I confess that it's been 50 years since I took shop classes in college and
while I've done some things regularly since then both professionally and as
part of my hobby work, I've had very limited experience in certain areas.
SO ...

I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped. Without thinking it through, I drilled
the hole and started tapping. But the tap's cutting length is only 1" and
the shaft behind it is too thick to pass though previously tapped metal.

A Google search reveals that there are some custom taps that are made for
extra long holes but for a one-off I don't need a custom tap. I think I
found that there are some types where the shaft is narrow enough to pass
through the previously tapped hole to allow deeper holes to be done, but the
nomenclature is confusing.

I need help and I'd love to learn the right terminology. As a start, to get
the project back on track, I'd really appreciate it if someone could tell
me, perhaps, the name and part number at ENCO for the right tap for my hole.
As a follow-up, perhaps a link or three to pages which explain the
differences would also be greatly appreciated.

TIA
Norm

On Fri, 09 Jan 2009 15:54:38 GMT, Norm Dresner wrote:

I confess that it's been 50 years since I took shop classes in college and
while I've done some things regularly since then both professionally and as
part of my hobby work, I've had very limited experience in certain areas.
SO ...

I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped. Without thinking it through, I drilled
the hole and started tapping. But the tap's cutting length is only 1" and
the shaft behind it is too thick to pass though previously tapped metal.


Do you need the whole length of the hole threaded?

If not, drill a clearance hole for the tap and keep going.

If you do, you could grind the shank of the tap for the extra quarter inch;
a cheap carbon tap in aluminium should be ok, especially if you have a good
sized tap hole and some wd-40 with which to lube the tap.

I presume you don't have a lathe - single-pointing with a boring-bar works.

Norm Dresner wrote:
I confess that it's been 50 years since I took shop classes in college and
while I've done some things regularly since then both professionally and as
part of my hobby work, I've had very limited experience in certain areas.
SO ...

I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped. Without thinking it through, I drilled
the hole and started tapping. But the tap's cutting length is only 1" and
the shaft behind it is too thick to pass though previously tapped metal.

A Google search reveals that there are some custom taps that are made for
extra long holes but for a one-off I don't need a custom tap. I think I
found that there are some types where the shaft is narrow enough to pass
through the previously tapped hole to allow deeper holes to be done, but the
nomenclature is confusing.

I need help and I'd love to learn the right terminology. As a start, to get
the project back on track, I'd really appreciate it if someone could tell
me, perhaps, the name and part number at ENCO for the right tap for my hole.
As a follow-up, perhaps a link or three to pages which explain the
differences would also be greatly appreciated.

TIA
Norm

There are several kinds of taps with extra-long shanks, called pulley
taps (from their use in tapping pulley hubs), extension taps, or long
reach taps.

The words you're interested in are "reduced shank" or "undercut shank".
An ordinary 1/4-20 pulley tap will have a 1/4" diameter shank, while a
reduced shank tap will have a shank smaller than the root diameter of
the thread. So you can keep going and going ...

Spiral point (gun) taps are particularly nice here, since they throw
the chips ahead of the tap and they don't clog the flutes.

In your case, see http://www.use-enco.com/CGI/INSRIT?PMAKA=325-4824
for #325-4824 -- a 6" long reduced shank 1/4-20 spiral point tap for
$20.95.

I've only used mine a few times, but I'm very glad I have it.

Tove

On Jan 9, 11:17*am, Tove Momerathsson wrote:
Norm Dresner wrote:
...

In your case, see http://www.use-enco.com/CGI/INSRIT?PMAKA=325-4824
for #325-4824 -- a 6" long reduced shank 1/4-20 spiral point tap for
$20.95.

I've only used mine a few times, but I'm very glad I have it.

Tove

Enco doesn't like my 3rd party cookie setting so I can't show you, but
"Nut Taps" are long ones with reduced shanks that fit through the
tapped hole. Pulley taps have thicker, stronger shanks to get past the
flange to the hub.

Grind the shank of a less valuable tap smaller beyond the threads. You
could tap the end of an aluminum rod for a handle to hold it and
protect the threads from overheating if it's carbon steel. It will be
weakened so don't use it unless you have to.

You can make a crude quickie tap for soft metal by grinding the end of
a screw conical and filing lengthwise notches or grinding a flat on
either side, like the end of a chisel.

Jim Wilkins

"_" wrote in message
...
| On Fri, 09 Jan 2009 15:54:38 GMT, Norm Dresner wrote:
| I've got a bar of aluminum that I had to drill and tap several 1/4-20
holes
| in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
| through the thickness (1") was a good refresher course, but the hole
through
| the height (1.25") has me stumped. Without thinking it through, I
drilled
| the hole and started tapping. But the tap's cutting length is only 1"
and
| the shaft behind it is too thick to pass though previously tapped metal.
|
|
| Do you need the whole length of the hole threaded?
|
| If not, drill a clearance hole for the tap and keep going.
|
| If you do, you could grind the shank of the tap for the extra quarter
inch;
| a cheap carbon tap in aluminium should be ok, especially if you have a
good
| sized tap hole and some wd-40 with which to lube the tap.
|
| I presume you don't have a lathe - single-pointing with a boring-bar
works.

I've thought of drilling a clearance hole for the top 1/4" or so, but it
bothers my sensibilities ... I may yet do it.

The tap I'm using is part of a set I bought from DRI around 1973 or so and
yes, I could probably grind the shank down but that seems like a lot more
work than it's worth, considering that new taps can be bought for $5-7.

And, right, I don't have a lathe.

Norm

only because its alum maybe try tapping as deep as you can with your
tap, get a 1/4 bolt or carriage bolt about 4" long and grind tip to
look like your tap or close and vise-grip and have at it.

On Fri, 09 Jan 2009 15:54:38 GMT, "Norm Dresner"
wrote:
snip
I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped. Without thinking it through, I drilled
the hole and started tapping. But the tap's cutting length is only 1" and
the shaft behind it is too thick to pass though previously tapped metal.
snip
Actually very long tapped holes are not a good idea. The slight
variation in lead between the tap and the hole will frequently
cause the tap to bind/break. You are attempting to tap 5
diameters deep.

A tap depth of 1 to 2 diameters [in your case 1/4 to 1/2 inch]
will be adequate. Indeed, it has been frequently demonstrated in
most cases even a 1 diameter tap depth [assuming good threads and
a reasonable thread percentage] will result in fastener breakage
before the threads will strip when loaded to destruction.

Without knowing your actual design, it would appear best to drill
a counter bore large enough to pass the tap shank, if you will be
using the drill press as a tapping alignment jig. If you tap from
the other side, the counterbore can be just enough to clear the
tap, say 5/16 or 9/32. It can be helpful to put a heavy chamfer
[or counterbore] on the side where the thread exits/enters as
this will keep the surface smooth/level, as you will tend to
raise a bur where the trap enters/exits the material. If you do
this remember to take the chamfer depth into consideration when
calculating the length of tapped hole.

Although soft, aluminum can be tricky to tap, so back off often
to break the chips, back out often and clean if the chips are
tending to pack in the flutes, use a tap wrench [a crescent
wrench is a sure way to break a tap] and use a good tap lube,
WD-40 if nothing else.

Good luck on the project, and let the group know how you make
out.


Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

On Jan 9, 11:50*am, Jim Wilkins wrote:
...

You can make a crude quickie tap for soft metal by grinding the end of
a screw conical and filing lengthwise notches or grinding a flat on
either side, like the end of a chisel.

Jim Wilkins

I thought of a variation on that during lunch, tried it, and it worked
pretty well. A home-made tool will probably cut with only one edge
anyway, so why make more?

I hand ground a bevel about 2/3 of the way across the end of a Grade 5
1/4-20 screw, trying for a 30 degree angle (it measures 33).
After filing the burrs off I used it to complete a hole tapped 1/4"
deep in 3/4" aluminum, with Tap-Free lube. It acted like a spiral
point tap should and spit out one long curled chip. The exit wound is
tighter than standard but another screw will go in with finger
pressure.

Jim Wilkins

On Fri, 09 Jan 2009 11:24:37 -0600, F. George McDuffee
wrote:

A tap depth of 1 to 2 diameters [in your case 1/4 to 1/2 inch]
will be adequate. Indeed, it has been frequently demonstrated in
most cases even a 1 diameter tap depth [assuming good threads and
a reasonable thread percentage] will result in fastener breakage
before the threads will strip when loaded to destruction.

Without knowing your actual design, it would appear best to drill
a counter bore large enough to pass the tap shank, if you will be
using the drill press as a tapping alignment jig. If you tap from
the other side, the counterbore can be just enough to clear the
tap, say 5/16 or 9/32. It can be helpful to put a heavy chamfer
[or counterbore] on the side where the thread exits/enters as
this will keep the surface smooth/level, as you will tend to
raise a bur where the trap enters/exits the material. If you do
this remember to take the chamfer depth into consideration when
calculating the length of tapped hole.
good advice

Gunner


"First Law of Leftist Debate
The more you present a leftist with factual evidence
that is counter to his preconceived world view and the
more difficult it becomes for him to refute it without
losing face the chance of him calling you a racist, bigot,
homophobe approaches infinity.

This is despite the thread you are in having not mentioned
race or sexual preference in any way that is relevant to
the subject." Grey Ghost

On Fri, 09 Jan 2009 15:54:38 GMT, "Norm Dresner"
wrote:


I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped.

Nut tap.

McMaster cat# 2583A12
Nut Hand Taps 1/4"-20, 4 Flute, 5" O'all Length
In stock at $40.95 Each

Or for a lot less than $40 you can grind down the shank of a standard
tap by hand. It won't be pretty, but it'll work.

--
Ned Simmons

On Jan 9, 1:58*pm, Ned Simmons wrote:
...
Or for a lot less than $40 you can grind down the shank of a standard
tap by hand. It won't be pretty, but it'll work.
Ned Simmons

http://picasaweb.google.com/KB1DAL/T...74956505595074

jw

"Norm Dresner" wrote in message
...
|
| I've got a bar of aluminum that I had to drill and tap several 1/4-20
holes
| in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
| through the thickness (1") was a good refresher course, but the hole
through
| the height (1.25") has me stumped. Without thinking it through, I drilled
| the hole and started tapping. But the tap's cutting length is only 1" and
| the shaft behind it is too thick to pass though previously tapped metal.
|
| I need help and I'd love to learn the right terminology. As a start, to
get
| the project back on track, I'd really appreciate it if someone could tell
| me, perhaps, the name and part number at ENCO for the right tap for my
hole.
| As a follow-up, perhaps a link or three to pages which explain the
| differences would also be greatly appreciated.
|
| TIA
| Norm

Thanks to everyone who answered. I've learned the term "Pulley Tap" and
while it might have been the ideal thing, I took the easy way suggested by
several people and ground down the shaft of the tap enough to clear the
threads for the final 1/8" or so.

Thanks again
Norm

On 2009-01-09, Norm Dresner wrote:
I confess that it's been 50 years since I took shop classes in college and
while I've done some things regularly since then both professionally and as
part of my hobby work, I've had very limited experience in certain areas.
SO ...

I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped. Without thinking it through, I drilled
the hole and started tapping. But the tap's cutting length is only 1" and
the shaft behind it is too thick to pass though previously tapped metal.

A Google search reveals that there are some custom taps that are made for
extra long holes but for a one-off I don't need a custom tap. I think I
found that there are some types where the shaft is narrow enough to pass
through the previously tapped hole to allow deeper holes to be done, but the
nomenclature is confusing.

Do you have a spin indexer? A surface grinder or a Tool &
Cutter grinder? Then grind the diameter of the shank down a little
below the root diameter -- and perhaps overlapping the last turn of
threads, for a length a bit over 0.250" removed from the shank,

Be careful with this, because it will probably be easier to
break the shank off in the workpiece.

I need help and I'd love to learn the right terminology. As a start, to get
the project back on track, I'd really appreciate it if someone could tell
me, perhaps, the name and part number at ENCO for the right tap for my hole.
As a follow-up, perhaps a link or three to pages which explain the
differences would also be greatly appreciated.

Look for a "reduced shank" (or something like that).

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
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