Stepper calibration questions

Hey, all. I've been continually tweaking and using my Ox derivative "Cebu" All has been working well, for the most part, especially since replacing the Z axis with C-Beam.

The problem is this - recently I tried to cut something that required a fairly close precision (cutting a row of .5" diameter holes .8475" deep in 1" thick padauk) and discovered that my machine was not tuned properly. Circles weren't round, and the diameter was too small by several hundredths of an inch.

So, I tightened belts (one of the y axis belts was not tight), squared things, etc. and cuts got better, but still off. Circles were now circular, but the size was too small.

I did some stepper tuning by measuring actual distance traveled vs. input, and wound up with $100=26.990 and $101=26.967. (grbl, of course!).

I set up a test cut pattern with a .5" circle profile, .5" circle pocket, 1" square profile, 1" square pocket, triangle, 1" circle profile, and 1" circle pocket.

When I run this in red oak, .25" deep, .125" per pass, with .25" 3-flute upcut mill, the pockets come out sized correctly, but the profiles are too small. Instead of 1" square or 1" diameter circle, they come out at about .982 or so.

Am I missing something here? Is this just due to the nature of the wood being cut, and I need to figure out some kind of compensation based on material?

Hmm, just went through the CAM setup, and realized the pockets are climb cut, and profiles are conventional. Should that make a large difference?

Appreciate any input!

-- John

 

tl;dr - Outside cuts (profile) are wrong dimensions, inside cuts (pocket) are correct size.

Let me clarify - the pockets are always the right depth (.25") and the X/Y dimensions are correct. It is the profile cuts that have the wrong X/Y dimensions. If cutter diameter was off, I would expect X/Y to be off for both pocket and profile cuts. I will measure and make sure it is correct.

-- John