The TRIM and EXTEND commands

by Will on November 23, 2010

I group the TRIM and EXTEND commands together because they’re basically equal and opposite. They are typically used quite commonly when drawing, but there are a few little tips for using them that can be really handy to know.

Basic Usage

Invoke the TRIM command. AutoCAD® then prompts you for a selection. A lot of people simply ignore this step and just use the default option to select all, but I tend to avoid doing this in nearly all cases. My reason for this is because you’re making AutoCAD® work harder if you select all. When you subsequently click an object to trim, AutoCAD® has to perform an intersection check with every single entity you selected, for each of the entities you selected to trim. So if you’ve got 10,000 entities in modelspace, and you selected to trim 50 lines, you’re asking AutoCAD® to perform 50 * 10,000 = 1 million comparisons. If AutoCAD® starts to hang and crashes, I wouldn’t place the blame entirely on AutoCAD…

 On the other hand, if you’d taken the time to select the entity you want to trim back to, you’re only asking AutoCAD® to perform 1 * 50 = 50 comparisons, which is drastically less than before. Get in the habit of doing this and you’ll avoid a lot of AutoCAD® hanging and possibly crashing.

What about the EXTEND command?

This is perhaps one of the most useful “quick tips” I’ve come across. I recommend that you do this right now – go into the CUI editor and remove the EXTEND command completely from your toolbars as you will never need to use it again. During the TRIM command, press and hold the SHIFT key to switch to extend m0de. That way you can tidy up all your loose ends without having to switch between the two commands.

Other Information

There also exists a LENGTHEN command, which you’d think to be very similar to the EXTEND command. You’d be right – the commands are very similar, but the LENGTHEN command has some very useful differences which make it worthy of a post of its own.

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