Marking Tool for Centerline on Square Tube (50 mm Radius)

This is a marking tool I designed for a project where I needed to scribe a line precisely down the center of a square tube with a 50 inch radius. It also works well with flat or straight edges. The tool is designed to hold a standard #2 pencil for easy, consistent marking.

Parts List:

• 1x Base
• 1x Scribe Arm
• 2x Threaded Knobs (thd-knob)
• 3x M4 Flat Washers
• 3x M4 x 20 mm Screws
• 1x M4 x 25 mm Flat Head Screw
• 5x M4 Heat-Set Threaded Inserts

Pencil Compatibility:

• Designed for: Standard #2 pencil (hexagonal or round barrel)

Printing Instructions:

• Material: PLA
• Nozzle Diameter: 0.4 mm
• Layer Height: 0.2 mm recommended

Assembly Notes:

• Threaded Inserts:
  Heat-set threaded inserts should be installed from the sides indicated in the assembly drawing. Ensure they are fully seated and aligned.
• Thumb Screw Assembly:
  The thumb screw is assembled by screwing one M4 x 20 mm screw into one of the thd-knob parts and tightening it snugly.
• Center Screw (Base to Scribe Arm):
  The center hole in the base is tapped for an M4 thread. Insert the M4 x 25 mm FHSCS from the bottom and tighten it snugly. This secures the screw in place and enables simpler adjustment of the scribe arm.
• Bearings:
  Two bearings are used on each arm to ensure the tool rides smoothly past the radiused corners of the square tubing. This improves consistency and stability during marking.