Hi,
I was wondering if it would be possible to tap the interior of a ~4"
diameter pipe? I can't imagine a tap so large...? Can I tap it on the
lathe, by somehow getting the cutterhead inside (I'll need to go back
to the shop on Monday to assess if it can)...? If not, are there
places that will economically tap it for me? Or, just rethink my
design to not require this; although it just makes the design better if
I can do it.

Secondly, is there a way to tap for acme-style threads; are such
threads preferred for higher-load applications like bringing together
to vise jaws?


thanks!
-Bernard Arnest

On 11 Mar 2006 20:28:20 -0800, "Bernard Arnest"
wrote:
Hi,
I was wondering if it would be possible to tap the interior of a ~4"
diameter pipe? I can't imagine a tap so large...? Can I tap it on the
lathe, by somehow getting the cutterhead inside (I'll need to go back
to the shop on Monday to assess if it can)...? If not, are there
places that will economically tap it for me? Or, just rethink my
design to not require this; although it just makes the design better if
I can do it.

Secondly, is there a way to tap for acme-style threads; are such
threads preferred for higher-load applications like bringing together
to vise jaws?


thanks!
-Bernard Arnest
===================================
It used to be commonly done and still can be.

The only special tools you need are a large diameter "boring" bar
to hold the tool and the Acme thread tool. The major problem is
that you must be very careful to not bottom out the boring bar!

I note that you are wanting to do a 4 inch diameter internal Acme
thread. How long/deep is the thread and is this a blind hole or
can the tool/bar go completely through the pipe?

Most likely you will wind up making a special fixture for a face
plate to hold the pipe and may need a steady rest if the length
is more than 1 diameter.

You may also wind up making a one off boring bar/tool holder and
block to mount it to the cross slide or compound. The compound
is better because you can set the compount to 14_1/2 degrees so
you are not taking a full width cut.

You are also going to need an acme thread gage [fishtail] to
grind the tool and set it square. The fence on most grinders is
not nearly accurate enough for this. See the pictures on a
fixture we made as a class project on my website at
http://www.mcduffee-associates.us/machining/thfnce.htm
and
http://www.mcduffee-associates.us/ma...g/tabanggg.htm

Please feel free to browse the entire site.

Unka George


Unka George
(George McDuffee)

What a country calls its vital economic interests are not
the things which enable its citizens to live, but the things
which enable it to make war. Petrol is more likely than wheat
to be a cause of international conflict.
Simone Weil (1909-43), French philosopher, mystic.
«The Power of Words», in Nouveaux Cahiers (1 and 15 April 1937;
repr. in Selected Essays, ed. by Richard Rees, 1962)

On 11 Mar 2006 20:28:20 -0800, "Bernard Arnest"
wrote:
snip
Secondly, is there a way to tap for acme-style threads; are such
threads preferred for higher-load applications like bringing together
to vise jaws?
snip
Even better for one-way loads like a vise are buttress threads.
Even harder to grind the tool for a buttress thread than for an
acme though. You almost need a surface grinder and fixtures.
Can be a royal pain to set square also as the "fish tail" gages
are not available.

Unka George
Unka George
(George McDuffee)

What a country calls its vital economic interests are not
the things which enable its citizens to live, but the things
which enable it to make war. Petrol is more likely than wheat
to be a cause of international conflict.
Simone Weil (1909-43), French philosopher, mystic.
«The Power of Words», in Nouveaux Cahiers (1 and 15 April 1937;
repr. in Selected Essays, ed. by Richard Rees, 1962)

I think it would be costly to buy a tap that size and you would also need a
large machine . But there are shops
that do nothing but cut threads. Any kind you can think of. And most machine
shops can cut threads. Look in Yellow pages under threads or threading.
I used to use Vescio Threading in Santa Fe Springs Ca
And they had a ton of threading machines maybe 50
of them and I think they also ground threads.
Jim
"Bernard Arnest" wrote in message
ups.com...
Hi,
I was wondering if it would be possible to tap the interior of a ~4"
diameter pipe? I can't imagine a tap so large...? Can I tap it on the
lathe, by somehow getting the cutterhead inside (I'll need to go back
to the shop on Monday to assess if it can)...? If not, are there
places that will economically tap it for me? Or, just rethink my
design to not require this; although it just makes the design better if
I can do it.

Secondly, is there a way to tap for acme-style threads; are such
threads preferred for higher-load applications like bringing together
to vise jaws?


thanks!
-Bernard Arnest

On 11 Mar 2006 20:28:20 -0800, "Bernard Arnest"
wrote:

Hi,
I was wondering if it would be possible to tap the interior of a ~4"
diameter pipe? I can't imagine a tap so large...? Can I tap it on the
lathe, by somehow getting the cutterhead inside (I'll need to go back
to the shop on Monday to assess if it can)...? If not, are there
places that will economically tap it for me? Or, just rethink my
design to not require this; although it just makes the design better if
I can do it.

Secondly, is there a way to tap for acme-style threads; are such
threads preferred for higher-load applications like bringing together
to vise jaws?


thanks!
-Bernard Arnest


yes.you can tap just about any size pipe.

However..depending on the length..it may be easier to single point
thread it in the lathe

Gunner



"A prudent man foresees the difficulties ahead and prepares for them;
the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3

According to Bernard Arnest :
Hi,
I was wondering if it would be possible to tap the interior of a ~4"
diameter pipe? I can't imagine a tap so large...?

I can. I've seen a web site showing the building of a 12"
diameter tap.

Can I tap it on the
lathe, by somehow getting the cutterhead inside (I'll need to go back
to the shop on Monday to assess if it can)...?

On a lathe, for making only one or a few, the thread should be
single-point cut, not made with a *very* expensive tap.

For making a *lot* of them, you might consider a collapsing tap,
mounted on a bed turret or on a lathe made from scratch as a turret
lathe. This is like a Geometric die head -- but inside out. It taps to
depth, then trips a release, and the chasers move to a reduced diameter
position, allowing you to withdraw the tap while the workpiece is still
spinning.

However -- for your purposes, I think that it is perhaps time to
learn to single-point cut threads -- first on the OD of something, and
once you have that right, then you try your hand at making them on the
ID. (First turn a "runout" groove at the end of the threads, to give
you someplace to stop the threading pass.

You don't say how long the workpiece is, but I suspect that at
4", you can't pass it through the spindle, so if it is short enough, you
can just hold it in the chuck, or when a bit longer, you'll need to set
up a steady rest to hold it concentric against the cutting forces.

If not, are there
places that will economically tap it for me?

Unless you happen to luck into a shop which already has a tap of
the desired thread, I consider *economical* tapping unlikely. But
economical internal threading is a different matter, and that should be
possible if the pipe is short enough -- or if the lathe is big enough.

Or, just rethink my
design to not require this; although it just makes the design better if
I can do it.

Secondly, is there a way to tap for acme-style threads;

Sure -- tap, or single-point thread on the lathe. Again, Acme
taps are expensive, and large ones are even more expensive, so
single-point threading makes more sense.

Note that part of this depends on the wall thickness of the
pipe, and the thread pitch desired. If the wall thickness is not
sufficient, you may have to select a smaller pitch. I threaded the OD of
some aluminum pipe to 20 TPI, because I did not need strength (these
threads were for screwing on endpieces to a waveguide antenna for
wireless internet frequencies), and because a more appropriate pitch
would come closer to cutting through the wall of the pipe.

are such
threads preferred for higher-load applications like bringing together
to vise jaws?

They are used for such applications -- in part because an Acme
thread can survive wear longer than a standard V thread.

Perhaps you should give a bit more detail about what you want to
do, and why (including dimensions like length) and you might get more
useful advice.

Good Luck,
DoN.

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