higbee ends for threads
Most of the machine screws depicted in McMaster Carr CAD files seem to
be like a threaded rod, chopped off arbitrarily then chamfered at 45
degrees. In designing optimal 3D-printed plastic threads, mass-produced
screws may be too simplistic to use for inspiration. And a general CAD
library may need to support two or three designs to cover the majority
of modeling applications.
-Curt
On 2/20/2023 3:23 PM, Adrian Mariano 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:
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.png
On Mon, 20 Feb 2023 at 23:06, 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:
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:
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:
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:
So lineiar decrease in diameter of the
thread? Something like this? I have two
views for clarity:
image.png
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:
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:
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:
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 Mon, Feb 20, 2023 at
06:37:37AM -0500, Adrian
Mariano 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.
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/
<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.
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On 21/02/2023 10:51, Revar Desmera wrote:
I pulled out my digital microscope and a beefy M5 screw to see if I can get a clearer view:
I've just seen those images of a rolled thread. You can tell it is a
rolled thread, the crest of thread is rough, the valleys of thread is
smooth. The rolling has pushed the threads beyond the end, leaving the
end recessed (cupped) , and no sharp edges. At the end, there is no
resistance to the rolling pressures, so crests are not fully formed,
instead they get pushed over the end..
This link explains the faults in your 5mm example, (stock too small, and
possibly wrongly or no bevelled end )- typical of the stuff sold by 'big
box stores '(no manufacturer name). Not a problem for many applications.
https://www.iqsdirectory.com/articles/screw-machine-product/thread-rolling.html
I saw in Raymond's post the link to the rolled thread forming process,
which indicates that the end chamfer is an essential part of that process.
So that means all mass produced screws are going to have chamfered ends.
Someone wrote me directly saying "I've forgotten what the question was
about" so just to clarify my intention in starting this thread, the
situation is this.
BOSL2 has threading and that threading capability is very general. It can
bevel the ends or not, on both nuts and bolts. It can use any thread
profile, user supplied or from a list of standard profile, with any number
of starts. It can create thread ends that taper away or are cut
away---blunt start or higbee, perhaps. The length of that taper can be set
to anything, a short amount for a sharp cut, or a long taper, even the 180
deg favored by nophead. You can change where the threads end, to provide
flagpole section alignment for Jordan. When the threads taper they taper
in diameter (thread depth/height) and they taper in the axial direction
(thread width). I can specify functional forms for both directions of
taper. The problem is not "I can't do it". The problem is the reverse, "I
can do too much".
Making users choose values for all of these different options would
overwhelm most users. Now people do CAD for different reasons. One reason
is to model some existing object. In that case, there is such a thing as
the "right" result. It matches or it doesn't. I don't care about this
case. People who want to do that can handle a zillion parameters and can
figure out how to get their model to match up with the target.
The case I care about is people who want to model things to USE them. A
person who wants threads to USE doesn't have a model of what the threads
are supposed to look like. For that person, I want default behavior that
is as good as possible, and I want guidance about when and how to deviate
from the defaults. And I want an explanation that justifies the default
behavior. So the question I am trying to answer specifically with regards
to thread ends is how should the threads end ideally? Is the answer
different for metal or plastic? Is it different if you're mixing metal and
plastic in one model (e.g. you're making a threaded hole in plastic to
receive a metal bolt). If there is not a single best answer then what are
the handful of best answers for different cases. And what is the
explanation behind it all: why is answer X the best result for a specific
situation? That is, what is the intuition that explains how to choose the
parameters?
It seems like the function of thread ends treatment is to minimize the risk
of cross threading and perhaps to make the screw easier to start. So what
accomplishes that? It seems like threads that decrease in diameter are
bad, because they can more easily slip in too far and engage in
cross-thread. It seems also reasonably clear that a sharp cut is bad
because corners are always bad, so the end should be somehow rounded. I
would imagine that the exact way it's rounded probably doesn't matter. But
I think the length of the taper and whether the taper is in depth and/or
width might matter. If I want to draw a picture that shows cross threading
happening and another picture that shows how a particular thread end (or
other modification) prevents it, what would that picture look like?
Someone told me, "there will be many answers, which will be OK for those
that live in the practical engineering world, where it is all about
compromises". If it's all about compromises, what are the compromises?
What trade-offs exist in how the thread ends are designed?
Oh, and another question I was trying to get an answer to is what I should
call the library functionality that specifies the thread ends. My erratic
correspondent insisted that it should be called "higbee" and that everybody
who works with hardware knows what that means. I had question about that
because (1) it wasn't even clear that the tapered thread on the plastic
bottle met the definition of Higbee, since it wasn't maintaining the full
thread width and (2) it seems like actually nobody has heard of higbee.
(I hadn't before getting involved in this.)
On Wed, Feb 22, 2023 at 1:25 AM Curt McDowell maker@fishlet.com wrote:
Most of the machine screws depicted in McMaster Carr CAD files seem to be
like a threaded rod, chopped off arbitrarily then chamfered at 45 degrees.
In designing optimal 3D-printed plastic threads, mass-produced screws may
be too simplistic to use for inspiration. And a general CAD library may
need to support two or three designs to cover the majority of modeling
applications.
-Curt
On 2/20/2023 3:23 PM, Adrian Mariano 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:
[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:
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:
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:
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:
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:
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:
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:
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:
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 Mon, Feb 20, 2023 at 06:37:37AM -0500, Adrian Mariano 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.
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.
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On 2/22/2023 8:13 AM, Adrian Mariano wrote:
Making users choose values for all of these different options would
overwhelm most users. Now people do CAD for different reasons. One
reason is to model some existing object. In that case, there is such
a thing as the "right" result. It matches or it doesn't. I don't
care about this case. People who want to do that can handle a zillion
parameters and can figure out how to get their model to match up with
the target.
Functions for machine screws, bottle caps, jar caps, flag poles, etc.
would allow most users to avoid dealing with the zillion parameters.
BOSL2 is an amazing library, and perhaps as it becomes the de facto
go-to for OpenSCAD, few here would have to worry about re-inventing
threads for the millionth time.
The case I care about is people who want to model things to USE them.
A person who wants threads to USE doesn't have a model of what the
threads are supposed to look like. For that person, I want default
behavior that is as good as possible, and I want guidance about when
and how to deviate from the defaults. And I want an explanation that
justifies the default behavior.
As a user, the above functions are what I want, but I'd also want them
to conform to industry standards. For example, something that screws
onto the top of a 2-liter bottle, or a vessel that can be sealed with a
Mason jar lid or screwed onto a Mason jar, or a plastic hole that
tightly accepts an M6 bolt, or a flagpole mount, or something that
screws onto a painter's extension pole, or just a container and lid
where the threads are indeed compatible with off-the-shelf containers
and lids.
So the question I am trying to answer specifically with regards to
thread ends is how should the threads end ideally? Is the answer
different for metal or plastic? Is it different if you're mixing
metal and plastic in one model (e.g. you're making a threaded hole in
plastic to receive a metal bolt). If there is not a single best answer
then what are the handful of best answers for different cases. And
what is the explanation behind it all: why is answer X the best result
for a specific situation? That is, what is the intuition that
explains how to choose the parameters?
The ideal shapes for those will certainly vary for metal, ceramic, wood,
plastic, rubber, etc. But even within a category, industries will have
spent years or decades perfecting the shapes, according to constraints
on ease of use, effectiveness, durability, manufacturability, cost,
safety (Higbee), etc. Is it even possible to list the situations, let
alone fully explain them and try to out-design the master engineers?
It seems like the function of thread ends treatment is to minimize the
risk of cross threading and perhaps to make the screw easier to
start. So what accomplishes that? It seems like threads that
decrease in diameter are bad, because they can more easily slip in too
far and engage in cross-thread. It seems also reasonably clear that a
sharp cut is bad because corners are always bad, so the end should be
somehow rounded. I would imagine that the exact way it's rounded
probably doesn't matter. But I think the length of the taper and
whether the taper is in depth and/or width might matter. If I want to
draw a picture that shows cross threading happening and another
picture that shows how a particular thread end (or other modification)
prevents it, what would that picture look like?
If you're like me, you're probably imagining 3D printed interior and
exterior threads. If in fact industry standards aren't sufficient due to
tolerances or 3D constraints/advantages, there could be an opportunity
to come up with a new standard. But it wouldn't be just a mathematical
experiment, would it? A great solution (or several) would require
extensive testing on a lot of prototypes of different ideas in different
methods and materials.
Oh, and another question I was trying to get an answer to is what I
should call the library functionality that specifies the thread ends.
My erratic correspondent insisted that it should be called "higbee"
and that everybody who works with hardware knows what that means. I
had question about that because (1) it wasn't even clear that the
tapered thread on the plastic bottle met the definition of Higbee,
since it wasn't maintaining the full thread width and (2) it seems
like actually nobody has heard of higbee. (I hadn't before getting
involved in this.)
I had never heard of it either. The Wikipedia page is short with few
references. There are three equivalent names: "Higbee cut", "convoluted
thread" and "blunt start thread" (ASME B1.7-2006).
Regards,
Curt
On Wed, Feb 22, 2023 at 1:25 AM Curt McDowell maker@fishlet.com wrote:
Most of the machine screws depicted in McMaster Carr CAD files
seem to be like a threaded rod, chopped off arbitrarily then
chamfered at 45 degrees. In designing optimal 3D-printed plastic
threads, mass-produced screws may be too simplistic to use for
inspiration. And a general CAD library may need to support two or
three designs to cover the majority of modeling applications.
-Curt
On 2/20/2023 3:23 PM, Adrian Mariano 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:
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.png
On Mon, 20 Feb 2023 at 23:06, 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:
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:
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:
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:
So lineiar decrease in diameter of the
thread? Something like this? I have two
views for clarity:
image.png
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:
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:
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:
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 Mon, Feb 20, 2023 at
06:37:37AM -0500, Adrian
Mariano 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.
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/
<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.
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Thanks, those alternative names get a lot more hits than Higbee and "blunt"
is the best description as a blunt start is unlikely to cut a new thread,
so stops cross threading. Chamfering creates a sharp edge where it
intersects the thread crest. The Higbee cut removes that.
On Thu, 23 Feb 2023 at 05:58, Curt McDowell maker@fishlet.com wrote:
On 2/22/2023 8:13 AM, Adrian Mariano wrote:
Making users choose values for all of these different options would
overwhelm most users. Now people do CAD for different reasons. One reason
is to model some existing object. In that case, there is such a thing as
the "right" result. It matches or it doesn't. I don't care about this
case. People who want to do that can handle a zillion parameters and can
figure out how to get their model to match up with the target.
Functions for machine screws, bottle caps, jar caps, flag poles, etc.
would allow most users to avoid dealing with the zillion parameters. BOSL2
is an amazing library, and perhaps as it becomes the de facto go-to for
OpenSCAD, few here would have to worry about re-inventing threads for the
millionth time.
The case I care about is people who want to model things to USE them. A
person who wants threads to USE doesn't have a model of what the threads
are supposed to look like. For that person, I want default behavior that
is as good as possible, and I want guidance about when and how to deviate
from the defaults. And I want an explanation that justifies the default
behavior.
As a user, the above functions are what I want, but I'd also want them to
conform to industry standards. For example, something that screws onto the
top of a 2-liter bottle, or a vessel that can be sealed with a Mason jar
lid or screwed onto a Mason jar, or a plastic hole that tightly accepts an
M6 bolt, or a flagpole mount, or something that screws onto a painter's
extension pole, or just a container and lid where the threads are indeed
compatible with off-the-shelf containers and lids.
So the question I am trying to answer specifically with regards to thread
ends is how should the threads end ideally? Is the answer different for
metal or plastic? Is it different if you're mixing metal and plastic in
one model (e.g. you're making a threaded hole in plastic to receive a metal
bolt). If there is not a single best answer then what are the handful of
best answers for different cases. And what is the explanation behind it
all: why is answer X the best result for a specific situation? That is,
what is the intuition that explains how to choose the parameters?
The ideal shapes for those will certainly vary for metal, ceramic, wood,
plastic, rubber, etc. But even within a category, industries will have
spent years or decades perfecting the shapes, according to constraints on
ease of use, effectiveness, durability, manufacturability, cost, safety
(Higbee), etc. Is it even possible to list the situations, let alone fully
explain them and try to out-design the master engineers?
It seems like the function of thread ends treatment is to minimize the
risk of cross threading and perhaps to make the screw easier to start. So
what accomplishes that? It seems like threads that decrease in diameter
are bad, because they can more easily slip in too far and engage in
cross-thread. It seems also reasonably clear that a sharp cut is bad
because corners are always bad, so the end should be somehow rounded. I
would imagine that the exact way it's rounded probably doesn't matter. But
I think the length of the taper and whether the taper is in depth and/or
width might matter. If I want to draw a picture that shows cross threading
happening and another picture that shows how a particular thread end (or
other modification) prevents it, what would that picture look like?
If you're like me, you're probably imagining 3D printed interior and
exterior threads. If in fact industry standards aren't sufficient due to
tolerances or 3D constraints/advantages, there could be an opportunity to
come up with a new standard. But it wouldn't be just a mathematical
experiment, would it? A great solution (or several) would require extensive
testing on a lot of prototypes of different ideas in different methods and
materials.
Oh, and another question I was trying to get an answer to is what I should
call the library functionality that specifies the thread ends. My erratic
correspondent insisted that it should be called "higbee" and that everybody
who works with hardware knows what that means. I had question about that
because (1) it wasn't even clear that the tapered thread on the plastic
bottle met the definition of Higbee, since it wasn't maintaining the full
thread width and (2) it seems like actually nobody has heard of higbee.
(I hadn't before getting involved in this.)
I had never heard of it either. The Wikipedia page is short with few
references. There are three equivalent names: "Higbee cut", "convoluted
thread" and "blunt start thread" (ASME B1.7-2006).
Regards,
Curt
On Wed, Feb 22, 2023 at 1:25 AM Curt McDowell maker@fishlet.com wrote:
Most of the machine screws depicted in McMaster Carr CAD files seem to be
like a threaded rod, chopped off arbitrarily then chamfered at 45 degrees.
In designing optimal 3D-printed plastic threads, mass-produced screws may
be too simplistic to use for inspiration. And a general CAD library may
need to support two or three designs to cover the majority of modeling
applications.
-Curt
On 2/20/2023 3:23 PM, Adrian Mariano 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:
[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:
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:
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:
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:
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:
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:
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:
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:
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 Mon, Feb 20, 2023 at 06:37:37AM -0500, Adrian Mariano 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.
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.
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Curt, the industry standards for threading specify the thread form and
pitch. At least when such standards exist. (There is for example, a
standard for plastic bottle threads but no standard for the threads of the
mating caps.) Conforming to those standard dimensions ensures that
modeled parts are compatible with standard parts.
The question of blunt start is different, because it's a tweak on the
threads that has no effect on compatibility. And in the context of metal
threads, it's too expensive to use so there's no standard for it, at least
not there. The plastic standards do specify thread ends, but they are
vague about it. It is not obvious to me that the ideal shape of the ends
of the threads must necessarily vary significantly across materials in the
manner that you suggest. My goal here was not to launch a new research
project, but to find somebody with existing knowledge on the topic.
There may be a larger question out there which is: given that I want to
design a mated pair of threads at a particular diameter and 3d print in
material X, what should the thread geometry be? I would guess that using
the plastic thread standard form would be better than using the standard
metal screw form. But maybe 3d printing has its own optimal thread form
that nobody has identified. That's an interesting question, but not
something I'm trying to figure out.
On Thu, Feb 23, 2023 at 12:57 AM Curt McDowell maker@fishlet.com wrote:
On 2/22/2023 8:13 AM, Adrian Mariano wrote:
Making users choose values for all of these different options would
overwhelm most users. Now people do CAD for different reasons. One reason
is to model some existing object. In that case, there is such a thing as
the "right" result. It matches or it doesn't. I don't care about this
case. People who want to do that can handle a zillion parameters and can
figure out how to get their model to match up with the target.
Functions for machine screws, bottle caps, jar caps, flag poles, etc.
would allow most users to avoid dealing with the zillion parameters. BOSL2
is an amazing library, and perhaps as it becomes the de facto go-to for
OpenSCAD, few here would have to worry about re-inventing threads for the
millionth time.
The case I care about is people who want to model things to USE them. A
person who wants threads to USE doesn't have a model of what the threads
are supposed to look like. For that person, I want default behavior that
is as good as possible, and I want guidance about when and how to deviate
from the defaults. And I want an explanation that justifies the default
behavior.
As a user, the above functions are what I want, but I'd also want them to
conform to industry standards. For example, something that screws onto the
top of a 2-liter bottle, or a vessel that can be sealed with a Mason jar
lid or screwed onto a Mason jar, or a plastic hole that tightly accepts an
M6 bolt, or a flagpole mount, or something that screws onto a painter's
extension pole, or just a container and lid where the threads are indeed
compatible with off-the-shelf containers and lids.
So the question I am trying to answer specifically with regards to thread
ends is how should the threads end ideally? Is the answer different for
metal or plastic? Is it different if you're mixing metal and plastic in
one model (e.g. you're making a threaded hole in plastic to receive a metal
bolt). If there is not a single best answer then what are the handful of
best answers for different cases. And what is the explanation behind it
all: why is answer X the best result for a specific situation? That is,
what is the intuition that explains how to choose the parameters?
The ideal shapes for those will certainly vary for metal, ceramic, wood,
plastic, rubber, etc. But even within a category, industries will have
spent years or decades perfecting the shapes, according to constraints on
ease of use, effectiveness, durability, manufacturability, cost, safety
(Higbee), etc. Is it even possible to list the situations, let alone fully
explain them and try to out-design the master engineers?
It seems like the function of thread ends treatment is to minimize the
risk of cross threading and perhaps to make the screw easier to start. So
what accomplishes that? It seems like threads that decrease in diameter
are bad, because they can more easily slip in too far and engage in
cross-thread. It seems also reasonably clear that a sharp cut is bad
because corners are always bad, so the end should be somehow rounded. I
would imagine that the exact way it's rounded probably doesn't matter. But
I think the length of the taper and whether the taper is in depth and/or
width might matter. If I want to draw a picture that shows cross threading
happening and another picture that shows how a particular thread end (or
other modification) prevents it, what would that picture look like?
If you're like me, you're probably imagining 3D printed interior and
exterior threads. If in fact industry standards aren't sufficient due to
tolerances or 3D constraints/advantages, there could be an opportunity to
come up with a new standard. But it wouldn't be just a mathematical
experiment, would it? A great solution (or several) would require extensive
testing on a lot of prototypes of different ideas in different methods and
materials.
Oh, and another question I was trying to get an answer to is what I should
call the library functionality that specifies the thread ends. My erratic
correspondent insisted that it should be called "higbee" and that everybody
who works with hardware knows what that means. I had question about that
because (1) it wasn't even clear that the tapered thread on the plastic
bottle met the definition of Higbee, since it wasn't maintaining the full
thread width and (2) it seems like actually nobody has heard of higbee.
(I hadn't before getting involved in this.)
I had never heard of it either. The Wikipedia page is short with few
references. There are three equivalent names: "Higbee cut", "convoluted
thread" and "blunt start thread" (ASME B1.7-2006).
Regards,
Curt
On Wed, Feb 22, 2023 at 1:25 AM Curt McDowell maker@fishlet.com wrote:
Most of the machine screws depicted in McMaster Carr CAD files seem to be
like a threaded rod, chopped off arbitrarily then chamfered at 45 degrees.
In designing optimal 3D-printed plastic threads, mass-produced screws may
be too simplistic to use for inspiration. And a general CAD library may
need to support two or three designs to cover the majority of modeling
applications.
-Curt
On 2/20/2023 3:23 PM, Adrian Mariano 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:
[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:
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:
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:
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:
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:
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:
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:
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:
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 Mon, Feb 20, 2023 at 06:37:37AM -0500, Adrian Mariano 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.
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.
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On 23/02/2023 11:34, Adrian Mariano wrote:
But maybe 3d printing has its own optimal thread form that nobody has
identified.
I guess you've got some testing ahead.
I'm not sure of the practical use, but then 50 years ago, I said
computer games would never catch on...
I just made up my own thread profile for 3D printed parts that has 45
degree slopes and a wide crest that are easier to print than 30 degree
pointy ones. It doesn't conform to any standards but it works for me. And
tapered lead-ins, which also work for me. Not quite the same as higbee
because mine start narrow when only the peak is above the minor diameter
and get wider as they get higher. Higbee starts wide and narrows as it gets
higher. Not sure if that works better, or is just more practical to make
when not 3D printing. Because it starts as a wide ramp I could imagine it
jamming on the crest when mis-aligned with the female thread whereas mine
would more likely engage.
When I wanted to print a bottle cap I couldn't find any proper data to feed
into my thread generator but I found a part on Thingiverse that fitted
perfectly when sliced with Cura. A rare thing.
[image: IMG_20220705_091939414.jpg]
On Thu, 23 Feb 2023 at 11:44, Raymond West raywest@raywest.com wrote:
On 23/02/2023 11:34, Adrian Mariano wrote:
But maybe 3d printing has its own optimal thread form that nobody has
identified.
I guess you've got some testing ahead.
I'm not sure of the practical use, but then 50 years ago, I said
computer games would never catch on...
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