advance.

Don't even try this. An HSS twist drill, which has been ground correctly
will tackle most steels, but the case hardened, or hardened ones.

Many years ago, I had to drill some incredibly hard steel on an
aircraft. Twist drills come in several varieties.

1 These are made of something akin to copper.

2 HSS twist drills come in 2 types, those made of chalk and break every
time you use one and those that are made of good metal that will take
and keep an edge and drill a hole

3 You now move up to cobalt drills that are a lot harder that HSS.

4 Next comes what is known as a C1150, harder still.

5 Above this comes the D 200 which was what I was using to drill the
aircraft steel. 3 by 2.5 mm holes and I had to go and grind a new
cutting edge on it. Beyond this, you have to go to solid tungsten
carbide drills.

Dave

On 30/09/2010 09:18, John wrote:
"F wrote in message
...
Frank Stacey wrote:
I was faced recently with trying to drill an 8mm diameter hole in a
piece of sheet metal 2-3mm thick. The sheet was a bit from an old
lawnmower blade. Sawing that off made me think this metal sheet might be
particularly hard.
I tried to drill a small diameter hole and gradually increase the
diameter with successive drillings. I was using a tower drill and bits
which had scarcely ever been used before. The drill was set at medium
speed of rotation. It worked for the first 2 diameters, 3& 5mm I think.
But at 7mm the bit just refused to bite. I tried another similar sized
bit from a different set, still no good. It was as if either the bits
were blunt or the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey



It is possible to get tungsten carbide metal cutting drills (solid or
inserts)for difficult steels .


There is a drill grinding technique that involves reducing the cutting angle
on the lips of the drill. It avoids the drill getting pulled into the metal.
In effect you are giving it a negative rake

Not quite, but it ends up very flat, but positive.

Dave

"Dave" wrote in message
...
On 29/09/2010 22:18, Spamlet wrote:
"Frank wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a
piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be
particularly
hard.
I tried to drill a small diameter hole and gradually increase the
diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3& 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from
a
different set, still no good. It was as if either the bits were blunt
or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


Next time drill first then cut, and the metal won't get so hot,

The metal should not be even warm when drilling. If it is, the twist drill
is not sharp.


Drilling with the work immersed in water or oil may help
too.

If the twist drill is a good one, then you won't need a coolant.

Once it gets hard: it's time to anneal or start again if you wanted to
preserve the original qualities of the metal.

For the metal to change state to hard, it would have to get to a very high
temperature.

As it will when you put your weight on a pedestaI drill so much that it
begins to squeal! This has happened to me plenty of times when trying to
utilise bits of scrap that looked the right size but turned out to be made
of the wrong stuff. I've melted cheap drill ends more than once, as I'm
sure others here must have done.

think you are confusing this with the bit polishing
the metal because it can't bite and cut.

At a pinch you can try a
glass drill, but the tungsten tips of those get very hot and soon fall
out
or snap. Then you could try enlarging your pilot holes with diamond
burrs.
Better to think of the proper approach in advance.

"Don't even try this."

Wot: not try the proper approach in advance!?

Your info on drill types is welcome and handy, in making that choice, but
most of us don't have much of a selection, and have to make best use of what
we have. In many cases we will just have a box of drills and are lucky
enough if we have one the right size that still works, let alone one of the
ideal material. The OP probably just picked up what looked like a handy
sized piece of scrap for the job, and only found its properties beyond his
equipment once started. Grinding out the hole he has may get him out of
trouble - and it certainly has for me on a number of occasions. Also, most
of the common tool sources like Screwfix tell one precious little about what
one is actually buying (Shudder to think of the number of use once and throw
away masonry drills I've bought afer reading ads that simply lie about what
they can do!)

Your handy list will help me choose my next set of drills.

S



An HSS twist drill, which has been ground correctly
will tackle most steels, but the case hardened, or hardened ones.

Many years ago, I had to drill some incredibly hard steel on an aircraft.
Twist drills come in several varieties.

1 These are made of something akin to copper.

2 HSS twist drills come in 2 types, those made of chalk and break every
time you use one and those that are made of good metal that will take and
keep an edge and drill a hole

3 You now move up to cobalt drills that are a lot harder that HSS.

4 Next comes what is known as a C1150, harder still.

5 Above this comes the D 200 which was what I was using to drill the
aircraft steel. 3 by 2.5 mm holes and I had to go and grind a new cutting
edge on it. Beyond this, you have to go to solid tungsten carbide drills.

Dave

On 01/10/2010 00:13, Spamlet wrote:
wrote in message
...
On 29/09/2010 22:18, Spamlet wrote:
"Frank wrote in message
...
I was faced recently with trying to drill an 8mm diameter hole in a
piece
of sheet metal 2-3mm thick. The sheet was a bit from an old lawnmower
blade. Sawing that off made me think this metal sheet might be
particularly
hard.
I tried to drill a small diameter hole and gradually increase the
diameter
with successive drillings. I was using a tower drill and bits which had
scarcely ever been used before. The drill was set at medium speed of
rotation. It worked for the first 2 diameters, 3& 5mm I think. But at
7mm the bit just refused to bite. I tried another similar sized bit from
a
different set, still no good. It was as if either the bits were blunt
or
the metal suddenly much harder.
I have tried sharpening the 7mm bit and added a drop of oil to the
cutting surface - less noise until the oil was gone then shrieking
loadly
before I stopped drilling.

Am I doing something (possibly everything) fundamentally the wrong way?
Any adivice would be much appreciated.

TIA
Frank Stacey


Next time drill first then cut, and the metal won't get so hot,

The metal should not be even warm when drilling. If it is, the twist drill
is not sharp.


Drilling with the work immersed in water or oil may help
too.

If the twist drill is a good one, then you won't need a coolant.

Once it gets hard: it's time to anneal or start again if you wanted to
preserve the original qualities of the metal.

For the metal to change state to hard, it would have to get to a very high
temperature.

As it will when you put your weight on a pedestaI drill so much that it
begins to squeal! This has happened to me plenty of times when trying to
utilise bits of scrap that looked the right size but turned out to be made
of the wrong stuff. I've melted cheap drill ends more than once, as I'm
sure others here must have done.

think you are confusing this with the bit polishing
the metal because it can't bite and cut.

At a pinch you can try a
glass drill, but the tungsten tips of those get very hot and soon fall
out
or snap. Then you could try enlarging your pilot holes with diamond
burrs.
Better to think of the proper approach in advance.

"Don't even try this."

Wot: not try the proper approach in advance!?

Your info on drill types is welcome and handy, in making that choice, but
most of us don't have much of a selection, and have to make best use of what
we have. In many cases we will just have a box of drills and are lucky
enough if we have one the right size that still works, let alone one of the
ideal material. The OP probably just picked up what looked like a handy
sized piece of scrap for the job, and only found its properties beyond his
equipment once started. Grinding out the hole he has may get him out of
trouble - and it certainly has for me on a number of occasions. Also, most
of the common tool sources like Screwfix tell one precious little about what
one is actually buying (Shudder to think of the number of use once and throw
away masonry drills I've bought afer reading ads that simply lie about what
they can do!)

Your handy list will help me choose my next set of drills.

You will find that C1150 and D 200 very hard to source. I have tried two
engineering suppliers and they hadn't even heard of them. I suspect you
would have to contact Dormer for info on them.

An HSS twist drill, which has been ground correctly
will tackle most steels, but the case hardened, or hardened ones.

Many years ago, I had to drill some incredibly hard steel on an aircraft.
Twist drills come in several varieties.

1 These are made of something akin to copper.

2 HSS twist drills come in 2 types, those made of chalk and break every
time you use one and those that are made of good metal that will take and
keep an edge and drill a hole

3 You now move up to cobalt drills that are a lot harder that HSS.

4 Next comes what is known as a C1150, harder still.

5 Above this comes the D 200 which was what I was using to drill the
aircraft steel. 3 by 2.5 mm holes and I had to go and grind a new cutting
edge on it. Beyond this, you have to go to solid tungsten carbide drills.

Dave

John wrote:
Alternatively, use one of the TCT wonder drills that
you see advertised. I've seen them drill files, hacksaws and bearings
and the do work. They look like masonry drill but take higher
temperatures.

Sounds interesting. Got any brand names?


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

The Medway Handyman wrote:
John wrote:
Alternatively, use one of the TCT wonder drills that
you see advertised. I've seen them drill files, hacksaws and bearings
and the do work. They look like masonry drill but take higher
temperatures.

Sounds interesting. Got any brand names?


they are the metal cutting carbide drills that I mentioned in the
earlier post,don't know the brand.

"F Murtz" wrote in message
...
The Medway Handyman wrote:
John wrote:
Alternatively, use one of the TCT wonder drills that
you see advertised. I've seen them drill files, hacksaws and bearings
and the do work. They look like masonry drill but take higher
temperatures.

Sounds interesting. Got any brand names?


they are the metal cutting carbide drills that I mentioned in the earlier
post,don't know the brand.

Most seem to be tiny drills and burrs for the jewellery purposes but there
are more links such as:
http://drillcity.stores.yahoo.net/
S