Design of Screw Jack

i) Inputs
a) Material Used
b) Yield strength
c) Allowable strength
d) Factor of safety
e) Nut Material
f) Design Load
g) lifting Height

Step 1 : Design of Screw

Allowable Shear Stress of Screw = 0.5 * Allowable Strength

= 54.765

Critical Cross Sectional Area of Screw= Ac =

Assuming Single Start Thread

Standard Available
Critical Cross Sectional Area of Screw (Ac) =
Major diameter of screw (d) =
Minor diameter of screw (d1) =
Pitch (P) =
Pitch Circle Diameter (d2) =
Inner diameter of Nut (dnut) =
 Check For Screw

direct compressive Stress 〖 (𝝈 〗 _𝒄) =

Torsional Moment For Screw

𝑀_𝑡𝑟=𝑊[𝑑_2/2 (tan⁡〖
∝ + 𝜇 〗 /(1−𝜇𝑡𝑎𝑛𝛼))]

For Single Start Thread

Load = Pitch

𝑡𝑎𝑛𝛼=2/(𝜋𝑑_2 )=

Mtr =

We have
where
Mtr
𝑀_𝑡𝑠=𝜋/16 〖𝑑 _1 〗 ^3𝜏 τ
d1

τ= 0.653614 Mpa

Then,
Maximum Nominal Stress

σmax = 2.24357573
Hence,
Allowable strength > Maximum Nominal S

Step 2 : Design of Screw Head

=
Hieght of Collor
Out side Diameter of Collor =
Diameter pin of Above Head =

Mean diameter of Collor (dc) =

Assuming Friction Between Harden Steel and Cast Iron

Step 3 : Design of Nut

〖〖(𝜎 〗 _𝑏 〗=^′)
Bering Pressure For Steel Screw

Bering Pressure For Phosphor Bronze 〖

〖(𝜎 〗 _𝑏 〗 ^′)

Number of Threads in Nut = 𝑖=4𝑤/( 〖 〖(𝜎

〖𝑑 _1 〗 ^2)))

Length of Nut (ln) = i*P 10

Length of Screw = Lift + Length of Nut +Margin

 = 1540 mm

Tensile Strength of Nut = 𝑤=𝜋/4 ( 〖𝐷 _1 〗 ^2− 〖𝑑 _

𝜎_𝑡𝑛𝑢𝑡

D1 = 92.2344119

Crushing Strength of Nut = 𝑤=𝜋/4 ( 〖𝐷 _2 〗 ^2− 〖𝐷 _

𝜎_𝑐𝑛𝑢𝑡

D2 = 96

Shearing of Nut w = (𝜋×𝐷_1)×𝐻×𝜏_𝑁𝑢𝑡

H = 1.68583367

Step :4 Checkingg For Buckling of Screw

𝐹_𝑐𝑟=𝐴_𝑐 𝜎_𝑦 (1−𝜎_𝑦/(4𝜋^2 𝑛𝐸)

n= Eulers Constant
𝑙=𝑙𝑖𝑓𝑡𝑖𝑛𝑔 𝑙𝑒𝑛𝑔𝑡ℎ+(𝑛𝑢𝑡
𝑙𝑒𝑛𝑔𝑡ℎ)/2

l = 1505

𝑘=√(𝐼/𝐴=) 𝑑_1/4

l=
 Fcr = 62835.7911

𝐹_𝑐𝑟>𝑊

Step 5: Design of Tommy Bar

Total Frictional Torque Mt = Mts + Mtc

= 𝑊[𝑑_2/2 ((𝑡𝑎𝑛𝛼+𝜇)/(1−

tan⁡〖
𝛼 =𝑙/(𝜋𝑑_2 ) 〗

=
μ

Mt= 167465.363

𝑀_𝑡=𝐹×𝑙_ℎ

Assuming that force applied by a person

lh = 558.217878

Checking For Bending

𝑀_𝑏/𝐼=𝜎_𝑏/𝑐

dh = 24.9768355

Step 6 : Design of Cup

Diameter of Cup at bottom D3 ≈

Diameter of Cup at Top D4 ≈

Height of Cup H2 ≈

Thickness of Cup t ≈

Efficiency of the screw (square thread )

𝜂=(𝑑_2 𝑡𝑎𝑛𝛼)/(((𝑡𝑎𝑛𝛼+𝜇)/(1−𝜇𝑡𝑎𝑛𝛼) 𝑑_2+𝜇_𝑐 𝑑

η 0.0932791
η 9.32791044

Checking For overhauling

𝑡𝑎𝑛𝛼≥(𝜇𝑑_2+𝜇_𝑐 𝑑_𝑐)/(𝑑_2−𝜇𝑢_𝑐

0.0379 ≥ 0.37198312

Hence it is self locking screw

Step 6 : Design of Body

(i) Length of Screw = lift + length of Nut + ma

= 1540

(ii) Height of Body = Length of Screw + Clear

= 1550

(iii) Diameter of Body at Top (D5) =

 =
(iv) Diameter of Body at the bottom inside (D6)

(iv) Outside Diameter of Body at the bottom (D7)

(iv) Thickness at base t1

(iv) Thickness at body t2

 C40 Steel h) Tensile Strength of Nut = 𝜎_𝑡𝑛𝑢𝑡 39.43 Mpa
328.6 Mpa i) Crushing Strength of Nut = 𝜎_𝑐𝑛𝑢𝑡 57.5.43 Mpa
109.53 Mpa j) Shear Strength of Nut = 𝜏_𝑐𝑛𝑢𝑡 19.715 Mpa
3 k) Youngs modulus = E 206800 Mpa
Phosphor Bronze
9810 N
1500 mm

* Allowable Strength

load
allowable
stress
89.5645029 mm^2

rew (Ac) = 4778 mm2

= 90 mm
= 78 mm
= 10 mm
= 84 mm =
= 90.5 mm
𝐿𝑜𝑎𝑑/𝐴_𝑐
𝑊/𝐴_𝑐 =2.05316 Mpa

where
Mtr Torsional Moment For Screw
W Load
d2 Pitch Circle Diameter
μ co=efficent of friction = 0.14 (for heavy machine Oil)

7.58E-03

6.09E+04 N-mm

Torsional Moment For Screw

Shear Stress
Major diameter of screw

𝜎_𝑚𝑎𝑥=1/2
[𝜎_𝑐+√( 〖𝜎 _𝑐 〗 ^2+4𝜏^2 )]

Mpa
> Maximum Nominal Stress Design is Safe

H1 = 135 mm
dco = 180 mm
D = 45 mm

2/3
[( 〖
𝑑 _𝑐𝑜 〗 ^3−𝐷^3)/( 〖
𝑑 _𝑐𝑜 〗 ^2−𝐷^2 )]

126 mm

n Steel and Cast Iron 𝜇_𝑐= 0.147

10.8 to 17.2 Mpa

nze 〖
〖(𝜎 〗 _𝑏 〗 =^′) 14 Mpa

𝑖=4𝑤/( 〖 〖(𝜎 〗 _𝑏 〗 ^′×𝜋(𝑑^2−

〖𝑑 _1 〗 ^2)))

0.44277265 ≈ 1 Threads

mm

h of Nut +Margin
=𝜋/4 ( 〖𝐷 _1 〗 ^2− 〖𝑑 _𝑛𝑢𝑡 〗 ^2 )
𝑛𝑢𝑡

≈ 94 mm

=𝜋/4 ( 〖𝐷 _2 〗 ^2− 〖𝐷 _1 〗 ^2 )
𝑛𝑢𝑡

mm

×𝐷_1)×𝐻×𝜏_𝑁𝑢𝑡

≈ 2 mm

_𝑦 (1−𝜎_𝑦/(4𝜋^2 𝑛𝐸)(𝑙/𝑘))

onstant 0.25
𝑔𝑡ℎ+(𝑛𝑢𝑡

mm

√(𝐼/𝐴=) 𝑑_1/4
k = 19.5

19.5 mm
 N

Design is safe

𝑑_2/2 ((𝑡𝑎𝑛𝛼+𝜇)/(1−𝜇𝑡𝑎𝑛𝛼))+(𝜇_𝑐 𝑑_𝑐)/2]

=𝑙/(𝜋𝑑_2 ) 〗 = 0.03791

0.147

d by a person = 300 N

mm

𝑏/𝐼=𝜎_𝑏/𝑐
𝐼=(𝜋 〖𝑑 _ℎ 〗 ^4)/64 𝐶=𝑑_ℎ/2

30 mm

dco = 180 mm
 2dco = 360 mm

70 mm

10 mm

(1−𝜇𝑡𝑎𝑛𝛼) 𝑑_2+𝜇_𝑐 𝑑_𝑐 ) )

2+𝜇_𝑐 𝑑_𝑐)/(𝑑_2−𝜇𝑢_𝑐 𝑑_𝑐 )

ift + length of Nut + margin

mm

Length of Screw + Clearance

mm

1.5*d2 126 mm
m inside (D6) = 2.25*d2 189 mm

he bottom (D7) = 1.5*D6 283.5 mm

= 2*H 4 mm

= 0.25*d 22.5 mm
 Design - Screw Jack

PARTS MATERIAL DESIGN CAD DRAWING

Cap C40 - Steel Done Select Select
Head C40 - Steel Done Select Select
Tommy Bar C40 - Steel Done Select Select
Nut Phosphor-Bronze Done Select Select
Screw C40 - Steel Done Select Select
End Stop C40 - Steel Not DoneSelect Select
Bottom Lid C40 - Steel Not DoneSelect Select

Inputs
Parameter Symbol Value Units
Total Lift Lt 1500 mm
Load W 1000 Kg
Thread type Square -NA-
Start type Single -NA-

Rod Material C40 - Steel -NA-

Youngs modulus 208000 MPa
Poissons ratio 0.3 -NA-
Yield strength 328.6 MPa
Ultimate strength 340 MPa
Shear strength 0 MPa
Chrushing strength 0 MPa
Tensile strength 0 MPa
Factor Of Safety 3 -NA-
Allowable strength 109.533333333333 MPa

Nut Material Phosphor-Bronze -NA-

Youngs modulus 0 MPa
Poissons ratio 0 -NA-
Yield strength 0 MPa
Ultimate strength 0 MPa
Shear strength 19.72 MPa
Chrushing strength 57.543 MPa
Tensile strength 39.43 MPa
 Design - Screw

Outputs
Parameter Symbol Value Units Formula
Allowable Shear Stress of Screw 54.7667 MPa 0.5 * Allowable Strength
Load Factor 1

Critical Cross Sectional Area of Screw-

calculated Ac-calc 89.5618 mm^2 Load to lifted* Load Factor
Critical Cross Sectional Area of Screw-
Selected Ac-std #N/A mm^2
Thread type Single
Core dia of the screw 6.1659 Lifting load * Load factor /
Thread type Start type Material
Select Select Select
Square Single C40 - Steel
Triangular Double Phosphor-Bronze
Cast Iron

Status Ac
Select -115
Done -58
Not Done -1
Purchased 56
113
170
227
284
346
415
452
707
855
1075
1385
1521
1662
2043
2376
2827
3318
3848
4185
4778
5411
0.5 * Allowable Strength

Load to lifted* Load Factor/Allowable stress

Lifting load * Load factor / Allowable stress

Assuming Single Start Thread

Standard Availabl
Critical Cross Sectional Area of Screw (Ac) 4778
Major diameter of screw (d) = 90
Minor diameter of screw (d1) = 78
Pitch (P) = 10
Pitch Circle Diameter (d2) = 84
Inner diameter of Nut (dnut) = 90.5
Material Youngs modulus Poisson ratio Yield Ultimate Shear Chrusing Tensile
C40 - Steel 208000 0.3 328.6 340
Phosphor-Bronze 19.72 57.543 39.43
Cast Iron
mm2
mm
mm
mm
mm
mm