After filing away more thoroughly the z-seam bulge and a general roughening of the entire surface (fine sandpaper), the surface was painted with a water-based acrylic. The paint was simply brushed-on and left to dry for about 10 or 15 minutes. After the paint was dry (but not hard), rubbed with a cloth/rag to make a smooth surface.
The above image shows the newly manufactured reproduction (top) next to the original ~1905 platen. The repro surface still shows the seam of the printing process, but the surface is smooth and it's less noticeable visually than it was. The thin layer of acrylic should not have any real effect on the resilience of the platen and it does help to even-out the surface. Result of this method is that it looks good and types fine, but it will have to be seen how durable a surface this is. Trial and error :)
Also, an improved replica of the platen knob was made. Because the knob needs to be tightened quite hard on the rod, it really did need a threaded metal insert. In this case, just as in the original, a hex-nut.
For fitting the replica knob on an original platen-rod, a UNF 8-36 nut should be fitted. If making one for a new M4-based platen, there's a model for an M4 nut too. Both versions can be downloaded here.
The 3D model is ideally printed with a small layer-height. For nicest results, of course a small nozzle will create a crisper profile and enable smallest layering.
Enable supports (tree) and set the support theshold to e.g. 20 degrees to avoid annoying supports in the central hole.
To finish the knob, insert a nut and fixate with a small drop of e.g. cyanoacrylate glue on a corner. With a few applications of paint and then light sanding, the surface can be made to imitate the surface of an original. (Pedestal-stand helps with painting.)
A glut of knobs! Of course only one needed per Blick - here on the Blickensderfer 5.
