Power Screws with different Types of Thread Profiles Video Lecture | Design of Machine Elements - Mechanical Engineering

Hello friends here in this video we will
see the Definition of Power Screw with
various thread profiles which are there
in case of Power screws so let us get
started here is the definition part of
power screws now as the name suggests it
is Power screws means screw which have
some Power so here I will write it down
that power screws are screws which
either receive power or which transmit
power so this is the simplest definition
of power screws that they are the screws
which either receive power or which
transmit power now I can say that from
this it is very much clear that power
screws are different in design then
screw fasteners screw fasteners are
nothing but those are the screws which
are used as a temporary joint like if we
have two screws then we are using them
as a temporary joint that is called as a
screw fastener but power screws since
they are transmitting power their design
is different from that of screw
fasteners next they must have sufficient
strength
to transmit power here it means that
power screws they should be strong
enough to transfer the power because
they are you mostly used in case of
machines where the power transmission is
of prime importance so the screw they
must have sufficient strength next they
should have adequate bearing area to
withstand forces means the power screws
they AR area should be such that they
should be able to resist high amount of
forces because they are used in such
machineries where always these screws
they would be subjected to some kind of
axial movement in the horizontal
direction or vertical direction so
always there are forces acting on such
kind of screws so this is the definition
part now I will draw some of the
commonly used thread profiles in power
screws thread profiles of
power screws now when I am starting from
the thread profile the most commonly
used thread profile which we have it is
a square threaded screw here the profile
is in such a way that it forms a square
so I am taking just this section now if
I draw the section here this is the
thread profile which has square threads
and it will look something like this now
this is the profile the first one I will
say that it is the profile of square
threads now square threads are mostly
used for power transmission and if I
want to indicate some of the common
distances if I take any point on this
thread and along its axis if I measure
the distance on the next thread for the
same point this distance would be called
as pitch
and now here I have this as the height
of thread denoted by H and this top
surface of the thread is taken as half
of pitch that is pitch by two so now
this is regarding the square thread
after this the second most commonly used
profile is of AK matrix here I am
drawing the profile of Acme threads this
is the cut section and here I will draw
the section lines now these are
Acme threads now again in case of Acme
threads I can show the pitch if I
measure the distance that is I take a
point on a thread on the next thread if
I take the point at the same location
and measure this distance it would be
called as the pitch and this pitch will
remain same throughout denoted by small
P next this top surface of the thread it
is taken as zero point three seven times
of pitch now as we can see from the
diagram compared to square thread square
thread was having ninety degree angle
like this it was in kind at ninety
degree but here in case of AK matrix
they are inclined at some other angle if
I extend these lines so they are at an
angle now this angle is called as two
beta that is the angle between the
thread flanks ACMA threads as I can see
here that at the bottom your area is
more so this offers additional strength
to AK mate rates compared to square
threads next the third type of thread
profile which we have it is called as
but earnest thread Here I am drawing the
thread profile for it
this is buttress thread profile mostly
used in machine vices
Here I am drawing the section for the
buttress thread now this is the profile
of buttress thread so now you're the
thread profile which I have drawn it is
called as buttress thread now in case of
buttress thread again as I have shown
the pitch for square and act methods
similarly here we are having the pitch
for buttress thread and this top surface
it is taken approximately equal to 0.125
times of pitch and here is the height of
thread and this angle as I extend this
vertical line and this inclined line
they will meet at an angle which is
inclined at 45 degree so that is the
inclination which we are taking for
buttress right now as we can see for
buttress thread also the area at the
bottom that is called as the core of the
thread so at the core the area is more
so this offers more strength for the
thread and buttress thread it is useful
for power transmission I will write it
down it is for power transmission
in both the directions that is if we are
using buttress read with the help of
that we can transfer the power in
forward direction as well as we can
transfer the power in the reverse
direction
so mostly buttressed rates they are used
in case of machine vices the where we
are clamping the workpiece that is in
case of a clamp we are attaching this
buttress thread to the machine table and
then we when we are rotating the handle
with the help of that this thread moves
forward or backward so when it is moving
forward or backward it has adequate
strength to transfer the motion and
mostly as I have told it is used in case
of clamps or in case of machine vices
square threaded screw they are used in
case of screw jack in case of universal
testing machine and even in case of
lathe machine as I talk about Acme
threads they are preferably used in case
of late machine where we are having the
lead screw of the lathe which is
continuously rotating and transferring
the carriage from one place to another
there we are having Acme traits to
transfer the motion so in this video we
have seen the definition of power screws
and the various thread profiles
available for power screws