Wise up to woodworking

Measuring and marking out

Ideally you will have 6, 12, 24 and 36in steel rules. The quality of these rules can vary enormously. I was tempted to buy three 6in rules as the price was so low – and I should have known better. One look and they went straight in the bin. The first 1/32in was missing completely!

So, spend a little more and get an easily read quality product.

I always check a new rule to ensure that it is telling the same story as the others.

You will also need a tape measure – a five metre tape is ample.

Use an HB pencil to mark wood and plywood, as it will not bleed through covering as a ballpoint pen will. A craft knife is another good way of marking as it gives a very defined boundary line, but obviously it can’t be used for any lines within the piece. Squares, large and small, are useful. My most used square is about 2in x 3in as not many components are wider than three inches.

The squares are always worth checking. Place it on a straight edge of a table or bench and draw a line. Turn it over and it should, of course, be parallel with the line. I bought two small steel squares recently and, on checking, found one of them to be out. As the blade was merely an interference fit in the base it was easy to put in a vice and tap the blade with a hammer to get it right.

Beware of the dreaded accumulative error. That occurs when marking, for instance, rib positions along a spar. From the datum, usually the spar root end, let’s say the first rib is at 12in, then it is 18in to the next rib and all the rest out to the tip. Rather than measuring rib to rib, each rib position is calculated from the datum so the measurements you use will be 12in, 30in, 48in, 66in etc.

This means that when you place your pencil and mark off if you are slightly out the inaccuracy will only ever be that much, whereas if you measure from rib to rib all the way along, and your small inaccuracy is always on the same side of correct, they will all add up and become a greater inaccuracy. From this, don’t think that an aircraft has got to be super accurate. It hasn’t. But if you aim for perfection, you are more likely to be in the right field at the end of the job than if you were a little slapdash.

While we are talking about spars you may well have eight of them, four wing panels with front and rear spars.

You don’t want the job of measuring out eight separately, so when your first one is done, use it as a pattern, clamp another spar to it flush with the datum, and use a square to transfer your rib positions to it. It may be worth saying here that this would not be a place to use a craft knife to mark out!

Cutting

One of the most useful tools in the workshop is the bandsaw. They can range in price from less than £100 to £1,000s. A small three-wheel saw, with a throat of around 12in is adequate, a larger one, with two larger wheels, is better, but will be more expensive. The disadvantage of the small three-wheeled saw is the small diameter of its wheels, because they are small is the reason there are three of them, the third one to the side pushes the blade out to allow the 12in throat. Why is that a disadvantage?

Every time the blade covers one ‘circuit’ the blade is flexed through a larger angle than if it was running around big wheels, and it is being flexed three times per circuit rather than two. This leads to fatigue in the weakest point of the blade, the welded join. So, on the saws with small wheels, it is relatively rare to junk a blade because it has gone blunt, it normally breaks far sooner than that.

Note that a bandsaw is not ideal for ripping down timber. Not only does it leave a poor finish, it will also follow the path of least resistance, which is wandering off and following some softer grain instead of the intended path. If you do rip with it, slow the feed rate down to snail pace.

Setting up a bandsaw

Inside your saw, when you take off the front cover, it is usual that there is a guide to each side of the blade, and a thrust bearing to the rear of the blade, above and below the table. The set of guides above will be attached to the blade guard that can be raised and lowered. Slacken these guides and move them clear of the blade. The top wheel is usually the one that allows the tracking of the blade to be adjusted. On the back of the saw, behind the top wheel there will be an adjustment for the ‘tilt’ of the top wheel. Ensure that your hands are well out of the way – it makes it more difficult to build an aircraft with fingers missing! Check the blade tension – the blade does not want to be slack, nor very taut. Turn on the saw and check that it runs on the centre line of the top wheel. If it doesn’t, slowly adjust the tilt until it does. The chances are that you will never have to adjust that again.

With the blade running centrally on the wheels, turn the saw off. Adjust the side guides to have about a 15thou (0.3mm) gap between the guide and the blade and the same for the rear (thrust) guides, these guides will be hardened steel on a budget machine and possibly roller bearings on a higher quality machine.

Put the front cover back on. The last thing to do is to check that the blade is cutting square to the table. The chances are that the manufacturer has given you the option to tilt the table to carry out an angled cut by making the table tiltable. I think I have utilised this feature once in the 20-year life of my little saw. The easiest way to do this is with a small square and make sure you lock it well when in position.

Razor saw

Very useful for cutting components in-situ without straining the structure. The secret of sawing is to always have at least three teeth in the cut. Imagine a carpenter’s handsaw of, say, 7 TPI.

When you start sawing a 4 x 2 on a workbench, initially the saw is close to parallel with the top surface of the timber, as the cut progresses, so the carpenter’s arm is slowly raised to the comfortable angle of 30-40° from the surface. If he had tried to start the cut at this angle the coarse teeth would have jammed on the corner of the timber.

The razor saw overcomes this problem by having so many teeth it is difficult not to get at least three in the cut. It can be placed on a line drawn on a plywood panel and moved backwards and forwards until it breaks through.

It is then an easy job to follow the line accurately to the corner, or hopefully to a radiused corner, as plywood can suffer from a stress riser coming from a square cut corner, just as steel and aluminium can.

Plane

A small smoothing plane can be useful, as can a bullnose plane. Use them to take the edge off stringers, and for tasks like shaping wood for wingtip bows.

Craft knife

I have a Stanley knife and a Swann Morton craft knife, which both have their uses. There is just one tip for when you want to carve back a plywood edge – don’t hold the knife square to the material surface.

If you do, you are asking the knife to part the plywood at 180°, and it won’t want to do it. If you angle the blade at about 45° from the surface the blade will tend to part the ply with one side rising and the other side falling.

Basically, the ply has somewhere to go. You can carve on the vertical when there is only a small way to go. Obviously, I am talking about thin plywoods here.

If you embark on a wooden project and you hit a stumbling block that you think I may be able to help you with then please do not hesitate to email me at dudleypattison@gmail.com ■