2. Requirements of a lathe

Bearing Centres - Faceplates - Tool Rests –Speeds

I hope that in the preceding chapter your interest in wood-turning has been roused and that you wish to 'do it yourself, as the various magazines and papers say these days.

Obviously, the old pole or Bodgers lathe will not be your choice for your workshop, so let us have a look at the basic requirements of your lathe to enable you to start turning.

As I have already said, the main items of any lathe are the headstock, tailstock, tool rest and lathe bed.

Headstock. This should have two good bearings, the left-hand one being, preferably, a ball thrust race, as this has to take a considerable amount of hard work when wood is being turned between centres. This is because the tailstock is held firmly into the wood and this exerts a pressure towards the left-hand side of the lathe. The right-hand bearing of the headstock is usually referred to as the main bearing and takes the thrust in a vertical plane.

It will be obvious that in turning between centres, or on a faceplate and when the chisel or gouge is cutting the wood, there is a tendency to lift the wood upwards, hence the need of a very good bearing here. I prefer this to be of the plain, tapered, adjustable type, so that play in the bearing can be kept to a minimum. Quite a few of the older lathes and particularly lathes used in the trade, have this bearing adjustable and made of phosphor bronze, some being very large indeed. Unfortunately, if the bearings are too large, the lathe will require quite a lot of horsepower to keep it going and I am sure the amateur will not want this type of equipment in the garden shed or workshop.

The headstock mandrel, as the main shaft is called, is usually fitted with a graduated pulley wheel of two, three or four steps to enable various turning speeds to be obtained.

I should mention here, that there are a few lathes where the electric motor is actually the headstock and that the various turning speeds are obtained by altering the speed of the motor by a variable resistance, or, as in the case of one American lathe, by means of a variable gearbox, built in the motor headstock assembly. The usual arrangement is by belt and pulley to a remote power supply.

To rotate the wood, there must be a pronged centre, fitted into the end of the headstock, either screwed in or a Morse taper push fit, which is quite common on amateur and professional lathes. These centres vary somewhat in shape according to manufacturers' whims, but are usually two- or four-pronged as shown in the diagram. The centre point should be about a quarter of an inch longer than the driving prongs or fangs, so that wood can be removed from the lathe and easily replaced if required. I prefer to use a four-prong centre, as, quite often, the two-pronged versions are easily twisted if one accidentally digs the tool into the work. I also find the four-prong centre gives a more positive drive in softish wood.

On small lathes, it is advisable to mark the end of the wood to be turned, by knocking the centre into the wood with a mallet before fitting it into the lathe. This prevents damage to the bearing, which could be caused if the tail-stock was overtightened. On larger lathes, the wood is placed between centres and the tailstock is turned and forces the work on to the prong centre, but you must have good bearings to stand this sort of treatment. Of course, when you are doing repetition work, if you are continually removing the centre and driving it into the work to be turned, you can get a little hot around the collar. It is the usual method, in the trade, to mount the wood between centres by guess-work, screw up the tailstock slightly, so that the wood is lightly held, and rotate the lathe by hand. The operator can easily see if the work is running true. If it isn't, just give it a tap with a piece of wood or your fist until it appears to be turning true. Judge this by eye. Now tighten up the tailstock and all is set.

After all that, perhaps you will appreciate what I am trying to stress about your driving centre. The good centre point will hold the work while you get it mounted dead centre and before the drive starts to rotate the work. Very few centres on the market do the job they are supposed to and it generally falls to the craftsman to shape them to his requirements. Figure 2 shows some typical driving centres although some awkward projects call for original ideas by the operator.

Tailstock. This is on the right of the lathe and its purpose is to hold the dead centre and support the end of the work when turning between centres, e.g. when making chair legs, etc. The tailstock must have two main adjustments. First of all, you must be able to move it bodily along the whole length of the lathe bed, and by means of a clamping device, lock it in any required position. Secondly, the part of the tailstock which holds the dead centre, must also be separately adjustable. This is usually by a screwed thread which will project or retract the centre and lock in any position. Most centres are held in the tailstock by means of a No. 1 or 2 Morse taper and can easily be removed by passing a tool through the hollow shaft. Some lathes have a self-ejecting device built in. This, of course, simplifies work a great deal.

There are three types of dead centres which are most commonly used, solid, cup and ball-bearing. The solid type have a point ground to 60 or 90 degrees, but have the disadvantage in that they usually work into the wood whilst turning and require continual lubrication and adjustment of the tailstock. The cup centre overcomes some of these disadvantages but unless well lubricated will heat up and burn the work. It must be appreciated that too much tension on the tailstock centre will have the effect of putting undue strain on the bearings at the other end of the lathe. Quite often when turning, you suspect something is wrong with your bearings or driving centre but the real trouble lies in the tailstock end. The ball-bearing centre overcomes all of these disadvantages and can be used continually with no attention whatsoever. They are more expensive than the plain centres but the extra expense is well worth it, for all the advantages obtained.

Figure 2. Some typical driving centres. (A) Two pronged centre. (B) Four pronged centre. (C) Plain or solid centre. (D) Cup or ring centre.

Some lathes have a tailstock which is easily removed from the bed completely. This is very useful when doing certain faceplate work. At least you do not get your elbow impaled on the dead center. Lathes manufactured by a few companies have tailstocks which are held in place by spring plungers and can quickly be released so that they drop away under the bed of the lathe and are well out of the operator's way.

Toolrest. So much then, for each end of the lathe. Now what about the middle, and I mean the tool rest. This is one part which really wants to be strong and well designed, as even in the best of hands it really has to take a hammering. With the small electric drill lathe, quite often this and other parts are made of die cast alloy and for the type of work undertaken this is quite satisfactory, but in larger lathes, say from 24 in. between centres, this is not really strong enough for the job. Cast iron or steel is much more satisfactory.

The actual design of the tool rest is another very impor­tant feature. You must have a rest which is easy and comfortable to use. Their design varies quite a lot. I prefer the square type of rest as this gives adequate sup­port for the tools and forms a natural guide for the fingers of my left hand which are holding the tool. Figure 3 will make this point clearer. Some woodturners will not agree on this point, but if you hold your tool lightly, as I want to show you, then the square type answers the purpose very well. People who hold their tools as if they weigh a ton, may prefer something different. Tool rests are manu­factured in various lengths and I would like to recom­mend having two or three of different length, say 6 in.,

Figure 3. Typical tool rest shapes.

10 in. and perhaps one of 18 in. for long slender work. In the trade, they quite often use a wooden rest running the whole length of the lathe. It is very useful for long work but for the type of work that the amateur is going to do, I would suggest that he leaves this type of rest alone until he has really got used to turning with a smaller more rigid tool rest. Still, if the idea appeals to you, there is no harm in making one up out of hardwood to suit your particular lathe. For repetition work the wooden tool rest has one great advantage. You can pencil on it details of design so that you do not have to keep referring to a pattern.

In all cases, the tool rest must be easily adjustable for height as this varies according to the type of work you are undertaking, and, of course, it must suit the habits of the operator.

Lathe bed. Some lathes in use in factories and old work­shops have a wooden bed consisting of two lengths of 2 in. × 10 in. pine spaced about 2 or 3 in. apart. The headstock is bolted through to one end and the tailstock with tool rests clamped and movable along the remainder, thus making a lathe of some considerable length if required. One feature of the wooden bed is that the whole lathe has a certain amount of springiness, which enables the work to be held more firmly between centres, without continually having to tighten the tailstock. Quite a few craftsmen still prefer this type to the modern all metal lathe. More modern types have pressed steel, flat cast iron, tubular steel or a solid round bar, all of which are quite satisfactory providing they are of ample proportions. I am very much in favour of the solid, round type, as it is much easier to keep clean and does not get blocked up with wood dust and chips.

Faceplates. Salad bowls, egg cups, plates, etc., are just a few examples of the type of work which is done using a faceplate to hold the wood to the lathe. Various methods are used for fixing the work to the faceplate. Two or three woodscrews is the most common. Some people prefer to stick the work to the faceplate and where screw holes would prove to be unsightly, then this method is very helpful. When you next take a walk round the store in your neigh­bourhood which specializes in woodware, pick up a few wooden bowls or plates and have a good look at their undersides. Some will have bases covered with felt or cork sheet, which is the usual method for hiding screwholes which held the article on the faceplate. Some will have bases which are polished, indicating some other method of chucking. Again, you may find a bowl which has no obvious clue as to how it was held on the faceplate.

For more general use, the woodscrew chuck is invaluable. This consists of a small faceplate, usually about 2 to 3 in. in diameter and having an ordinary woodscrew fixed to its centre, either by being welded or clamped by a special locking device. The advantage of the latter is that the wood­screw can easily be replaced, if it should be damaged. Another feature of the woodscrew chuck is the ease with which the wood can be readily removed, and in repetition work this is most important. Having just the one central fixing screw, it will be seen that when the wood has been removed, it is quite a simple matter to replace it in its previous position, whereas with the normal type of face­plate, with its multiple screw fixing, it is sometimes quite impossible to remount the wood in its original position if more work has to be done. There is no reason at all why quite large bowls cannot be turned on the woodscrew chuck and recently, at an exhibition, I surprised quite a few people, including myself, by turning a mammoth bowl of over two feet in diameter on this type of chuck. Providing your cut­ting tools are used in the correct manner, you will not have any trouble with this useful attachment. The question of using your cutting tools correctly is a very important aspect of woodturning, if trouble is to be avoided, and in a subse­quent chapter I hope to make you quite happy on this point.

I have mentioned a lot about bowls only to show you that faceplates and faceplate chucks are quite a problem and it is difficult to make any hard and fast rule about them. Such a lot depends on the type of work to be undertaken. I shall go into this in greater detail in the chapter on faceplates and bowl turning.

So much then for the essential parts of the lathe, which I hope will help you to understand the lathe more thoroughly. No doubt you may be able to suggest other features but I hope that by the time you have reached the end of this book, most of your queries will have been answered.

Speeds. One thing which was lacking in the primitive lathe, was a constant source of power and speed, but thanks to the small electric motor, we can quickly overcome both of these problems. The speed at which your lathe must run depends entirely on the diameter and balance of the wood on the lathe. You will understand that if your lathe has one fixed speed, say 2,000 r.p.m., you must exercise great care on the larger diameter work, as any unbalance of the work will cause vibration and probably the wood will fly off the lathe, causing you injury if you should be in the way; but if the wood were only 2 or 3 in. in diameter, all would be well. There are quite a few technical books on wood machining and in them you will find all sorts of equations and formulae, telling you what speed the outside of the wood should travel in feet per minute. This is all very well and interesting, but as most lathes have only three or four speeds at which they can run, then we must have some rule of our own which will help us to choose the most practical speed at our disposal. I have found the following speeds satisfactory, assuming of course, that the piece of wood is true and mounted centrally on the lathe.

Diameter in inches r.p.m.

1-2                               3,000
2-4                               1,500-2,000
4-6                               1,000-1,500
6-8                               750-1,000
8-12                             450-750

You will see that as the diameter of the work increases so the speed of the lathe must decrease, but if your lathe has not a speed range as shown, do not be disheartened. You just choose a speed which corresponds as near as you can get to those which I've suggested. It will be possible to turn at higher speeds than I've shown, but there is a great disadvantage in turning too fast, and that is the heating up of the cutting edge of your tools, so you may turn faster, and create a fine shower of shavings, but you will be spending twice as long trying to keep your tools sharp. Owners of lathes driven by electric drills will find the speed of the drill is higher than the speeds I have men­tioned, but this is quite all right, as by the design of the machine, there is a restriction on the maximum diameter of work which can be tackled. Some types of drills are now fitted with a two-speed device which makes the tool more flexible.

If the work, when it is placed on the lathe, is unbalanced due to rough cutting out, it will be necessary to turn at a much slower speed until the work has trued up. The amount of vibration set up on your workbench will soon give you the clue that you are turning at too fast a speed. One final point on speed, and that is your choice of electric motor, and here I would suggest one of not less than 1/2h.p. and supply­ing a constant speed of 1,425 r.p.m. This, fitted with a three-or four-step pulley wheel, will supply all the range of speeds for turning anything up to 12 in. in diameter.

Quite often one is offered a choice of electric motors when buying a lathe, either 1,425 r.p.m. or 2,800 r.p.m. Both are quite suitable for lathe work, but if large diameter work is contemplated, e.g. salad bowls, etc., I would prefer to have the slower speed for greater flexibility. The faster motor could be used with a counter shaft to reduce the speed, but I don't like lathes festooned with additional belts and pulleys.

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