Printing - lines are invisibly thin

I tried to print to a laser printer on a letter size paper.
My drawing looks fine in the Print Preview, and I have set the B/W mode on.

However, the printout results in all lines (and dimensions) that are not explicitly set to a wider width rendering as so thin as to be invisible.  

I think modern printers are something like 1200dpi, so it may be trying to render the default line as 1/1200", which is not visible.

Is there any setting to improve printing of default-width lines?

There is no extra setting to improve the printing of default-width lines. The default width is 0.00mm.
You have to take care of setting a proper line width when drawing, or change it afterwards via properties, or attributes, or layer attributes. Out of the box the line width is "By Layer", and in the layer attributes it is 0.00 mm.
This constantly produces troubles for newbies. Some while ago I already have suggested to change the default width to practical 0.25mm out of the box, but there seems to be some hesitation to do so, probably to stay with AutoCAD conventions. But I don't have access to AutoCAD, so I don't really know how they do it.

Thanks!

I started looking for a way to select by attribute.  Is there a way to select all lines with a width of 0.0mm?  
I didn't want to select all (by dragging around the whole drawing), because I had already changed some lines to a custom width.

I tried searching for that concept in the new manual, but of course I don't know the terminology, so I don't know what to search for.

Also, where do I set the default line width in the default layer for future drawings? I don't see that under Options / Application Preferences
( I did find and set dimension width under Current Drawing Preferences, and I found the Layer Attributes which set it for this drawing. )

There is no selective filter option. More advanced commercial cad programs do have this, I know. Maybe in a couple of years...
If you have already changed the width of some lines, you can select those with the mouse, then do a "Invert Selection" and use "Attributes" to convert only the rest.
You can't set the default line width for the entire application. But you can set up and save an empty drawing with your settings and use this as a template for future drawings.
You can even set this for automatic start up for a new drawing in  Application Preferences - Path - Template.  

This might be why I can't see anything I've drawn on the screen.  What does that mean, 0 width lines?  Isn't a 0-width line nothing at all?

This might be why I can't see anything I've drawn on the screen.  What does that mean, 0 width lines?  Isn't a 0-width line nothing at all?  I'm coming from Gimp.  On the other hand, in the world of math, all lines are zero width, by definition, a line is a straight figure whose points lie upon themselves when viewed from one end, a "breadthless length" as Euclid says.  Still, everyone uses a piece of chalk when drawing one, so the people in the back of the room can see it.  Are lines all you can draw, maybe this is part of my problem.  I need a rectangle, that is, a plane figure, not a line figure, that is, one who is colored in.  Can't seem to find the color-this-thing-in button, can't figure out how to select the rectangle once you've made it, can't seem to find the paint bucket tool, can't figure out what the icons mean, or how to make them big enough to be seen.

--nerodog