For the reconstructed ship of the line 'De Delft' a total of around 1100 blocks are required. There are currently 700 ready, in various types and sizes. Blocks are made for guiding rope, to control forces and to help with hoisting. Blocks are made using a different number of sheaves (or pulleys): single-sheave, double-sheave and triple-sheave (even up to a maximum of 7-sheave). One of the rooms at the yard is set up as a block mill: there are a number of large workbenches with bench vices, a large barrel of linseed oil and cabinets full of tools.
The blocks for the 'De Delft' are made in the traditional way by hand; sawn, drilled, gouged and planed. The block-maker has written a manual for block-makers, which is used by the students.
When making the blocks some traditional techniques and materials are used, as well as some modern techniques and materials because it is handier or because the original materials are no longer available. For example, the sheaves over which the ropes run were previously made from lignum vitae, which has self-lubricating properties. Lignum vitae is a protected type of timber which can no longer be obtained. The sheaves for 'De Delft' are therefore made from polypropylene, a strong plastic. The sheaves are turned on a lathe. The grommets (strops) around the blocks are also made from Leoflex synthetic rope because it lasts longer than traditional manila rope which rots away from the inside out in fresh water.
Materials and tools
The shells for the blocks of 'De Delft' are made from elm. The shells are constructed from various processed planks of elm that are bonded together. Elm is a tough, water-resistant and easy to machine type of wood. Shells were previously made from a single piece of oak that was riled and gouged into the required shape.
A workbench with a vice is required for making shells, plus various gluing clamps for securing the work pieces during processing. Additional handy tools include an electric band saw, planer/thicknesser machine, lathe and bench drill. Hand tools, such as drills, planes, gouges and rasps are also used. Always make sure that the tools are sharp in order to prevent the wood from splintering or chipping. Adhesive is also used for gluing together the various pieces of wood from which the shell is constructed. A metal axle pin is used, which should preferably be made from stainless steel. A square piece of leather is also used to seal off the axle pin hole. Finally, you require a barrel of linseed oil into which the shells are submersed in order to saturate the wood with oil to make it waterproof.
It is handy to work using jigs in order to obtain the correct shape. You can make them yourself from cardboard, hardboard or plexiglas. The jigs are best made from a drawing.
Proceed with the following steps to machine a block of wood into a shell:
- You start by sawing a number of pieces of wood from a plank of elm for the cheeks, the sheave spacers and the crown and tail spacers. For sawing make sure that you measure the required pieces accurately and that you saw them accurately. Correct operation of the block requires precision. Do not use wood with knots because these weaken the wood. Every type and size of block has its own sawing sizes. The block-maker for 'De Delft' has produced a table of sawing sizes. NB If you want to make more blocks of the same size then it is handy to immediately saw more planks to size so that you can finish them in batches.
- Once the pieces of wood have been sawn to size they are planed to the correct thickness using a planer/thicknesser machine.
- One side of the crown and tail spacers is hollowed out (to form the swallow and the breech) to allow the rope to be inserted through the block. The spacer is hollowed out using a rounded plane and a gouge to form a semi-circle. Make sure that you leave enough wood on the sides of the area hollowed out so that wood does not splinter off. Any sharp edges should be smoothed using sandpaper.
- The wooden parts of the shell (cheeks, sheave spacer and crown and tail spacers) are joined together by gluing and securing using wooden dowels.
- First of all, make the correctly sized wooden dowels by turning slightly oversized square sticks to the correct thickness dowels on a lathe. Here too, the dimensions must be precise.
- Before the parts of the shell can be glued you need to drill the axle pin hole and the dowel holes in the wood. To prepare for drilling set out the parts of the shell first, in the correct sequence. Place the cheeks (and for multiple sheave blocks the sheave spacers as well) against each other and clamp them together using the gluing clamps. Now mark the precise position of the axle pin hole.
- An auger bit is used for drilling the axle pin hole. This is a very long drill bit that you can fit into a bench drill. The drill bit has the same diameter as the axle pin that you will insert into the hole later. Before drilling holes make sure that the wood pack is completely secure underneath the bench drill, for example in a vice or by using large clamps or brackets.
- The dowel holes can now be marked off. To do this you also add the crown and tail spacers to the pack in the correct position. Add sheave housing packing pieces at the position where the sheaves will be located later. Insert a fitted pin in order to keep all components in the correct position. All of the components can now be re-clamped together using the gluing clamps. The correct positions for the dowels can now be marked off.
- An auger mounted in a bench drill is also used to drill the dowel holes but this time you use a smaller diameter auger. The wooden pack, now with the crown and tail spacers in between, has become thicker. Drilling the dowel holes is precision work – therefore work with patience and accuracy. Do not apply too much pressure on the drill bit in order to prevent the drill bit from wobbling. Let the drill bit do the work and allow it to drill into the material slowly. If the wood pack has become too thick to be able to drill through the entire hole in one go it may be necessary to drill the dowel hole from two sides, whereby you have to drill through precisely opposite the first drill hole. This is an even more precise job. It is preferred that several people work on this so that it will be easier to operate the bench drill.
- Now that the axle pin hole and the dowel holes have been drilled, you mark the correct position of the wooden parts by numbering them on the ends using a pencil. You can now release the gluing clamps and place the individual parts next to each other, safe in the knowledge that later, with the glue applied, you will be able to reassemble them in the correct sequence.
- Glue the wooden parts together using water-resistant wood glue (do not use D4 adhesive!), that you spread onto the bonding faces of the wood parts using a spatula. Place a piece of cardboard on the workbench first in order to prevent the glue getting everywhere. Place one cheek on the piece of cardboard. Now coat the underside of a dowel with glue and insert this dowel into the cheek. Repeat this for the other dowels. The next wood parts are assembled in sequence (crown/tail spacer, sheave spacer) after you have coated the faces with glue using the spatula. Finally, slide the last cheek over the dowel holes. All of the wood parts have now been reassembled. Now insert the fitted pin through the axle pin hole and clamp all parts together using gluing clamps. Leave the glue to set for at least one day. Once the glue has set properly you can cut away any surplus glue using a paring chisel. The protruding parts of the dowels can also be sawn off now.
- The shell now has its rough shape, even though it is still a square pack of wood parts. You can now give the shell its oval shape. This is done using a band saw. Using the correct jig you now mark the required oval on the cheeks and then saw off pieces of wood using the band saw, keeping outside of the pencil line. This creates a rough oval shape. The last pieces of wood can now be sawn off carefully, up to the pencil line, using the band saw.
- The outside of the shell that you have just sawn into its rough oval shape using the band saw is now smoothed using a small block plane. To do this you secure the shell in the vice using an auxiliary timber that you secure to one of the cheeks using a length of stuffing, two washers and a nut. Use the jig for checking when the shell fits precisely through the jig.
- The cheeks can now be given their rounded shape. The best way of doing this is to use a normal disk, though there are also block-makers who prefer to use a paring chisel. Shave the wood with the grain and work from the long sides towards the short sides. Finish off using a block plane in order to prevent removing too much material in one go. Use the jig to check when the cheeks have reached the required curvature.
- The next woodworking operation is to form the scores. The strop is a very strong piece of rope that is applied around the shell. The strop has two functions: to suspend the block from the stop and to confine the axle pin. The score is a recess in the shell to prevent the strop from slipping off the block, even when excessive force is exerted on the block. The score runs from the crown of the block downwards and its width is that of the strop rope wound with thick tarred twine. At the mid-point of the shell the score has virtually no depth and gets deeper the closer it gets to the short sides. The score is made by marking off the width of the score on the cheeks. The wood is then removed using a sharp gouge, working from the centre of the shell towards the short side. On the short side the score has a depth of approximately a semicircle. The pencil line can be cut very slightly and carefully using a paring chisel so that the score is given a nice straight line.
- The woodworking on the shell is now complete. Now suspend the shell from a piece of twine into a barrel of linseed oil so that the shell is covered by the linseed oil. The shell is left submerged in the linseed oil for a week so that the wood draws in the linseed oil completely. The linseed oil makes the wood water repellent and extends its working life. After a week in the linseed oil bath the shell is allowed to drip-dry and then dry.
- The axle pin and the sheave or sheaves for the block are now made on the lathe. The axle pin is made from stainless steel and the sheave from polypropylene, a strong plastic. A square is formed on one end of the axle pin.
- Now insert the sheave or sheaves into the shell and insert the axle pin through the shell. On the side with the square end the axle pin cannot be pushed through. Fix a small square piece of leather on the other side, using four small stainless steel nails in each corner to secure it to the wood.
- Finally, make the strop. To do this, take a piece of Leoflex rope, which is synthetic rope with a steel core. The piece of rope must be long enough to be able to go around the shell, in the score, and be able to create a loop at the crown of the shell through which you can push your hand. For handling the rope see the skill ‘splicing’. Once the ends of the strop rope have been spliced together you whip the entire strop securely using tarred twine. This creates a very rigid loop that you will only be able to distort slightly with effort. The loop is then placed in the scores and drawn tightly upwards. At the crown of the shell you draw both sides of the strop together and whip these together tightly over a few centimetres using tarred twine. Attach the tarred twine securely so that it cannot come loose. The shell is now enclosed within the strop and the block can be hung up by the loop in the strop at the crown.