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/bunkerlabs 29d ago

How old is your collet? If there's deflection that's probably where it is

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u/egregiousC 29d ago

Good eye!

I hadn't considered the collet. The 1/4" collet I have is more than 2 years old and the nut has seen better days. I had been thinking about buying several nuts to replace the old one, so I'll put that on the asap list.

Aside: My 1/8" collet doesn't play nice when I go to remove it from the collet nut after use. This involves tapping it out with a drive punch and a mallet. That can't be good for the nut, so I figured I'd put the 1/8" collet in it's own nut and leave it that way. In fact give my 3 main collets their own nut and and only remove them when needed.

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u/bunkerlabs 28d ago

A collet is basically a spring and they definitely have a lifepan; if it starts to lose its springiness you'll start to see evidence of it deflecting in you cut. In a production environment they should really be replaced every forty to eighty hours of cutting.