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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › CNC Machining › G-Code Programming for CNC Mills and Lathes › Lesson 9
MFG-CNC14-04 · Lesson 9 · 18 clock hours · lab

Safe Program Prove-Out on a Live Haas CNC Machine

Objective. Students execute a safe, step-by-step prove-out sequence—lockout/tagout energy verification, single-block mode, 0% feed-rate override, dry run, air-cut—on a live Haas mill before engaging the first workpiece.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Prove-Out Exists

A CNC program looks correct on screen. It may simulate cleanly in CAM software. Neither guarantee means it is safe to run on a live machine with a real workpiece in the vise. Toolpath offsets can be wrong, work coordinate systems can be misset, and tool-length values can be entered incorrectly. Prove-out is the structured sequence that catches those errors before the spindle meets metal—or a fixture, or a clamp, or an operator's hand. Every professional shop has a prove-out procedure; Haas Technical Education Centers teach this sequence as a core operating skill, and NIMS competency standards require machinists to demonstrate controlled program verification.

Step 1 — Lockout/Tagout Before Any Setup Work

Before you load a program, install a tool, or reach inside the work envelope for any reason, the machine must be in a zero-energy state. Federal OSHA 29 CFR 1910.147 (the Control of Hazardous Energy standard, commonly called LOTO) requires a written procedure for every piece of equipment. Your shop's posted procedure for the Haas VF-2 lists each energy source: 480 V three-phase electrical supply, hydraulic pressure (tool-changer and drawbar), and pneumatic pressure (air blast and chip conveyor).

The six required steps every time:

1. Notify all affected personnel.

2. Identify all energy sources using the machine's LOTO procedure card.

3. Isolate — turn the main disconnect to OFF and close the hydraulic and pneumatic shut-offs.

4. Apply your personal lock and tag to each isolation point; use a hasp if multiple workers are involved.

5. Release/restrain stored energy — bleed hydraulic pressure, exhaust air lines, allow the spindle to come to a complete stop.

6. Verify zero energy — use an approved voltage tester on the panel terminals to confirm no live voltage; watch the hydraulic pressure gauge drop to zero.

Your instructor must sign your LOTO checklist at step 6 before you proceed. There is no shortcut and no partial credit. Any safety deviation means stop, restore energy under supervision, and retest from step 1.

After setup is complete, restore energy in reverse order—remove locks only after all personnel are clear of the work envelope.

Step 2 — Loading the Program

With the machine powered and the door closed, navigate to the LIST PROGRAMS screen on the Haas control. Insert the USB drive into the control panel port, locate your verified student program file (`.nc` or `.tap` extension), and transfer it to the machine's memory. Always confirm the program number on the Haas display matches the program you intend to run. A wrong program number is a common source of crashes. Scroll through the code on the Haas editor and visually confirm the tool-call blocks (T1, T2, etc.) and the work-coordinate call (G54 or as assigned).

Step 3 — Single-Block Mode and 0% Feed-Rate Override

These two controls together give you full authority over machine motion.

With both controls set, press CYCLE START once per block, reading each G-code line on the screen and watching the tool path display. Confirm that rapid moves clear all clamps and fixtures with visible daylight between the tool and the obstruction.

Step 4 — Dry Run

Press the DRY RUN button (indicator light on). In Dry Run mode the machine ignores programmed feed rates and uses a single operator-selectable feed rate for all moves. This lets you sweep through the program quickly to check geometry without worrying about incorrect `F` word values. Dry Run does not suppress spindle rotation unless you also cancel the spindle command—your shop checklist will tell you whether to run the spindle or not during this phase. Keep Single-Block on for the first dry-run pass.

Step 5 — Air-Cut at 25% Feed

Remove the workpiece (or confirm it is absent). Turn off Dry Run, return FOV to 25%, and run the program in memory mode (not single-block if you are confident in the geometry, or keep it on for additional caution). The tool cuts air following the exact programmed path at 25% of the programmed feed rate. Watch the tool-path display, listen for unexpected sounds, and watch the spindle load meter. The load meter should read near zero in an air-cut because there is no material resistance. Any unexpected spike means investigate before adding stock.

Step 6 — Incrementing to Full Feed Rate

After a clean air-cut, the instructor approves advancing to stock. Increment FOV in 25% steps—25%, 50%, 75%, 100%—pausing at each increment to observe the spindle load meter and listen to the cut. Record each reading in your prove-out log. Compare the observed spindle load to the estimated cutting power you calculated during programming. Large discrepancies suggest a tool-engagement problem or an incorrect offset.

Alarm Codes

If the Haas control displays an alarm, press RESET, read the alarm number and message on the screen, and record both on your log sheet. Look up the alarm in Section of the Haas Operator Manual covering alarms. Common prove-out alarms include axis travel limits (verify work-coordinate origin) and tool-length errors (re-measure and re-enter the offset). Do not restart the program until the root cause is corrected and documented.

Key terms9

Lockout/Tagout (LOTO)An OSHA-required procedure for isolating all hazardous energy sources on a machine—electrical, hydraulic, pneumatic—applying personal locks and tags, and verifying zero energy before any setup or maintenance work inside the machine.
Single-Block ModeA Haas control mode (SINGL BLK) in which the machine executes one line of G-code per press of CYCLE START, allowing the operator to inspect each move before it occurs.
Feed-Rate Override (FOV)A knob on the Haas operator panel that scales the programmed feed rate from 0% to 200%, giving the operator real-time control over how fast the cutting tool advances into the work.
Dry RunA Haas control mode that replaces all programmed feed rates with a single operator-selected rate, used to verify tool-path geometry at a convenient speed without cutting forces from the programmed F words.
Air-CutA prove-out pass in which the program runs at a reduced feed-rate override with no workpiece in the fixture, so the tool follows the exact programmed path through air, confirming clearances and motion before stock is engaged.
Spindle Load MeterA real-time display on the Haas control showing the percentage of rated spindle power being consumed; used during prove-out to detect unexpected cutting forces, tool problems, or offset errors.
Work Coordinate System (WCS)The coordinate origin set by the operator (typically G54–G59 on a Haas) that tells the control where the programmed zero point is located on the actual workpiece or fixture.
Rapid OverrideA separate override knob or setting on the Haas control that scales rapid traverse (G00) speed independently of the feed-rate override, allowing safe slow-motion verification of rapid moves during prove-out.
Alarm CodeA numbered error message displayed by the Haas control when it detects a fault—such as an axis travel limit, spindle overload, or program error—that stops machine motion and must be diagnosed and documented before restarting.

Worked examples4

1. Your student program contains the line `G01 X3.500 Y1.250 F12.0`. You are running the air-cut with FOV set to 25%. What actual feed rate will the machine execute?
  1. Identify the programmed feed rate from the F word: F12.0 = 12.0 in/min.
  2. Identify the override percentage: FOV = 25% = 0.25.
  3. Multiply: Actual feed rate = 12.0 × 0.25 = 3.0 in/min.
Answer: The machine will feed at 3.0 in/min during the air-cut.
2. After a clean air-cut you increment FOV in 25% steps through your first actual cut. At 75% FOV the spindle load meter reads 48%. The program's F word is 10.0 in/min. What actual feed rate is running, and if the load at 100% FOV scales roughly linearly, what load would you expect at full feed?
  1. Actual feed rate at 75% FOV: 10.0 × 0.75 = 7.5 in/min.
  2. Spindle load scales approximately with material removal rate (MRR), which is proportional to feed rate under constant depth and width of cut.
  3. Estimated load at 100% FOV: 48% × (100 / 75) = 48% × 1.333 = 64%.
  4. 64% is well below the 100% alarm threshold, so advancing to 100% FOV is reasonable.
Answer: At 75% FOV the machine feeds at 7.5 in/min with a 48% spindle load. At 100% FOV the expected spindle load is approximately 64%, which is within normal operating range.
3. During single-block prove-out you press CYCLE START and the Haas executes a G00 rapid move to Z0.100 above the part. The next block is `G01 Z-0.500 F8.0`. Your FOV is at 0%. What happens when you press CYCLE START for that next block, and why?
  1. G01 is a linear feed move governed by the programmed F word and the feed-rate override.
  2. FOV is at 0%, which scales the feed rate to 8.0 × 0.00 = 0.0 in/min.
  3. With a commanded feed rate of zero, the axis motion is suppressed; the control will hold at the current position.
  4. Single-Block mode also means only this one block would attempt to execute before the control stops again.
  5. Result: pressing CYCLE START will not move the Z axis because FOV at 0% prevents feed motion.
Answer: The Z axis will not move. FOV at 0% suppresses all feed motion, so the G01 block executes with zero axis travel. This is the intended safety behavior during the first single-block pass.
4. Your program calls tool T3 with a tool-length offset stored in register H3. You accidentally entered the offset as +2.3450 instead of -2.3450. The part zero is on the top face of the stock. During the air-cut at Z0.500 above the part, where will the tool tip actually be relative to part zero?
  1. The control applies the tool-length offset to position the tool tip at the commanded Z coordinate.
  2. With the correct offset of -2.3450, the control shifts the tool tip down by 2.3450 in to place the tip at the programmed Z.
  3. With the wrong offset of +2.3450, the control shifts the tool tip up by 2.3450 in instead of down.
  4. The error between correct and incorrect offset = 2.3450 - (-2.3450) = 4.6900 in.
  5. At a commanded Z of +0.500 (0.500 in above part zero), the tool tip will actually be 0.500 + 4.690 = 5.190 in above the part surface rather than 0.500 in above it.
  6. This means the air-cut will show the tool far above the expected position—the spindle load meter will read zero, which is correct for an air-cut, but the tool path display and visual observation will show the tool is not where it should be.
Answer: With the sign reversed on H3, the tool tip will be approximately 5.190 in above part zero when commanded to Z0.500. The air-cut will still look safe (no crash), but the tool is nowhere near the workpiece surface. Correcting the offset sign is required before engaging stock.

The math in this lesson2

Learners find tool tip error from a tool-length offset entered with the wrong sign.
7.NS.17.RP.3
Brush up in the math halls at newSchoolWorks.com:
In class: Complete a lockout/tagout demonstration on the Haas VF-2: isolate hydraulic and electrical energy, apply personal lock, verify zero energy with approved test method, then restore under instructor supervision before operating the machine—documented on a LOTO checklist. · Load a pre-written student program into the Haas control via USB; run a full prove-out sequence using the shop's posted prove-out checklist (single-block on, FOV at 0%, dry run on, confirm all rapids clear fixtures, then air-cut at 25% feed); stop at any alarm and document the alarm code and corrective action. · After a successful air-cut, increment feed-rate override to 100% in supervised increments of 25%, noting spindle load meter readings and comparing them to the calculated cutting power; record findings in a prove-out log sheet.
Materials: Haas VF-2 CNC mill; pre-written student program (verified in simulation); LOTO kit (personal lock, hasp, tag, energy-isolation checklist); shop prove-out checklist; prove-out log sheet; Haas operator manual Section on Program Operation
Check: Instructor observes and signs LOTO checklist confirming all six energy-isolation steps completed correctly; prove-out log must document every step in sequence; any safety deviation = immediate stop and retest. 100% compliance required—no partial pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Workplace Safety and LOTO
1. During LOTO on the Haas VF-2, after you turn the main disconnect to OFF and apply your lock, what must you do before reaching inside the work envelope?
CNC Machine Operation
2. What is the primary purpose of running a CNC program in Single-Block mode during prove-out?
CNC Machine Operation
3. You set the feed-rate override (FOV) to 0% before pressing CYCLE START on a G01 move. What will happen?
CNC Machine Operation
4. During a prove-out air-cut with no workpiece in the fixture, the spindle load meter shows a 35% reading. What does this most likely indicate?
CNC Troubleshooting
5. A machinist loads a program and the Haas control displays a travel-limit alarm before any cutting takes place. What is the correct immediate action?
CNC Machine Operation
6. Which prove-out step should always be completed before incrementing the feed-rate override above 0% to engage actual stock?
G-Code Programming and Math
7. A student's program line reads `G01 Z-0.750 F15.0`. FOV is set to 50%. What actual feed rate will the control command?
Workplace Safety and LOTO
8. When multiple students are working on the same machine during a setup exercise, which LOTO practice is required so that no individual can accidentally restore energy while another person is inside the work envelope?
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