A methodical, disciplined approach to work is essential if accuracy and fine workmanship are to be achieved. Whatever the job may be it has to be ‘set out’, parts have to be prepared and identified, cut to size and test assembled.
Do not rush blindly into cutting parts from a list before first checking carefully. Look over the drawings. Check measurements on them, then check the list. If it is possible, make a full size drawing from the scale details, then check for cutting. Timber is costly these days and an error in cutting can waste a lot of valuable material. There is still an old saying, doubly true these days: ‘Measure twice, cut once’.
To give an example of setting out and preparing a job let us consider a typical small project for the home or school workshop. The stool is 305 x 305 x 305 mm. Legs are 32 mm. Top rails are 32 X 19 mm and the bottom rail is 25 x 19 mm placed 76 mm from lower ends of legs.
The basic procedure, which generally is the same on all projects, is first to place all legs together in the vice, with ends approximately level and face sides and edges arranged as shown in. Then carry out all gauging, squaring, marking and measuring from these surfaces.
Next, mark out all similar pieces, together, while they are held in the vice or cramps. This is not only quicker but far more accurate than marking each piece separately.
Do not forget that there are often right hand and left hand parts to a job, therefore, when doing the marking out arrange the face marked components in pairs. Marking out for the rails is shown in.
Reference has frequently been made to a marking knife. There is a tool by this name, with a pointed and bevel-edge blade. But a trimming knife of the Stanley type can be used to mark out, and this has other uses. Where sawing has to be done across the grain use a marking knife, or a sharp pencil of moderate hardness, say 2H. Mark out all corresponding pieces for that part of the job at the same time, before doing any sawing.
Remember that the marking out for one part of a joint must correspond exactly with the other part, and not be made slightly bigger or smaller. Always shade in the waste. It is so easy to cut out the wrong part of a joint, or even saw on the wrong side of a line.
Returning to the rails, place them in the vice, ends level and face edges up. Square across to the dimension given. This dimension is known as the shoulder length. In this case it is arrived at by subtracting the thickness of two legs from the length: 305 – = 241 mm, or 12 – = 9Viin.
Check and re-check all marking out. An accurately cut joint will not fit if it is made in the wrong part of the wood. Acknowledge that old saying ‘measure twice, cut once’ without having to learn it the hard way!
One is central, the other is offset. The latter gives slightly longer tenons.
With a mortise gauge mark in the tenon size, and gauge from the face side, setting the gauge to the chisel you will use. For gauging the legs, pins of the gauge are not changed but the stock must be moved to give either a central mortise or an offset one, as shown in.
The kinds of errors that can occur when setting out are shown in. Incorrectly squared lines around the work is one. Lines should meet at every corner. At the gauge lines do not align on edge of end, probably because the gauge was not set with pins central, or the gauge was not always kept tight against the face side.
In the gauge lines are correct on the face side but not on the face edge. Correct position is shown dotted. This error arises through failure to keep the gauge stock against either the face side or the face edge.
After tenons have been sawn they must be cut to length and also have their ends mitred if. Both can be done on a mitre block or in a mitre box. Length of tenons must be slightly less than depth of mortise.
A mitre box is used for larger size work and provides better control of the saw and is therefore more accurate. Either can be purchased or made in the workshop. Blocks screwed to the base provide a grip for the vice.
Assembling the parts, cleaning up, securing the assembly and applying the finishes are stages that logically follow setting out. No matter how well made a joint may be, a light stroke with a plane, rub with glasspaper or some other cosmetic operation is needed to enhance the appearance of the work before applying polish, varnish or whatever the final process may be.
Cleaning up is the process of removing all pencil and other marks from the work, making the surfaces smooth, and preparing the job for the application of the ‘finish’. Joggles or horns are usually left on until after assembly, then removed and. In the rails are thinner than the legs so the cleaning up procedure is slightly different.
Rails are cleaned up on their faces before assembly and joints do not have to be levelled as in. Outer surfaces of legs can be cleaned up before or after assembly.
When glasspapering around a joint part should be done first, always finishing with part. This helps to reduce the amount of cross-grain papering, and therefore scratching.
To do its job effectively the smoothing plane should be kept quite sharp, with the blade, cap iron and mouth prepared as described earlier. The aim with the smoothing plane is to skim over the work so that everywhere is covered, and yet the minimum of wood is actually removed. A close eye should be kept on the surface as planing proceeds to see if there is any tearing of grain. Any tendency of the fibres to tear can usually be corrected by reversing the work and thereby, in effect, planing the opposite way.
Glasspaper varies in its granule size, from ‘flour’, which is very fine, to ‘strong 2’, which is coarse. For most work two grades are sufficient, starting with either grade M or F2 and completing with grade 1 ½ or 1. The following points should be noted when glasspapering. 1. Use a cork, rubber or wood block to support the paper. Do not work over flat surfaces with the paper held in the hand. 2. Hold the work firmly, either in a vice or cramped to the bench top. 3. Apply plenty of pressure; working slowly this way is much more effective, and far less tiring, than trying to do the job hurriedly. 4. Work with the grain whenever possible. Working across the grain, especially with coarse glasspaper, will scratch the surface and this will show up under a clear finish. Direction of working is not so important for a painted finish. 5. Do not glasspaper joints. A poor fitting joint is not improved by glasspaper and a good joint can easily be spoiled.
Other types of abrasive paper are available but they all do the same job and are used in the same manner as glasspaper. An exception is ‘wet-and-dry’ paper, which should not be used directly on a raw wood surface.
By the very nature of its purpose the cleaning up stage comes towards the end of a job when all the joints, shaping, cutting and fitting have been carried out. However, it cannot always be left until last and, broadly,the following is the procedure:
Before assembly, clean up those parts which cannot be reached after they have been put together. Those parts which can be tackled by plane and glasspaper after assembly are left until the work is glued up. This stage will often include levelling off joints and adjusting surfaces.
Occasionally work is assembled without adhesives but for the vast majority of jobs glue of one sort or another is employed.
Scotch, or bone, glue is rarely used these days as it has many disadvantages compared with modern glues; it is still used by some craftsmen for special jobs such as veneering.
P ½ adhesive, which is a white emulsion that dries to a clear transparent film, is a good general-purpose woodworking assembly glue and is widely used. It is bought ready for use and is applied cold. This adhesive provides a satisfactory bond with materials allied to woodworking such as cork, leather and fabrics, and is clean and simple to use. It is not a waterproof glue however and is therefore limited to indoor use. It will also cope with plastics laminates, but only if pressure is applied over all the surface until the glue sets.
A more satisfactory ‘adhesive for bonding plastics laminates to wood is one of the many ‘impact’ or ‘contact’ types. Makers’ instructions must be followed and the result should be a bond so successful that it is impossible to break. Impact adhesive can also be used for veneering but it is not the best glue for normal assembly work.
For external work, and boatbuilding in particular, special resin-type glues are used. They are completely waterproof and are usually bought in powder form. They may be ‘one-part’ which incorporates a hardener, or ‘two-part’ where the hardener is separate.
Epoxy resins, usually sold in two-tube packs of resin and hardener, are useful for special applications of bonding metal surfaces to wood, or other dissimilar materials.
For most jobs, and especially for the man with little experience, it is advisable to have a trial run of assembling a piece of work with everything fitted ‘dry’. This means that the work can be checked to ensure that it will, in fact, go together correctly, and with joints that are not too tight. While so assembled, it is advisable to mark each part of each joint so that when gluing the work will be re-assembled the same way.
This is simply a strip of wood with one end pointed. The point fits in one internal angle and the diagonally opposite angle is marked on the other end of the lath. The lath is then reversed to the other angles and if the frame is square the mark will coincide. A better pattern is shown at where two pointed laths slide over each other. They can then be held together and transferred to the other angles.
Small frames can be checked with a try-square. Check also corners A, B and C. Cramps should be applied as indicated by arrows and scrap wood should be used under the cramps to protect faces of the work.
Bowing of sides can occur as the result of using a single cramp in the centre of the job, or when cramps are incorrectly positioned. Thick pads of wood also reduce the chances of bowing.
Being methodical is one of the essential disciplines of assembly work. Such cramps as are to be used should be set out and prepared at the ‘dry-run’ stage and scrap wood pads collected to place between jaws and work to prevent bruising and marking. Nails, screws, wedges or pegs to be used during assembly should be set out on the bench beforehand. In addition a container of clean water and some cloth swabs should be to hand for wiping off surplus glue before it hardens. Glue, once set, is very difficult to remove and if any smears of glue, however slight, dry out on parts that are to be clear varnished or polished, they will ‘grin’ through the polish as areas of a different shade to the natural wood colour you hope to achieve.
P ½ glue can be applied directly from its plastics container if it has a nozzle, or with a brush or spatula if in a can. Do not be too generous but also do not be ‘greedy’. Apply enough to wet all contacting areas without a lot of excess which will have to be mopped off later.
After applying the glue, check and cramp up without delay. Makers specify an ‘open’ time for their adhesives and usually it is slow enough to allow plenty of time for correct assembly. But the sooner the work is assembled and at rest for setting the better will be the bond. If things do go wrong, dismantle, mop off the glue while it is still wet, and start again. Partially set glue will not give a good bond. By the same token an incorrectly glued up assembly can rarely be put right once the glue has set.
Do not forget that cramps can exert a great deal of pressure. Use just enough to hold the assembly firmly – too much can distort the work.
When the right-hand cramp is tightened it will pull the corner over, thus correcting the misalignment.
In a frame which is badly twisted, or ‘winding’, is shown. Here, ends of cramps must be moved vertically up or down in order to pull the frame free from twist.
To test for correct alignment sight with the eye, as in. Surfaces of rails are in line. When viewed at right angles to the first observation point the legs should also be in alignment. The whole frame should be flat, or ‘out of winding’.
All this is the counsel of perfection. It may sound formidable but in reality it is not; just the application of some common sense, patience and pride in achievement.