Thread rolling is normally used in the making of external threads, as
on a shaft, for example. It is a lower quality thread than a cut
thread. Inexpensive threaded rod that can be purchased in a hardware
store is the best example I can think of to demonstrate rolled thread
quality. It is generally used when the cost of the item needs to be as
competitive as possible.
You can cut the threads that you need very easily, by drilling a
17/32" hole, 5/8" deep for a 5/8-11 thread, which is standard, or by
drilling a 9/16" hole for a 5/8-18 thread which is a fine thread, then
using a starting tap, followed by a plug tap, for the last few threads
at the bottom of the blind hole. If you require a lot of holes to tap,
you will need "coated taps", and a good quality lubricant, as Titanium,
is about as tough a metal to machine as you will find.
I hope this helps you.
G. De Angelis
I would take slight issue with you on being an inferior quality.
Rolled threads are used on high tensile bolts due to the grain flow
it produces, therefore yielding far greater strength. Aero engine
bolts are rolled and ground. The inferior quality may certainly be
attributed to the final form, therefore the follow on grind
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Boy, someone gave you some misinformation.
Thread Rolling is Superior in many respects:
Depending upon material but here are some highlights and advantages
for thread rolling.
Thread rolling is widely accepted as the fastest and preferred method
of economically producing uniform smooth, precise threads of superior
In penetrating the surface of the blank, the rolls displace material
to form the thread roots, and force the displaced material radically
outward to form the thread crests.
Cold working of metal during thread rolling improves thread form
physical characteristics and mechanical properties. When thread is
rolled, the structure is deformed and the surface is hardened.
Increased surface hardness results in thread form properties that are
superior to those of the original material.
Grain structure is maintained with rolled threads, in continuous
unbroken lines following contours, increasing tensile and shear
The smooth flanks of rolled threads provide better surface contact
with mating threads. The burnished roots and flanks are free from
chatter, tearing or cutter marks that can serve as a focal point or
stress and starting point for fatigue failures.
Rolled threads maintain consistently closer tolerances and uniformity
than cut thread. Thread rolling is unique in its ability to maintain
accuracy of the original set up during long runs of high-speed
production. Dies do not change appreciably during the life of the
rolls. They do not wear like other types of threading tools.
What you see at a hardware store is commercial grade probably a 1A
tolerance or even a looser application. As well as the rods in the
hardware store are handled none too carefully.
FYI, a lot of aerospace fittings and fasteners require rolled threads
because of increased thread sheer strength and quality.
It's a one pass operation.
I don't have the pitch nor my technical data handy, but I'm guessing
without a geared head spindle you'll need an honest 15-20 horsepower
depending on the pitch. Or about 30-40 haaspower.
I wouldn't want to bet I could do it.
Titanium (alloys do differ) generally work hardens and that can make
for some humongous forces and at some point you can exceed the ultimate
strength and just fracture the metal.
D Murphy wrote:
I found a picture of a roll forming tap. It was not what I thought, I
expected "rollers". It looks to me like you just drive a screw into the
hole and create threads that way. Now I understand why it takes so much
torque and why you need "venting".
Cut threads are not an option. It is a very high stress, very high
fatigue forged aircraft part: a helicopter tail rotor.
Thanks for all the excellent information, I may be asking for quotes.
and many more.
Because of the high force/friction involved in internal thread
forming in titanium, your choice of tap lubricant may be
critical. Some of the best friction reducers such as
MolyDisulfide may also contaminate the metal.
Has anyone tried a lube containing teflon?
Good luck and let the group know how you make out.
Unka' George [George McDuffee]
On Theory: Delight at having understood
a very abstract and obscure system
leads most people to believe
in the truth of what it demonstrates.
G. C. Lichtenberg (1742-99),
German physicist, philosopher.
Aphorisms "Notebook J," aph. 77
(written 1765-99; tr. by R. J. Hollingdale, 1990).
On Fri, 12 Jan 2007 17:37:44 -0600, F. George McDuffee
Good point. Probably have a bit of trouble if you try to use toilet
water :-). I use CutMax 570 cutting OIL, which has a rather high
sulfur and chlorine content. The largest roll tap I've ever had the
chance to run in TI, was a 3/8-16. It was a while back, but IIRC, I
ran the entire 350 pc. order with one tap.
Rolling ID threads is not a problem. Do it all the time. You simply
need a roll tap, or also referred to as a Thread Forming, Cold
Forming, or Roll Forming Tap. You can start by using it just like you
would a cut tap, although you will most likely find that you can run
it at a faster rpm.
You're going to need some HP behind that tap. Don't know what kind of
machine you're using, but I run 1/2-13 roll threads on my 5C Gang
Lathe rather often, and it works quite well. It groaned a bit the last
time I used a 5/8" CUT tap, and, although I've never tried it, I'm
quite certain that it wouldn't pull the 5/8" roll tap. But then, it's
pretty wimpy. Hopefully you have a machine with plenty of power.
Find some taps with oil grooves. You're going to have enough fun
without having to deal with the hydraulic resistance of the oil
compressing in the bottom of the hole. The Greenfield taps have 4 oil
grooves, and really do work well. Some of the local (Escondido/San
Diego) tooling suppliers stock them, but you can also get them from
McMaster Carr or MSC. OSG taps are another good choice, but I don't
know if their larger diameters have oil grooves or not. The 1/4-20's I
have here do not.
Does the print REQUIER rolled thread? If not your going to need some
horsepower, a very good setup and very good lubricant.
When I use to roll external threads in titanium years ago we needed to
use an induction heater and roll them hot because the machines HP
could not do it cold depending upon the thread size and length.
In my opinion it is almost always easier, better and faster to cut
titanium than roll it.
If you have a choice, thread mill. Otherwise cut tap. Only use a roll form
tap if the drawing requires it. Assuming you need to roll form the threads,
you need to consult a tap drill chart for roll form threads. The tap drill
size will be different than a cut tap. It should be right around the pitch
diameter. For best results use as low of a thread engagement percentage as
is allowed. IOW, use the largest tap drill size that is permissable.
Also if the drawing calls for a tight tight tolerence on the thread, then
you should ream the hole before tapping. Probably not a bad idea in any
Run the roll form tap at around 20 SFM or so for 6Al-4V. Use a cutting oil
if possible. If you have to use water soluble, make sure it has an EP
additive in it. If you are doing this on a VMC consider putting a cup of
oil or tapping fluid on the table somewhere out of the way, then dip the
tap into oil before tapping. Or seeing as they are blind holes, you can
program an optional stop before tapping and fill the holes with oil.
I hope you have a machine that has some serious low end torque, especially
if it's a coarse pitch thread. Otherwise don't even bother, you'll stall
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