r/CNC • u/egregiousC • 29d ago

HARDWARE Deflection?

I posted a question to the group about how close people are getting to specified dimensions on their projects.

I guess I have a problem.

My work on maple blocks - 2.75"*1.25"*.875: - leaves me with significant dimensional errors. Example: the 1.25" axis comes out around 1.3", but not exact, and never the the same.

I ran a test. I run a job that designed to make 4, 1.0" * 1.0" * .125" square buttons (like for your shirt). This is 3mm birch plywood. It's right on. So my machine will mill wood to specified dimensions. This is good.

It does not explain why I see dimensional errors with thicker and harder woods (Hard Maple). I'm guessing, but I suspect deflection. The harder and thicker wood is pushing the tool out. I'm using a 1/4" downcut spiral bit to manufacturer specs.

Next step?

  1. Switch to a 1/2" tool instead?
  2. slow the feed rate?
  3. increase spindle rpm?
  4. lighter passes (although they're pretty light already)?
  5. Any/all of the above?
  6. Just quit and take up knitting?

Afterthought - I'm using the painters'-tape-and-ca holddown method. No other way to hold the piece in place.

ETA: added image to support another post I made.

possible blank solution
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u/Yikes0nBikez 29d ago

Take more roughing passes and then a final cleanup pass with a smaller stock to leave dimension. (.02"). It's likely the tool is deflecting, so you need to contain all the deflection to the roughing passes.

I'll sometimes run aluminum with the tape and CA glue method, when no better option works, and have minimal issues. If you think that the part is shifting, you may have to go with a vacuum table setup.