[Cordless Crazy]

If I want to form a M8 thread in a piece of sheet steel, what size hole do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

"Cordless Crazy" wrote in message
...

If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

Sorry it's not an exact answer, but from what I remember from my distant
days at BT Fulcrum, it is certainly no greater than a mm. But don't take my
word for it - try it out, but don't force the tap if the hole is too small,
as they are very brittle.

-- JJ

"Jason" wrote in message
. uk...

"Cordless Crazy" wrote in message
...

If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

Sorry it's not an exact answer, but from what I remember from my distant
days at BT Fulcrum, it is certainly no greater than a mm. But don't take
my
word for it - try it out, but don't force the tap if the hole is too
small,
as they are very brittle.

-- JJ


Why don't you first do an internet search: -

e.g. http://www.newmantools.com/tapdrill.htm
Jaymack

Cordless Crazy wrote:
If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?


Its not hugely critical. The tap will be more or less tapered for a
thread in sheet..I'd guess at around a 6.5mm or 1/4" hole meself.

In use, the taper tap will remove as much metals as it needs to, but go
slow, use oil, and work it backwards and forwards till it runs freely
before advancing it the net half a turn or so. If it binds, rotate
backwards and forwards till it frees up and proceed.

"John McLean" wrote in message
...

"Jason" wrote in message
. uk...

"Cordless Crazy" wrote in message
...

If I want to form a M8 thread in a piece of sheet steel, what size
hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

Sorry it's not an exact answer, but from what I remember from my distant
days at BT Fulcrum, it is certainly no greater than a mm. But don't take
my
word for it - try it out, but don't force the tap if the hole is too
small,
as they are very brittle.

-- JJ


Why don't you first do an internet search: -

e.g. http://www.newmantools.com/tapdrill.htm
Jaymack



or even better: - http://www.simetric.co.uk/sidrill.htm

Jaymack

On Sat, 1 Apr 2006 08:06:39 +0100, Cordless Crazy
wrote:


If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

6.8mm is the correct size, according to "Machinery's Handbook".

--
Frank Erskine
Sunderland

"Frank Erskine" wrote in message
...
On Sat, 1 Apr 2006 08:06:39 +0100, Cordless Crazy
wrote:


If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

6.8mm is the correct size, according to "Machinery's Handbook".

--
Frank Erskine
Sunderland

===================
My chart shows some variation depending on the pitch of the thread.

Fine thread (0.75) - 7.2mm drill, medium thread (1.00) - 7mm drill, coarse
thread (1.25) - 6.8mm drill. If you're not sure what the pitch is it would
be sensible to start with the smallest hole and if the tap binds go to the
next larger drill hole.

Cic.

In message , The Natural
Philosopher writes

In use, the taper tap will remove as much metals as it needs to, but go
slow, use oil, and work it backwards and forwards till it runs freely
before advancing it the net half a turn or so. If it binds, rotate
backwards and forwards till it frees up and proceed.

1/2 turn forward and then a 1/4 back to break off the swarf, according
to my apprentice supervisor, nearly 50 years ago:-(

regards

--
Tim Lamb

"Cordless Crazy" wrote in message
...

If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

The rule for any metric thread is the nominal size minus the thread pitch
which for a standard 8mm thread is 8 - 1.25 = 6.75mm
--
Dave Baker
www.pumaracing.co.uk

"Cicero" wrote in message
. uk...

"Frank Erskine" wrote in message
...
On Sat, 1 Apr 2006 08:06:39 +0100, Cordless Crazy
wrote:


If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

I am thinking 2mm less or is that too much?

Would that make it a 6mm hole?!?

6.8mm is the correct size, according to "Machinery's Handbook".

--
Frank Erskine
Sunderland

===================
My chart shows some variation depending on the pitch of the thread.

Fine thread (0.75) - 7.2mm drill, medium thread (1.00) - 7mm drill,
coarse
thread (1.25) - 6.8mm drill. If you're not sure what the pitch is it would
be sensible to start with the smallest hole and if the tap binds go to the
next larger drill hole.

Cic.

and if its a different tap.......

standard M8 tapping drill size is 6.8mm

Regards Jeff

On Sat, 1 Apr 2006 17:01:15 +0100, Tim Lamb
wrote:

|In message , The Natural
|Philosopher writes
|
|In use, the taper tap will remove as much metals as it needs to, but go
|slow, use oil, and work it backwards and forwards till it runs freely
|before advancing it the net half a turn or so. If it binds, rotate
|backwards and forwards till it frees up and proceed.
|
|1/2 turn forward and then a 1/4 back to break off the swarf, according
|to my apprentice supervisor, nearly 50 years ago:-(

Bi Hek that brings back memories!
The first thing we had to do was to file a cube with all sides within 1
thou of each other from a bit of round bar ins dia by 1 ins long.
--
Dave Fawthrop dave hyphenologist co uk Google Groups is IME the *worst*
method of accessing usenet. GG subscribers would be well advised get a
newsreader, say Agent, and a newsserver, say news.individual.net. These
will allow them: to see only *new* posts, a killfile, and other goodies.

"The Natural Philosopher" wrote in message
...
....
In use, the taper tap will remove as much metals as it needs to, but go
slow, use oil, ...

I would guess that an EP grade would work best. The tapping lubricant I buy
is more like a grease than an oil though.

Colin Bignell

"Cordless Crazy" wrote in message
...

If I want to form a M8 thread in a piece of sheet steel, what size hole
do I initially drill?

If the sheet metal is thin, you are better off using a clinch nut:

http://www.allproducts.com/fastener/...131163225.html

The ones in the top row are applied with a pop rivet gun, for which you need
one with an appropriate mandrel. The ones in the bottom row are inserted
using a press.

Alternatively, you can drill out a small hole and use a tapered drift to
enlarge it. That will throw up a heavy burr on the back of the sheet, which
increases the length of thread you can cut. You can also use a special punch
to press a hole of that form.

Colin Bignell

In message , Dave Fawthrop
writes

|1/2 turn forward and then a 1/4 back to break off the swarf, according
|to my apprentice supervisor, nearly 50 years ago:-(

Bi Hek that brings back memories!
The first thing we had to do was to file a cube with all sides within 1
thou of each other from a bit of round bar ins dia by 1 ins long.

Crumbs. I was an *electrical technician* so that sort of precision was
not reached.

There was the occasion when one of the craft lads filed the master to
suit his test piece which put the rest of us out.

Leaning on the saddle of the only lathe in the dept. took another 10
thou off the work.

Happy days.

regards

--
Tim Lamb

Cicero wrote:


My chart shows some variation depending on the pitch of the thread.

I'm glad that some one brought this up in the thread (sorry about the pun).

Fine thread (0.75) - 7.2mm drill, medium thread (1.00) - 7mm drill, coarse
thread (1.25) - 6.8mm drill. If you're not sure what the pitch is it would
be sensible to start with the smallest hole and if the tap binds go to the
next larger drill hole.

Pitch is the determining factor in the drill size, as metric threads
have symmetrical pitch/ thread depth.

Dave

In article
Cicero wrote:
snip
If you're not sure what the pitch is it would
be sensible to start with the smallest hole and if the tap binds go to the
next larger drill hole.

If you're not sure what the pitch is it would be sensible to measure it.

"Rob Morley" wrote in message
t...
In article
Cicero wrote:
snip
If you're not sure what the pitch is it would
be sensible to start with the smallest hole and if the tap binds go to
the
next larger drill hole.

If you're not sure what the pitch is it would be sensible to measure it.


====================
If the OP had been aware that there are three possible pitch sizes and knew
how to measure his tap then he probably wouldn't have asked a question in
the first place.

I supplied good data which the OP could match against the information
stamped on the tap he intended to use. In the unlikely event that his tap
didn't show full information then a common sense thing to do would be to
start with the smallest tapping hole and change to a larger hole if
necessary.

Cic.

In article
Cicero wrote:
snip
If the OP had been aware that there are three possible pitch sizes and knew
how to measure his tap then he probably wouldn't have asked a question in
the first place.

Surely it's better to explain the differences, and how to measure them?

I supplied good data which the OP could match against the information
stamped on the tap he intended to use. In the unlikely event that his tap
didn't show full information then a common sense thing to do would be to
start with the smallest tapping hole and change to a larger hole if
necessary.

That's a good way to break a tap if you're not familiar with the torques
that they can withstand. Adnittedly not a problem with 8mm and mild
steel sheet, but with smaller taps and tougher metal it can end in
tears. There again, while he said it's sheet steel it would have to be
pretty thick to take an 8mm thread. Nobody mentioned the difference
between taper, second and plug either.