Gantry height for Printrbot 1405?

[tabicat]

I'm trying to configure Cura for a Printrbot 1405, and one of the things it asks me is the gantry height. I've read a few web pages on the topic, but I still don't understand it. How do I measure the gantry height on a 1405?

[RetireeJay]

The safest answer would be zero.

This would only come into play if you were printing more than one object on the bed, finishing one object before moving on to the next object, so for most people most of the time it doesn't matter because the most common practice is to print all the objects on the bed simultaneously.

[tabicat]

Wouldn't printing one at a time produce better prints? Having the head travel back-and-forth between two objects slows down prints significantly and spews lots of strands in between the objects.

[RetireeJay]

It depends on the object. Having two objects on the bed is actually a recommended practice when one object is tall but very small, so that it can cool down between layers and avoid getting mushed out of shape. Think of the smokestack on Benchy. This is actually a feature built into some slicers (building a sacrificial column so that the desired print comes out right). Although just slowing the print speed down seems to work fine, not needing to use the sacrificial column.

Yes, when the nozzle moves between objects it does tend to leave threads. Having it execute non-printing moves as quickly as possible reduces the threading somewhat, and also keeps the chamber nearly full of molten plastic for when it starts the next extruding move.

Most Printrbots have fairly large structures surrounding the nozzle (fan shroud, Probe, and extruder support). These are just two or three mm higher than the nozzle, so the space available on the bed to print a new object if there is a competing object already on the bed is quite limited; you'd have to keep that entire structure away from Object 1 while printing Object 2. I suppose on my Plus I might just barely be able to squeeze four objects onto the bed for that kind of serial printing. If I did that, the gantry height (the height of my X-axis rails and support) would be 7mm. But I'd much rather just print one object at a time and take it off the bed before printing the next (or print all the objects simultaneously, cleaning up the threads afterward). That way, if a print messes up (like becoming detached from the bed) it only messes up one print, not several.