Gotcha! Thank you, that did the trick.

Thanks all for the comments here, very happy that many are enjoying my design :D To Tafelspitz: When I mounted the knob I found that the casing (transparent that will light up in blue when on) for the knob has a small hole on its backside inside the Ultimaker (in front of the print bed). You need to rise the print bed to and through that hole I could fit for example a smaller screwdriver and push the knob out, no damage done.

Thank you for this, I just printed it successfully. Could anybody please tell me how to get the "old" knob off the machine without breaking anything?

Thank you for this model Viktor. This jog shuttle dial is nice to use and much easier than the silly flat knob used on the Ultimaker 2+. A suggestion to people wanting to print this: first check the diameter of the knob shaft on the printer (when you remove the existing knob). Potentiometer shaft diameters vary with supplier. I looked through my electronics part box and found there was a wide variation. The dial knob I printed was way too loose. I finally fixed it by using a sleeve of heatshrink tubing over the pot shaft and reaming out a shallow funnel shape at the opening of the knob shaft hole with a scalpel. After a tiny squirt of silicone I gently pushed the new dial knob onto the shaft. Perfect fit with no wobble or mushiness.