Just made another top and have got really good holes , best so far. Having tried various approaches before, this time I drilled all the 3mm holes using Parf2, then I routed my microjig slots between the holes and then when it came to drilling the 20mm holes I used a microjig clamp on the drilling guide which prevented any movement or rocking and I could clamp the guide even if it was in the middle of the table, before I only clamped from the edge and found these holes a better fit than the others but now all are the same nice fit.