[spaco]

Several good ideas in the other posts.
You probably know that there are 3 kinds of basic taps:
Taper
Plug
Bottoming.

Taper taps have as many as 6 to 10 tapered threads,
Plug taps, 3 to 5 or so and,
Bottoming taps, about 1 1/2.
Depending on which tap you are using, your tailstock chuck is going
to slip sooner, the taper tap being deeper in the hole and therefore
straighter before the friction goes 'way up.
If you are buying your taps at the hardware store, you are probably
getting "plug".
I like using the dead center in the tailstock to align with the hole
in the end of the tap or in the tap wrench. But, I also have a little
device that is a spring loaded "center" for the tailstock or mill
spindle that does the same thing while freeing you from having to crank
to keep the tap aligned.
Also, could it be that your tap(s) are worn out? Causes same problem.
Be sure to countersink the hole, too. Try a new GOOD one anyway. I
always keep one brand new tap of the most used sizes so I have a way to
check if I suspect that the tap I'm using might be dull. (A REAL
machinist would probably throw the things away on a regular basis).

Pete Stanaitis
-------------------------

Carl Boyd wrote:
I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am leary
to cut internals. I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

[Carl Boyd]

I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am leary
to cut internals. I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

[chipswarf]

Hi, Carl

Does your tap have a female center at the back? I think you'd be
better served, after starting the tap, to put a hard center in the
tailstock and use it to align the tap. Turn the tap with a wrench
while keeping tailstock pressure on the center. You can start the
thread this way also, and save your chuck jaws the beating they take
when the tap slips. Put a nice countersink in the hole before starting
the tap. I was taught this way when going through the USAF machinist
course in (gad!) '69.

You are backing off the tap every half-turn or so, to break the chips,
are you not? That greatly eases the job.

If you supply yourself, or make, internal threading tools, you'll
enjoy the results. If you doubt your grinding, you can start by
screwcutting with a pretty-good tool, and finish with the tap. That'll
provide better alignment, too. Have fun, I sorta envy where you are on
the learning curve. I had fun learning all this stuff.

Mark

On Jun 28, 9:10*pm, "Carl Boyd" wrote:
I have had a problem on a couple of my recent projects. *Both involved
1/2"-13 inside threads. *Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. *Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? *I have cut a few external threads, but am leary
to cut internals. *I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

[Carl Boyd]

Mark

Thanks for the advice.

My taps do not have a female center in the back.

I did not countersink, the one that came out straight had a fairly long 1/2
inch counter bore that I am sure helped to keep the tap straight. I'll
remember the counter sink idea.

Yes I am backing the, but it seems to cut fine for about 2 turns and then
get tight. Thats when I back it off.

I have ground my own external threading tools, the nuts fit the threads
fine, I have no idea if they meet spec or not. Grinding for an inside
thread seems harder, maybe, I'll give it a try.

CarlBoyd

"chipswarf" wrote in message
...
Hi, Carl

Does your tap have a female center at the back? I think you'd be
better served, after starting the tap, to put a hard center in the
tailstock and use it to align the tap. Turn the tap with a wrench
while keeping tailstock pressure on the center. You can start the
thread this way also, and save your chuck jaws the beating they take
when the tap slips. Put a nice countersink in the hole before starting
the tap. I was taught this way when going through the USAF machinist
course in (gad!) '69.

You are backing off the tap every half-turn or so, to break the chips,
are you not? That greatly eases the job.

If you supply yourself, or make, internal threading tools, you'll
enjoy the results. If you doubt your grinding, you can start by
screwcutting with a pretty-good tool, and finish with the tap. That'll
provide better alignment, too. Have fun, I sorta envy where you are on
the learning curve. I had fun learning all this stuff.

Mark

On Jun 28, 9:10 pm, "Carl Boyd" wrote:
I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly
off
axis.

I had assumed that I would start the thread on axis with the tailstock
chuck
and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am
leary
to cut internals. I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

[Martin H. Eastburn]

How about using a Steady Rest to keep the tap on center away from the
tail stock. Fixed or 'traveling' rest.

The tap would have to be round or ground round if not.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Carl Boyd wrote:
I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am leary
to cut internals. I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd




----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.pronews.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= - Total Privacy via Encryption =---

[Leo Lichtman]

"Martin H. Eastburn" wrote:
How about using a Steady Rest to keep the tap on center away from the
tail stock. Fixed or 'traveling' rest.
^^^^^^^^^^^^^^^^^
Maybe cobble some way to hold a nut to serve as a steady rest. If your
steady rest has three arms, maybe they would hold a hex nut on axis.

[F. George McDuffee]

On Sat, 28 Jun 2008 22:10:49 -0400, "Carl Boyd"
wrote:

I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am leary
to cut internals. I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

===========
Sometimes a taper tap in a straight hole without a guide can be a
problem. It may be helpful to use a taper reamer and then thread.
The thread quality will also be higher, and a taper reamed hole
is generally needed for dryseal quality threads.

for examples see
http://www.hermanscentral.com/produc...cfm?sid=google
http://www.use-enco.com/CGI/INPDFF?P...PARTPG=INLMK32
most mill supplies should stock.


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).

[flash]

There used to be a tool called an "Extension Tap Holder", I believe. I had
one in ancient history, but it got lost in moving. It looked like an
ordinary Tee-handled tap holder, with a shaft extending coaxially from the
tool, (opposite the tap), and it had a bearing: ie, the tap-holder swiveled
on the extension shaft. You would put the shaft in a chuck on the
tailstock, run the tailstock in until the tap was just taking a bite in the
hole in the end of the workpiece, and turn the tap by hand, keeping pressure
lightly with the tailstock.

I think that would get your job done right.

I have used the dead-center point in the back of the standard tee-handle
tap-holder method, with decent results.

However, these showed up in a Google search.


http://www.patentstorm.us/patents/4818158.html

http://www.vintageprojects.com/machi...ttachment.html

And this might just be overkill:
http://nbutterfield.com/d.aspx

But this one looks simple and could do the job. I think I'll make one for
myself, anyway.
http://homemetalshopclub.org/project.../lathetap.html

And this guy has taken this idea to a higher level of the craft.
http://members.shaw.ca/aldobler/
(Scroll down to the last article)

About half-way down this page, "Tailstock Tap Holder"
http://www.stellar-international.com...lstock%20Drive



Maybe something there will work for you.

Flash




"Carl Boyd" wrote in message
m...
I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly
off axis.

I had assumed that I would start the thread on axis with the tailstock
chuck and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am
leary to cut internals. I currently have no tools to cut internals
threads but I suppose I need some if that is the only way to do this.

CarlBoyd

[F. George McDuffee]

On Sun, 29 Jun 2008 00:22:17 -0400, "Flash"
wrote:
snip
I think that would get your job done right.

I have used the dead-center point in the back of the standard tee-handle
tap-holder method, with decent results.
snip
====for current production see ====
http://www.use-enco.com/CGI/INPDFF?P...MITEM=318-0150
most mill supplies should have something similar in stock.



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).

[Steve Lusardi]

Carl,
Your procedure is fine. I have used the same one hundreds of times and never
had a problem. I believe you are starting straight, but your thread is
probably not deep enough to prevent applied side trust to tilt the tap. It
is ultimately the applied side thrust that is causing the problem. Once the
thread is adequately started (4-5 threads), removing the work to a vise and
using a T wrench will go a long way to control side thrust. Pay careful
atention to the side yhrust and you will be fine.
Steve


"Carl Boyd" wrote in message
m...
I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly
off axis.

I had assumed that I would start the thread on axis with the tailstock
chuck and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am
leary to cut internals. I currently have no tools to cut internals
threads but I suppose I need some if that is the only way to do this.

CarlBoyd

[[email protected]]

On Jun 28, 7:10*pm, "Carl Boyd" wrote:
I have had a problem on a couple of my recent projects. *Both involved
1/2"-13 inside threads. *Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. *Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? *I have cut a few external threads, but am leary
to cut internals. *I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

Drills aren't necessarily going to bore straight, best to use an
internal boring bar after starting the hole with a smaller drill. Tap
shanks are hard, the chuck jaws aren't going to hold the shank and
spinning the tap in the jaws isn't going to improve them. I use a T-
handle tap wrench with an accurately centered center hole for doing
this sort of thing in the lathe, if the tap is a larger size, it will
have center holes and I use a dogbone. In either case, I use a dead
center in the tailstock to align the tap. I lock the headstock while
doing this and it's all manual, not under power. I go about 1/4 to
half a turn before backing out and breaking the chip off. Getting in
a hurry leads to busted taps and more work.

If you need to use these screw holes for location, don't do it! As
I've said before, threaded fasteners are to be used in tension and
only for fastening parts together. Design in a feature, ledge,
collar, whatever, to locate your two parts or drill, ream and insert
dowel pins to do the location. Then it doesn't matter so much how
much your tapped holes are off. If you just gotta have threaded holes
accurately located, then you've got to bore and single-point thread in
the lathe. The only way you get good at it is to do it! Chuck up
some scrap and practice! If you've got a threaded lathe spindle, make
an external copy of the nose for practice, then make an internal mate,
these come in handy. You can go down in size as you get better at
it. If you don't have a threading gauge, get one, they're cheap.
About the only way you can grind and set up tool bits.

The South Bend Lathe book shows a set of threading stops that used to
be available. I made a set of these and the time spent making and
learning to use them was well worth it, particularly for internal
threading. I also made a set of boaring bars and bits, for the
smaller sizes I ground 1/4" Tantung bits, these last a long time
without sharpening and puts off the time when you've got to stop and
sharpen in the middle of a hole. Learning to pick up threads again in
the middle of a job is another skill, internals are more fun than
externals.

Stan

[Jim Wilkins]

On Jun 28, 10:10*pm, "Carl Boyd" wrote:
I have had a problem on a couple of my recent projects. *Both involved
1/2"-13 inside threads. *Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. *Two out of three times the thread ended up significantly off
axis.

I had assumed that I would start the thread on axis with the tailstock chuck
and it would stay on axis when I finished by hand.

What is a better procedure? *I have cut a few external threads, but am leary
to cut internals. *I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd

Others have given good advice, so I'll only add a few hints.

The tailstock on my lathe droops from student abuse. When it's
properly centered front-rear it turns a parallel cylinder and the
droop isn't evident. Check yours. I think the tendency was to
manufacture them on the low side of tolerance so the buyer could shim
it higher if he noticed.

I use a very short Collis center-drill holder to start a hole because
a chuck is off too far. A chucked drill bit jumps upwards noticeably
when it starts into the hole, although they usually drill true within
0.005" or better. They sell tap holders which are like square Morse
collets.

The female center hole in a chuck arbor will guide a pointed-end tap
fairly well because it doesn't extend out as far as a chuck. A female
cup center works better if you can find one. Sometimes closing the
chuck jaws enough to bear on the tap's conical end guides it
straighter than chucking it. I grind shallow flats in the shank end of
the threads for a wrench.

Make the part long and bore a straight guide section that the tap
barely bites into, or make a slip-on guide. I make my custom tooling
for standard drill rod sizes rather than specific for a job. 0.500"
and 1.000" have worked well so far.

Tap from the wrong side with a *sharp* spiral-point tap and good
tapping fluid. The exit should be straighter and tighter than the
entrance. If the tap starts way off you can bore the hole out a
little.

A long nut / extension / pulley tap shows any angular error in the
chuck and then flexes back parallel to minimize it, assuming the hole
is straight. Spiral point nut taps are the most generally useful if
you have to buy those expensive things new.

Use a hand-held angle grinder to rough out an internal threading bit
quickly. They cut fast and cool and are a lot safer than trying this
on a chop saw. Make the shank recess at least as long as the width of
your bench grinding wheel. If you cut even a rough partial thread with
it the tap will cut much easier. Internal threading goes easier if you
swing the compound back behind the ways so it feeds directly into the
cut. If at all possible cut a good-sized groove to end the thread in.
A good, easy practice part is threaded bushings to hold screws
straight and centered on the threads. Mine are the length of a 5C
collet's gripping surface and recessed so a 1/2" long screw will
protrude a little.

What you did works fine on my mill but not on my lathe.

Jim Wilkins

[Carl Boyd]

Thanks for all the good advice. I went out to the shop and looked at what I
had. The tap I was using was a plug tap, It does not have a center hole,
but I found I have a couple of old Tap wrenches in the back of the box that
have center holes in the back.

I have been on the lookout for quality taps and have picked up a few UB 3
tap sets, but not in this size yet.

Thanks again.

CarlBoyd

[Jim Wilkins]

On Jun 29, 11:48*am, "Carl Boyd" wrote:
...
but I found I have a couple of old Tap wrenches in the back of the box that
have center holes in the back.
CarlBoyd

I have quite a few of those and except for one Starrett they hold taps
crooked.

[John]

Carl Boyd wrote:

Thanks for all the good advice. I went out to the shop and looked at what I
had. The tap I was using was a plug tap, It does not have a center hole,
but I found I have a couple of old Tap wrenches in the back of the box that
have center holes in the back.

I have been on the lookout for quality taps and have picked up a few UB 3
tap sets, but not in this size yet.

Thanks again.

CarlBoyd



This type of holder will make taping with the tailstock much easier.


http://business.search.ebay.com/mors...0QQsacatZ12576


it will hold the tap in position and will not let it slip. You will
need a sharp tap and cutting oil to do a good job. Dull taps you give to
your enemies. (or learn to sharpen them)


John

[DoN. Nichols]

On 2008-06-29, Carl Boyd wrote:
Mark

Thanks for the advice.

My taps do not have a female center in the back.

A 1/2-13 without a center hole? That sounds like cheap taps.
Smaller taps 10-32 and smaller) may have a male center instead of a
female center. I don't think that I have ever seen a 1/2-13 with that,
however.

The spring-loaded center gadget which was mentioned before has a
replaceable follower -- one for the female center taps, and one for the
male center taps.

I did not countersink, the one that came out straight had a fairly long 1/2
inch counter bore that I am sure helped to keep the tap straight. I'll
remember the counter sink idea.

Yes -- the counterbore will certainly help to guide the tap in
straight. Starting with a taper (starting) tap will help too.

Tapping in the lathe tailstock chuck could be helped by using
gun taps (spiral point taps), which chase the chips ahead of the tap
instead of collecting them in the flutes where they can jam if not
cleared by frequent backing. But you can't go all the way to the bottom
of a blind hole with those, because the buildup of chips gets too big.
Use the gun tap to start the threads, and switch to a plug tap to
continue down to the bottom -- or finish up with a bottoming tap if you
need maximum thread length.

I forget whether you mentioned the workpiece material. A thread
forming (rolling) tap instead of a thread cutting tap can deal with
such holes without generating chips if your workpiece is not too hard --
but it needs a different staring hold diameter. The standard will jam
it and break it off in the holes.

Note that there are releasing tap holders made (designed to
mount in a turret on the lathe, but you can adapt them to the tailstock
or the carriage). These feed in with the tap until you reach a stop
(part of the turret -- if you are doing carriage work, you'll have to
set up a bed stop). Once you reach the stop, the tap self-feeds for
about another turn after which it disengages a dog clutch in the tapping
head, so the tap is free to spin. Then you reverse the spindle and pull
back on the tap holder to back the tap out of the hole. This (of
course) needs a gun tap or a thread-forming tap, since it offers no
provisions for backing out every half turn or so.

Yes I am backing the, but it seems to cut fine for about 2 turns and then
get tight. Thats when I back it off.

Hmm -- you should back more frequently than that -- before it
gets tight -- unless you have a gun tap or a thread forming tap.

I have ground my own external threading tools, the nuts fit the threads
fine, I have no idea if they meet spec or not. Grinding for an inside
thread seems harder, maybe, I'll give it a try.

A 1-2" internal thread is a rather tricky one to start with (too
small). Learn using something larger first, like a 1" ID. Among other
things, the direction to crank the cross-feed to clear for backing out
is different from external threading, and it is easy to make a mistake
with old habits. And a larger hole lets you see things like how close
to the bottom of the hole you are getting. For small holes, run your
tool in without cutting (spindle not turning) until it hits the bottom
of the hole. Then back it out a little and put some bright-colored tape
around the shank lined up with the end of the workpiece to tell you when
to disengage the half nuts. Then, start the spindle, crank the tool out
(into the workpiece walls) to cut a groove to full thread diameter, and
move it slowly by hand towards the bottom of the hole to produce a
runout groove at the bottom of the threads, so you don't have to be
totally precise as to when you disengage the half-nuts.

And one particularly important factor in the single-point
internal threading on your lathe is what is the minimum spindle speed.
Especially when first cutting internal threads, you want it slow enough
so that your reflexes are a lot faster than what you need. My 12x24"
Clausing will go all the way down to 35 RPM at the slowest belt speed
plus back gear. This is probably where you want to be for your first
internal threads. Later you can speed up to whatever you are
comfortable with.

Some of the small import lathes have a minimum speed which is
frightening when considering internal tapping. :-)

[ ... ]

If you supply yourself, or make, internal threading tools, you'll
enjoy the results. If you doubt your grinding, you can start by
screwcutting with a pretty-good tool, and finish with the tap. That'll
provide better alignment, too. Have fun, I sorta envy where you are on
the learning curve. I had fun learning all this stuff.

Note that the relief angles will be reversed for internal
threading.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

[Doug White]

Keywords:
In article , Jim Wilkins wrote:
On Jun 29, 11:48=A0am, "Carl Boyd" wrote:
=2E..
but I found I have a couple of old Tap wrenches in the back of the box tha=
t
have center holes in the back.
CarlBoyd

I have quite a few of those and except for one Starrett they hold taps
crooked.

I bought three brand new Starrett tap wrenhces about 10 years ago. NONE
of them would hold a tap straight. They appeared to have switched
from machined to investment cast jaws. I sent them all back & they
replaced the jaws with ones that were a bit better, but not exactly
perfect. I was more than a bit disappointed, especially given the
prices.

Doug White

[Carl Boyd]

A 1/2-13 without a center hole? That sounds like cheap taps.
Smaller taps 10-32 and smaller) may have a male center instead of a
female center. I don't think that I have ever seen a 1/2-13 with that,
however.

I am using a Craftsman Tap, I've gotten a lot from the set, although I am
sure
they are not industrial quality, I don't consider them cheap (i.e. Harbor
Freight is cheap).
A good set bought new would cost me more than my lathe. Budget has been
tight but
may loosen up some next year. I picked up 3 Union Butterfield, 3 tap sets
last month at
reasonable prices. I'll continue to keep my eyes open.


I forget whether you mentioned the workpiece material. A thread
forming (rolling) tap instead of a thread cutting tap can deal with
such holes without generating chips if your workpiece is not too hard --
but it needs a different staring hold diameter. The standard will jam
it and break it off in the holes.

The workpiece material has varied from CRS to an old lawn mower crankshaft.


Yes I am backing the, but it seems to cut fine for about 2 turns and then
get tight. Thats when I back it off.

Hmm -- you should back more frequently than that -- before it
gets tight -- unless you have a gun tap or a thread forming tap.

2 turns is pretty much where it starts to get tight. When just starting I
do
tend to back off quicker, but when the tap is well started I turn until I
feel the resistance increase. A 4 flute 1/2-13 tap has a fair amount of
room for chips before they start to bind up. With some taps and some
materials I back up every 1/4 turn. Why is 1/2 turn the magic
number?


Some of the small import lathes have a minimum speed which is
frightening when considering internal tapping. :-)

My 16" LeBlond goes pretty slow. I cant remember of the top of my
head but I believe it is under 20 RPM


Note that the relief angles will be reversed for internal
threading.

My external tools I ground with symetrical relief angles and pretty
much just eye balled them, but I have not done any very coarse theads.


Good Luck,
DoN.

Thanks, I need it.

CarlBoyd

[DoN. Nichols]

On 2008-07-01, Carl Boyd wrote:

A 1/2-13 without a center hole? That sounds like cheap taps.
Smaller taps 10-32 and smaller) may have a male center instead of a
female center. I don't think that I have ever seen a 1/2-13 with that,
however.

I am using a Craftsman Tap, I've gotten a lot from the set, although I am
sure
they are not industrial quality, I don't consider them cheap (i.e. Harbor
Freight is cheap).
A good set bought new would cost me more than my lathe.

Well, yes -- if bought new and all at once. I have a lot of
taps which I have bought a few at a time. I tend to prefer gun taps for
general use, even when hand tapping.

But I also got a set of TRW taps -- 0-80 through something like
1"-8 -- all three taps and a corresponding die. Metal boxed, with a
molded foam liner which accepted all of the taps and dies and kept them
in place. Large -- something like 3' wide by 2' deep IIRC. A ridged
rubber liner under the lid which you can use to set taps on and not
damage them. The whole thing went for a little over $100.00 -- but it
had no photo, and I was just taking the description as true at that
price. When I got it, it looked as though none of the taps or dies had
ever been used. :-)

You can also get good taps with matching drills in a special
index. I've picked up one of those for common metric sizes, and the
taps are TiN coated gun taps so I am quite pleased with them.

Budget has been
tight but
may loosen up some next year. I picked up 3 Union Butterfield, 3 tap sets
last month at
reasonable prices. I'll continue to keep my eyes open.

Good luck there. And watch eBay too -- though this was close to
ten years ago,a nd things have changed over the years.

I forget whether you mentioned the workpiece material. A thread
forming (rolling) tap instead of a thread cutting tap can deal with
such holes without generating chips if your workpiece is not too hard --
but it needs a different staring hold diameter. The standard will jam
it and break it off in the holes.

The workpiece material has varied from CRS to an old lawn mower crankshaft.

O.K. I would probably go for HRS for roll tapping, unless I
were to consult with the tap vendor to pick the right version for the
material. 360 brass and aluminums would be my material of choice for
roll taps without some research.


Yes I am backing the, but it seems to cut fine for about 2 turns and then
get tight. Thats when I back it off.

Hmm -- you should back more frequently than that -- before it
gets tight -- unless you have a gun tap or a thread forming tap.

2 turns is pretty much where it starts to get tight. When just starting I
do
tend to back off quicker, but when the tap is well started I turn until I
feel the resistance increase. A 4 flute 1/2-13 tap has a fair amount of
room for chips before they start to bind up. With some taps and some
materials I back up every 1/4 turn. Why is 1/2 turn the magic
number?

Because beyond that is where chips in some materials curl into a
complete circle and can sometimes pretty much lock the tap in place.
Backing off to cut the chips shorter increases your chances to keep the
taps from breaking off in the wokrpiece. But I don't back at all with
gun taps, since they are designed to put the chips out of the danger
zone.


Some of the small import lathes have a minimum speed which is
frightening when considering internal tapping. :-)

My 16" LeBlond goes pretty slow. I cant remember of the top of my
head but I believe it is under 20 RPM

Great! That would be a good choice to start with. Plenty of
time to train your reactions.


Note that the relief angles will be reversed for internal
threading.

My external tools I ground with symetrical relief angles and pretty
much just eye balled them, but I have not done any very coarse theads.

O.K. The last personally ground threading tools which I have
made were for cutting an ACME thread on a test stub, and then an
internal ACME thread in bronze on a replacement nut for a friend's log
splitter. There, I wanted the minimum clearance for strength, so I had
to calculate the helix angle and grind specific clearance angles on each
side -- and I did manage to make my first try for the internal thread
with the reverse of the needed angles -- fine for making a left-hand
thread, but not for what I needed to make. :-)

BTW For tapping the end of the shaft -- perhaps you should turn a
guide bushing to slip over the OD of the shaft and provide a
hardened hole to hold the tap centered while you're starting.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

[[email protected]]

On Mon, 30 Jun 2008 20:49:33 -0400, "Carl Boyd"
wrote:


A 1/2-13 without a center hole? That sounds like cheap taps.
Smaller taps 10-32 and smaller) may have a male center instead of a
female center. I don't think that I have ever seen a 1/2-13 with that,
however.

I am using a Craftsman Tap, I've gotten a lot from the set, although I am
sure
they are not industrial quality, I don't consider them cheap (i.e. Harbor
Freight is cheap).
A good set bought new would cost me more than my lathe. Budget has been
tight but
may loosen up some next year. I picked up 3 Union Butterfield, 3 tap sets
last month at
reasonable prices. I'll continue to keep my eyes open.


I forget whether you mentioned the workpiece material. A thread
forming (rolling) tap instead of a thread cutting tap can deal with
such holes without generating chips if your workpiece is not too hard --
but it needs a different staring hold diameter. The standard will jam
it and break it off in the holes.

The workpiece material has varied from CRS to an old lawn mower crankshaft.


Yes I am backing the, but it seems to cut fine for about 2 turns and then
get tight. Thats when I back it off.

Hmm -- you should back more frequently than that -- before it
gets tight -- unless you have a gun tap or a thread forming tap.

2 turns is pretty much where it starts to get tight. When just starting I
do
tend to back off quicker, but when the tap is well started I turn until I
feel the resistance increase. A 4 flute 1/2-13 tap has a fair amount of
room for chips before they start to bind up. With some taps and some
materials I back up every 1/4 turn. Why is 1/2 turn the magic
number?


Some of the small import lathes have a minimum speed which is
frightening when considering internal tapping. :-)

My 16" LeBlond goes pretty slow. I cant remember of the top of my
head but I believe it is under 20 RPM


Note that the relief angles will be reversed for internal
threading.

My external tools I ground with symetrical relief angles and pretty
much just eye balled them, but I have not done any very coarse theads.


Good Luck,
DoN.

Thanks, I need it.

CarlBoyd



Greetings Carl,
I (almost) never have trouble with tapping in the lathe. When tapping
the tap is gripped hard enough in the drill chuck so that it doesn't
slip until the tap starts to bottom. Of course, large taps or really
tough materials may make the tap slip in the chuck. Tap sets often
have taps made for hand tapping. These taps will have 4 flutes instead
of two or three. And the chips do pack into the flutes. Stringy
materials like mild steel can pack up real tight because the chip
tends to be continuous. This why the tap is backed off every so often.
I generally use spiral point taps or roll taps. The spiral point taps
push the chips ahead of the tap and so don't tend to fill the flutes.
If you examine the end of a spiral point tap you can see how it will
push the chips forward. Also, the tap thread is actually ground with a
decreasing pitch diameter at the end of the tap. This makes them cut
easier. Hand taps just have the first threads ground away at an angle.
Spiral point taps do pack chips into the bottom of the hole though. So
blind holes can be a problem. I try to use roll taps whenever I can
because they don't make chips and they make better threads. Roll taps
require a larger hole because the metal is only displaced during
tapping. The holes also need to be closer to the exact size because of
the metal being displaced. A slightly oversize hole will result in the
minor diameter being too large and a slightly smaller hole will
require much more torque and may break the tap. Roll (AKA form) taps
work best in ductile materials. This means that wrought aluminum,
copper and most of its alloys, mild steel, most stainless steels and
zinc are good candidates for roll tapping. Some cast aluminums and
some cast irons do not tap well with roll taps. The metal fractures
from the displacement and this weakens the threads. The weak thread
may not be obvious until it fails under pressure.
Cheers,
Eric

[ignator]

On Jun 30, 7:49 pm, "Carl Boyd" wrote:
snip

I am using a Craftsman Tap, I've gotten a lot from the set, although I am
sure
they are not industrial quality, I don't consider them cheap (i.e. Harbor
Freight is cheap).
A good set bought new would cost me more than my lathe. Budget has been
tight but
may loosen up some next year. I picked up 3 Union Butterfield, 3 tap sets
last month at
reasonable prices. I'll continue to keep my eyes open.

snip
I have learned that Craftsman tap and die sets are what's call
rethreading sets. The are high carbon steel, not HSS, and it makes a
big difference as they last much longer and cut soft-semihard steel,
unlike the high carbons which dull very quickly, and is most likely
the source of your problem.
I have used the same technique of chucking the tap in the tail stock.
It generally works great.
If the dies are all hex in the set, this is a indication that they are
high carbon. HSS will be clearly marked on them if they are.

SteveK