Performing basic shop computation

Information Sheet 8.2.1 : Basic shop formulas and equations

When the cutting tool or workpiece diameter and the spindle speed in RPM are known,
it is often necessary to calculate the cutting speed. In this event, the following formulas are
used.

As in the previous formulas, N is the RPM and D is the diameter of work (if turning) or
diameter of cutter for operations that uses rotating cutting tool.

Study this Example:

Calculate the cutting speed in feet per minute and in meters per minute if the spindle of a 3/4
inch (19.05mm) drill is 400 RPM.

ENGLISH METRIC

Step 1: Write the formula to calculate
spindle speed

Step 2: Substitute the given values to the
formula and calculate for the final
answer.

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204 April 28, 2010 3

Information Sheet 8.2.1 : Basic shop formulas and equations

Machining Time

This is the estimated time to finish a given workpiece on the Lathe Machine.

Formula: L Finish cut time = L
Rough cut time = Feed x RPM

Feed x RPM

Where:
L = Length of the portion to be machined
Feed = Set feed on the Lathe machine
RPM = Computed spindle speed

Study this given Example:

Calculate the approximate time to machine this given workpiece:

Given data
Material: 70mm Dia. X 150mm tool steel
Cutting speed of tool steel: Rough cut = 21

Finish cut = 27
Feed: 0.5 Rough cut

0.25 Finish cut

Solution:

1. In turning this piece, first thing to do is turn it to 68 Dia.

Rough cut Rough Time = 135 = 2.81 min.
RPM = (1000) (21) = 21,000 = 96 RPM (0.5) (96)

(3.14) (70) 219.8

Finish cut Finish Time = 135 = 4.25 min.
RPM = (1000) (27) = 2,7000 = 127 RPM (0.25) (127)

(3.14) (68) 213.5

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204 April 28, 2010 3

Information Sheet 8.2.1 : Basic shop formulas and equations

2. The next step is to turn Dia. 68 to Dia. 60.5 Rough Time = 115 = 2.35 min.
(0.5) (98)
Rough cut
RPM = (1000) (21) = 21,000 = 98 RPM

(3.14) (68) 213.5

Finish cut Finish Time = 115 = 3.24 min.
RPM = (1000) (27) = 27,000 = 142 RPM (0.25) (142)

(3.14) (60.5) 189.9

3. The next step is to turn Dia. 60.5 to Dia. 56 Rough Time = 45 = 0.81 min.
(0.5) (110)
Rough cut
RPM = (1000) (21) = 21,000 = 110 RPM

(3.14) (60.5) 189.9

Finish cut Finish Time = 45 = 1.17 min.
RPM = (1000) (27) = 27,000 = 154 RPM (0.25) (154)

(3.14) (56) 175.8

TOTAL Machining time: 1. 2.81 + 4.25 = 7.06 min.
2. 2.35 + 3.24 = 5.59 min.
3. 0.81 + 1.17 = 1.98 min.

14.63 minutes

Thus, the minimum time to finish the workpiece is 14.63 minutes. It is important to note that the
time for set-up is not included in the computation.

Tap drill size

To produce an internal thread a hole should be drilled and cut a thread in it by means of
a hand tap. Tap drill size is the size of the drilled hole before tapping. Although theoretically
the diameter of the drill is equal to the minor diameter of the bolt for which the internal thread is
to be used, in practice tap drill sizes are somewhat larger than the minor diameter.

Formula: Tap drill size (TDS) = Major diameter (MD) – Pitch (P)

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204 April 28, 2010 3

Information Sheet 8.2.1 : Basic shop formulas and equations

Let’s review the thread specification: 10 means Major diameter and 1.5 means Pitch
For Metric threads: M10 x 1.5 1/2 means Major Diameter and 1/14TPI means Pitch
For English threads 1/2 14TPI

Study this Example:

1. Calculate the tap drill size for M10 x 1.5

Formula: TDS = MD – P TDS = 10 – 1.5 = 8.5mm

Thus, if you are to create an M10 x 1.5 internal thread, you should use an 8.5mm drill bit
in drilling the hole before tapping.

2. Calculate the tap drill size for 1/2 14TPI

Formula: TDS = MD – P TDS = 1/2 – 1/14 = 3/7 inch

Thus, if you are to create ½ x 14TPI internal threads, you should use a 3/7in. drill bit in
drilling the hole before tapping.

Conversion of units

Measurement is a very important factor in machining operation. Since there are 2
system of measurement (English and Metric), it is essential for a machinist to learn how to
convert English to metric and vice versa.

Conversion factors: 1 cm = 10 mm
Study these examples 1feet = 12 inches
1 inch = 25.4 mm
1 inch = 2.54 cm

A. Converting inches to millimeters = 76.2 mm
Convert 3 inches to millimeters
Conversion factor: 1inch = 25.4 mm
3 inches x 25.4 mm
1 inch

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204 April 28, 2010 3

Information Sheet 8.2.1 : Basic shop formulas and equations

B. Converting millimeters to inches
Convert 101.6 millimeters to millimeters
Conversion factor: 1inch = 25.4 mm
101.6 mm x 1 inch = 4 inches
25.4 mm

C. Converting centimeters to inches
Convert 35 centimeters to inches
Conversion factor: 1inch = 2.54 cm
35 cm x 1 inch = 13.78 inches
2.54 cm

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204 April 28, 2010 3

Worksheet 8.3.1 : Worded Problems

Learning outcomes:
8 Manipulate and use basic shop formulas
Learning Activity:
8.3 Calculating shop requirement

General Instruction: Solve for the following worded problem. Use the space provided after
the problem for your solution and box your final answer. Erasures
means wrong. You have 35 minutes to answer this worksheet.
(5 points each)

1. Calculate the approximate time to produce the given workpiece.
Given data
Material: 60mm Dia. X 110mm tool steel
Cutting speed of tool steel: Rough cut = 21
Finish cut = 27
Feed: 0.5 Rough cut
0.25 Finish cut

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 8

Worksheet 8.3.1 : Worded Problems
2. What should be the RPM of the drilling machine if you are to drill a 10mm hole on an
aluminum plate that has a cutting speed of 100 m/min?

3. What is the diameter of the drill if you are instructed to create an M16 X 2.0 internal
thread?

4. The cutting speed of a piece of work in a lathe is 250 ft. per minute. If the diameter is
2 ½ inches, what must be the revolutions per minute?

5. What is the diameter of the drill if you are instructed to create an M5 X 0.8 internal
thread?

6. A shafting of annealed tool steel 3 ¾ inches in diameter is turned in the lathe with a
cutting speed of 30 m/min. what should be the spindle speed?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 8

Worksheet 8.4.1 : Worded Problems

Learning outcomes:
8 Manipulate and use basic shop formulas
Learning Activity:
8.4 Calculating shop requirement

General Instruction: Solve for the following worded problem. Use the space provided after
the problem for your solution and box your final answer. Erasures
means wrong. You have 30 minutes to answer this worksheet.
(5 points each)

1. Calculate the approximate time to produce the given workpiece.
Given data
Material: 60mm Dia. X 110mm tool steel
Cutting speed of tool steel: Rough cut = 24
Finish cut = 30
Feed: 0.5 Rough cut
0.3 Finish cut

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 8

Worksheet 8.4.1 : Worded Problems
2. What should be the RPM of the drilling machine if you are to drill a 14mm hole on an
MS plate that has a cutting speed of 30 m/min?

3. What is the diameter of the drill if you are instructed to create an M6 X 1.0 internal
thread?

4. The cutting speed of a piece of work in a lathe is 250 ft. per minute. If the diameter is
4 ½ inches, what must be the revolutions per minute?

5. What is the diameter of the drill if you are instructed to create an M12 X 1.75 internal
thread?

6. A shafting of annealed tool steel 1 ¾ inches in diameter is turned in the lathe with a
cutting speed of 30 m/min. what should be the spindle speed?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 8

Worksheet 9.1.1 : Number Problems

Learning outcomes:
9 Identify information about the blueprint
Learning Activity:
9.1 Identifying information about the blueprint

General Instruction: Given below is a working drawing of a part. Answer the following
Questions below. Write your final answer on the box after each
question. Erasures means wrong. You have 25 minutes to answer this
worksheet.

1. How many drilled holes are there?
2. What is the center distance of the two drilled holes?
3. What size of drill is used in the drilled holes?
4. What radius forms the front of the plate?
5. What type of line is drawn through the center of

a drilled hole?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7

Worksheet 9.1.1 : Number Problems

1. What is the largest diameter?
2. What is the overall length?
3. How many holes are drilled through the flange?
4. How many degrees apart are they spaced?
5. For what size screw must they be drilled?
6. What is the size and angle of chamfer?
7. What is the diameter of the recess on the right

end of the piece?
8. What is the depth of the recess?
9. What type of section view is shown?
10. What is the smallest size to which the hole through the

center can be bored?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7

Worksheet 9.4.1 : Identifying missing dimensions

Learning outcomes:
9 Solve for information needed to produce the given product
Learning Activity:
9.1 Solving for missing dimensions

General Instruction: Given below is a working drawing of a part. Answer the following
Questions below. Use scratch paper for your solution and
write your final answer on the box after each question. Erasures means
wrong. You have 25 minutes to answer this worksheet.

1. How thick is the workpiece?

2. What is the overall width (B)?

3. What is the overall length (A)?

4. What is the clearance (C) between the
body and the back of the plate?

5. If you are given a 420mm x 360mm x 28mm raw
material, how many workpiece can you produce?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7

Worksheet 9.4.1 : Identifying missing dimensions

1. What is the overall length of the part?
2. What is the dimension (A)?
3. What s the dimension (B)?
4. What is the dimension (C)?
5. What is the diameter of the drill to be use on M8?
6. What is the diameter of the drill to be use on M6?
7. What is the diameter of the drill to be use on M4?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7

Worksheet 10.2.1 : Identifying missing dimensions

Learning outcomes:
10 Perform basic shop computations
Learning Activity:
10.2 Performing basic shop computations

This is the working drawing of a product. Fill up the required information and answer the given
questions on the next page. This drawing is the reference of all the questions.

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7

Worksheet 10.2.1 : Identifying missing dimensions

Direction A:
Below is a sample of tools and materials requisition form. Fill up the required information if you
are ask to make 100 pieces of object 1 and 50 pieces of object 2

Specification of materials Quantity

Object 1
Object 2
Cutting tool for Obj.1
Cutting tool for Obj.2

Direction B:
Answer the following questions below. Use the next page to have an organize solution and
write your final answer on the box provided before the question.

1. What is the approximate time to finish a piece of object 1?

2. What should be the spindle speed of the milling machine in creating
object 2 if you are using a cutting speed of 27 m/minute and a ¾ end
mill cutter?

3. What is the size of the drill bit that you should for object 2?

4. What is the spindle speed of the drill press for drilling the holes on object 2
if you have a cutting speed of 27 m/min?

5. What is the measurement of dimension A?

6. What is the measurement of dimension B?

7. What is the measurement of dimension C?

8. What is the Specification of the hand tap to be used on object 2?

For questions 9 and 10, write YES or NO

9. You are ask to make 50 pieces of object 1. Do you steel need to request
for materials if you already have a 5/8 diameter x 22.5 cm. long mild steed
round bar?

10. You are ask to make 100 pieces of object 2. Do you steel need to request
for materials if you already have 4 pieces of 170mm x 220mm x 12mm
thick Mild steel plate?

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7

Worksheet 10.2.1 : Identifying missing dimensions

Code No. Perform Basic Shop Computations Date: Developed Date: Revised Page #
MEE722204
April 28, 2010 7