The following is excerpted from Chapter 4 of “The Solution at Hand: Jigs & Fixtures to Make Benchwork Easier” by Robert Wearing. The book covers a wide swath of useful material, from building workbench appliances for planing, to making handscrews (and many other ingenious clamps), some simple tools that you cannot buy anywhere else, to marking devices that make complex tasks easier.
There can be few readers who enjoy buying cramps. Unlike some other tools they do not make anything. Nevertheless, they are essential. Generally they are bought and used as four of a size. The major disadvantage is that good iron G cramps are very expensive for what they do, and because four are required, that cost is multiplied four-fold. Apart from the cost, iron G cramps have another disadvantage. They can easily damage the work; consequently wood blocks must be used to prevent this. Juggling these while the glue sets can be a problem for the single-handed worker. The G cramp with its swivelling foot cannot give that light nip at the very tip as can many of the cramps illustrated later. Though obviously G cramps have very great strength, it should be remembered that good joints require only to be pulled, not crushed together.
These tools are much less common than they were a generation ago. Nevertheless they have several advantages over the much more numerous G cramps. They are lighter in weight, they do not damage the work and, of course, they can be made. Jaw length can vary between 12″ (300 mm) and 4″ (100 mm). They are usually square in section and are made from any close-grained hardwood. The screws can be of wood, if a wood screw box is available, or can be of bought metal screwed rod. The latter would be of a smaller size. The metal screws can be screwed, glued and even pinned into chisel-type handles and wood screws can be similarly fitted if it is required to cut out some of the woodturning.
It must be stressed that both the threaded holes are in the same jaw, in this illustration the lower one. In use the through screw makes the preliminary grip then the second shorter one screws into a cavity in the upper jaw, thus increasing the pressure.
Another Simple Handscrew
This derives directly from the traditional wooden handscrew, and from the metalworkers’ “Toolmakers’ clamp.” In addition to the advantages already stated, the handscrew can grip in a depression or confined space, particularly useful in repair work. A variety of sizes is possible using threads of 5/16″ (8 mm) or 3/8″ (10 mm). The positions of the screw holes in relation to the sizes of block is shown in Fig. 2.
Prepare a piece of dense hardwood for the jaws. This should be just over twice the jaw length and planed to the finished width and thickness. Saw to produce the two jaws and square one end of each by shooting board or disc sander. Cramp them together and mark the centre lines for the holes. Separate and square the lines onto all four faces. On one jaw gauge the centres for the cylindrical nuts. Note the positions of these centres. They are not central in the jaws. Drill these holes using a sawtooth, dowel or lip and spur bit. The engineers’ twist drill will not start accurately enough. If this is the only tool available, put through a small pilot drill first. If working entirely by hand, bore from both sides to ensure squareness and avoid later twist when the tool is assembled.
The holes for the screws are marked centrally on the other (top) face then drilled. Note that one hole does not go through. Saw and plane the tapered jaws and round off the back corner slightly. The wood jaws, now complete, can be treated with linseed oil or given several coats of shellac or polyurethane varnish.
Turn or file up two cylindrical nuts slightly shorter than the jaw thickness. Drill centrally then tap for the selected thread. Cut the screws to length and clean up the ends. Clear any burr here by running on an ordinary nut. Make a small metal pellet and drive this into the blind hole.
The handles may be turned or benchmade to a hexagonal form. They are best drilled in the lathe. Grip the handles in the vice and cut the internal thread using the taper tap only. Force in the screwed rod, using two locked nuts. Turned handles can now have two flats planed on them. Assembly is quite straightforward. Finally, close the jaws and trim off any projecting end.
In use try to keep the jaws parallel. First tighten the centre or clamping screw. Then apply pressure with the outer or pressure screw. With a little experience, the operation is quite quick. Grip the centre handle with the left hand and the outer one with the right. Now clockwise rotation of the right hand tightens the jaws.
Two Easy Cramps
The following two cramps, the “Handscrew” and “An Adjustable Cramp,” are both easy and cheap to make yet are really useful cramps to have about the workshop. Furthermore, they need neither special equipment nor skill in metalworking. All the requirements can be bought from a good hardware or DIY store. The reader is recommended to make these cramps four at a time.
The materials to be purchased for these cramps are lengths of screwed rod, 3/8″ BSW or M10, hexagon nuts and washers to suit and 4″ file handles.
Fig. 3 closely follows “Another Simple Handscrew.” Produce the jaws, accurately square and to size. Having cramped them together, mark the hole centres. First complete the top jaw of the drawing. Preferably using a sawtooth bit or a flatbit, bore the two holes for the nuts. These are 5/8″ (16 mm) which is the size across the flats of the nut. The depth is slightly more than the nut thickness. On the same centre, drill through with a 3/8″ wood drill. Enlarge these through-holes to give a loose fit either with a large twist drill or with a round file. Using a piece of the screwed rod, a hexagon nut and a large-diameter washer, force a nut into each hole.
The lower jaw has one oversized through-hole and one blind hole – the hole into which a 3/8″ steel pellet is forced.
The file handles are best bored in the lathe. Tap them 3/8″ (M10) to a depth of 1-1/2″ (40 mm). A tap suitable for a limited use in wood can be made by filing four tapered flats on a piece of screwed rod and then fitting two lock-nuts, very firmly tightened. With two lock-nuts temporarily on each screwed rod, two handles can be forced on. Assembly is straightforward. Remember that the scrap screw needs a washer under the ferrule.
It is unlikely that the nuts will work loose. If this does happen, thoroughly de-grease and return with a dab of epoxy resin glue. In use, aim to keep the jaws parallel for the most effective grip.