How to crop large format paper I've got drawings and other art on 18x24 inch and larger format papers.

How can I inexpensively crop these papers so that the edges are straight and the corners perfectly right angled?  Professionally so?
The simple DIY way

Use a ruler along the line to be cut. Use a cutter.



The more professional way

Use a paper guillotine.

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The advantage of the ruler + cutter is that you can cut lines anywhere, anyhow, even holes. The guillotine will help you get cuts perpendicular to one edge, and the cuts must start at one edge of the sheet.