These wheeled implements present several difficulties in designing them to give perfect satisfaction. They may damage the floor, be hard to push or be noisy to operate.

Wheels

Metal wheels on a hard, smooth floor will satisfy the first two conditions, but will be very noisy. A soft rubber-tyred wheel will make a loaded truck considerably harder to push, and when as is frequently the case, the workers can only just propel a truck with metal wheels, it is nearly certain that if rubber tyred wheels be fitted, that they then cannot move it without more help. It seems to be completely lost sight of by many people that, if either the floor or the wheel surface be other than perfectly hard and rigid, then the effect of putting load on will cause an appreciable depression of the floor or wheel, or both. This depression travels along as the truck moves, and causes work, maybe hard work. Frequently if the wheel happens to be rubber tyred, it is stated to cause " suction" on the floor ; this is quite wrong, there is no suction in any way, the added resistance is simply that due to the moving of the depressed place either in the floor, or wheel, or both. This depression varies in amount, depending upon the load, and upon the material in use, the lighter the load, and the harder the material, the less is the depression and therefore the easier is it to move the truck. In many cases there is no objection to using, say a concrete floor and metai wheels, except only that due to the great noise. In that case a compromise has to be made between quietness and slightly harder running obtained by using, say a hard rubber wheel.

Trucks

Now all wheels wear considerably less if just rolled along as against being rubbed sideways across the floor, yet it is a fairly common sight, at the turn of a gangway or passage to note that the floor has been cut up badly by truck wheels. This means that they did not roll round the corner, but were scraped or rubbed around. There is something defective with the wheels or the truck design, and both should be well examined to discover the cause of the floor damage. The ideal wheeled truck would be mounted upon four wheels, one at each of the corners of the truck base, and each mounted in a swivelling castor. A compromise on the question of first cost is to have two swivelling castors at one end, one at each corner, and at the other end to have two fixed axle wheels. If this type of truck be pushed preferably from the swivelling wheel end, it will be found to steer easily round any corner, without skidding or rubbing the wheels across the floor. Another point to avoid in arrangement of wheel position on the truck is that of fixing the wheel at each end in the centre of the width of the end, as this means that if the load comes on one corner more than another, then the truck tilts up at the opposite corner, a wheel should come under each truck corner.

General

The question of the wheel diameter is an important one, small wheels are less expensive than large ones in first cost, but it does not end there, trucks on large wheels are much easier to push than if mounted on small wheels, therefore the operators finding this are likely to put more load per journey on the trucks with large wheels. Dirt, pieces of string, etc., on the floor can much more easily twist round the axle of a small wheel than a large one, and generally this goes on until the wheel jams, and has a flat rubbed on it, resulting in a new wheel being required. Some have fitted ball or roller bearings on to their truck wheels ; this does decrease the running friction, but still a heavily loaded truck is hard to get moving, many quite forget that the load has inertia, and that energy does have to be put into it merely to overcome this. It is quite impossible to get, say a truck loaded with 12cwt. moving at the same speed as one with 6cwt., when exerting the same push in the same time, more energy must be put into the heavier load, and this is sometimes blamed on to the truck or the wheels. It should be remembered that a truck loaded with 12cwt. moving at 3 miles per hour would be difficult to stop quickly by hand, yet it is perhaps expected to easily be able to get it moving at that speed quickly, and without undue exertion. Always therefore if a loaded truck be harder to push than it should be, it must be due to a defect in either the floor or the wheels and axles, and if the floor be good, then it must be either the wheel or axles. Examine the floor first, if this is good, then pass on to see whether (1) the axles are a good lit in the wheels (2) the axles are well oiled and free. (3) the wheels do not rub anywhere sideways (4) they do not set or distort under the load, (5) they are not too small for the state of the floor. (1), (2) and (3) are easy to settle : (4) is not easily done, the best way is to measure whether the centre of the wheel axle gets nearer to the floor as the load comes on, and this will require to be carefully measured for, with say inside callipers from the wheel centre to floor, standing the wheel for the test on a metal plate. If the wheel does distort, consider well whether the wheel is wide enough for its work. With regard to (5) one has to be guided by the conditions, one floor might be good enough for 2in. wheels, and another floor bad even for tfin. wheels, in any case the large wheel turning more slowly must be better as regards axle friction than the small one. The ideal condition for floor and wheels will be, say a concrete floor, the wheels to be made of something just not so hard as the floor, and which will not distort under load, and will run without noise, using trucks that will turn round corners without side skid. The nearest approach to this ideal wheel material at present appears to be hard rubber.

A word might be said on swivelling castors, they are made of many patterns and designs. The best have good ball hearings with large diameler ball rare, so made and adjusted that they will turn easily-even when loaded. Cheap indif ferent designs have slack, rough, and small diameter ball or roller races, and these are much worse than good plain bearings. In any ease the best and most ample design that can be afforded should be fitted, and kept well greased and properly adjusted.