CENTRAL INSTITUTE OF PLASTICS ENGINEERING & TECHNOLOGY
Question Bank
COURSE : DPMT
SEMESTER : FOURTH
SUBJECT : MACHINESHOP TECHNOLOGY II
(5 marks – question)
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1. Explain horizontal milling machine with neat
sketch?
Ans.
a. Column
The column
houses the spindle, the bearings, the gear box, the clutches, the shafts, the
pumps, and the shifting mechanisms for transmitting power from the electric
motor to the spindle at a selected speed.
b. Knee
The knee
mounted in front of the column is for supporting the table and to provide an up
or down motion along the Z axis.
c. Saddle
The saddle
consists of two slide ways, one on the top and one at the bottom located at 90º
to each other, for providing motions in the X or Y axes by means of lead
screws.
d. Table
The table is
mounted on top of the saddle and can be moved along the X axis. On top of the
table are some T-slots for the mounting of workpiece or clamping fixtures.
e. Arbor
The arbor is
an extension of the spindle for mounting cutters. Usually, the thread end of an
arbor is of left hand helix.
f. Base
The base of
the milling machine, along with the column, is the major structural components.
They hold, align, and support the rest of the machine.
g. Spindle
The spindle
holds the tool and provides the actual tool rotation.
h. Spindle Reverse Lever
The position
of this lever determines the spindle direction. The three positions of the
handle are; In, Middle, and Out. The middle position is the neutral position.
Never move the spindle reverse lever when the spindle is turning.
i. Spindle Speed Selection Lever
The spindle
speed selection lever is used to change the spindle R.P.M. setting. This type
of machine has a geared head so the spindle speed can only be changed when the
spindle is stopped.
j. Spindle Clutch Lever
The spindle
clutch lever engages the spindle clutch to the motor. By manipulating the
spindle clutch lever the operator can start and stop the spindle.
k. Feed Rate Selection Lever
The feed rate
selection lever is used to change the feed rate setting. The feed rate settings
are expressed in inches per minute.
l. Motor Start and Stop Buttons-
The motor
start and stop buttons control the power to the main motor for the machine.
2. Explain vertical milling machine with neat sketch?
Ans.
a. Milling head
The milling
head consisting the spindle, the motor, and the feed control unit is mounted on
a swivel base such that it can be set at any angle to the table.
b. Ram
The ram on
which the milling head is attached can be positioned forward and backward along
the slide way on the top of the column.
c. Column
The column
houses the spindle, the bearings, the gear box, the clutches, the shafts, the
pumps, and the shifting mechanisms for transmitting power from the electric
motor to the spindle at a selected speed.
d. Knee
The knee
mounted in front of the column is for supporting the table and to provide an up
or down motion along the Z axis.
e. Saddle
The saddle
consists of two slide ways, one on the top and one at the bottom located at 90º
to each other, for providing motions in the X or Y axes by means of lead
screws.
f. Table
The table is
mounted on top of the saddle and can be moved along the X axis. On top of the
table are some T-slots for the mounting of workpiece or clamping fixtures.
g. Arbor
The arbor is
an extension of the spindle for mounting cutters. Usually, the thread end of an
arbor is of left hand helix.
h. Base
The base of
the milling machine, along with the column, is the major structural components.
They hold, align, and support the rest of the machine.
i. Spindle
The spindle
holds the tool and provides the actual tool rotation.
j. Spindle Reverse Lever
The position
of this lever determines the spindle direction. The three positions of the
handle are; In, Middle, and Out. The middle position is the neutral position. Never
move the spindle reverse lever when the spindle is turning.
k. Spindle Speed Selection Lever
The spindle
speed selection lever is used to change the spindle R.P.M. setting. This type
of machine has a geared head so the spindle speed can only be changed when the
spindle is stopped.
l. Spindle Clutch Lever
The spindle
clutch lever engages the spindle clutch to the motor. By manipulating the
spindle clutch lever the operator can start and stop the spindle.
m. Feed Rate Selection Lever
The feed rate selection
lever is used to change the feed rate setting. The feed rate settings are
expressed in inches per minute.
n. Motor Start and Stop Buttons-
The motor start and stop buttons control the power to the main motor for the machine.
3. Explain Construction of indexing head with neat sketch?
Ans.
Indexing is an operation of dividing a
periphery of a cylindrical workpiece into equal number of divisions by the help
of index crank and index plate. A manual indexing head includes a hand crank. Rotating
the hand crank in turn rotates the spindle and therefore the workpiece. The
hand crank uses a worm gear drive to provide precise control of the rotation of
the work. The work may be rotated and then locked into place before the cutter
is applied, or it may be rotated during cutting depending on the type of
machining being done.
Most dividing
heads operate at a 40:1 ratio; that is 40 turns of the hand crank generates 1
revolution of the spindle or workpiece. In other words, 1 turn of the hand
crank rotates the spindle by 9 degrees. Because the operator of the machine may
want to rotate the part to an arbitrary angle indexing plates are used to
ensure the part is accurately positioned.
Direct
indexing plate: Most dividing heads have an indexing plate permanently attached
to the spindle. This plate is located at the end of the spindle, very close to
where the work would be mounted. It is fixed to the spindle and rotates with
it. This plate is usually equipped with a series of holes that enables rapid indexing
to common angles, such as 30, 45, or 90 degrees. A pin in the base of the
dividing head can be extended into the direct indexing plate to lock the head
quickly into one of these angles. The advantage of the direct indexing plate is
that it is fast and simple and no calculations are required to use it. The
disadvantage is that it can only be used for a limited number of angles.
Interchangeable indexing plates are used when the work must be rotated to an angle not available on the direct indexing plate. Because the hand crank is fixed to the spindle at a known ratio (commonly 40:1) the dividing plates mounted at the handwheel can be used to create finer divisions for precise orientation at irregular angles. These dividing plates are provided in sets of several plates. Each plate has rings of holes with different divisions. For example, an indexing plate might have three rows of holes with 24, 30, and 36 holes in each row. A pin on the hand crank engages these holes. Index plates with up to 400 holes are available. Only one such plate can be mounted to the dividing head at a time. The plate is selected by the machinist based on exactly what angle he wishes to index to.
4. Explain about Care and Maintenance of Milling Cutters?
Ans.
· The life of a milling cutter can be greatly
prolonged by intelligent use and proper storage. General rules for the care and
maintenance of milling cutters are given below.
· New cutters received from stock are usually
wrapped in oil paper which should not be removed until the cutter is used.
· Take care to operate the machine at the proper
speed for the cutter being used, as excessive speed will cause the cutter to
wear rapidly from overheating.
· Take care to prevent the cutter from striking
the hard jaws of the vise, chuck, clamping bolts, or nuts.
·Whenever practical, use the proper cutting oil
on the cutter and workpiece during operations, since lubrication helps prevent
overheating and cutter wear.
· Keep cutters sharp. Dull cutters require more
power to drive and this power, being transformed into heat, softens the cutting
edges. Dull cutters should be marked as such and set aside for grinding. For
further information on cutter grinding.
· Thoroughly clean and lightly coat milling
cutters with oil before storing.
· Place cutters in drawers or bins so that their
cutting edges will not strike each other. Hang small cutters on hooks or pegs,
and set large cutters on end. Place taper and straight shank cutters in
separate drawers, bins, or racks provided with suitable sized holes to receive
the shanks.
5.Explain about selection of Milling Cutters?
Ans.
Consider the following when choosing milling cutters:
· High-speed steel, stellite, and cemented carbide cutters have a distinct advantage of being capable of rapid production when used on a machine that can reach the proper speed.
· 45° angular cuts may either be made with a 45° singleangle milling cutter while the workpiece is held in aswivel vise, or with an end milling cutter while the workpiece is set at the required angle in a universal vise.
· The harder the material, the greater will be the heat that is generated in cutting. Cutters should be selected for their heat-resisting properties,
·Use a coarse-tooth milling cutter for roughing cuts and a finer-toothed milling cutter for light cuts and finishing operations.
· When milling stock to length, the choice of using a pair of side milling cutters to straddle the workpiece, a singleside milling cutter, or an end milling cutter will depend upon the number of pieces to be cut.
6. What is the advantages, disadvantages and applicationsof milling machine?
Ans.
Advantages
1. The metal is removed at a faster rate as the cutter has got multiple cutting edges and rotates at a higher speed.
2. It is possible to perform machining by mounting more than one cutter at a time.
3. The table of the machine can be moved to a n accuracy of 0.02mm.
4. It is very useful since various cutters and precise tools ca n be machined.
5. Special attachments can be mounted on the machine to perform operations that are performed in other machine tools.
Disadvantages
1. The cost of the milling machine is high.
2. As milling cutters cost is high, the investment for procuring tools is more.
3. The production cost will increase if we carry out the operations performed in a shaper or a drilling machine with a milling machine.
Applications
They are usually used to machine flat surfaces, but can also produce irregular surfaces. They can also be used to drill, bore, cut gears, and produce slots
7. Explain working and construction of surface grinding machine with neat sketch?
Ans.
Base: It acts as a support for the entire assembly and also acts as an absorber of vibrations.
Hand Traversing Wheel: This traversing wheel is used to adjust the worktable in a longitudinal direction i.e. the worktable can be moved in forward and backward direction by means of Hand Traversing Wheel.
Cross Slide Hand wheel: This hand wheel is used to adjust the worktable in up and down direction so that the workpiece is to be placed in exact dimension w.r.t. the Grinding wheel.
Work Table: It is the place where the workpiece is to be held properly.
Column: It is the vertical column where wheel head, Wheel Guard and Abrasive Wheel are mounted.
Wheel Head: It is the compartment which has to be moved up and down so that the grinding wheel can touch the workpiece.
Vertical Feed Hand Wheel: This hand wheel is used to provide the feed to the wheel head in a vertical direction which also indicates the depth of cut from the surface of the workpiece.
Wheel Guard: It acts as a cover on the grinding wheel to avoid the accidents.
Abrasive Wheel: This is the main tool which is used to remove the material from the surface of the workpiece. It is coated with abrasives and thereby the accuracy obtained is very high.
Coolant: The Coolant used in Surface Grinding Process is used to cool the work region so that heat cannot be dissipated into the workpiece and grinding wheel.
Working principle
· Surface Grinding Machine uses a rotating
abrasive wheel to remove the material from the surface of the workpiece so as
to create a flat surface with a high surface finish.
· The grinding wheel revolves on a spindle and
the workpiece is mounted on a reciprocating table.
· The reciprocating table moves in a forward or
backward direction and the workpiece is adjusted with respect to the grinding
wheel position.
· When the power supply is given and suitable
speed is provided to the grinding wheel, the grinding wheel rotates on the
surface of the workpiece so as to remove the material from the surface of the
workpiece till high accuracy is obtained.
· The Aluminum oxide, diamond, silicon carbide, and cubic boron nitride (CBN) are four commonly used abrasive materials for the surface of the grinding wheels.
8. Explain the procedure to follow in balancing a wheel?
Ans.
The procedure to follow in balancing a wheel is as follows:
1. Mount the wheel on its sleeve. (In case of wheels with arrow markings, the stenciled arrow should point upwards). Tighten the flange bolts evenly and only enough to hold the wheel firmly.
2. True the wheel so that it is in running truth on its own sleeve.
3. Remove the wheel and sleeve assembly from the grinding machine. Insert the proper size balancing arbor and then place the arbor with the wheel on the balancing stand.
4. Remove the two balance weights from the wheel sleeve.
5. Allow the two wheels to turn until it has come to rest with the heavy side down.
6. Draw a chalk mark on the side of the wheel at the exact top (directly opposite the heavy side).
7. Replace the two balancing weights in the flange groove with their adjacent endsmeeting under the chalk mark. Tighten the weights just enough to hold them in position temporarily.
8. Give the wheel a quarter turn. The wheel may not remain at rest in this position; move the weights gradually and equally from the chalk mark until the balance is established.
9. Give the wheel a half turn. Test for balance and then keep turning the wheel for a complete revolution, stopping and checking for balance at about eighth of a revolution.
10. Now tighten the balancing weights securely.
11. Carefully rest the wheel on the floor, remove the balancing arbor and mount the wheel in the grinding machine. Finally re-true the wheel preparatory to grinding.
9. Draw the wheel balancing in grinding machine?
Ans.
10. Draw the standard types of wheels?
Ans.
11. Explain Dressing and truing of grinding wheels?
Ans. Dressing
Dressing removes loading and breaks away the glazed surface
so that sharp abrasive particles are again presented to the work This is done
with various type of dressers A common type of wheel dresser, known as the star
dresser,
· For precision and high finish grinding, small
industrial diamonds, known in the trade as bors are used.
· Diamond or group of diamonds is mounted in a
holder The diamond should be kept pointed, since only the point can be used for
cutting
· This is done by the holder down at a 1515°angle
and using a new surface each time the wheel is dressed
· Good supply of coolant should be used when dressing with a diamond, as overheating can cause the diamond to fracture or drop out of its setting Very light cuts only may be taken with diamond tools.
Truing
Truing is the process of changing the shape of the grinding
wheel as it becomes worn from an original shape, owing to the breaking away of
the abrasive and bond
This is done to make the wheel true and concentric with the bore,
or to change the face contour for form grinding Truing and dressing are done
with the same tools, but not for the same purpose.
12. Explain about glazing and loading?
Ans.
Glazing
When the surface of a grinding wheel develops a smooth and shining
appearance, it is said to be glazed. This indicates the abrasive particles on
the wheel face are not sharp.
Loading
When soft materials like aluminum, copper, lead, etc are
ground the metal particles get clogged between the abrasive particles this
condition is called loading, The effects of a glazed or a loaded grinding wheel
are almost the same.
13. What are the advantages of surface grinding machines?
Ans.
Surface grinding machines are used wildly in manufacturing processes. These grinders use rotating wheel to produce finishing to metallic, nonmetallic objects at desired shape. Less investment is required for this type of machines. Below are key advantages of surface grinding machine as follows
1.Surface grinding can be performed on abrasive, metallic, non metallic, hard, soft materials.
2. It gives perfection in output while grinding process taking place on any material.
3. After surface grinding process material obtained is of high quality finished.
4. Surface grinding machines are available in automatic or in manual mode. Some companies offer both type of mode through their machines.
5. Working principle of surface grinding machine is simple. It is not complicated process so its easy to deliver quality output.
14. Explain about cutting fluids and disadvantages of grinding wheel imbalance?
Ans. 1. Cutting fluids
Recommended cutting fluids
Soluble mineral oil and pure water are mixed in the ratio of 1:40 or 50 (depending upon the grinding wheel) and is used for grinding the following materials
· Cast iron or hardened steel
· Soft steel
· Connected carbide tools (using silicon wheel)
2. Disadvantages of grinding wheel imbalance
·It will affect the strength of grinding wheel
spindle and increase the fatigue stress.
· It will cause abnormal wear and tear of
bearings.
· It will cause grinding wheel vibration and
decline of machining precision.
· The grinding stress increases and grinding
wheel is easy to fracture.
· Abnormal and uneven wear.
15. What is consideration to select a suitable specification of grinding wheel?
Ans.
1. The material to be ground and its hardness
ABRASIVE: Aluminum oxide for steel and steel
alloys.
Silicon
carbide for cast iron, non-ferrous and non-metallic’s.
GRIT SIZE:
Fine grit for brittle materials. Coarse grit for ductile materials.
GRADE: Hard grade for soft materials. Soft
grade for hard materials.
2. The amount of stock to be removed
and the finish required
GRIT SIZE:Coarse grit for rapid stock removal
as in rough grinding.
Fine
grit for high finishing.
BOND: Vitrified for precision cutting. Rubber
for high speed cutting.
3. Wet or dry
GRADE: Wet grinding, as a rule, permits use of wheels at
least one grade harder than that of dry grinding without danger of burning the
work.
4. The wheel speed
BOND: Standard vitrified wheels are not exceeding 2,000mpm,
Standard organic bonded wheels(Rubber or Epoxy) are used of
most applications over 2,000mpm up to 6,000mpm.
NOTE: Do not exceed the safe operating speed
shown on a wheel tag or blotter.
5. The contact area of grinding
GRIT SIZE: Coarse grit for large contact
area.Fine grit for small contact area.
GRADE: The smaller contact area, the harder wheel.
16.Draw a cylindrical grinding machine with and types?
Ans.
This machine
is used to produce external cylindrical surface Surfaces may be straight,
tapered, steps or profiled
Broadly there are three different types of
cylindricalgrinding machine as follows
· Plain centre type cylindrical grinder
· Universal cylindrical surface grinder
· Centre-less cylindrical surface grinder
17. Draw and explain principle of centreless grinding?
Ans. Support and feed of the workpiece is
provided by using two wheels (regulating and grinding) + work rest.
· Regulating wheel of rubber bonded abrasives. It
rotates the work by friction, with a speed of 0.25 – 1 m/s. (much slower than
the wheel)
· Both wheel rotate in the same direction to move
the work.
·The work rest support the work. The axial
movement of the work – piece is obtainedby tilting regulating wheel at (50 –
70).
· Feed can be calculated F= Ø x RPM x sinØ
(in/min)
· very productive and work must not be supported.
18. Draw the method of centreless grinding with explanation?
Ans.
A. Through-FEED GRINDING - The piece of one
diameter is fed on one side and is passed between the wheels, e.g. preparing
for thread rolling
B. INFEED GRINDING - For form grinding:
To install the
piece, the rest and the regulating wheel have to be moved back; when the work
is in, the regulating wheel is adjusted to the required position.
· parts with multiple diameters can be ground;
·for curved parts, wheel with a profile is used
in ball grinding for bearing
C. END FEED GRINDING – both wheels are tapered
and tapered work/stock bar is fed from one side, until reaches the stop.
19. Advantages and Disadvantages of center-less grinding?
Ans. ADVANTAGES
1. No mounting
of workpiece required
2. Size of the
work easily controlled
3. No
deflection of the workpiece
4. Very
reproductive process
5. No high
skilled operators are required (only setters).
DISADVANTAGES
1. Pieces with
flats and key-ways cannot be ground
2.
Concentricity and the cylindricity are not assured
3. Machines
are very specialized.
20. What is selection of grinding fluids?
Selection of a grinding fluid depends upon the work-wheel material
combinationand environmental conditions
a) Grey cast iron:
Generally dry for its self lubricatingproperty, or air blast for cooling
and flushing chips
b) Steels: If machined
by HSS tools, soluble oil (1: 20 to 30) for low carbon and alloy steels and
neat oil withEPA for heavy cuts. Often steels are machined dry bycarbide tools
for preventing thermal shocks.
c) Aluminum and its alloys: Preferably machined dry,otherwise
light but oily soluble oil or straight neat oil orkerosene oil for stringent
cuts.
d) Copper and its
alloys: Water based fluids aregenerally used, but oil with or without inactive
EPA fortougher grades of Cu-alloy are also used.
e) Stainless steels and Heat resistant alloys: High performance soluble oil or neat oil with
high concentration with chlorinated EP additive.
21. What are the work holding devices and attachments in grinding machines?
Ans. Work
holding devices are
1. Steady rest for cylindrical grinding.
2. Chucks and fixtures for other grinders
3. Magnetic chucks used on surface grinding.
Magnet chucks
There are
two types of magnetic chucks a) direct current, b) permanent magnet
The direct current chucks, made both
rectangular and circular shapes having pulling power. Only magnetic materials
such as iron and steel, will actually hold in the chuck. The magnetic chuck
holds the work by exerting a magnetic force on it. All parts held on a magnetic
chuck should be demagnetized after the work is finished.
Attachments
to improve grinding results
They include wheel reciprocating attachments for better
finish, ultrasonic cleaning device and electrolytic attachments to aid in
grinding extremely hard material.
22. Define tool and cutter grinding with neat sketch?
Ans.
Tool grinding may be divided into two
subgroups: tool manufacturing and tool re-sharpening. There are many types of
tool and cutter grinding machine to meet these requirements. Simple single
point tools are occasionally sharpened by hand on bench or pedestal grinder.
However, tools and cutters with complex geometry like milling cutter, drills,
reamers and hobs require sophisticated grinding machine commonly known as
universal tool and cutter grinder. Present trend is to use tool and cutter grinder
equipped with CNC to grind tool angles, concentricity, cutting edges and
dimensional size with high precision.
23. What is the safety precautions followed in grinding machines?
Ans.
·
Wear goggles for all grinding machine
operations.
·
Check grinding wheels for cracks before
mounting.
·
Never operate grinding wheels at speeds in
excess of the recommended speed.
·Never adjust
the workpiece or work mounting devices when the machine is operating
·
Do not exceed recommended depth of cut for the
grindingwheel or machine.
·Remove
workpiece from grinding wheel before turning machine off.
· Use proper wheel guards on all grinding machines.
24. What are the factors affecting the grain size, structure & Bonding Material?
Ans. Factors affecting
the grain size
·
The softer and more ductile the material, the
coarser the grain size.
·
The larger the amount of stock to be removed,
the coarser the grain size.
·
The finer the finish desired, the finer the
grain size.
Factors affecting the structure
·
The softer, tougher, and more ductile the
material, the wider the grain spacing.
·
The finer the finish desired, grain spacing
should be.
·
Surfacing operations require open structure
(wide grain spacing).
·
Cylindrical grinding and tool and cutter
grinding are best performed with wheels of medium structure.
Factors affecting the Bonding Material
·
Thin cutoff wheels and other wheels subject to
strains require resinoid, shellac, or rubber bonds.
·
Solid wheels of very large diameters require a
silicate bond.
·
Vitrified wheels are usually best for speeds up
to 6,500 SFPM and resinoid, shellac, or rubber wheels are best for speeds above
6,500 SFPM.
·
Resinoid, shellac, or rubber bonds are
generally best where a high finish is required.
·
25. Draw and explain mounting the grinding
wheel
Ans.
The proper
mounting of a grinding wheel is very important. An improperly mounted wheel may
become potentially dangerous at high speeds. The specified wheel size for the
particular grinding machine to be used should not be exceeded either in wheel
diameter or in wheel width.
The following
four items are methods and procedures for mounting grinding wheels:
Note that the wheel is mounted between two
flanges which are relieved on their inner surfaces so that they support the
wheel only at their outer edges.
This holds the wheel more securely with less
pressure and with less danger of breaking. For good support, the range diameter
should be about one-third of the wheel diameter.
The spindle hole in the wheel should be no more
than 0.002 inch larger than the diameter of the spindle, since a loose fit will
result in difficulty in centering the wheel. If the spindle hole is oversize,
select another wheel of the proper size. If no others are available, fit a
suitable bushing over the spindle to adapt the spindle to the hole.
Paper blotters of the proper size usually come
with the grinding wheel. If the proper blotters are missing, cut them from
heavy blotter paper (no more than 0.025-inch thick and place them between the grinding
wheel and each flange. The blotters must be large enough to cover the whole
area of contact between the flanges and the wheel. These blotters serve as
cushions to minimize wheel breakage.
When
installing the grinding wheel on the wheel spindle, tighten the spindle nut
firmly, but not so. Tight that undue strain will be put on the wheel.
26. Explain the method and procedure for grinding a formed milling cutter?
Ans.
·
Formed milling cutters are usually ground with
a cup or dish grinding wheel of medium grain (36 to 60 grain).
·
It is important that formed cutters be ground
only on the face, never on the land. Grinding the land destroys the shape of
the cutter. Also important, the face must be ground so that the exact rake
angle is retained or the cutter will cut unevenly.
·
Formed cutters are ground by radial grinding.
Correctly ground cutter teeth are shown at A and B. At A, the tooth is ground
without rake; only cutters originally shaped without rake should be reground
without rake. At B, a correctly ground tooth is shown with positive rake. Rake
angles are commonly between 10° and 15° from the radius passing through the
cutting edge, 12° being the most commonly used angle. The tooth shown at C, has
excessive positive rake this tooth will gauge, making an excessively deep cut,
and the cutting edge will dull rapidly with hard materials.
·
On new cutters, the back of each tooth should
be ground accurately before grinding the face. This procedure is recommended so
that an accurate reference surface is provided for the index finger of the grinding
machine attachment. Another method of assuring this alignment is by mounting
another cutter containing the same number of teeth on the same arbor with the
cutter being ground. With the second cutter properly aligned and locked in
place, the index finger can be used against the second cutter’s teeth.a
·
The grinding wheel should be set up so that the
wheel traverse is aligned with the face of one tooth. The alignment should be
checked by moving the grinding wheel away from the cutter, rotating the cutter,
and rechecking the traverse on another tooth. After this alignment is
accomplished, the depth of cut, is regulated by rotating the cutter slightly,
thus maintaining the same rake angle on the sharpened cutter. The depth of cut
should never be obtained by moving the cutter or grinding wheel in a direction
parallel to the wheel spindle. Doing this would change the rake angle of the
cutter.
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Thanks for the messages.