Another Lumberjocker asked for plans for my One-Handed Clamp (Picture #1). So far as I know this type of specialty clamp was originally devised for building lapstrake boats. In lapstrake boats the laps are clamped together for riveting which requires reaching across the full width of the new plank with the clamp. But this clamp also comes in handy at times for other deep-reaching, and/or one-handed clamping needs. I decided to publish a copy of my patterns here for anyone who needs them.
The photos are of my clamp patterns laid on a layout grid (picture #2), which you can use to reproduce them for yourself. Each square of the grid is one inch, but you could scale them up or down within reason. Just remember, if you make them too big they will be hard to use with one hand. Note the picture of the finished clamp shows a jaw opening of about 1/2 – 3/4” when closed. That choice was made for my own needs but your needs may differ. Remember, you must consider the thickness(es) of the materials you are clamping.
Depending on your own needs, the thickness of the stock used for your own version should be a minimum of 3/4” on up to 2” or so. (anything thinner than about 3/4” will allow the jaw ends to spring sideways under strain) Note also the exaggerated ‘bow’ or curve built into the jaws. This is to allow for clearance around anything you may need to reach over or around with the jaws, as well as to allow for a little ‘spring’. Most any hardwood could be used for these, but I prefer white ash for its springiness, toughness and relatively light weight. Hickory would rival or exceed ash for springiness and toughness, although perhaps a little heavier material, and I have also made them from oak.
The semi-circular ‘boss’ or receiver for the cam was made with a Forstner bitt. A diameter of 1-1/2 to 2” seems to be about right. (you can see my blog for making 'half-a-hole' if you wonder how). And since large Forstner bitts are fairly expensive you could also make your bosses with either a bandsaw with a fine blade, or a jig saw. However made, they should be made accurately. You can probably ‘lap’ them to smooth with sandpaper if you make them with a saw. And, the same thing goes for the cams themselves of course. That said, the fit between the cam and its boss needs to have a little room or slop about 1/16” or less.
Even though I much prefer the looks of sawn cams, I have also made them from sawn round stock turned on a lathe or made on the bench. In this case the toggle levers are separate pieces, inserted in holes bored for them and glued in place rather than sawn as part of cam itself as in the pictured version. I learned you must be careful here to insure the grain in the round itself is at or near a right angle to the toggle lever to keep the round from splitting under strain. (See sketch, Picture #3)
The metal links on my clamps are of 1/8” x 1/8” steel strapping and go on both sides of the jaws, but anything close will serve. They are held with 1/4” machine screws of sufficient length for the stock. You could make your clamps adjustable by drilling more holes in the straps, but keep in mind the distance between the holes will be multiplied by roughly two at the jaw ends. You need to pay particular attention to where you drill the holes in the clamp jaw and cam for the machine screws to maximize your clamp action. You might make your own patterns and experiment in two dimensions before you commit to actually building the clamps. This is important when considering the jaw opening in the closed position. Another thing to mention is the straps are normally located about 45-50% of the distance from the hinge end to the jaw end. Almost anything can be used for a hinge since there is no strain imposed there. I have used leather, webbing and even cabinet hinges. (picture #4 shows webbing for a hinge). The main advantage a fixed hinge has is that it helps keep the jaw ends aligned.
I hope anyone who is interested can use these patterns to make their own versions of these handy clamps!
-- "Never let your dogma get run over by your karma!"