Re: Helical milling drill holes with endmill #pcbgcode #drill #helical

John Johnson

I'd forgotten how tedious and terrible development is without a debugger and the ability to step through code and inspect variables 🙁

On 8/10/22 2:45 PM, John Johnson wrote:

Hello Folks,

I've been thinking about and working on the long-requested (ca. 2018) feature that would let one mill holes of different diameters using an endmill.

I would like your input.

  • Is this useful?
  • Do let me know if you have suggestions on gcode. My knowledge on this is limited. I would like to support as many controllers as possible (TurboCNC (happy to see TCNC is still around!), Mach3, grbl, LinuxCNC, etc.), so make it as generic as possible.
    • I'm thinking G03 (counter clockwise) for all holes.
    • From what I've read, using IJ is preferable over R, and I recall from my experience R arcs can get whacky.
    • I'm thinking 4x 90° arcs to make a circle. Again, to accommodate as many controllers as possible.
  • I'm concerned about holes that are larger than 2x the tool diameter.
    • For example, in the image attached, the tool is 0.015"/0.381mm and the holes are 0.020"/0.508mm, 0.035"/0.889mm, and 0.050"/1.27mm. There is a 0.005"/0.127mm post in the center hole, and 0.020"/0.508mm on the right-hand hole.
      • The debris left in the center (see attached pics), which could potentially become ensnared by and break the tool.
    • One way to eliminate this is as two (or more) holes, a smaller one to full depth, then larger ones.
      • This would probably need "pecking."
    • I could also use a sort-of center-out strategy, where the cutter starts in the center, then mills at increasingly larger diameters until the desired size is reached. Rather than the helical path shown, I would probably just plunge some amount in the center, then start milling the concentric circles at that depth out to the max diameter, plunge at the center a bit deeper, rinse and repeat.
  • How do we control chip load?
    • Step down for Z axis as an absolute amount (e.g. 0.25mm/0.010") per pass?
      • Sounds reasonable.
    • What about increasing the diameter if concentric holes or multiple passes are used?
      • Could be a fixed maximum, I suppose, or some percentage of the tool diameter.
  • Code that generated the images is attached.
    • Let me know what you think about it too. I just generated it in Excel for the time being.

Would appreciate your input and expertise!



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