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The BIG CNC has been retired and replaced with the Forest Scientific CNC Router


Other Reminders


This reminder page is NOT a substitute for being trained on the CNC by a qualified HackPgh member.

This reminder page is NOT a substitute for using your brain and taking appropriate precautions.

ALWAYS closely monitor the CNC while it is operating.

ALWAYS wear SAFETY GLASSES and other appropriate safety gear when operating the CNC.

ALWAYS wear HEARING PROTECTION when operating the CNC.


This set of reminders is organized roughly as a step-by-step in the sequence necessary to actually use the router.

Here are some useful terms to look up. I will add to this list as further terms come to mind, or as people ask questions.

  • Spindle (aka router or dremel)
  • Mill End
    • or Cutting Mill
    • or Cutting Tool
    • or Cutting Head
    • or Dremel Bit
    • or Router bit
  • Bed
  • Spoil Board

Note: The big CNC router is based on the "low rider" design.

CNC Operation Overview

The big CNC takes instructions in GCode.

Create the CNC design in a program like VCarve or Easel (see below).

Export the design to GCode if your software supports that.

Otherwise export to SVG or DXF, and from there use another software tool to convert the SVG or DXF file to GCode.

Use UGS (Universal GCode Sender), running on the MacBook attached to the big CNC, to send the GCode to GRBL, running directly on the big CNC hardware.

GRBL, running on the hardware built into the big CNC, converts the Gcode into CNC motor actions.

To use the big CNC successfully you need to:

  1. create your design appropriately
  2. export your design to GCode
  3. prepare the CNC spoilboard
  4. prepare the work piece on the CNC (secure it with screws)
  5. prepare the spindle (set speed, change router bit)
  6. zero out the spindle in all 3 axes
  7. copy the Gcode to the MacBook
  8. send the Gcode from the MacBook to the big CNC hardware
  9. IMPORTANT: monitor the big CNC while it cuts
  10. clean up the big CNC after you're done

These steps are covered in more detail below.

Big CNC Basics


End stops are on the to do list, but until then there is nothing to stop the CNC spindle from running right off the end of the rails if you tell it to do so. So check your design carefully.

The big CNC has 2 buttons:

  • A red stop button on one end
  • An E-stop on other end

There is a MacBook at end of the CNC that runs the control software, UGS (Universal Gcode Sender).

Get the MacBook's password from somebody trained to use the big CNC.

Start UGS; the icon to run UGS is located on the MacBook GUI's dock, it's a black terminal window icon.

Check the USB cable from the MacBook to the big CNC hardware.

Using the UGS GUI on the MacBook, click in the upper-left corner, 2nd icon, to enable manually moving the spindle.

  • X is length
  • Y is width
  • Z is height

The UGS GUI "Play" button (triangle facing right) sends the GCode to GRBL, which translates the GCode into electrical signals that move the spindle.

The UGS GUI "Pause" buton (two vertical bars) temporarily pauses the spindle motion, for example if you need to clear sawdust away or some other action.

BE CAREFUL when the router is running.

The UGS GUI "stop" button (square) stops the spindle entirely and will result in having to replace the work piece with a fresh piece to start over.

CNC CAD Software

VCarve is highly recommended for creating CNC designs.

HackPgh has a FULL license for VCarve Pro on the desktop machine by the (paper) printer area on the "clean" side o the shop.

HackPgh also has a makerspace site license for VCarve; download the Vcarve Pro trial and install it, then get the makerspace member's license number from the board. This license will enable almost all actions with VCarve Pro, except exporting the design to GCode or other non-proprietary formats. Work on your design on your own installation of VCarve, then use the printer station desktop machine's installation of VCarve to export your design to GCode for running on the CNC.

Another popular app is Easel, it's not as powerful but it's easier to learn, and open source and free.

When creating a design, remember to:

  1. Use a big enough seat to have room for screws.
  2. Remember to include tabs in your design.

Tabs are small gaps in the cuts, usually on the perimeter of the piece being cut, sometimes internally. Tabs provide connections from the piece to the remaining wood. Otherwise the piece being cut out may come loose and cause problems. At a minimum, subsequent cuts may be off. At worst, the router might fling a piece of wood and present a safety hazard.

Preparing For A Cut

Before cutting a design on the big CNC, set up a "spoil board", a sacrificial sheet of wood to protect the CNC bed. Fasten the spoil board down to the bed with 1/4 x 20 Brass Machine Screws at the perimeter. Then attach your project to the auxiliary spoil board.

Note: Members should ONLY use brass screws to anchor things to the auxiliary spoil board. Members should ALWAYS: a) use brass screws and brass screws ONLY b) NEVER use steel screws or anything harder than brass c) use an auxiliary spoilboard. d) use 1/4 x 20 brass machine screws to anchor the auxiliary spoilboard to the main bed. e) use brass screws (with a pilot hole) to anchor the work piece to the auxiliary spoilboard The reason to use brass instead of steel screws is that the brass is soft and the router bit will cut the brass, rather than vice versa. If you break a steel bit off in MDF, we will be unable to resurface the MDF using the fly bit

Running A Cut

IMPORTANT NOTE: NEVER leave the CNC unattended while running.

  1. Change the bit in the cutting head to an appropriate bit.
  2. Zero out the cutting head to the workpiece.
  3. Set the spindle speed manually (on the spindle).
  4. Turn the spindle (router) power button on manually.
  5. Click the UGS GUI Play button to start the cut.

Adjust the spindle speed MANUALLY on the spindle itself, it is not controllable from UGS or GCode.

Remember, you MUST monitor the CNC while it's working.

In the event of an emergency, hit the E-Stop button.

In the event of a non-emergency problem, click the UGS GUI "stop" (square) or "pause" (two vertical bars) buttons.

ALWAYS use the UGS GUI jog buttons to raise the Z axis BEFORE clicking "Return to Zero".

WATCH the rails, brush dust off them before it accumulates enough to interfere with the wheels.

Zeroing Out The Head

"Zeroing out" means picking a corner of the work piece to use as the origin point/starting point.

Use the "jog" (arrow) buttons on the GUI for UGS to zero out cutting the head to the work piece. To enable the jog buttons, click the 2nd icon in the upper-right corner of the UGS GUI.

To zero a specific axis, click on the display of the right, upper corner of that axis value.

Zeroing the Z-Axis (Height)

  1. place a sheet of paper under the cutting head
  2. lower the spindle using the Z axis jog button (on the GUI) until the cutting head touches the work piece
  3. lower the head until you cannot pull the paper out without a little resistance.
  4. but NOT so much that the paper tears
  5. Click "Reset Zero"; DO NOT click "Return to Zero"

Changing the Bit in the Cutting Head

IMPORTANT: ALWAYS turn off power to the spindle before working on the spindle.

  1. Undo the clamps on the gray metal tube.
  2. Hold in the buttons on the black collar on the spindle.
  3. Pull the spindle out.
  4. Use a wrench to loosen the bit.
  5. Insert the new bit.
  6. Use a wrench to tighten the bit.
  7. Reinsert the spindle in the holder.
  8. Make sure the buttons on the black collar click closed.
  9. Re-do the clamps on the gray metal tube.
  10. Turn on power to the spindle.