I am not an expert but I think normal machine screws that you can buy the
thread at the end tapers in diameter, so it sort of follows a chamfer. My
thread library supports that and a simple chamfered end, which is what you
get when you cut a threaded rod and then chamfer the end.

Higbee seems to be cutting off the crests of the leading treads, making
them flat topped. It seems to be a second pass on a CNC lathe that uses a
flat ended grooving tool to remove the sharp crests left by the threading
tool when it meets the chamfer.

On Sun, 19 Feb 2023 at 22:11, Adrian Mariano avm4@cornell.edu wrote:

I think a normal thread is created by tapping the thread onto a rod or into
a hole.  Possibly a chamfer is applied afterwards.  I think this is done
for normal machine screws because it's cheap and fast, not because it is
good.  In the context of 3d printed parts, there is no reason not to choose
the best option, because we aren't paying a machinist.  Furthermore, the
knife-thin edge that arises when you carry threading out to the end of a
rod is probably not the best shape for 3d printing anyway, so why do that?
Maybe the chamfer helps reduce it, but it's not the best solution.  And it
sounds like the chamfer isn't ideal for preventing cross threading.  My
erratic correspondent seemed to think that threads made the "standard" way
were worthless in 3d printed plastic if the parts were going to be
disassembled and reassembled multiple times, though I admit that I don't
understand why.  He seemed to think---possibly based on experience with
failed parts?--- that such threads just wouldn't last, and that the higbee
end is essential.

On Sun, Feb 19, 2023 at 5:39 PM nop head nop.head@gmail.com wrote:

I mainly model threads I can buy or make myself, rather than 3D print. I
don't think machine screws are tapped rods. I think they are stamped out.
They don't have higbee ends. They have tapered ends and I find that also
works fine for large 3D printed threads like screw tops for jars.

[image: image.png]

I don't remember seeing anything with a higbee thread but instead of
tapering inwards it gets truncated inwards instead. Perhaps it cross
threads less because the lack of sharp crest stops it tappings its own
thread but it isn't how normal screws are made.

On Sun, 19 Feb 2023 at 23:07, Adrian Mariano avm4@cornell.edu wrote:

I looked for info on how screws are made and it sounds like the normal way
is indeed to press them between a pair of flat dies.  This process could
not make a higbee end.

https://www.wuerth-industrie.com/web/media/en/pictures/wuerthindustrie/technikportal/dinokapitel/Kapitel_04_DINO_techn_Teil.pdf
https://www.accu.co.uk/p/105-how-is-a-machine-screw-made

Second link has a video of a factory.  I guess the chamfer on the end is
included in the die?

But still the question of optimal thread ends remains.  Look at a jar or
plastic bottle and you will see smooth tapering thread ends, not ends that
run off the end like the picture above.  For example, SP400 threads:

[image: image.png]

So this seems like a better model for how 3d printed threads should look
than die pressed threads in metal.  We are not constrained---we can make
the thread end in 3d printed models.  And it sounds like that's better
design, so that's what should be done.

On Mon, Feb 20, 2023 at 2:13 AM nop head nop.head@gmail.com wrote:

That bottle thread is just tapered off much faster and then doesn't go
right to the end of the tube. I think my library does it over half a turn.
Here is a drill case I printed and it never cross threads.

[image: image.png]
It is different with fine thread in metal though as it is much easier to
cross thread if say you put a steel screw into brass.

On Mon, 20 Feb 2023 at 11:38, Adrian Mariano avm4@cornell.edu wrote:

On 2/20/23 06:39, Adrian Mariano wrote:

The only comment I can make is not expert, I'm not a pro machinist, just
a retired broadcast engineer. But I have used it many times, I have 4
cnc'ed machines I rebuilt from manual stuff and converted to cnc.

The ability to control the entry and withdraw profiles that LinuxCNC's
G76 canned threading can do, normally used where threading the middle of
a rod to make a bolt or nut, where the single tooth cutter is ramped
from its baseline to the depth of the thread being cut on this pass,
internal thread or external being auto selected by the base line being
inside or or outside of the thread G76 has a length for that, normally
used to give a fraction of a turn profile for the ends of the thread.

Normally used for the entry, aka the right hand end of the thread, the
other end, visualize that as at the underside of a bolts head, is either
subject to a precut groove to give the tool room to withdraw at an
achievable speed. Or you can just let the withdraw ramp out to a bolt
shank diameter withdraw as long as the tool doesn't actually touch the
underside of the head.

But this old Iowa farm kid thinks outside of the box now and then, and
needing a compression method of attaching the drive from the motor,
where an un-machined end of a ball screw is inserted to a slotted sleeve
that is intended to be compressed to grip the screw as effectively as a
weld w/o the distortions you get from the welding heat. The slots, cut
to the depth of the socket drilled, are done with EDM because its very
precise and leaves no burrs to interfere with the fit. So I found I
could make a tapered thread, length of taper cut being one turn less
than the length of the thread, doing the thread ahead of the EDM
slotting, and I made nuts out of stock 3/8" nuts to fit it, both at 50
tpi. On a 7x12 cnc'ed lathe.

It got me the grip I needed, precisely on center with no runout And
never a hint of wanting to cross-thread because the working space was
way to small to get any fingers in to guide it. That was a decade + back
up the log and has not been touched since. So I'll make the claim that a
long enough straight taper cannot be cross threaded. Its self
correcting. I'd assume that characteristic would survive down to a taper
done as a single turn. 1/4 turn ramps I'm less certain of.

This is control you don't get using taps and dies. And its a single data
point from multiple such uses experience. YMMV.

Take care & stay well, all.

Cheers, Gene Heskett.

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/

On Mon, Feb 20, 2023 at 06:37:37AM -0500, Adrian Mariano wrote:

I checked out your link, because I didn't think the shape of a screw
could be pressed between two dies.

Turns out the ROLL the pre-screw between the two dies. In hindsight
The hint was there with the /flat/ dies, but for sure they cannot be
FLAT because that'd make them "cylindrical" instead of a screw.

(If I'm honest... I'd make the dies round (on the outside of a big
wheel (*)) so that you can rotate them. rotate them in opposite
directions so that the screws remain stationary.  Then turn one
slightly faster so that after enough rotations it drops down between
the two big dies after enough of an impression has been made. Feed a
new pre-screw in due time. I'd think one machine can then thread 36000
screws per hour easily.)

Roger. 

(*) You can calculate the size of the required wheel by knowing
howmany rotations of the screw you want between the dies (i.e. length
of the trajectory from original cylinder to "finished screw" )

--
** R.E.Wolff@BitWizard.nl ** https://www.BitWizard.nl/ ** +31-15-2049110 **
**    Delftechpark 11 2628 XJ  Delft, The Netherlands.  KVK: 27239233    **
f equals m times a. When your f is steady, and your m is going down
your a is going up.  -- Chris Hadfield about flying up the space shuttle.

Thinking some more about it, I think higbee only makes sense when you have
a thread already made and you want to clean up the end. The optimal end
shape is simply tapered when you can mould it or 3D print it.

On Mon, 20 Feb 2023 at 14:45, Rogier Wolff R.E.Wolff@bitwizard.nl wrote:

On 19/02/2023 22:09, Adrian Mariano wrote:

It depends somewhat on the the way the bolt or stud is manufactured, and
its final application. For example, the screws that hold a switch plate
to the wall box, will have a short length at core diameter, so that it
can 'find' the tapped hole in said box, and allow the  bolt to be
straight, thus avoiding cross threading.

If threading a bar in a lathe, it is usual to bevel the end, and remove
sharp edges with a file, say, or if a quantity of them, by tumbling.

For common, mass produced  thread-rolled bolts, the rolling process does
not normally leave sharp edges at the bolt end (and the end is recessed,
unless shaped for a specific application, e.g, shaft locking socket screws.)

Bottles and caps, also have to be easily removed from the mould. there
is usually a 'skirt' on the cap, and a short plain end of the top, to
allow it to be more easily aligned.

Large diameter, fine pitches are easy to cross thread, if you do not
know the technique, (for example the threads those holding a wheel hub
to the vehicle axle (and some hubs on some vehicles, often have lh
threads, to add to the novices fun...)

I've never heard of Bigbee, I think it is merely the manufacturer of
bolts/machinery, like GKN. Not mentioned  in my 1990 Machinery handbook,
so get the guy to send you a decent drawing.

Whatever single solution you use, it will be wrong for many applications.

On 2/20/2023 8:48 AM, Raymond West wrote:

I have occasionally wondered why this isn't more common.

My Scout troop has flagpoles with two segments that screw together, and
they're sometimes a pain in the neck to get together because you have to
have them perfectly aligned - and when the people doing it are 11 or 12
years old, that's hard.

They're sort of like this, though this one looks like the threaded
section is really short.  I don't understand why they don't have a half
inch or so of straight plain core to get everything aligned before the
threads start to engage.

Gene, I wasn't quite able to follow your explanation.  Are you saying that
you tapered one turn of thread at the end?  And what does that mean?
Tapered how?

On Mon, Feb 20, 2023 at 9:32 AM gene heskett gheskett@shentel.net wrote:

So "simply tapered" is not well-defined.  Tapered how, and over what
length?  In both directions or just one?  And why is that clearly
optimal.

On Mon, Feb 20, 2023 at 9:55 AM nop head nop.head@gmail.com wrote:

Tapered by making the thread diameter decrease until it is below the minor
diameter and disappears. I do it linearly over half a turn but your bottle
example was much less.

Higbee removes the crests instead because the thread is already formed at
the nominal diameter. It can either ramp down gradually or be completely
removed with a rotary milling tool leaving a short ramp due to the tool
radius. See https://www.youtube.com/watch?v=MUojDLAaBiE

On Mon, 20 Feb 2023 at 21:49, Adrian Mariano avm4@cornell.edu wrote:

Raymond, your focus is on classic fabrication approaches.  But I don't care
about classic fabrication approaches particularly.  The question is what is
actually best.  When you really care, what do you do?  First of all, for
clarity here are some screw forms.  The basic threaded rod has nasty sharp
edges:

[image: image.png]
So we can make things better by adding a bevel, which softens the edge,
reducing, but not eliminating that sharp edge.  This is an improvement, but
clearly not optimal.

[image: image.png]
The Higbee patent is here:  https://patents.google.com/patent/US447775A
[image: image.png]
And there's a direct implementation.  Now the question of what, exactly,
qualifies as a Higbee end is not so clear.  It seems like one critical part
of the patent is that the full thread form is present, so it doesn't reach
the end of the shaft.  But the exact end?  Not sure that this matters.  So
is a long taper still a higbee?  I don't know.  It appears that the term
"Higbee" has fallen out of favor and if you look in your machinist handbook
it will be called "blunt start thread".

Blunt Start Thread: “Blunt start” designates the removal of the
incomplete thread at the starting end of the thread. This is a feature of
threaded parts that are repeatedly assembled by hand, such as hose
couplings and thread plug gages, to prevent cutting of hands and crossing
of threads. It was formerly known as a Higbee cut.

https://www.thomasnet.com/articles/machinery-tools-supplies/screw-thread-systems-types-terminology-and-dimensions/

The higbee cut was performed by filing off the incomplete thread at the end
that was left by the thread forming process, whatever it was.  Clearly
nobody is going to make the thread taper in width if they are filing the
thread down, so tapering in width isn't even a possibility here.  The
patent says it's supposed to be "full width".  In fact, it seems like full
width is maybe important because isn't cross threading enabled by thin,
fractional threads?  That suggests that maybe tapering in width is
undesirable.

Here then is the SP400 thread form as we have it in BOSL2.

[image: image.png]
This is specifically intended to comply with the SP400 standard, which
specifies a runout taper of a vaguely identified length.  This is a
standard for plastic bottle threads.
https://www.isbt.com/threadspecs-downloads.asp

I inspected some screws I have on hand.  The regular screws look like my
second picture: threads with a small bevel at the end.  My wall plate and
other electrical screws do not have the pattern described by Raymond, which
would in essence be a higbee or blunt start end.  Instead they have a much
longer bevel, something like this:

[image: image.png]
I think this is a cheap way of creating the alignment system Raymond
described.  I suspect that actually doing what Raymond said is too
expensive, because it involves post-processing each screw.  I also think
this is the reason that Jordan's flagpole doesn't work that way: it would
increase the cost of the screws by 10x or more.

So Raymond said, "whatever you do it'll be wrong some of the time".  I
think I disagree.  The only way that's true is when you're trying to model
to match some specific specification, like you WANT to show a bad screw the
way screws are actually made.  I think that in fact there should be an
optimal screw form that will not be wrong, and that's what I should produce
by default.  The only way I can see this not being true is if somehow the
ideal screw form varies radically with material.

My correspondent seemed to think that the term higbee was "well known" and
that it made sense to use it as the parameters in the library.  I'm not
sure sure, though threadlib does also use the term higbee for its tapering
thread ends.  Searching for information on higbee doesn't turn up tons of
material.

On Mon, Feb 20, 2023 at 11:50 AM Raymond West raywest@raywest.com wrote:

So lineiar decrease in diameter of the thread?  Something like this?  I
have two views for clarity:

[image: image.png]

[image: image.png]
Why would you want to extend the taper for a full half-turn.  My
correspondent was a little self-inconsistent, but suggested a much
shorter length, and it seems like a shorter length is better.  In fact, I
wonder if really very short is best.  Doesn't the section where the
diameter of the thread is reduced enable you to hop over it to
crossthread?  It seems like the abrupt end of the threads is the key to
success here:  you can't hop into the next thread because you have a full
thread in the way.  That's why I wonder if tapering is even a good idea as
compared to a more abrupt stop.  On the other hand, maybe the bottle makers
know what they're doing?  Their standard doesn't specify this, but in
their drawings it looks like about a quarter of a right angle, so ~20
degrees.  My correspondent seemed to think it should depend on the pitch
size of the threads, and nothing to do with angle, though.

On Mon, Feb 20, 2023 at 5:00 PM nop head nop.head@gmail.com wrote:

I do it over half a turn because that is what my machine screws look like
they do and that is what I am trying to realistically draw.

On Mon, 20 Feb 2023 at 22:28, Adrian Mariano avm4@cornell.edu wrote:

You have machine screws where the threads taper at the ends?  Like I
said...mine don't do that.  The end is just beveled.

On Mon, Feb 20, 2023 at 5:33 PM nop head nop.head@gmail.com wrote:

Yes. The only things I have bevelled are leadscrews and studding cut to
length that I bevel myself on a grinder. I have never seen a higbee end.

On Mon, 20 Feb 2023 at 22:37, Adrian Mariano avm4@cornell.edu wrote:

I've never seen a higbee end either.  But I've also never seen a machine
screw with a tapered thread like you are describing.  You have screws where
there is a full thread that gradually disappears by decreasing radius into
the shaft, and it's not because of a small bevel on the end?  Mine all have
the shaft beveled.

On Mon, Feb 20, 2023 at 6:02 PM nop head nop.head@gmail.com wrote:

[image: IMG_20230220_230829904.jpg]
That is what it looks like to me. Excuse the rubbish photo, I only have a
phone with me.

This is my attempt to model what I see.

[image: image.png]

On Mon, 20 Feb 2023 at 23:06, Adrian Mariano avm4@cornell.edu wrote:

The pic is a alas too rubbish for me to tell what' going on, but it looks
like it might be like my screws, which have a beveled end, not the feature
you're describing.  Note that it's a small bevel, like the size of one
thread, so it has the effect of cutting off part of the thread and could
produce the illusion of an intentional taper like you're describing.  I
inspected my screws under 10x magnification to figure out what was going
on.

On Mon, Feb 20, 2023 at 6:17 PM nop head nop.head@gmail.com wrote:

The last part of the thread tapers down to the minor diameter just where
the screw ends. You can see the crest is still intact but the diameter is
smaller in the photo.

Bevelling removes the crest of the last threads and looks different.

[image: image.png]

On Mon, 20 Feb 2023 at 23:23, Adrian Mariano avm4@cornell.edu wrote:

Here is a slightly better picture of a screw I also took here when there
was daylight,

[image: IMG_20210115_123701878.jpg]

On Mon, 20 Feb 2023 at 23:30, nop head nop.head@gmail.com wrote:

I still can't tell what's going on in your pic, but your model image of
beveling is wrong.  It's got a crazy huge bevel that touches several
threads.  The bevel only hits one thread most of the time.  Beveling looks
a lot like your second pic.  Here is beveling.  It looks sort of like a
decreasing crest height, but it is something different.  (Now that I think
about it, I'm really not sure what your thread model is.  You think you
have screws where the thread form shrinks in diameter but stays the same
width?  How would that be manufactured?)

[image: image.png]

On Mon, Feb 20, 2023 at 6:40 PM nop head nop.head@gmail.com wrote:

It stays the same pitch but the visible width reduces because the wider
part is below the surface.

Bevelling makes a sharp edge but my screws don't have a sharp edge. The
picture I posted was of leads screws, which do have bevelled ends and
multistarts.

On Tue, 21 Feb 2023 at 00:43, Adrian Mariano avm4@cornell.edu wrote:

To manufacture it I assume they press the screw between dies that have a
taper at the bottom.

On Tue, 21 Feb 2023 at 01:08, nop head nop.head@gmail.com wrote:

Wouldn't you need a die that had inverse threads that got wider and wider?

On Mon, Feb 20, 2023 at 8:11 PM nop head nop.head@gmail.com wrote:

Yes it would need to get wider so the gap gets smaller.

It would be difficult to make with a lathe or a circular die, hence why I
think higbee exists. You need a rotary tool in the toolpost to make the
abrupt version but the gradual ramp down can be created with a flat nosed
grooving tool on a CNC lathe.

I have a CNC lathe at my summer residence so I might have a go sometime.
The last thread I CNC cut I started with a chamfer before single point
threading. But with a chamfer you get a thin edge where the chamfer
intersects the threads crest.

On Tue, 21 Feb 2023 at 01:51, Adrian Mariano avm4@cornell.edu wrote:

Actually the die top surfaces would be parallel as the minor diameter
doesn't change. The depth of the groves would have to decrease at the end.

On Tue, 21 Feb 2023 at 08:29, nop head nop.head@gmail.com wrote: