Pro 5 Pockets too large, slots too small

Just starting to learn how to use my machine (SO5) and figured a simple box was a good place to start, but I can’t get a tight fit between parts - every lid is too small and pocket too large (like 0.3mm deviation per part). It feels like I’m missing something simple or fundamentally misunderstanding what’s happening so looking for any thoughts before I start designing parts with windage. I didn’t expect a perfect fit, honestly expected they wouldn’t go together at all, but is this normal deviation in wood?

I designed up a dummy part to be cut as one job then separate the halves to make sure I wasn’t introducing any funny business between jobs, but still things are off. Other things I’ve tried:

  • Swapping cutters (using cutters from Carbide 3D, so I shouldn’t have goofed on the cutter diameter, especially in Carbide Create)
  • Using two types of cutters (201 vs 251)
  • confirmed cutter diameter
  • Changing from Carbide Create to F360
  • Changed stock material from Maple to plywood
  • Switch from Imperial to Metric units
  • Checked every fastener I can find

I’m scratching my head - the parts are measuring the wrong way for play in the router

Here’s the part designed and processed in metric in F360 with no sanding on the face, just knocked off fuzz on the long edges. Don’t mind the measurements too much since this is pretty soft material for calipers, mostly just trying to help visualize the problem.

Good news is it was super easy to get everything assembled and running!

Seems almost as though the cutter is removing more material than it should. Could be a symptom of runout. I would check for runout and see if it can be adjusted as shown by NYC CNC:

Also make sure you are using the precision collets that should have been in one of the setup boxes and not what came in the router box (if any was present).


Not necessarily. If you are conventional cutting, the force of the cutter if there is slop, runout will pull the cutter into the material, taking off too much. Try a test with climb cutting & see how it measures.
It looks like you are getting very close to the same deviation in both directions, so your calibration is likely pretty good.

Just a question, I am assuming you are looking for a tighter fit between the cutout and what was cut? Why a 1/4" bit? Why not use a 3/16 or 1/8? Are you doing a contour cut with no inset, inner or outer? What measurement is right for what you set to cut?

Yup, swapped collets and this is what I get!


Good food for thought - it’ll take me some time to remember about forces from the cutting edge

You have to rough out and leave stock for a light finish pass.

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