Tuesday 16 November 2021

Printing Issues (again)


I'm using this model, a 1:100 scale Artilleriewagen, to try to iron out some issues I've been getting with my resin prints.

You can see some diagonal lines running across the turret where something has shifted during printing — I don't know yet what caused that, and some research is in order.

It has happened at least twice, and as a result the profile of the turret has been distorted. Not enough to make it unusable; I've had worse misalignments in cast components from commercial manufacturers, but it's annoying.

It may just be that the various bolts and screws on the platen and rail need tightening, and that's always a good first step. Or it may be that the FEP is getting a bit flaccid.

More successful is the rigidifying of the box-like body of the model.

I like to hollow the models for printing, partly because it means they use up less resin, but mostly because having less contact area on the FEP at any given level makes a suction-created print failure less likely.

Having as much as possible of the non-visible bottom surface cut away gives me maximal access to the interior for washing away uncured resin, which means less chance of warping and cracking problems later. It also gives more access to the innards for the UV curing lights.

However, especially on a boxy model like this, thin walls means a less rigid and strong model. I could keep the walls thicker, but in this instance I've also added some internal bulkheads which provide a great deal of strength to the whole thing, as well as supporting the tabs on which the wheels are set. These bulkheads are 2mm thick, and I could probably halve that in safety.

Something that I find a bit annoying is that because 3d printing takes so long, every time I change a variable to test what's going wrong, it takes another few hours before I can see the results of my change. Hey-ho, I'll just have to learn to reign in my impatience.

Thursday 11 November 2021

BP-44 Armoured Locomotive


The BP-44 was a WWII German armoured locomotive, used to propel mixed AA, anti-tank, artillery and infantry transport trains.

Germany didn't use armoured trains as much as others, such as the Soviet Union, but they did have some. Generally speaking, armoured trains tended to fall out of favour over the course of the war as road or tracked vehicles were more flexible and became ever more potent, and railway tracks were very vulnerable to sabotage and aerial attack.

This is a 1:100 scale model for 15mm gaming. It was designed by a chap called Tolawdjk, and came from Thingiverse.

I hollowed the model in Chitubox to 1mm walls, and it printed fine. However, it does flex very easily under finger pressure, having such large flat panels (curved surfaces being self-reinforcing) and it could probably do with some internal support structures. I've read that Chitubox can create infill structures that don't impede resin escape, but I can't figure out how to do that (I'm using the free version). I think probably the easiest option for me would be to save the hollowed model from Chitubox as STL, import it into Blender to add the support struts and/or bulkheads, cut a great big hole in the floor, and re-export it to STL.

And if you want to field a BP44 armoured train on your wargames table, but you can't be faffed actually modelling one, then you could just grab a bunch of clump foliage flock and dump it along the railway track :)

This was Pz75, surrendered to the Americans at Hagenow in May 1945.

Process Notes