Rectangular Cycles for Turning Centers

CNC Applications

A Common Task

This is a common turning task – rapid to depth, feed to length, feed clear of the diameter, rapid back to the starting point.

This cut takes four blocks to program, a rapid, two feeds, and another rapid.

Select this link tostart the animation.

What is a Cycle?

• Normally, we only perform one positioning or cutting task in each block.

• However, tasks such as the four block turning sequence just provided are so common that control designers have incorporated CYCLES to reduce programming time.

• A cycle combines multiple moves into a single programmed block.

The Rectangular Turning Cycle

To use the rectangular turning cycle, you must first position the cutter at the Cycle Start Point. The cutter will also end up at the cycle start point at the end of the cycle. The program looks like this:

G90 Xnewx Znewz Fnewf

The cutter rapids to the newx diameter, feeds to the newz length, feeds to the starting X value, and then rapids back to the starting Z value. You get four blocks for just one programmed!

2

3

4

1

CycleStartPoint

New XPosition

New ZPosition

Additional G90 Notes

• The rectangular turning cycle (G90) is modal which is handy for repeat cuts.

• You can change newx and newz in succeeding cuts, and you can add a feed rate on any cut or just use the previous one.

• G90 only works in the direction shown. There are additional cycles for facing, boring, and turning towards the tailstock.

• What does G90 do on a machining center? (Hint: it has nothing to do with cycles.)

A G90 Turning Example

Ø4.000

0.500

1.5002.250

Ø3.000 Ø3.500

We will turn the 3.000” and 3.500” diameter steps on this part at 800fpm using the 80 degree C shaped insert in tool 2.

Follow Planning and Programming Steps (1-5)1. Examine drawing2. How will we hold the raw material – in a 3 jaw chuck.3. Decide what cutters to use – given hard, coated carbide C shaped

insert, and the cutting speed is also given (800fpm). We’ll use constant cutting speed (css) and let the machine calculate and adjust the RPM based on the X position of the cutter.

4. Write down the exact sequence of operations:A. Rapid position the cutter in Z 0.25” away from the face.B. Rapid position the cutter 0.125” away from the part in X (radial).C. Take 0.125” radial cuts (0.25” from diameter) using the G90 turning

cycle. Note: we are not taking finishing cuts in this example.D. Program end.

5. Convert the sequence of operations to a program:Program StartTurn the StepsProgram End

The Program

Program Start

Cap the RPMSet the cutting speed to 800fpm, forward direction.Rapid 0.25 away from part in Z.Rapid 0.125” radial distance from the part in X, coolant on.First rectangular cycle cut removing 0.25” from diameter.Finish the larger step, G90 is still active.First cut on the second step, notice new Z value.Final cut on the second step.

Program End

% O999G20 G40 G99 G28 U0 G28 W0T0202 G54G50 S4000 G96 S800 M3 G0 Z2.5X4.25 M8G90 X3.75 Z0.5 F.012X3.5X3.25 Z1.5X3.0M9 M5 G28 U0 G28 W0 M30 %

ActionProgram Codes

The Animation

Remember, the animation does not show the difference between rapid and feed moves. When actually run on the machine, the rapid moves are much faster than the feed moves.

Select this link tostart the animation.