Safety in CAM: Simulation, Dry-Run Protocol, and OSHA Considerations

Objective. Students will explain the mandatory simulation and dry-run steps required before cutting, identify the PPE required during dry-run and live-run stages, and demonstrate Mastercam Verify as the first line of collision prevention.

Why Simulation and Dry-Run Both Matter

Mastercam Verify lets you watch a digital tool cut a digital workpiece before a single chip falls on the shop floor. It catches tool-path errors, incorrect depth settings, and obvious collisions in the safe environment of your screen. That makes it the first line of collision prevention in any CNC workflow. However, Verify cannot replicate every real-world variable: machine backlash, workholding flex, fixture interference, or an operator who forgot to update a tool-length offset. That is why industry and best practice require a physical dry run on the machine after simulation — and why you must understand both steps before you ever press Cycle Start on a live cut.

The Simulation-to-Dry-Run-to-Live-Run Protocol

Follow these eight steps in order every time you move a job from CAM to the machine:

1. Complete CAM programming. Toolpaths are fully defined, feeds and speeds entered, and post-processor selected for the target control (e.g., Haas).

2. Run Mastercam Verify. Animate the entire operation. Confirm the stock is fully machined to design intent, no tool gouges the part or fixture, and no rapid motion plows through the workpiece.

3. Inspect the NC file. Open the posted G-code in a text editor or the machine's editor. Confirm the correct program number, tool-change sequence, and that no obviously wrong coordinates (e.g., Z+10 when you mean Z−10) appear.

4. Set up the machine. Mount and torque the workholding, load and measure all tools, enter tool-length and diameter offsets, and set the work coordinate system (WCS) origin.

5. Perform a dry run — air cut at reduced feed, no coolant, guards closed. Set feed-rate override to a low percentage (commonly 25–50 % of programmed feed). Let the spindle run at programmed speed or reduce it. Watch the entire program execute with the tool above or away from the stock so you can verify motion sequence and clearance.

6. Perform a first-piece run at reduced feed with coolant. Feed-rate override remains reduced. Stop after the first operation to measure the workpiece against the drawing.

7. Adjust offsets as needed and confirm dimensions. Bring feed rate to 100 % only after the part meets print.

8. Document and sign off. Complete the pre-run safety checklist, record offset values, and note any deviations.

Never skip or swap these steps. Verify cannot substitute for a physical dry run, and a dry run cannot substitute for proper simulation — each catches different classes of error.

PPE Requirements During Dry Run and Live Run

The hazards present during a dry run are nearly identical to those during a live cut: rotating spindle, possible unexpected axis motion, and sharp tooling. Required PPE does not decrease just because you are not cutting metal yet.

Safety glasses or face shield — required any time the spindle turns or axes move. Flying chips, coolant mist, and debris are present during live cuts; broken tooling or a dropped insert can occur even without stock.
Hearing protection — required when noise levels exceed OSHA action levels. High-speed spindles and coolant pumps can reach those levels even during air cuts.
Closed-toe, leather or equivalent footwear — required at all times in the machining area.
No loose clothing, dangling jewelry, or unsecured hair — entanglement hazards around rotating spindles apply equally during dry run and live run.
Cut-resistant gloves — worn during workholding setup and when handling sharp stock or tooling, but removed before operating controls or reaching near moving machinery.

OSHA Machine Guarding Requirements and the Dry Run

OSHA General Industry standards on machine guarding require that hazardous points of operation be guarded so that no part of a worker's body can enter the danger zone while the machine is in motion. For CNC mills this means the enclosure doors must normally be closed and interlocked during spindle rotation or axis movement.

When an operator must observe motion with guards open — for setup, probing, or certain dry-run observation tasks — the machine must be operated in a reduced-speed or single-block mode using an enabling device (sometimes called a three-position enabling switch or deadman switch). The enabling device is held in the mid-position to allow motion; releasing or gripping it fully stops the machine. This requirement reflects the principle that open-guard operation is only permissible at speeds low enough that the operator can react and stop motion before injury occurs. Identify at least two applicable OSHA machine guarding requirements and record them in your lab log as required by this lesson.

Key rule: guards open + full spindle speed = prohibited. If you must see the cut in progress, use the machine's window, camera system, or reduced-speed enabling-device mode per the Haas operator manual procedure.

Mastercam Verify: First Line of Collision Prevention

Verify (accessible from the Toolpaths menu or the Verify toolbar) renders the stock as a solid body and removes material in real time as the simulated tool moves. You can pause, rewind, and inspect from any angle. Features that help prevent real collisions include:

Gouge detection — highlights where the tool would cut below the programmed surface.
Collision detection — flags contact between the tool holder, arbor, or collet and the workpiece or fixture when holder geometry is defined.
Stock comparison — overlays the finished part model on the machined stock so you can see excess or missing material.

Verify requires that you have correctly defined holder geometry and fixture models for collision detection to be meaningful. A simulation that uses a generic holder may miss a real holder-to-fixture collision on the machine.

Pre-Run Safety Checklist Summary

Before pressing Cycle Start for any dry run or live run, confirm and document:

Correct program number loaded on the control
Feed-hold and emergency-stop buttons located and tested
Workholding torqued to specification
No personnel inside the machine envelope
All tool offsets entered and verified
Guards in proper position or enabling device in use
PPE donned by all personnel in the area

Sign and date the checklist. This document is your record that the safety protocol was followed and is required for the competency check in this course.

Key terms10

Mastercam VerifyA simulation tool within Mastercam that animates toolpath motion against a digital stock model to detect gouges, collisions, and incomplete material removal before any physical cutting takes place.

Dry RunA physical test of a CNC program on the actual machine with the tool positioned to cut air (away from or above the stock), run at reduced feed-rate override, and without coolant, to verify program motion before cutting real material.

Feed-Rate OverrideA control knob or setting on a CNC machine that adjusts the programmed feed rate by a percentage, allowing the operator to slow axis motion during setup, dry run, or first-piece cuts.

Enabling DeviceA three-position switch (deadman switch) required when operating a CNC machine with guards open; held in the mid-position to allow reduced-speed motion and released or fully gripped to stop the machine immediately.

Machine GuardingPhysical barriers and interlocks required by OSHA General Industry standards to prevent operator contact with hazardous points of operation such as rotating spindles and moving axes.

Gouge DetectionA Mastercam Verify feature that highlights locations where the simulated tool would cut deeper than the programmed surface, indicating a toolpath error that must be corrected before machining.

Work Coordinate System (WCS)The programmable zero-point origin set on the CNC control that relates G-code coordinates to a specific location on the workpiece or fixture, established before any dry run or live run.

Pre-Run Safety ChecklistA signed, dated document confirming that all required safety verification steps — program number, emergency-stop access, workholding torque, personnel clearance, and PPE — have been completed before Cycle Start.

Collision DetectionA Verify feature that flags contact between the tool holder, collet, or arbor and the workpiece or fixture during simulation, requiring accurate holder geometry to be defined for meaningful results.

Single-Block ModeA CNC control mode that executes one block of G-code at a time each time the Cycle Start button is pressed, allowing step-by-step verification of program motion during setup or dry run.

In class: Instructor-led discussion of the simulation-to-dry-run-to-live-run protocol used in industry, emphasizing that Mastercam Verify does not replace machine dry-run at reduced feed and without coolant; students write the protocol steps in their own words and submit · Students review an OSHA General Industry standard excerpt on machine guarding and identify which machine guarding requirements apply to CNC mills during a dry run with guards open (e.g., enabling device / decreased speed requirements), recording findings in lab log · Students role-play a pre-run safety checklist for a simulated Haas mill dry run: verify program number, confirm feed-hold and emergency-stop reachable, check workholding torque, confirm no personnel in machine envelope, then sign and date the checklist
Materials: OSHA General Industry standards (relevant machine guarding sections), Haas Mill operator safety manual, printed pre-run safety checklist, Mastercam Verify (demo), lab computers
Check: Written protocol and signed safety checklist reviewed; pass = all eight simulation-to-dry-run protocol steps correct and in order, at least two applicable OSHA machine guarding requirements cited accurately, checklist signed with all fields complete

Practice check8

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