I while ago I was reading an article in a woodworking magazine that got me started thinking about clamps. What is a clamp, really? If you're talking about sheets of paper, a clamp might be a staple, or a paper clip or a binder clip, or even a rubber band. For wood, there are spring clamps, C-clamps, bar clamps, pipe clamps, strap clamps, wooden handscrew clamps,hold-down clamps, toggle clamps, corner clamps, and probably others I've never heard of. You can even use clothes pins for small projects. For use with metal, you can add things like vise-grip clamps of several sorts, magnetic clamps, etc.
A clamp is really nothing but a device to hold something where you want it. The old, venerable bumper jack for a car is really a special kind of ratcheting clamp. It holds a big piece of metal, glass, rubber and plastic (a car) off the ground while you cuss at it (and hopefully, fix it). The screw-type frame jacks (also called "scissor" jacks) that most cars come with today are a different kind of "clamp" that does the same job more safely. Things like a vise or drill chuck or lathe jaws and dogs can be used to hold things while you work on them while they're moving! Clamps can be very easy-to-use, crude, and cheap - like a rubber band or a clothes pin, or even a combination of 2 washers, a bolt, a nut and a scrap piece of wood (see picture). Or they can be very precise, complicated and expensive. (Check the price of a lathe chuck sometime - be sure you're sitting down first).
The most common clamps seem to consist of some form of a "U", "V" or "C" or sometimes even an "X" or "XX" (like old-fashioned ice tongs or a "Gorilla Gripper®" for carrying plywood sheets) with some way of tightening the thing to apply holding power where it's needed - generally either a spring (which could even be a rubber band) or a screw of some kind. Some bar clamps use either a ratcheting or friction mechanism to make "quick release" clamps.
Step 1: Think About What You Need to Clamp - and Ways to Do It
The point of all this is that, before you spend a small fortune on a wide variety of specialized clamps, you should think about what you are trying to hold and how it can be done. Often these specialized clamps will be used rarely - sometimes only once or twice! If you're trying to hold a chair together while you're re-gluing a loose rung, a good clamp can be a piece of surgical rubber tubing - sort of a big tubular rubber band - a long bungee cord, or a piece of rope or paracord tied around it with a stick to twist it tight. I've use all of these methods before.
Commercial corner clamps are great for 90° corners, but what if you are trying to glue a five, six or 8-sided picture frame? If you can find a clamp to do this, it'll cost a fortune. With a table saw or miter saw, a little bit of scrap lumber, some glue, and a few bolts, you can quickly make your own for very little. I'm showing a couple of pics of a 120° corner clamp I made for a large hexagonal shadow box I wanted. (The digital angle gauge shown is very helpful for miter work of almost any kind. They're about $20-25 on Amazon.com but probably available other places too.)
If you need a really big C-clamp and don't have one big enough, cut a 2x4 a little longer than the thickness you need then use two more pieces of 2x4 across the ends and squeeze them together with the twisted rope trick if you just want something fast for a single use. If you expect to need it more often, you can add a couple of hinges, perhaps some wider jaw ends, a piece of threaded rod and a couple of nuts and washers to pull the jaws in the direction you want. And, when you're done, take it apart and use the pieces for something else.
Step 2: Look on Instructables and YouTube for Ideas
Instructables and Youtube are fantastic sources for successful, proven DIY clamps and jigs. One of the sweetest ideas for clamps to edge-glue panels I've ever seen is here on Instructables at https://www.instructables.com/id/4-Way-Panel-Clamp... by Silver Paddleboards
If you need a clamp to hold two relatively long pieces together all along an edge, a piece of 2" PVC pipe (or larger diameter, depending on your needs) slightly longer than the length you need to clamp, ripped in half, then placed over what you want to clamp. Use a number of bolts and nuts in holes along the length to squeeze them together. PVC pipe is pretty easy to cut lengthwise on a table saw as long as you have a riving knife behind your blade (also sometimes called a "splitter") so that the pipe doesn't "grab" the blade. DON'T EVEN TRY TO RIP PVC PIPE ON YOUR SAW IF IT DOESN'T HAVE THIS FEATURE! If you want to make sure of alignment, you can almost cut through the second (top) side of the pipe while you're ripping it, leaving kind of a "hinge".
Step 3: Low-Clearance Clamps - With Mods
I recently discovered the benefits of using a "door board" (also called a circular saw edge guide or a makeshift track saw guide) for a circular saw such as https://www.instructables.com/id/Perfect-Cuts-With... (When you make it yourself, you can call it whatever you want.) But one of the problems with them is that often a regular C-clamp, used to hold them in place, interferes with the depth of cut for the saw. A low-clearance clamp really helps! Rockler has something very similar to mine called "Universal Fence Clamps" and sells them for $19.99 a pair. I made a couple out of some 1/4"-20 x 5-1/2" bolts (properly called cap screws - they're only partially threaded), washers, wing nuts, and some scrap 1x2 - total cost, about $1 each. I cut the heads off the bolts, stuck about 1-1/2" of the un-threaded portion in my vise, stuck a piece of 1/4" pipe over the part that was sticking up and bent it about 90°. (A little over a 90° bend doesn't hurt.) You can use a hammer instead of the 1/4" pipe, but you're more likely to mess up the threads on the bolt. This gave me an L-shaped bolt. Then I took about a 2" long scrap of 1x2 and drilled a 1/4" hole in one end of it. I've found that it helps if the hole angles just a bit. If you drill holes both through the side and the edge, it makes it just a little more versatile because you can change how you orient this piece to clamp thicker or thinner stock. Slide the threaded end of the bolt (opposite the bent end) through the hole in the block so that the legs sticking out angle towards each other a bit, put on the washer and the wing nut and you have a low-clearance C-clamp. It will stick up just over 1/4" above your guide, not enough to interfere with your saw. If you're cutting relatively thin stock such as 1/4" or 1/2" plywood, you may have to thread the bolt up higher with a threading die, use a thicker block for the jaw, or bend the bolt in a different place, but I didn't want the threads on the bolt cutting into anything so these were the kind of bolts I chose. If you need a non-marring version, take another scrap of 1x2, drill a hole in the side and stick it over the metal end - the fixed jaw (see picture) or even just put a piece of plastic tubing or a few layers of masking tape over the end.
Instead of the wing nut, you can use a regular nut welded or brazed to a short piece of steel flat stock that has a rod through the other end to form a crank. That makes it quicker to tighten and loosen. Or just drill and tap the flat piece to fit the threads of the L-bolt. You're making it - do it however you want to. You can try it my way, then come up with a way that works better for you.
Step 4: Possible Variations and Alterations
There are lots of variations available. Much larger. stronger versions made of 3/8" or larger All-thread rod and nuts would be easy to make. In fact the ease and low cost of making customizable jaws for these clamps makes them perfect for making mitered or contoured jaws out of 1x2 or 2x4 scrap blocks using a bandsaw, scrollsaw, and/or a router. They could be built up out of layers of MDF or made from aluminum or steel tubing. The can even be quickly padded with leather, rubber or polystyrene foam and a little contact cement. If you need special, custom jaws, you can even mold something with plaster of Paris, Bondo, or casting resin on top of the wooden blocks. Your only limit is your imagination. Just think - you could even form the bolt into a C instead of an L and make your own C-clamps.
Step 5: Conclusion
These are very versatile, cheap and useful clamps. I'll be using more of them to mount an auxiliary half-fence for my table saw (another Instructable on this to follow).
I'm sure I'll find other uses for them. I hope you do too. And I hope this has given you some useful ideas, perhaps saved you some time or money. Maybe it will even help you to think more "outside the box" and come up with better, cheaper, more efficient ways to accomplish what you want.
Maybe you'll even become an inventor.