DMS CNC Router Class
Lesson 4: Workholding and Offsets
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Introduction: Workholding and Offsets

It's important to determine workholding before CAM programming.

Workholding Options

The bed of the DMS is a thick acrylic sheet. It is drilled in a 6" hole pattern, with 3/8"-16 threaded brass inserts in each hole.

  • Over-tightening a fastener can pull the insert out of the table.

Spoiler Board & Clamps

  1. Clamp a spoiler board to the table.
  2. Screw your material to the spoiler board. Use a minimum of 4 screws, and more for large projects.

Make sure that the tool will not collide with a clamp or screw.

  • Brass screws will not damage the tooling in the case of a collision.

Threaded Inserts & Step Clamps

  1. Hold the work with a step clamp.
    • The clamp should be level.
  2. Support the end of the clamp with a step block.
  3. Insert a threaded stud through the clamp into the table insert.
  4. Tighten a nut on top of the clamp.
    • Use a minimum of 4 clamps, and more for large projects.

Make sure that the tool will not collide with a clamp.

Double Sided Tape

  1. Clean the table and material.
    • Tape will not stick to damp or dusty materials or MDF.
  2. Apply tape to your workpiece.
  3. Press firmly to adhere the material to the table.
  4. Test the adhesion before starting to cut your project.

Tape works better on short wide items than tall narrow ones.

Establish Your Work Offset

Set the Work Offset (G54)

You must use the same Work Coordinate System (WCS) you chose in your CAM program.

You have 3 options when setting the Work Offset.

  1. X, Y & Z at the corner
  2. X & Y at the corner, Z in the middle
  3. Air pass
    • X & Y at the corner, very high Z

Move the tool tip to Work Home

  1. Perform a tool change.
    • Choose a drill bit or small diameter tool to make finding your WCS easier and more accurate.
  2. Jog the tool to Work Home.
  3. Press MDI. (F4)
  4. Type G53 & press Cycle Start.

Set X & Y at the corner

  1. Press ESC to go up one level.
  2. Press User. (F5)
  3. Press Load Zero Offsets. (F2)
  4. Press Load G54 Offsets. (F1)
  5. Press Clear All Offsets. (F6)
  6. Press Yes. (F1)
  7. Press Exit. (F7)
  8. Press Load G54. (F1)
  9. Press X & Y. (F1) & (F2)
    1. The status for each axis will change to loaded.
  10. Press Exit three times. (F7)
    1. This will return you to jog mode.

You have set your Work Coordinates for X & Y. Now, you must decide where to set your Z axis.

Set the Z Work Coordinate

Reposition and set Z

The following steps will set Z, and also enable the machine to calculate exactly where the tool tip is located, even when moving the B & C axis.

  1. If needed, jog the machine to where you want to set Z.
  2. Press MDI. (F4)
  3. Type G48S0 (zero, not the letter) & press Cycle Start.
  4. Type G53 & press Cycle Start.
  5. Type D[tool number] & press Cycle Start.
  6. Type G48S1 & press Cycle Start.
  7. Press ESC.
    • You should be at the jog menu.
  8. Press User. (F5)
  9. Press Load Zero Offsets. (F2)
  10. Press Load G54. (F1)
  11. Press Z. (F3)
    • This will set your Z offset.

Confirm that your WCS has been correctly set.

  1. Press Exit (F7) 3 times.
  2. Press MDI. (F4)
  3. Take a photo of the screen.
    • Include the X, Y & Z values.
    • This will allow you to return to Work Home in the case of a problem.
  4. Type G54 & press Cycle Start.
  5. Check values of X, Y & Z.
    • Z should be 0.
    • X & Y will be 0, unless you jogged the machine to set Z.