I have around 300 A4 pages. I want to compile these into a book-like form. So I have a 3-Ring Binder. I don't have a 3-Hole Punch. I am looking for DIY method where I can do it in the smartest way without buying a punching tool.
If you have a hot melt glue gun you can achieve a similar result to professional book binding by making a cover out of a piece of card the same size as 2x the front sheet plus the thickness of the sheets (it needs to cover the front, back and the edge), pre-folding the edges of the spine, then loading up the spine area with melted glue and pressing it onto the side of the book. If you can't load the spine with glue and keep it all melted, you can re-melt the glue using an oven or heat gun, or you can place all the papers on the card and (having an assistant hold the papers firmly in place) tou can lay glue at the bottom of the spine, presson, open the gap back up and lay another line of glue, working your way up. Practice before ruining your 300 page masterpiece
If you don't have a hot melt glue gun you can achieve a similar job with normal wood glue: fix two sheets of wood at right angles and tip them slightly, so as to create something like the device that holds a music book open for a piano player, place your covering card (folded) in the device, load the spine area up with PVA/woodglue and sit the pages in the glue. After some time (a few hours), carefully remove the whole lot from the support and set them down so the spine can dry more effectively
In the past I've had reasonable success in using a drill to drill through a stack of paper clamped between two pieces of wood. Clamping pressure makes the paper behave like wood and drill more neatly. Tying the holes with string in neat knots makes for a cute, hand made look that if gotten right can add a shabby flair rather than making it look overly home made
Commercial solutions to the problem often involve a plastic clamp, or a multi hole punch (a comb binder) that punches 20+ holes in the document then has a set of metal fingers that opens up a plastic roll that is threaded through the 20+ holes. You also occasionally see documents printed in a certain order on double size paper so that when folded and stapled they form a book. 300 pages wouldn't be done in one go, but you might see it broken into 5 lots of upto 64 pages (requiring 16 sheets of paper, 4 document pages per sheet, 16 being a reasonable folding limit), stapled or sewn and then the stapled booklets bound together by gluing. This could be replicated at home if you can work out the page numbering for printing (most print dialogs have booklet printing options)