How can I create an portable object in Illustrator that will render anything beneath it transparent?

Question

I'm creating knitting charts in Illustrator CC on a Mac. Every chart has a lined grid on which I place symbols. Most of the symbols are one square high and wide, so they fit right within the black gridlines. Some symbols, however, span several columns, and the gridlines beneath them can't show through. I don't want to create symbols that have a white background that will cover the gridlines because the backgrounds for the charts are sometimes shaded and the white will show up. So I need for the multi-column-wide symbols to be able to render anything beneath them as transparent so that the gridlines don't show through the symbols.

Photo #1 shows how the gridlines are showing through the red-outlined symbol. #2 shows how I want it to look - I cut the gridlines so you could see the look I want.

How can I do this? I've tried knockout groups and zeroing out the opacity, but neither has worked, and I don't know if I'm doing something wrong. I have made it work once or twice in the past, but when I try to use the old symbols in a new chart, they don't work.

Answer 1

A knockout group is exactly what you need. A knockout group however, only affects the transparency of that specific group. I'm guessing you didn't group the objects that you wanted to punch the transparency through.

An easier option if you want the transparency to knockout all the way to the artboard is a Page Knockout Group. This is easier because you don't need to worry about which group you're working in—it will always punch through everything.

Simply select the object and from the Transparency panel dropdown menu, check "Page Knockout Group". Then drop the opacity down to 0. If you only want to knockout a specific fill or stroke then you can open the Appearance panel and drop the opacity on that specific stroke or fill or whatever you want to knockout: