Need to know: Turning Feeds and Speeds
Learn the concept to ace the test
The interview preparation series contains ideas and concepts you need to know for common tests such as the NIMS and for interview preparation.
Cutting feeds and speeds are foundational knowledge required for anyone who plans on being anywhere near a machine shop. Prepare for interviews and the NIMS test by knowing the definitions.
Cutting Speed Definition: The distance the work moves past the tool based on the number of feet that passes the tool in one minute and is given in surface feet per minute
Feed Definition: The machine movement that causes a tool to cut into or along the surface of a work piece
RPM (Revolutions per minute): The measurement used to determine the speed that the workpiece turns.
Other topics be prepared to answer are applying the formula or calculating different rates or speeds based on the relationship between different components. See sample questions below for details.
Sample Questions
Which of the following statements best defines cutting speed:
Cutting speed is based on RPM and is the amount a times a tool revolves in 1 second
Cutting speed is based on the diameter of the tool and is given in surface revolutions per minute
Cutting speed is based on the distance the work moves past the tool based on the number of feet that passes the tool in one minute and is given in surface feet per minute
Cutting speed is based on revolutions per diameter of the tool and is given in feet per inch
You’ll likely get this question in the exam, the key is to just memorize the definition of cutting speed. The key to answering this question is memorizing the definition of cutting speed.
Which of the following statements best defines feed?
The machine movement that causes a tool to cut into or along the surface of a work piece
The distance the work piece moves past the tool in one minute
The revolution of the tool per minute
The diameter of the tool correlated to the distance the tool moves in one second
When calculating the RPM for a turning operation, the machinist uses _________ instead of the diameter of the tool.
Tool nose radius
The diameter of the work piece
Cutter speed compensation
Surface feet per minute
On a lathe, the surface speed increases with diameter while the tool remains stationary therefore to calculate the RPM based on cutting speed the operator takes into account the diameter of the workpiece.
What is the RPM needed to drill a ∅.750” hole in mild steel with a cutting speed of 100 SFM on 3.50” diameter stock (use 3.82 for the constant)?
262.5 RPM
286.5 RPM
123 RPM
509 RPM
You can plug the values into the formula to get the diameter.
A part is being turned at 250 RPM with a feed rate of .008 inches per revolution. How long will it take to make one pass if the part is 10.625 inches long?
4.25 minutes
5.30 minutes
1.75 minutes
2.10 minutes
Calculate the time it takes with the following formula: T=length of pass / feed rate * IPM = 10.625/(250*.008)
Identify the proper formula for determining the RPM for a turning operation:
(CS • 3.82) / D
D / (CS/3.82)
(D • 3.82) / CS
(D •CS) / 3.82
This is a straight comprehension question for the which, if you memorize the formula, you can just apply.
How is a feed rate designated on a lathe?
Feet per second
Inches per minute
Feet per revolution
Inches per revolution