Making Rope Stropped Blocks
Have you ever secretly yearned for some of the pictuesque gear of the old squareriggers, deadeyes and lanyards, tarred hemp and canvas buckets, salt horse casks and handy billies?
Have you ever tossed in your bunk on a windy night, cussing away as the noisy deck block clattered and banged away just above your ear?
If so, you need some rope stropped blocks. There was a time when all blocks were rope stropped. They were made in endless variety, each designed for a specific job, tested and proved through the years by hard usage. They were handmade by men who were masters and took pride in their craft.
A block is a single or multiple pulley. In use, a block is fixed to the end of a line, to a spar, or to a surface. A line (rope) is reeved through the (pulley) sheaves, and maybe through one or more matching blocks at some far end, to make up a tackle. 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-sheaves).
HOW TO MAKE A MORTISED
ROPE STROPPED BLOCK
The Sheave: The first step in making the block is actually to select the size and type of sheave you want to use. The sheave is a solid cylindrical wheel, and round its circumference is a groove one-third of the thickness of the sheave deep, in which the rope works.
Historically, it is commonly made of lignum-vitae; but when used for very laborious purposes, it is coaked in the middle with metal.
Today, the best type of sheave is a commercially made self-contained ball-bearing sheave. The ball bearings will minimize friction, and give you a very long life. There are several manufacturers including Harken, and Ronstan. The Harken #160 bullet sheave is a good choice for small boat/yachting use and can handle a line of up to 5/16", in comparison a Harken #265 "big bullet" can handle a line up to 3/8".
Alternatively, you could also buy commerically made metal or plastic (nylon) sheaves. The better sheaves usually have as stainless steel bushing which prevents the plastic from deforming. You can get these from a variety of sources, at a fairly low cost. A very good economical choice is Duckworks Boat Building supplies.
Lastly, you can make your own sheaves, the traditional method is to make them out of lignum vitae, a hardwood which is self-lubricating. Lignum vitae is very rare and hard to source nowadays, - but it can be had from specialty wood working supply stores, such as Lee Valley Tools, Woodcraft, Rockler Woodworking and Hardware, or Exotic Woods USA. In lieu, you could also use other suitable hardwoods such as walnut or locust. In terms of cutting the sheaves, the traditional method is to either turn a dowel on a lathe, and then part-off the sheaves. If you dont have a lathe, a hole saw can work just as nearly well, and then the groove can be made by running a bolt through the middle to make a mandrel, so it can be turned and scored.
Other materials for making sheaves include UHMW (Ultra High Molecular Weight) polyethylene, which is soft enough to be worked with wood working tools, self lubricating, and impervious to moisture. It can be obtained in small quantities from wood working suppliers such as Lee Valley Tools. Alternatively, you could also use those cheap plastic cutting boards, the white ones, which would be suitable enough for smaller sheaves.
In terms of making your own sheave, the formula for the traditional dimensions are given in The Elements and Practice of Rigging And Seamanship, 1794, by David Steel as:
"the thickness of the sheave is one-tenth more than the diameter of the rope it is intended for, and the diameter of the sheave is five times the thickness."
So basically, this means a 1/2" rope should have a sheave about 5/8" wide, and a diameter of about 3 1/8" according to the traditional means. In comparison, a 1/4" line would have a sheave width of about 3/8", and a diameter of 1 1/2" to 1 5/8" in. In terms of the depth of the groove, according to David Steel, "the outer circumference hollowed one-third of its thickness, that the rope may embrace it closely".
In our blocks, we used commercially manufactured sheaves, the cost can range from $3-30, but knowing that we have a long-life well working sheave with minimal chance of failure is nice piece of mind.
STEP 1: To make a mortised block, the first step is to find a nice solid piece of wood to cut your block from. Traditionally, the best woods to use are hardwoods with an interlocking grain that resist splitting and cracking but are easy to carve and won't dull chisels. Elm or Ash is preferred for creating blocks, and has been the choice for centuries. However, today, many exotic woods are available that not only have great properties, but also an awesome estethic appeal, examples include: canary wood, rosewood, sycamore and black walnut. You can order these species through mail-order suppliers, such as Lee Valley Tools.
However, our preference is to use local species whenever possible, such as a re-purposed old walnut plank, or wood cut from a tree. If you are going to use wood cut from "your own backyard" make sure that it is throughly dried and seasoned. If you don't, the "green" wood may split and crack during the drying process ruining your blocks.
In our case, we used wild cherry. Cherry wood is very hard, and can definitely be difficult to work with hand tools, but it has a very nice grain, and is readily available in our area. The heartwood of cherry is also very durable to rot and decay.
A nice well seasoned piece of wild cherry
that we plan to use for our wooden blocks
STEP 2.: Once you have selected the wood, you will need to cut it to the size of your block. A good rule of thumb is that the block width should be three times the width of your rope, for example, if you have a 1/2" rope, your block should be at least 1 1/2". In terms of height, a general measure is twice the diameter of your sheave. You can always trim and shave down excess bits of wood, but you can't add wood back
We cut the cherry to the size we needed for our mortised blocks.
As far as the general shape, the first blocks used in ships were simply a square block, but by forming the block, the improved shape not only reduces weight, but prevents marring of the deck and spars and will not be as prone to getting fouled up in the rigging. The traditional shape of wooden rope blocks is similar to an egg, with an oval appearance, however you can use your own discretion to determine your own shape.
We drew out the rough oval shape of our block to be
cut out of the "blank" with a bandsaw.
STEP 3.: Cut the block to your desired shape, an egg shape is traditional, but it doesn't hurt to be a little creative - and you may want distinctive looking blocks. A "clump block" is nearly circular. The diagram below of a tradition block is from the Marlinspike Sailor, by Hervey Smith.
An example of a "traditional rope stropped single block"
We rough cut the shape of our block with the bandsaw, we will further finish
by using hand tools such as a rasp and sandpaper.
STEP 4.: Now that the block is cut to shape, it is time to mark the location of the mortise. In a typical block the swallow (the space above the pulley) is usual larger at the top than the bottom. In sizing the mortise, you want to make sure then length is at least 1 1/2 times the diameter of your sheeve. The mortise should only be as wide as the sheave can spin freely, too much play in the sheave will create wobble, and require the use of shims.
Mark the shape of the mortise
it should be longer than the sheave.
The mortis is marked and ready to be hollowed out.
The traditional method of hollowing out a mortise is to use an auger, or a hammer and chisel. In the early 1800's in England that had a special machine in the dockyards in Portsmouth. Today, we can also use a fixed router and table or a plunge router with a jig.
Master woodworker Ian Kirby still makes mortises with a hammer and chisel.
Click hereTo find out more on this method from Rockler.
Here is another method: Lumberjocks
Of course there are other methods, one could use a brace and a bit, or a drill press, and finally a router. In our case, we opted to use a router jig for a plunge router since we planned on making a number of blocks. While less traditional, even with the router jig, we required fine tuning the mortise by hand with a rasp and file.