The polelathe is constructed from timber in such a fashion as to make it portable but still rigid enough to turn accurately. There are a number of points that you should take into consideration when building a lathe, some of which will be important to you, some of which should not be ignored and others where you can use your own judgment. Use structural or furniture grade timber. The better you make your lathe, the more likely it will be a joy to use. Choose hardwood for preference or dense softwood if you have that. The lathe will take a lot of knocks and blows so resilience is a prime consideration. I used mainly english chestnut, because that is what was available. Others have used oak, ash, beech and pine. Some have recycled timber from sofas, tables and floors. For those of you in the USA hickory could make a fine lathebed. None of the metalwork need be anything other than mild steel, including the centres. Threaded rod of 10 & 12mm together with nuts and generous sized washers will suffice for both centres and fixing bolts.
Firstly, you will be standing at this lathe balancing on one foot and pumping the treadle with the other. Your hands will be busy and your back must be straight. The effort involved is about that of a brisk walk. The ergonomics of your lathe are important. Take a tape measure, hook it under your heel and measure to the top of your hip bone when you stand up straight. You are building a lathe for You and this is the height of the top of the lathe bed. It may seem tall but stick with it or suffer back pain and misery. The centres will be between 6" & 8" ( 15-18cm) above the bed. Make the bed as long as you can reasonably accomodate, this may be dictated by how long a piece of timber will safely and comfortably fit into your car. Remember, any turning over about 2'6" (76.2cm) is likely to need a 'steady' to prevent it whipping and chattering as you try to turn it. Polelathes may have a double or single piece of timber serving as the bed. The design described is a double bed. The end frames are made in such a way as to have parts under tension, torsion and compression when assembled. This gives a rigid support that does not work loose or slacken with age.
The easiest way of getting all the angles and lengths right is to draw a full size plan of the end frame on a large piece of paper. Pin it to the floor and mark off your timber against it. This way you will not have to struggle with calculating angles and triangles. Include the marker lines so that you can easily see where to mark your wood when it is laid on the drawing. The bottom of A has a tennon that fits into a recess cut into the end of C.
The socket cut for the tennon on the bottom of A in C should be a good fit side to side and the external face should be accurately cut. However extend the socket quarter of an inch further in towards the central leg to make it easier to assemble and dis-assemble. The top of A is not a tennon but wedges up against the end of the lathebed and the central leg. The force required to hold the legs into this position comes from the following construction.
1. Cut the leg B half an inch (12mm) shorter than on your plan.
2. Drill a 10mm hole centrally into the bottom of B.
3. Slightly widen the very start of the hole to 12mm.
4. Screw a 110mm (4.5") length of 12mm threaded rod into the bottom of the leg until about 50mm is in the wood.
5. Drill a 20mm hole 10mm deep centrally in the bottom of C and then continue the hole with a 12 mm drill right through. The 20mm hole will form a recess for the nut that goes on the end of the rod inserted in B and passed through C.
6. Drill two 20mm recesses and 12mm holes through the lathebeds D and the top of the legs B
Now when the beds (D) are bolted tight to the legs (B), angles (A) are inserted into the base (C), held in place while the nut on the rod is tightened pulling the base (C) hard up into a slight bow caused by B being slightly shorter than drawn. The force of this will pin the angles (A) tightly in place between the base and the bed. It is actually easier to assemble the lathe upside down. Bolt both B s to the upturned lathebeds (D) and then put a C in place with a nut two turns onto the rod. Slip the two angles (A) into place, gravity will hold them once they are in and resting on the bed. Tighten the nut and repeat the other end. now turn the lathe over. You should find that the whole thing holds together quite rigidly. The wear feet serve several purposes apart from preventing wear on the base. The lathe will stand better on uneven ground and is more stable due to the weight being transferred to the ground via the extremities of the base, rather like standing with your feet apart.
Hint: to screw threaded rod into wood you can do the following; take two nuts and thread them onto the piece of rod. If you then tighten one against the other they will lock on the rod. Now you can wind the 12mm rod into a 10mm hole so that it forms its own thread in the timber. Remove the nuts by reversing the locking procedure. I did this four years ago and the rods have shown no sign of pulling out.
Hint: Use 10mm threaded rod and drill 20mm recess with 12mm holes to attach the bed to the legs to make it easier to line up and slip the bolts in. Use stout washers wherever nuts would come into contact with wood so that the wood does not get chewed up.
The two inch gap between the beds serves as a location slot for the bits that carry the centres, these are variously known as poppets, puppets or stocks. Whatever the name they serve the same purpose. They will require accurate work but it is not desperately difficult.
Use the same 12mm rod in a 10mm hole method for the centres. Mark the centre of the rod and gently grind the centres at about 45 degrees, they do not need to be a sharp point so concentrate on an even cone. The headstock centre needs about 30mm of rod clear of the stock. The tail stock centre should pass right through and have 4" (100mm) out of the rear for a handle to be attached. Soak the tailstock hole in linseed or other oil so that when the centre is inserted it can be screwed in and out to set work up in the lathe. It will be tight but changes in air moisture will mean sometimes it is looser than others. To begin with use two nuts locked together on the rear and a spanner or wrench to screw it in and out. Later you can turn a nice knob to fit on the end, locking it in place with a locking nut.
The lower part of the stocks pass between the beds and are held in place by a wedge. The wedge can be improved in the following ways;
* Glue leather to the upper surface so that it grips the bottom of the lathebeds.
* Chamfer the edges so that the wedge is less likely to split when hit by a mallet.
* Drill a 6mm hole through the side of the thin end and once the wedge is inserted through the stock, push a thin peg of wood through the hole. This will allow you to loosen the wedge without it falling on the floor every time since the peg will prevent it passing back through the stock.
I used Elm and Scotts Pine to make my stocks. Avoid Oak and Chestnut since the tannin will eat the metalwork. It is well worth the effort of carefully rounding off all the sharp edges on your lathe. I got used to avoiding the edges but then I lent my lathe for a demonstration leading to a bloodstained lathe and a turner with sore knuckles.
The tool rest does not need to be adjustable for height. The height should be level with the centres. Some lathes are fitted with a simple bar rest that is attached to the stocks for support. However I prefer a scheme that allows more flexibility with regards to positioning. Described below is an independent tool rest that allows close positioning for effective turning.
A handle could be added to the wooden disk although I find I can tighten the tool rest sufficiently just by turning the disk. Glue leather to the bottom of the tool rest to improve the grip onto the bed. The tool rest is best made of a strong dense wood. You could use marine ply about 1" thick. The main thing is that it should transmit the force applied to the gouge by the work to the bed without distorting. Make the slot just wider than 12mm so that the rest can be adjusted easily. The brass strip is a refinement that I found useful. Recessing it into the top of the rest and epoxy resin have secured mine for two years.
The treadle can be as simple as a stout stick, indeed, I have seen a bodger use just this when demonstrating. Not because of any misguided machismo but because he left his at home by mistake. A better idea is to make one that is comfortable to use over a long period. Contrary to what you might expect it is not the leg doing the treadling that starts to ache first. It is just as important to make sure the foot you stand on has a flat surface on which to rest. The back foot also serves to anchor the position of the treadle. To this end the treadle is attached to a board about 18"(45cm) wide by 15"(40cm) front to back. My favoured treadle has a board made from 6mm plywood, thick enough to be robust but not so thick as to present an uncomfortable ridge if my foot is partly over the edge. The treadle itself need only be made of softwood. I use parts of an old leather belt to make the hinges. Metal hinges will tend to buckle on uneven ground whereas leather copes well. The treadle needs to be about 3ft (1m) long. If it is longer it will have a longer stroke but the cord will be at an acute angle to the work.
A rounded end to the bottom of the treadle will help prevent the treadle creeping forward as you work. The treadle ends should rest on the ground and not on the board, so make sure there is enough slack in the hinges to allow this. Attach the cord to the treadle head by a simple double half hitch to form a slip noose around the head. To shorten your cord to the desired length, just wind it onto the head a few turns. Round off the top of the treadle bar so that it it comfortable for your foot when pressing down on the treadle. To work the treadle, stand with one foot on the board and press down on the treadle bar and release it. A nice steady rate of about once a second is fine.
The spring that returns the treadle to the raised position after each downward stroke can be made in several different ways.
Traditionally, it would have been a long pole, up to 20 ft (6m) in length. Often it would have been a tall sapling such as one finds growing among more mature close planted woodland. These tend to be long, spindly and will not survive under the canopy of the older trees. Ideally it should be about 2" (5cm) at the base and 1" (2.5cm) at the tip. In use the base is anchored to the ground or the base of a stout tree. An A frame of stout timber provides the fulcrum over which the pole is bent as the treadle cord pulls it down. A shorter pole will give a shorter, more snatchy action. Using such a pole is like riding a bike that it too small for you - painful and inefficient. The setting up and adjusting of the traditional pole requires some practice. Moving the fulcrum point along the pole will change its behaviour. Bodgers refer to this as 'tuning' since you are trying to make the natural frequency of the pole match with your natural frequency when pushing the treadle.
A simple alternative to the pole is to use a bungee cord or bicycle inner tube in place of a pole. It may not be elegant but it is a pretty good substitute. Points to note are that the distance between the supports of the bungee and the height of the bungee above the lathebed should be as great as is practical otherwise you will find in the first instance that the bungee reaches full stretch before the treadle hits the ground, and in the second instance the treadle cord pulls the bungee down to the work and the bungee then becomes a menace to the operator. Use an anorak toggle, the type with a spring in it to fix the treadle cord to the bungee so that you can release it easily. If you tie it on directly the knot will tighten onto the bungee making adjustment difficult.
A more complex alternative is the bow and bobbin. My experiments with this are covered elsewhere.