Tools for Woodworking

The versatile G-cramp

After a vice, the G-cramp is the most useful gripping tool you can have for holding wood down as you saw, drill or mark out, and for holding small pieces for gluing.

The commonest sizes are from 50 mm (2 in) to 200 mm (8 in), the measurements indicating the maximum usable opening. Smaller sizes close completely when screwed down; sizes above 100 mm (4 in) have a short thread and leave an opening of about 50 mm between the jaws. It is worth having at least two cramps, a 200 mm and a 100 mm, as a basic kit.

Never tighten G-cramps other than with the hand — using a spanner may bend the body. Always use ‘softening’ between the work and the cramp jaws, to avoid denting wood. If you are gluing soft materials, such as expanded polystyrene, use two flat pieces of wood, wider than the work, to spread pressure and avoid local distortion.

When cramping wedge-shaped pieces together for gluing, use a second cramp placed crosswise to stop the glued surface from slipping. Put waxed paper or newspaper between the softening for the second cramp and the glue-line, to prevent the softening from sticking.

If a cramp is not secured straight, or the glue is slippery, the pieces to be joined may shift as the cramp is tightened. To correct this, use a second cramp crosswise, or tighten the work in the vice.

Holdfast — for horizontal gripping

The holdfast is a common tool in the wood- working trade but seldom found in the home workshop, for no other reason than that its true value is not widely enough known. It holds long timber and panels firmly down on to the bench. Because of its strong grip, softening must be put be- tween the holdfast’s foot and the wood being worked on.

Apart from holding wood down directly, the holdfast can be used to grip wood indirectly, to jut over the edge of the bench, ready for grooving or rebating. This is done by using a beam and a support to transfer the grip to the work.

To fit a holdfast, drill a hole in your bench to take the cast-iron collar which comes with the tool. The best position for the collar is 350-450 mm (14-18 in) from the end of the bench opposite the vice. Centre it across the width of the bench and fit it flush with the bench top. If your bench is flimsy, strengthen it locally with an inch-thick hardwood block, glued and screwed under the working surface at the point at which you fit the collar. The holdfast can be stored out of the way, and slipped into position when needed.

Sash cramps — for large jobs

Sash cramps are for holding large work while it is being glued. They consist of two adjustable shoes on a long bar. One shoe is adjusted by sliding along the bar and securing with a pin, the other tightens up like a vice jaw.

To place a sash cramp, first pin one shoe in position so that the distance between the shoes is slightly greater than the width of the work; place the work between the jaws and tighten by screwing up the other shoe gently. Do not overtighten by using a spanner to force the shoe. Always use softening between the shoes and the work.

Light sash cramps have a rectangular section bar; stronger versions have a T-section bar. Sizes range from 600 mm (2 ft) for lighter versions to 2 m (7 ft) for T-bar cramps. Plug-on lengthening bars can be fitted to shorter types.

Three 1220 mm (4 ft) sash cramps are a good basic kit. Alternatively you can buy the cramp ends only and make your own bars out of hardwood, preferably beech or oak. Do not buy cheap cast-iron heads, as they break easily.

When sash cramps are in use, the bar always bends upward. To prevent the bar from touching the work, always put 5 mm (¼ in) wood-spacers between the work and the bar at the shoe ends. To prevent the work from being curved by the pressure of the cramp, use three or four bars — two below and one or two above it. This counterbalances the bending action of the bars. Always check the work for flat with a straight-edge before the glue dries.

Always place cramps squarely on to the work, as they distort if crooked. Cramps can be used to straighten up frames which are out of true: check the diagonal measurements from corner to corner; if they are not identical, the frame is out of square. Correct this by putting the cramps on slightly out of true, so that when they are tightened gently, they pull the frame back square.

When gluing up frames which have through mortise joints, the cramps have to be set away from immediately over the joint. This will cause the frame to bend slightly. To overcome this bending, release the cramps slightly before the glue is completely dry and then place a cramp at either side of the joint while the wedges are hammered home.

Mitre cramp

The quickest and easiest way to ensure true, firm corners when making picture frames is to use a mitre cramp. A variety of patterns are on the market, including a version which doubles as a mitre box, allowing you to cut as well as cramp the wood accurately.

Wooden handscrew

This traditional tool grips both parallel and tapering work. It has a wide gripping area, but gives nothing like the pressure of a G-cramp.

To use it, open the jaws to the approximate size by holding one handle in each hand and winding them simultaneously; place the jaws round the work, tighten the inner screw and then the outer screw, thus levering the jaw on to the wood. Because of the handscrew’s light grip and its wooden jaws, softening is not usually needed.

Carver rack cramp

An expensive but extremely strong and quickly adjusted cramp for general purpose work.

The adjustable foot can be removed and used as a jack.

Do not use force to increase the tightness of the cramp; the tommy bar is an intended length to prevent overstrain

Home-made cramping devices

Once you have a bench vice and a set of G-cramps, you will be able to cope with most cramping jobs. However, if jobs beyond their scope occasionally occur, you can often improvise with your own cramps rather than go to the expense of buying a set of, say, sash cramps.

Large frames can be held together while glue dries by looping cord around them and tightening with a peg. Pack the frame with paper or woodblocks to avoid marking the wood.

Frames can also be cramped by tightening a cord around four corner blocks. Make the blocks from glued and screwed pieces of wood, notched to take the cord, which is tightened by a peg. Make sure that the frame is square by checking that the diagonal measurements tally.

Pairs of wedges (`folding wedges’) are an invaluable cramping aid. They can be used with a couple of straight wooden strips to hold large frames or flat work, such as a table top made from boards: screw the strips parallel to each other on a flat surface, put the frame between them, and tighten up by hammering in the wedges against each other.

For lighter jobs, use folding wedges with screws instead of the strips.

Frames can be held on a bench by screwing a temporary stop at the back and holding the work between it and an L-shaped block in a vice.

For a large bookcase or similar carcase, make a wooden frame to fit round it, then use wedges to tighten up.

With ingenuity you can improvise cramps by using anything from Bulldog clips to pails of water stood on a plank.

22. June 2011 by admin
Categories: Hand Tools, Woodworking | Tags: , , , | Comments Off on Tools for Woodworking

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