[ath]

Originally Posted by Moonraker

This is true but we have to work with what we got.

I too, always insert a space before and after an em dash except where it occurs at the end of a sentence.

Not really. If 'what you got' produces results of a quality you cannot accept, you also have the choice of using something else.

Inserting ordinary spaces around em dashes produces a fairly ugly result in general: the space can become far too big (especially with poor line-breaking algorithms). And even when the spaces stay reasonably small, the overall space still is too large for the intended effect. The length of the em dash is not unimportant -- adding two spaces on either side makes it into a considerably more eyestopping separation than it should.

A better choice may be to use whatever special-width spaces are available -- I've seen zero-width spaces used to good effect.

A more practical approach may be to avoid em-dashes, and instead use en-dashes -- they are better with word spacing on both sides.

While I remember -- if your choice of spacing fail to make the end of a sentence clear to the reader, you have failed as a typesetter. If you use word spaces around dashes, a dash at the end of a sentence requires special treatment so as not to confuse the reader into believing that the next sentence should be considered part of the previous one. The standard spacing rules for em dashes don't lead to such confusion -- if you alter them, you have to take on and manage the consequences as well.

An extra space at the end may do the trick: as long as you take the precaution of avoiding dashes at the end of lines. If you cannot do so, ... again, if the tool you work with doesn't allow you to do a proper job, you put it away, and use something better.

I believe en dashes are used to show a range of something so should not be used instead of an em dash.

Often, but that is because en dash is more of a tie between the numbers on each side, while the em dash has a somewhat different function. It's not because there's some sacred rule about it -- it is because it works optically.
You can't add spaces around it, and still expect it to work.