Printing a 15mm STL file - part 1

 

Prepping a File

As I mentioned in a previous post I purchased a STL file for the Hotchkiss Geschutzwagen 39H a while ago, this being one of the vehicles used by 21st Panzer Division in Normandy. This conversion of the  French Hotchkiss H39 saw the turret removed and replaced with an open-topped armored superstructure that could house either a 7.5cm PaK, or 10.5cm artillery piece.

• 7.5 cm PaK40(Sf) auf Geschützwagen 39H(f): A tank destroyer version (Marder I).
• 10.5 cm leFH 18(Sf) auf Geschützwagen 39H(f): A self-propelled artillery version.

I paid $5.50 for the file which when opened in the slicer ( I use BambuStudio) provides the following models. These are already scaled for 1:100 (15mm) so no rescaling is required.

 

In order to optimise the print quality I try to avoid printing a vehicle in one piece and look to find ways of cutting the file to allow it to be broken into sperate parts that can be best aligned on the print bed to reduce the amount of supports required and so improve print quality. The slicer software includes a "cut" feature which allows a cut to be made across a model, but with the cut surfaces being repaired so they remain solid. This is a very powerful feature, but while a cut can be angled in all three axis, it will always be across all of the model captured by the cutting too.

This cut produces these two parts 

Using this feature I try and cut out the tracks so I can rotate them through 90° and lay them on their side. This removes the need to support the upper track element. With this model the guns are already provided as separate files and so I have broken this model down to the two track halves and the two hull elements 

I have rotated the lower hull part through 90° to ensure a flat surface on the print bed. I will now print the parts in separate batches so if any print fails for any reason it only affects one or two parts.

Printing the file

Generally if the first layer of a print goes down without issue there is a good chance the rest of the print will complete without issue. I therefore try and keep an eye on the printer for the first couple of layers. If I see any issues I will often cancel the print and try again so as to ensure the best quality print I can achieve. (I am no expert at this and there are likely a great many other tricks and tips that can be used to improve print quality - but this time last year I knew nothing about any of this).

For all my vehicle printing I use a 0.02mm nozzle, which is the finest offered for the printer. This allows for a line of molten filament to be laid down on the print bed which is 0.22mm wide and 0.06mm high which seems to be about the limit for problem free printing. Print time for this model broke down into four elements, the gun, lower and upper hulls and the pair of tracks is about 4 hours. Using a larger print height you can reduce the time, but often with a reduction in quality. 

I'll be back for part 2 once the printer has stopped whirring.