Speed and Feed Calculation for Dummies

The basic information is the speed the cutting edge is going through the material. If a round cutter or a round part you calculate the outside diameter times pi to get the distance the cutting edge is traveling. A simple formula is: RPM = (3.8 x CS)/dia. RPM = Rev. per minute

CS = cutting speed in feet per minute or meters per minute.

dia. = diameter of cutter or work when turning

The cutting speed is selected by the type of material being cut, the type and material the cutter is made of, the type of cut being made and the stiffness of the machine and setup.

Example: Aluminum part solid in vise being cut with 1/2" carbide end mill

1) normal cutting speed range for aluminum with carbide is 200 to 1000 feet/min. This information is what is given by the cutter MFG. in charts and varies according to material, operation, and cutter.

2) vise is a solid clamping way to hold part

3) If machine is small bridgeport or low HP machine you could try 300 ft/min to start

This would be RPM =(3.8 x 300) / .500 = 2,280 RPM

This would be OK for roughing or finishing by varying the feed rate, depth and type of cut in the job if the machine and job does not vibrate to much.

NOTE: IF CUTTER IS A BALL NOSED END MILL AND YOU ARE CUTTING ON THE BALL TIP THE CUTTING SPEED IS MUCH slower THEN CUTTING ON THE OD OF THE CUTTER.

The FEED RATE is measured by how much is cut by each individual tooth of the cutter

and is know a the chip load per tooth. In the above example if the cutter was 2 flute cutter you would feed it appox. half as fast as a four flute cutter with the same chip load. On a solid carbide 1/2" cutter in aluminum you can feed it .001" (finish) to .007" roughing for each tooth (flute- cutting edge) 2.28" x 2 =4.56" / min finish feed rate for a two flute cutter. Or 31.92" / min roughing feed rate for a two flute cutter.

Your depth of cut is determined by how strong the sit-up and machine is and the power to drive the cutter.

NOTE: It is best to program for what you think will run but start the job running with the feed rate turned down to 10 or 20% to start and increase till you see what is safe to run the job at. Same thing for the speed, but crank up the speed before you crank up the feed. Good Luck

GOD'S BLESSINGS

Bill