[Fredxxx]

All through the Screwfix and Toolsatan website there are many examples
of metric bolts and nuts but they never seem to specify the pitch.

Wikipedia article:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread

suggests there are course and fine threads.

The Tapping sets sold by Screwfix often contain, for example, M6 x 0.75
and M6 x 1.0

Please spare my confusion which would be considered "standard", fine or
course?

[Clive Arthur]

On 27/03/2017 22:59, Fredxxx wrote:
All through the Screwfix and Toolsatan website there are many examples
of metric bolts and nuts but they never seem to specify the pitch.

Wikipedia article:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread

suggests there are course and fine threads.

The Tapping sets sold by Screwfix often contain, for example, M6 x 0.75
and M6 x 1.0

Please spare my confusion which would be considered "standard", fine or
course?

Coarse is standard. Fine is special. I work in electronics and almost
never see metric fine threads.

Cheers
--
Clive

[Clive George]

On 27/03/2017 22:59, Fredxxx wrote:
All through the Screwfix and Toolsatan website there are many examples
of metric bolts and nuts but they never seem to specify the pitch.

Wikipedia article:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread

suggests there are course and fine threads.

The Tapping sets sold by Screwfix often contain, for example, M6 x 0.75
and M6 x 1.0

Please spare my confusion which would be considered "standard", fine or
course?

The article to which you refer confirms the answer which my namesake
gave you. It's in the Designation section (and it's there twice...)

"If the pitch is the normally used "coarse" pitch listed in ISO 261 or
ISO 262, it can be omitted (e.g., M8)"

"If, for instance, only M20 is given then it is coarse pitch thread."

But thank you for asking the question - it made me look it up and learn
something myself :-)

[T i m]

On Tue, 28 Mar 2017 00:00:19 +0100, Clive George
wrote:

On 27/03/2017 22:59, Fredxxx wrote:
All through the Screwfix and Toolsatan website there are many examples
of metric bolts and nuts but they never seem to specify the pitch.

Wikipedia article:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread

suggests there are course and fine threads.

The Tapping sets sold by Screwfix often contain, for example, M6 x 0.75
and M6 x 1.0

Please spare my confusion which would be considered "standard", fine or
course?

The article to which you refer confirms the answer which my namesake
gave you. It's in the Designation section (and it's there twice...)

"If the pitch is the normally used "coarse" pitch listed in ISO 261 or
ISO 262, it can be omitted (e.g., M8)"

"If, for instance, only M20 is given then it is coarse pitch thread."

But thank you for asking the question - it made me look it up and learn
something myself :-)

On the subject of thread pitches ... I had to re-establish where we
were on our 3D printer recently when updating the firmware and
re-checking the stepper motor steps to distance_moved figures.

The motors are .9 degree per step and the printer Z (vertical) axis is
directly driven using two lengths of M8 stud. The 'default' pitch for
M8 is 1.25mm and so each complete rev of the motor would raise the
head 1.25mm, therefore 320 steps [1] would raise it 1mm (so that was
the 'steps / mm' value) and therefore the minimum vertical increment
was 1 step = 0.003 mm. ;-)

Given that the head tends to be moved up ~.3mm at a time (each printed
layer), that means it takes 100 whole steps to do so, potentially
making such movement pretty accurate. However, because it's just
'studding' and so really designed to bolt things together, I'm not
sure the resultant accuracy (linearity) is actually that good (but not
bad). ;-)

I understand the preferred mechanism for such a role is engineering
leadscrew and whilst that is a much coarser pitch, it's supposed to be
more accurate (linear) and still much better than the X or Y axis that
are around only 10 steps / mm (so .1mm / step 'resolution') and rely
on toothed belts and pulleys.

Cheers, T i m

[1] The electronics sub divides a single motor step (in this case) by
16x (using current / phase control or some such) so for the firmware
and the Z axis that's 5120 steps / mm!

p.s. Because our printer has (typically for such machines) no movement
feedback / servo mech it can only assume that an instruction to step
say 10000 steps results in 10000 actual steps made. That's why I am,
even nearly 2 years after building and running the printer pretty
regularly, still fascinated / amazed that it can all stay in sync,
even after running a print job for ~6 hours! How many million steps
have been made over all 3 directions?!

p.p.s. I'm also amazed (as in 'Standing on the shoulders of giants')
how you can add things like live filament diameter measurement when
you tell the firmware the distance between the measurement device and
the extruder ('print head') and it 'considers' any change in filament
diameter as it would be by the time (distance) it travels the extruder
and adjusts the filament speed accordingly to compensate.

And you can print / build such things for yourself. ;-)

http://www.thingiverse.com/thing:454584

[Andy Burns[_13_]]

T i m wrote:

because it's just 'studding' and so really designed to bolt things
together, I'm not sure the resultant accuracy (linearity) is actually
that good (but not bad). ;-)

I understand the preferred mechanism for such a role is engineering
leadscrew

not a ballscrew?

[T i m]

On Tue, 28 Mar 2017 07:29:26 +0100, Andy Burns
wrote:

T i m wrote:

because it's just 'studding' and so really designed to bolt things
together, I'm not sure the resultant accuracy (linearity) is actually
that good (but not bad). ;-)

I understand the preferred mechanism for such a role is engineering
leadscrew

not a ballscrew?

No, I don't think so Andy, or not that I'm aware of anyway. shrug

The reasons I have seen are that they are not generally good VFM for
3D printing because they are often 'chunkier' than the straight
leadscrew / stud type mechanism and because of that, they also carry
more inertia and so put more strain on the stepper motors etc.

They are also 'too accurate' in that they would completely outstrip
the abilities of laying melted plastic filament (and wouldn't be fast
enough to use on the X and Y axis).

Am also not sure if ballscrews 'like' stepper motors and so are
typically used in closed loop mode with std servo motors?

I think they would use belts on the Z axis of these d-i-y level 3D
printers but they wouldn't enjoy the head dropping onto the print
table when the power was turned off. ;-)

I understand ballscrews really come into their own when you need to
push say a CNC cutter into the workpiece, not really something
required on a 3D printer.

Are there any diy / small 3D printers that use ballscrews that you use
or are aware of Andy?


Cheers, T i m

p.s. I'm probably going to buy the 3D printer off my mate soon that he
bought on the understanding that 'we' built it g (he's moving and
doesn't have the room) and I did consider getting some leadscrews to
'upgrade' it. However, the existing M8 ss studs and twin (one spring
against the other) nuts seem to be doing the job ok so I might not
bother. ;-)

[Andy Burns[_13_]]

T i m wrote:

Are there any diy / small 3D printers that use ballscrews that you use
or are aware of Andy?

I've seen some homebuilt CNC routers (with steppers) that use them, and
assumed they would have the same advantage for 3D printers, i.e. lower
friction, better accuracy, it might be that since you need little force
for 3D printing they're not required ...

[newshound]

On 3/28/2017 4:53 AM, T i m wrote:
On Tue, 28 Mar 2017 00:00:19 +0100, Clive George
wrote:

On 27/03/2017 22:59, Fredxxx wrote:
All through the Screwfix and Toolsatan website there are many examples
of metric bolts and nuts but they never seem to specify the pitch.

Wikipedia article:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread

suggests there are course and fine threads.

The Tapping sets sold by Screwfix often contain, for example, M6 x 0.75
and M6 x 1.0

Please spare my confusion which would be considered "standard", fine or
course?

The article to which you refer confirms the answer which my namesake
gave you. It's in the Designation section (and it's there twice...)

"If the pitch is the normally used "coarse" pitch listed in ISO 261 or
ISO 262, it can be omitted (e.g., M8)"

"If, for instance, only M20 is given then it is coarse pitch thread."

But thank you for asking the question - it made me look it up and learn
something myself :-)

On the subject of thread pitches ... I had to re-establish where we
were on our 3D printer recently when updating the firmware and
re-checking the stepper motor steps to distance_moved figures.

The motors are .9 degree per step and the printer Z (vertical) axis is
directly driven using two lengths of M8 stud. The 'default' pitch for
M8 is 1.25mm and so each complete rev of the motor would raise the
head 1.25mm, therefore 320 steps [1] would raise it 1mm (so that was
the 'steps / mm' value) and therefore the minimum vertical increment
was 1 step = 0.003 mm. ;-)

Given that the head tends to be moved up ~.3mm at a time (each printed
layer), that means it takes 100 whole steps to do so, potentially
making such movement pretty accurate. However, because it's just
'studding' and so really designed to bolt things together, I'm not
sure the resultant accuracy (linearity) is actually that good (but not
bad). ;-)

I understand the preferred mechanism for such a role is engineering
leadscrew and whilst that is a much coarser pitch, it's supposed to be
more accurate (linear) and still much better than the X or Y axis that
are around only 10 steps / mm (so .1mm / step 'resolution') and rely
on toothed belts and pulleys.

Cheers, T i m

[1] The electronics sub divides a single motor step (in this case) by
16x (using current / phase control or some such) so for the firmware
and the Z axis that's 5120 steps / mm!

p.s. Because our printer has (typically for such machines) no movement
feedback / servo mech it can only assume that an instruction to step
say 10000 steps results in 10000 actual steps made. That's why I am,
even nearly 2 years after building and running the printer pretty
regularly, still fascinated / amazed that it can all stay in sync,
even after running a print job for ~6 hours! How many million steps
have been made over all 3 directions?!

p.p.s. I'm also amazed (as in 'Standing on the shoulders of giants')
how you can add things like live filament diameter measurement when
you tell the firmware the distance between the measurement device and
the extruder ('print head') and it 'considers' any change in filament
diameter as it would be by the time (distance) it travels the extruder
and adjusts the filament speed accordingly to compensate.

And you can print / build such things for yourself. ;-)

http://www.thingiverse.com/thing:454584

Perhaps you need a variant on the system once used for ruling
diffraction gratings. This has a fine pitch screw and a *long* nut
lined, iirc, with cork so that pitch errors average out. Can't for the
life of me remember the name of it. Standard Physics A-level in the
1960s. I guess photo litho methods replaced ruling soon after. Can't
persuade Google to divulge the name.

[newshound]

On 3/28/2017 2:33 PM, newshound wrote:


Perhaps you need a variant on the system once used for ruling
diffraction gratings. This has a fine pitch screw and a *long* nut
lined, iirc, with cork so that pitch errors average out. Can't for the
life of me remember the name of it. Standard Physics A-level in the
1960s. I guess photo litho methods replaced ruling soon after. Can't
persuade Google to divulge the name.

The brain kicked in eventually, it is a Merton Nut

https://en.wikipedia.org/wiki/Thomas_Ralph_Merton

[T i m]

On Tue, 28 Mar 2017 22:18:33 +0100, newshound
wrote:

On 3/28/2017 2:33 PM, newshound wrote:


Perhaps you need a variant on the system once used for ruling
diffraction gratings. This has a fine pitch screw and a *long* nut
lined, iirc, with cork so that pitch errors average out. Can't for the
life of me remember the name of it. Standard Physics A-level in the
1960s. I guess photo litho methods replaced ruling soon after. Can't
persuade Google to divulge the name.

The brain kicked in eventually, it is a Merton Nut

https://en.wikipedia.org/wiki/Thomas_Ralph_Merton

Interesting, thanks. ;-)

Cheers, T i m

[T i m]

On Tue, 28 Mar 2017 14:33:02 +0100, newshound
wrote:

snip

The motors are .9 degree per step and the printer Z (vertical) axis is
directly driven using two lengths of M8 stud. The 'default' pitch for
M8 is 1.25mm and so each complete rev of the motor would raise the
head 1.25mm, therefore 320 steps [1] would raise it 1mm (so that was
the 'steps / mm' value) and therefore the minimum vertical increment
was 1 step = 0.003 mm. ;-)

Given that the head tends to be moved up ~.3mm at a time (each printed
layer), that means it takes 100 whole steps to do so, potentially
making such movement pretty accurate. However, because it's just
'studding' and so really designed to bolt things together, I'm not
sure the resultant accuracy (linearity) is actually that good (but not
bad). ;-)

I understand the preferred mechanism for such a role is engineering
leadscrew and whilst that is a much coarser pitch, it's supposed to be
more accurate (linear) and still much better than the X or Y axis that
are around only 10 steps / mm (so .1mm / step 'resolution') and rely
on toothed belts and pulleys.

snip

Perhaps you need a variant on the system once used for ruling
diffraction gratings. This has a fine pitch screw and a *long* nut
lined, iirc, with cork so that pitch errors average out.

That's a clever idea. ;-)

Can't for the
life of me remember the name of it. Standard Physics A-level in the
1960s. I guess photo litho methods replaced ruling soon after. Can't
persuade Google to divulge the name.

I think the 'bottom line' (outside of 'don't fix what's not broken'?)
is that some lead screws could both speed up the z axis (quicker
homing etc) whilst potentially providing better linearity.

I also understand that stainless steel nuts running on ss threads
might 'gall' more easily that non stainless steel nuts / threads? This
is good when it's being used as a fastener but not if you want a
freely running joint?

This is quite interesting:

http://www.protoparadigm.com/news-up...n-3d-printers/

Cheers, T i m

[Fredxxx]

On 27/03/2017 22:59, Fredxxx wrote:
All through the Screwfix and Toolsatan website there are many examples
of metric bolts and nuts but they never seem to specify the pitch.

Wikipedia article:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread

suggests there are course and fine threads.

The Tapping sets sold by Screwfix often contain, for example, M6 x 0.75
and M6 x 1.0

Please spare my confusion which would be considered "standard", fine or
course?

Many thanks to Clives for clearing this up.

If I had read the wikipedia article a more carefully ........