I've been "practicing" with mill threading with a tap. At least for now,
I really can't see dropping a couple of hundred bucks on a 'proper'
threading mill bit, so I've been fooling with a modified tap. I do this
about once in a blue moon. But I have a project that requires a lot of
1.5" holes to be tapped 1" deep at 10tpi.

I started with a 3/4"x 10tpi tap, and ground off all but one flute.

It works - ehh... - OK, but the surface finish sucks. Partly, that's
likely due to having to mill conventional, since the lead of the threads
is in that direction.

I'm thinking it might also be partly due to the rest of the teeth on that
flute sort of "rubbing" the work, and maybe also due to the thickness of
the flute (so the teeth are slightly over-cutting the top and bottom
shoulders of the vee on entry and exit from the profile.

So I'm thinking of removing all but four or five teeth, and thinning the
flute -- but this is my only 3/4x10 tap/thread mill to work with, and I'd
rather not ruin it just trying out an idea.

Any of you folks fooled around with doing thread milling by modifying a
tap; and does it do decent work?

Thanks,
Lloyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
I've been "practicing" with mill threading with a tap. At least for now,
I really can't see dropping a couple of hundred bucks on a 'proper'
threading mill bit, so I've been fooling with a modified tap. I do this
about once in a blue moon. But I have a project that requires a lot of
1.5" holes to be tapped 1" deep at 10tpi.

I started with a 3/4"x 10tpi tap, and ground off all but one flute.

It works - ehh... - OK, but the surface finish sucks. Partly, that's
likely due to having to mill conventional, since the lead of the threads
is in that direction.

I'm thinking it might also be partly due to the rest of the teeth on that
flute sort of "rubbing" the work, and maybe also due to the thickness of
the flute (so the teeth are slightly over-cutting the top and bottom
shoulders of the vee on entry and exit from the profile.

So I'm thinking of removing all but four or five teeth, and thinning the
flute -- but this is my only 3/4x10 tap/thread mill to work with, and I'd
rather not ruin it just trying out an idea.

??? Didn't you say you already basically ruined as a regular tap ???

I have made taps out of bolts before. They work good for chasing a thread,
but only fair for tapping a smooth hole. I have made taps out of acme
threaded rod before. They work awesome in plastic, and horrible in
aluminum. Ok. I have some threaded couplers made out of aluminum I tapped
with one, but it was a nightmare.

For tapping with the mill I have a small 3/16 right hand boring bar and a
3/16 left hand boring bar that have a nice 60 degree point. I use these
with Mach 3 NFS threading wizard, or if I am being anal I create a helix in
CAD, and then tool mops relative to it in CAM.

I've never used an actual tap on one of my mills. I do use a small tapping
head on one of the drill presses though. Nor have I deliberately broken a
tap... the truth of which is not necessarily born out by the number broken
taps I have thrown away...

If any of that helps... Yeah! I am a hero. If not, then I'll waive the
consulting fee.

"Bob La Londe" fired this volley in news:1HU0r.8235$I%
:

??? Didn't you say you already basically ruined as a regular tap ???

Yeah, but it's my only one, and it's "sort of" working as a threading mill
right now. Just don't want to make it worse.

I started out with a 3/16" boring bar, Bob. It was too flexible, and just
sang to beat the band. The tap cuts quietly.

I'll try making up a LH boring bar, and cutting in climb.

Lloyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 70...
"Bob La Londe" fired this volley in news:1HU0r.8235$I%
:

??? Didn't you say you already basically ruined as a regular tap ???

Yeah, but it's my only one, and it's "sort of" working as a threading mill
right now. Just don't want to make it worse.

I started out with a 3/16" boring bar, Bob. It was too flexible, and just
sang to beat the band. The tap cuts quietly.

I'll try making up a LH boring bar, and cutting in climb.

Lloyd


You can always make a much bigger boring bar.

On Tue, 21 Feb 2012 15:28:49 -0700, Bob La Londe wrote:

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 70...
"Bob La Londe" fired this volley in news:1HU0r.8235$I%
:

??? Didn't you say you already basically ruined as a regular tap ???

Yeah, but it's my only one, and it's "sort of" working as a threading
mill right now. Just don't want to make it worse.

I started out with a 3/16" boring bar, Bob. It was too flexible, and
just sang to beat the band. The tap cuts quietly.

I'll try making up a LH boring bar, and cutting in climb.

Lloyd


You can always make a much bigger boring bar.

You beat me to it. With nearly 3/4 of an inch of hole to play with, you
should be able to make a nice stout boring bar and use an insert for the
sharp part.

Not, mind you, that I've ever done this myself -- I've ground tools for
inside single-point threading out of tool steel, but I haven't made an
actual monotonous rod.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Tim Wescott fired this volley in
:

You beat me to it. With nearly 3/4 of an inch of hole to play with,
you
should be able to make a nice stout boring bar and use an insert for
the
sharp part.


Yeah... I'm going to have to run the trig on the point. Obviously, since
it's cutting a little on the lagging bottom shoulder and a little on the
leading top shoulder, then unlike a regular 60-degree point, it's going
to have to be a smaller angle.

And that may very well be why my tap isn't giving a decent cut, yet.

Lloyd

On Tue, 21 Feb 2012 16:04:51 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

I've been "practicing" with mill threading with a tap. At least for now,
I really can't see dropping a couple of hundred bucks on a 'proper'
threading mill bit, so I've been fooling with a modified tap. I do this
about once in a blue moon. But I have a project that requires a lot of
1.5" holes to be tapped 1" deep at 10tpi.

I started with a 3/4"x 10tpi tap, and ground off all but one flute.

It works - ehh... - OK, but the surface finish sucks. Partly, that's
likely due to having to mill conventional, since the lead of the threads
is in that direction.

I'm thinking it might also be partly due to the rest of the teeth on that
flute sort of "rubbing" the work, and maybe also due to the thickness of
the flute (so the teeth are slightly over-cutting the top and bottom
shoulders of the vee on entry and exit from the profile.

So I'm thinking of removing all but four or five teeth, and thinning the
flute -- but this is my only 3/4x10 tap/thread mill to work with, and I'd
rather not ruin it just trying out an idea.

Any of you folks fooled around with doing thread milling by modifying a
tap; and does it do decent work?

Thanks,
Lloyd


have you heard of the Devlieg microbore line?
http://tinyurl.com/79g7e25

A very rigid bar holds a brazed carbide insert. Grind the insert to a
60 degree angle but with a lot of relief on the bottom (for threading
right hand going down)

You really need a good baldor carbide grinder and preferably an
optical comparator to check your grinding. Given all this, single
point thread milling "werks grate"

Karl Townsend fired this volley in
:

have you heard of the Devlieg microbore line?
http://tinyurl.com/79g7e25

Karl,

I can't even imagine how an adjustable boring bar would help in this
case. I have an adjustable boring head of the off-set slide type.

But insert-style (indexable carbide, and not) internal threading tools
are a LOT cheaper, and in this case, more flexible than that... those
cartridges are outrageously expensive.

The grinding of a healthy relief on the bottom is important, but more
important would be grinding the angle to less than 60-degrees to make up
for cutting on the lag and lead.

A single-point threading mill would give its best profile when as small a
cutter radius as possible, commensurate with enough stiffness and thread
depth.

LLoyd

"Bob La Londe" wrote in message
...
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 70...
"Bob La Londe" fired this volley in news:1HU0r.8235$I%
:

??? Didn't you say you already basically ruined as a regular tap ???

Yeah, but it's my only one, and it's "sort of" working as a threading
mill
right now. Just don't want to make it worse.

I started out with a 3/16" boring bar, Bob. It was too flexible, and
just
sang to beat the band. The tap cuts quietly.

I'll try making up a LH boring bar, and cutting in climb.

Lloyd


You can always make a much bigger boring bar.


I have a single point one I made up by off-hand grinding an old 5/8 many
years ago that I still occasionally use for 3/4 and larger npt--it takes
several minutes to actually machine a thread this way as opposed to only
taking a few seconds when an actual thread mill that has multiple teeth is
used....

Also, where a single point tool is used, you're still probably better off to
finish by chasing with an actual tap afterwards.

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
Tim Wescott fired this volley in
:

You beat me to it. With nearly 3/4 of an inch of hole to play with,
you
should be able to make a nice stout boring bar and use an insert for
the
sharp part.


Yeah... I'm going to have to run the trig on the point. Obviously, since
it's cutting a little on the lagging bottom shoulder and a little on the
leading top shoulder, then unlike a regular 60-degree point, it's going
to have to be a smaller angle.

And that may very well be why my tap isn't giving a decent cut, yet.



A modified tap is NEVER going to give you a decent cut unless you completely
grind away all but one flute, then grind all but one tooth off of the
remaining flute, and THEN grind a portion of the upper face of the single
remaining tooth away in a manner that provides a proper primary clearance
angle on BOTH sides of the resultant 'vee' tooth form.

"PrecisionmachinisT" wrote in message
...

"Bob La Londe" wrote in message
...
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 70...
"Bob La Londe" fired this volley in news:1HU0r.8235$I%
:

??? Didn't you say you already basically ruined as a regular tap ???

Yeah, but it's my only one, and it's "sort of" working as a threading
mill
right now. Just don't want to make it worse.

I started out with a 3/16" boring bar, Bob. It was too flexible, and
just
sang to beat the band. The tap cuts quietly.

I'll try making up a LH boring bar, and cutting in climb.

Lloyd


You can always make a much bigger boring bar.


I have a single point one I made up by off-hand grinding an old 5/8

END MILL

many years ago that I still occasionally use for 3/4 and larger npt--it
takes several minutes to actually machine a thread this way as opposed to
only taking a few seconds when an actual thread mill that has multiple
teeth is used....

Also, where a single point tool is used, you're still probably better off
to finish by chasing with an actual tap afterwards.

On Tue, 21 Feb 2012 19:10:34 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Karl Townsend fired this volley in
:

have you heard of the Devlieg microbore line?
http://tinyurl.com/79g7e25

Karl,

I can't even imagine how an adjustable boring bar would help in this
case. I have an adjustable boring head of the off-set slide type.

But insert-style (indexable carbide, and not) internal threading tools
are a LOT cheaper, and in this case, more flexible than that... those
cartridges are outrageously expensive.

The grinding of a healthy relief on the bottom is important, but more
important would be grinding the angle to less than 60-degrees to make up
for cutting on the lag and lead.

A single-point threading mill would give its best profile when as small a
cutter radius as possible, commensurate with enough stiffness and thread
depth.

LLoyd

ya, you want about 1/2 or at most 2/3 diameter from single point tool
to bore on thread mill. I scored a whole set of micro bores real
cheap, also drawers and drawers of inserts. I like to grind the form
on just the brazed insert with the baldor and then put it on the
optical comparator. I've done threads, timing pulleys, and gears this
way. Works a treat.

Probably a case of use what you have.

karl