I have just got a new Creality K1 Max printer to replace my old hand me down Creality CR-10 Smart. I have printer off a small project that has 4 holes in two 15mm x 40mm x 5mm mounting ears for clearance holes for some wood screws.They were drawn in the CAD object as 3.5 mm diameter but when printed were only 3.1 mm diameter.
The holes in the same item printed on my old CR-10 come out spot on 3.5 mm. Other holes of various diameters printed on the CR-10 have also come out right. Both printers have 0.4 mm nozzles, are using the same filament with, as far as I can see the same slicer settings. I am using the Creality slicer V7.1. As I am about to print a number of pieces which will have heat set inserts installed I need the holes to be to close tolerances. As an experiment I printed a test piece with 5 holes of varying diameters, 2.5, 3.1, 4, 5, and 6 mm. measuring them they came out as, 2.1, 2.7, 3.6, 4.7, and 5.8 mm ( the holes were, .4,.4,.4,.3,.2 mm smaller).
I then made another test strip with the diameter of the holes increased by .4 mm for the first 4 and .2 for the 6 mm one. The resulting holes were, 2.6, 3.3, 4.1, 5.0, and 6.0 mm. For ones I design myself I can experiment to find the right size, but for .stl files down loaded from elsewhere that won’t work without a lot of hassle.
Has anyone got any suggestions as to why this new printer is making the holes considerably smaller than designed? The first pic is of the test pieces. The upper one of the nominal size and the lower one is with the dia. increased to bring them up to nominal size. The difference is obvious, especially in the smaller holes.

On a different note, I have been trying to increase the wall thickness of embedded holes without any success. Can anyone tell me if it is possible to increase the thickness of the wall around a hole relative to the rest of the wall thicknesses? I can do it by increasing the number of wall loops form 2 to say 5, but that does it for all of the walls, but that just wastes filament.
Is there any way to do it independently? If I make a nest of cylinders and embed it in a solid, when printed it just reverts to the normal wall thickness, if it stands up separately it is the same thickness of the nest. I am guessing that once it is embedded in the solid it just disappears and becomes part of the solid. The second pic shows three sets of 4 identical nested cylinders, two embedded in the solid the third standing on its own.
Note in the upper example the walls of the two embedded ones have been reduced to the thickness of the external walls, while the stand alone one retains its full thickness. In the lower example I have increased the wall loops from 2 to 5, now the walls around the holes are thicker but so are all the walls.

The reason I want to do it is two fold, I want to tap a hole with a 16TPI thread and the thickness of two wall loops is less than the thread depth, also the wall thickness is insufficient for the larger heat set inserts.

John