[deadlykitten]

hello if you wish, keep an eye on this thread i will share "stuff" about metrics

0 2 hero

after i replied in a few threads about threads, my solutions were found complicated; i don't find them so, but easy

to eliminate doubts, i thought of explaining this as simple as i can, because if i would post directly a technical document, i don't think that it will be easy to asimilate

so i thought of a set of simple and clear steps

( . . . . . . . . . . . . . . . . . . . . . . . . )

Simple is harder than complex ...

When the solution is simple, God is answering. Albert Einstein

[deadlykitten]

threads, or however were they called back then, had various shapes ... they were not alike, also not very different

sometimes it was only a single part : the "screw / father" or the "nut / mother" ; i can imagine some ancient applications for a "screw", like lifting materials, or in a mine ?!?! but for a "nut" i can not say ...

sometimes there were bought "screw" & "nut", so there was something like an "threaded ensemble"

they were built to deliver a function

[deadlykitten]

and time passed and the dinosaurs got screwed, or someone planted all those skeletons around earth

some bing-bang here or there, some flashy lights, some requests to repair or replace threads

if i have a threaded part, and it broke, can i just get another ? > this means that the craftsman must ensure "repetition"

but the craftsman is so far !! replacing will take too much time ! this time we should order more than one > this means "stock"

until our craftsman will deliver, we must get one from somewhere else > this means " stealing / borrowing " ... i guess they are synonyms

suddenly, the stock from the craftsman arrives all parts look good, but they don't fit ! > the craftsman retired

thx god, the borrowed part did work > this means that the craftsman can not ensure "stability"

we must have a good stock, right here ! let's craft them ourselves ! > this is "reverse enginerring"

but let's try also to use parts from our last stock delivered by the craftsman > this is "practical thinking", and it leads to "variations"

and so, the idea of interchangeability was born

[deadlykitten]

so there were threads delivering functions some functions were commonly used, and for them interchangeability was required

and exactly how one man salutes another, or how the sun rises, someone said : let's use for metrics the 60 degree zig-zag - attached image

what i mean is that it just happened, the conditions were favorable, and the idea remained

from a technical perspective, this come naturally

maybe the "60" was not intended, maybe at the begining it was other value ...

theory says that the pitch is the distance measured on the middle line of this geometry, thus the blue line is the correct way to represent the pitch, at least from a theoretical perspective / however, once this is understood, also the yellow line is correct i like more the yellow one ...

this may be considered a reference design ; it's time to put it in practice

[broby]

Pitch is measured from the same point on each thread to the next identical point on the SAME thread along the axial line. So when you say you like the Yellow rather than the Blue line in your diagram, there is NO DIFFERENCE.
Don't forget to mention that the PITCH is not the same as LEAD especially when it comes to multistart threads.
You are making a bloody great mountain out of a mole hill.
Seems like you have just reached the point in your apprenticeship where you have discovered threading... Trying to impress a lady are you?

[deadlykitten]

Pitch is measured from the same point on each thread to the next identical point on the SAME thread along the axial line. So when you say you like the Yellow rather than the Blue line in your diagram, there is NO DIFFERENCE

hy bought blue and yellow have same dimension : pitch

theoretical, this dimension makes sense only when it is on the axial line, like the blue one; this is the key of thread shape design

Don't forget to mention that the PITCH is not the same as LEAD especially when it comes to multistart threads

PITCH is not the same as LEAD especially when it comes to multistart threads > satisfied ?

You are making a bloody great mountain out of a mole hill. Seems like you have just reached the point in your apprenticeship where you have discovered threading...

please be patient until i finish if i will post directly the technical document, it will be hard to understand it

also, here : http://www.cnczone.com/forums/okuma/...uot-value.html , i was the only one delivering a H value, and you mixed up the H and the D value from the thread cycle ; so be patient

Trying to impress a lady are you?

always

[deadlykitten]

when this 60degree zig-zag goes in practice, some adjustments are required, because is hard to craft those sharp edges : so some radius will appear

in image 1 you may see the theoretical shape for the nut ( blue ) and for the screw ( yellow ); as you can see, the nut goes on the "circle secant" when the screw goes among "radius", and vice-versa

like this some comfort is created near those sharp edges; also this geometry is easier to craft

in image 2 you may see the dimensions for those secants ...

[deadlykitten]

so, the base parameters for metric threads design, are : pitch and 60degree

the base parameters for adapting this design for crafting are those secants&radius, which are relative to "pitch"

all this is in attached image ; screw and nut can not be seen here, but the reason why it looks like this is described in the previous post

[deadlykitten]

in the attached image 5, is the reference design for nut ( blue ) and for the screw ( yellow )

these designs, shapes, are determined, thus anyone can draw them for a specific pitch ; for another pitch, is just a matter of scaling

how same pitch can be on different diameters, this design is floating; anchoring it / determining it's position for a specific diameter is shown in image 6

[deadlykitten]

in image 7 is the simplified representation of image 6 from previous post

this image contains the shape for bought screw and nut, for a specific thread dimension

[deadlykitten]

when this parts are crafted, some "play" must be achieved between them

in image 8, the nut shape ( blue ) is a bit lifted, while the screw shape ( yellow ) is a bit lowered; thus some "play" is achieved, and the screw can go inside the nut with by using a relative normal torque

if "play" is minimal, than more torque is required

[deadlykitten]

"play" must be controled, and this means that the nut and the screw should have their "nominal lines" at a specific distance from the theoretical thread design

in image 9 is the "nominal axis for the theoretical thread design"

by translating this line for bought screw and nut, some play is achieved ( image 10 )

[deadlykitten]

if you take the "nominal axis for the theoretical thread (nafttt)" and represent it acrross the simetry line for the nut / screw / threaded asamble, the "flanc diameter" appears

some consider the "flanc diameter" as the most important dimension when talking about a thread; some others consider the "nafttt" to be the most important

it may be reffered as : nominal, primitive, zero line, neutral fiber, etc > in the end is the same thing words and drawings only describe this "thing"

[deadlykitten]

"play" is relative to "theoretical flanc diameter", thus :
...... " nut flanc diameter " = " theoretical flanc diameter " + " nut play "
...... " screw flanc diameter " = " theoretical flanc diameter " + " screw play "

bought " nut flanc diameter " and " screw flanc diameter " are dimensions, fix numbers

to craft them, tolerances are needed, because mechanics is much more about "tolerances", than "numbers"

in mechanics, numbers deliver rigidity; tolerances deliver functionality

[deadlykitten]

please check attached image :

" nut flanc diameter " = " theoretical flanc diameter " + " nut play " , " nut play " = 2 x " nut offset "
" screw flanc diameter " = " theoretical flanc diameter " + " screw play " , " screw play " = 2 x " screw offset "

tolerances are :
... 2 x " T nut " for " nut flanc diameter "
... 2 x " T screw " for " screw flanc diameter "

( * )

" screw or nut offset" may be 0 : h7 / H7

[ " T screw " under the yelow line ] + [ " T nut " over the blue line ] = normal thread

[ h7 ] + [ " T nut " under the theoretical flanc diameter ] = high torque / permanent thread

... and so on

[deadlykitten]

in the attached image is a " common thread ensemble + tolerances "

"play" is always positive, and "minimal play" is enough for bought parts to work / deliver

[deadlykitten]

threads are designed to work near the " flanc diameter " ( red zone in attached image ), thus a thread will deliver same functionality if "screw diameter is smaller" or/and "nut diameter is bigger"

in practice, this means that more materials is removed before threading and threading durations is decreased

thus, a thread has 2 sets of tolerances : "flanc tollerances" and " tolerances before threading "

sometimes, the "threaded ensemble length", thus the distance where the nut and the screw are in contact, is regarded as "precision" ; like this, to increase the "ensemble length", may be enough to "decrease the OD of the screw" and/or the "ID of the nut"

[deadlykitten]

so, a metric thread is characterized by :
- diameter
- pitch
- flanc dimension : flanc positions + flanc tolerance
- dimension before threading : positions + tolerance

so far it was theory ; i will continue with the practical side

a full thread insert is designed on most used / common thread tolerances

knowing how this tolerances work allows:
... significantly reducing the cutting duration
... better thread control