How To Make Rope Stropped Blocks

How To Make Rope Stropped Blocks

Making Rope Stropped Blocks

Mortised Rope Stropped Block

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). 

A block was originally a block of wood with a hole in it for a rope to reeve through. To save friction the hole was enlarged to take a pully-wheel or sheave. Then the surplus wood was cut away from the outside of the block, leaving a wooden shell. This was grooved to take a rope strop spliced round the block to secure it in place as required. When the wooden shell split the block was useless. The next improvement was the 'iron-bound block' in which the strop or hook was rivetted to an iron case carrying the sheave and its pin, the wooden shell serving to stiffen the case. Today the larger modern blocks are made of metal, and friction is further reduced by roller-bearings between the sheave and its pin.
There are various types of blocks that are used in sailing. Some blocks are used to increase mechanical advantage and others are used simply to change the direction of a line.

There are basically  two sorts of block construction: mortised blocks, and made or built blocks.
 
A mortised block is made from a single piece of wood, that is mortised or hollowed out to fit a sheave, some of the largest morticed bloacks are 28 inches in size, or over two feet! However, typically for small boat use, a mortised block is about 3 inches in size.
 
A made or built block can be constructed to any size, and is used on both small and large blocks. Some of the largest made blocks are up to fifty inches in size! The number of pieces it is composed of depends upon the number of sheaves; as the partition between each sheave is a separate piece, they are bolted together by four bolts or rivets, two at the top, and two at the bottom, and are typically  fitted with metal sheaves, and a shoulder to one side of the shell.
 
The size of a block is denoted by the length, and its classification by the flatness or thickness of the shell, the number of sheaves, the number of scores, and the quality of the stropping.
 
For instance - if a shell of a block is 6 ins. in length, it is called a 6-in. block ; if it is 10 ins., 15 ins., or 20 ins., it is called a 10-in., 15-in., or 20-in. block, according to whatever length the shell might be.
 
A block, if one sheave, is called a single block; two sheaves, a double block; three sheaves, a treble; four sheaves, a fourfold block, and so on, according to the number of sheaves.
 
If one score, it is termed a single score block; if two scores, a double scored block.
 
There are rope strops and iron strop-blocks,  can be both double and single. The rope stropping is fitted in various ways: for instance, single strops, double strops, and two single strops, according to the stand the block is required to have to establish a fair lead with any given point. 
 
A block is supposed to carry a rope one-third its length in circumference : that is to say, a 6-in. block a 2-in. rope, an 8-in. block a 2½-in. rope, a 9-in. block a 3-in. rope, and so on.
 
Types of sailing bloacks 
Various types of sailing blocks - including the stropped block
 
Parts Of A Rope Stropped Block
 
Parts Of A Block
Parts of a rope stropped block
1. Shell
The shell is the outer housing for the block. The shell holds the sheave (pulley) and pin in place and is surrounded by the rope strop. A shell can be made of wood or iron. Commonly used woods are : ash and elm.
 
2. Sheave
Is the wheel on which the rope travels, and can be ade of plastic, metal, lignum-vitae, or iron. In some cases the sheave can contain roller bearings to reduce friction. In small boats, a variety of manufacturers make sheaves with delrin ball bearings, for example the Harkin 160, bullet sheave.
 
3. Pin
Is the axle on which the sheave sits. It usually has a head on one end, and passes through the centre of the shell. The pin is typically made of metal, either stainless steel, iron or brass. However, in older times, lignum-vitae or hardwood might be used on smaller blocks.
 
4. Crown & Tail 
The ends of the shell, the crown is at the top of the shell, and the tail at the bottom, usually the score in the tail is slightly longer and wider than the crown.
 
5. Swallow
Is the open part between the sheave and shell.
 
6. Score
Is the groove in the outside part of the shell to take the strops either single or double scores, according to what the blocks are required for. Double-scored are always double-stropped.
 
7. Strop
A strap, especially a short rope whose ends are spliced together to make a ring known as a gasket, that serves as a band to support the block. Strops can also be made of metal or iron.

HOW TO MAKE A MORTISED
ROPE STROPPED BLOCK

 

Nylon Sheeve

1.THE SHEAVE

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.

Block Mill
In 1794, a block mill was used to create large sized sheaves.

2.THE BLOCK

rope block shell

Block Diagram
Basic Block Diagram from
The Marlinspike Sailor, by Hervey Garrett Smith

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.

cherry wood
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

cherry wood
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.

Shaping
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. 

Rope Stropped block diagram
An example of a "traditional rope stropped single block"

 

cutting to shape
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 mortise
Mark the shape of the mortise
it should be longer than the sheave.

mortise
The mortis is marked and ready to be hollowed out.

3.THE MORTISE

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.

Mallet and Chisel 
Master woodworker Ian Kirby still makes mortises with a hammer and chisel.
Click hereTo find out more on this method from Rockler.

mortise and chisel
Here is another method: Lumberjocks

 


hand brace and bit mortise
The brace and bit method of making a mortise

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.


A simple plunge router jig
makes block mortises quick and easy

 


 

How To Make Rope Stropped Blocks - Part 2

3. Boring the Pin Hole

The next step is to bore the pin hole. In doing this it is best to use a drill press, and a clamp or jig to hold the block in place, a misalignment of the bore hole for the pin can create some difficulties. In the absence of a drill press this can all be done with a hand drill, but take care to ensure that the pin hole is absolutely square to the block. Any major misalignment of the pin will result in a block inclined to jam its sheave. 

Finally, you will want to score the block to help hold the strop in place. The scoring can be done with a round file, and you may want to round the edges and sand down the outside of the block to a smooth finish.

If you cut a tenion, you can place the mortise of the block over the tenion, and use it to hold your block while you file away at the excess wood. The tenion can be clamped in a vise or held in your hand. 

A simple block holder
A simple "block holder" to make filing and rounding easier

block
Filing, scoring and sanding the block to shape
 

4. Finishing the Block Shell

A microplane rasp is a great tool for helping to finish your block. In some cases it has been suggested to use a round over cove bit to help round the edges. You can also achieve similar results by using a sanding disk. In any event, you will definitely want some kind of pocket rasp. All of a sudden coffee and lunch breaks become "boat building" time as you can rasp away at your wooden block!

microplane shaping rasps
The original Microplane© Shaping Rasp is a great
tool for working on wooden blocks

Once you have finalized the shape, and sanded it smooth, it is time to finish the block to prevent cracking and splitting. There are various methods of finishing the block, it can be covered in epoxy resin, soaking in oil, or varnished.  The traditional method of soaking in linseed or tung oil is very effective, offering a nice patena and good protection.

People have known about the unique properties of linseed oil for several thousand years. Linseed oil penetrates into wood, protecting it from moisture and rot.

Use boiled or double boiled linseed oil for best results. The raw linseed oil is purified and refined through the addition of oxygen to produce boiled or "cooked" linseed oil. This process eliminates protein and improves aspects such as the drying time, shine and purity. Even though linseed oil that has actually been boiled is still available -- it's called heat-treated or polymerized oil -- most of the boiled linseed oil sold these days that you find in the "big box" stores such as Home Depot, Canadian Tire, Home Hardware, or Lowes is raw oil that has been mixed with chemical additives to speed up the drying time. For wood finishing, you should use only boiled linseed oil. Thus, boiled linseed oil, though, is not boiled. The actual boiling of some varnish oils changes their drying characteristics. With linseed oil, though, it is the addition of certain solvents that causes linseed oil to dry more quickly, acting as if it were boiled. This makes it a better product for preserving tool handles, decks, and furniture.
 
Double boiled linseed oil contains a blend of driers (no lead) and inhibitors to get a high quality product that will dry to the touch in 8 to 10 hours. Also, with the inhibitors added, they ensure the final product will not be attacked by mold or mildew.
 
If you do plan to use raw linseed oil you will need to put it through a "boiling process" first. In this procedure, fill a can with raw linseed oil, submerge the shell and heat it gently until it starts to boil, cooking it for a minimum of a half an hour. The longer you "cook" the oil the better, it is suggested that you "cook" the oil for about three hours. In performing this process be careful not to overheat the oil, which could cause it to combust, or burn since it is cold pressed - it is not necessary to use a high heat.
                                     
To avoid having to heat the oil, a simpler method is to fill a container with purified double-boiled linseed oil. The quality of linseed oil you use is very important, take care to use only boiled or double boiled linseed oil in this process.
 
You can get boiled linseed oil from a variety of mail order sources, or in your local hardware store, some are mail order suppliers listed here:
 
Allback purified linseed oil
J
amestown Distributors

American Rope and Tar
 
Once you have submerged the shell in linseed oil, let it soak in the oil for about a week, once you are finished soaking the oil, wipe off the excess, and let it dry for another week. By soaking the shell for a long time, the wood pores are more completely filled and checking and cracking is prevented. The linseed oil will provide an excellent weatherproof finish that will not mar or crack.
 
Alternatively, you could also use tung oil. This oil, which is pressed from the nuts of a tung tree, was introduced to the West from China about 1900. It was useful for making superior, water-resistant varnishes, especially for outdoor use.
 
You apply tung oil just like linseed oil by sumerging the shell in a can. Tung oil comes from China, however, so it has a certain mystique. Because few people really knew what tung oil was anyway, many manufacturers began packaging varnish thinned about half with paint thinner and labeling it “tung oil,” “tung oil finish,” or “tung oil varnish.” Others further muddied the waters by calling their thinned varnish Val-Oil, Waterlox, Seal-a-Cell or ProFin. Tung oil doesn’t contain driers. It takes two or three days to dry adequately in a warm room when all the excess is wiped off. Real tung oil has a distinct smell that clearly separates it from wiping varnish and oil/varnish blends, both of which have a varnish-like smell. 

You can obtain 100% tung oil from mail order supplies like Lee Valley Tools.
 
5. Making the Pin
A pin can be made from a variety of materials. Traditional pins in the 18th century were made of of lignum-vitae, or cocus; When made of wood, the diameter of the pin is the thickness of the sheave. When made from metal, the pin can usually be about 1/16" larger than one-half the thickness of the sheave.
 
The strongest and best quality pin is made from silicon bronze. You can order a silicone bronze rod or find a silicone bronze bolt and cut it down to size and grind the head.
 
That being said, silicone bronze can be very expensive, and being a very hard metal it can be difficult to cut. A source for silicone bronze rods can be found here:Duckworks BBS.
 
Alternatively, stainless steel or naval brass rod could be used. Naval brass is soft and is easy to work with, and in small sheaves is more than strong enough to handle the job. For large sheaves,  and depending on the quality of the sheave silicon bronze or steel will work better over time.
 
For our pin, we found a marine hardware store locally that still sold brass bolts, we found a bolt long enough to fit through the shell, and cut off the threads, leaving just the head and the smooth part of the bolt.
 
Brass Bolt
A brass bolt serves as our "pin" we simply cut the
threaded part off, leaving a smooth axle.
Special thanks to Steveston Marine and Hardware
 
Once the bolt was cut to size, we ground down the head of the bolt, so it was similar to a brass "lynch pin" - flat and thin.
 
brass pin
The finished pin with the head ground round and flat.
 
brass pin
Our "homemade" brass pin.
 
We then fit everything together and made sure that the sheave spun freely in our shell. We then "countersunk" the head of the pin, so it fit flush in the bore, so that the strop would fit nicely in the groove.
 
fitting it together
we fit it all together and checked for fit and finish and then
countersunk the head of the pin so if fit flush with the groove
 
 
 

How To Make Rope Stropped Blocks - Part 3

6. Making the Rope Thimble
The thimble is the eye that the strop streches around that allows it to attach to another rope or spare. While a metal thimble is not a neccesity, it does add strength to the rope strop, and also prevents chafing of the rope against shackles and other attachments that might otherwise cut through the rope strop.
 
The common thimble is an oval eye shape, and can be readily purchased at most hardware stores. While functional, the modern thimble does not have quite the salty look as the traditional round brass thimble of yesteryear.
 
brass thimble
Manilla round brass Thimbles for a more traditional look
 
The manilla brass thimbles provide a much more traditional look, they can be ordered from a specialty marine supply store for example, Duckworks BBS, and R&W Rope.
 
However, the cost of thimbles can be rather high if you need to make alot of blocks, with a 3/4" thimble which handles a 3/8" runnign a nearly $5 a thimble, it can be cost prohibitive.
 
Alternatively, while not brass, you can make your own thimble out of some old copper tubing, which gives a similar aesthetic appeal, but is considerably less expensive.
 
Start by obtaining a length of coper tubing in the diameter that you need; generally speaking a 3/4" I.D. tube is about right for most small boating thimbles.
 
The fist thing is to cut the tubing into the width you need, a standard size chart for commercial thimbles is a good rule to work from, and a slightly larger I.D. would not hurt since we need to work within the standard sizes of copper tubing.
 
That being said, copper tubing of an I.D. of 3/4" should work for rope from 1/4"-1/2". It is a good idea to use a commerical size chart to get a good idea of the size of thimble you require for the thickness of rope strop you plan to use. A standard 1/4"  strop would need a rope thimble about 1" wide and an I.D. of 3/4."
 
To make the thimble we first cut a ring about 1" from the length of tube using a metal cutting bandsaw blade.
 

we marked off a 1" section of pipe to make our rope thimble.
 
cutting rope thimble
Cutting the the timble piece on the bandsaw -
make special care to make sure that your cut is square
 

A successfully cut section of pipe to use as the basis for our thimble. If you are wondering how wide to cut it, basically allow for 1/4" more than the actual outer diameter of the finished thimble. O this means a 3/4" wide thimble should have a width of about 1".
 
copper thimble
A piece of copper tubing cut to size for our thimble.
 
The next step requires the use of two medium sized ballpeen hammers. The first one needs to be securily mounted so it doesnt move. We clamped it up against our cast iron lathe.
 
ballpeen hammer
A ballbeen hammer clamped down to a secure surface
 
Next, take the length of copper tube that was cut to the size of the thimble and place it square on the ballpeen hammer.
 
ballpeen
Tap the copper section with another ballpeen hammer of the same size.
 
 
Begin tapping the top of the copper tube with a ballpeen hammer of the same size. Making small quick taps, the bottom of the copper tube should begin to "flange" outwards. 
 
thimble
The bottom of the copper tube should begin to flange outwards.
 
making a coper thimble
Another view of the thimble

 
Once you have a reasonable flange started, then flip the thimble over, and begin the process on the other end. once you have decent flanges started, then you can place it ona flat surface and using the flat end of the hammer you can even out the flange shape with a few taps.
 
copper thimble
Place the thimble on a flat surface to even out the flange.
 
finished thimble
The finished thimble
 
rope thimbles
Tons of rope thimbles made easily and cheaply

 
 
7. Making the Rope Strop
 
The "strops" or strap is made up of a rope grommet or "grummit" as a sailor would say. To the landlubber they are sometimes referred to as quoits. They are also sometimes commonly refrerred to as "beckets". 
 
In any case a rope strop is simply a rope ring of a single strand about itself 3, 4, or 6 times over. There are many different kinds of rope, but for this kind of a strop the easier to work with is three strand braid. To complicate matters, rope can come in different materials, traditionally tarred hemp was used because of its superior qualityies. Today, hemp rope can be difficult to find but there are some suppliers, alternatively one could work ith manila, but usually the manila found in most retail outlets is not of yachting quality and is of low strength, and unless tarred deteriorates rapidly.
 
In contrast to organic rope, there are three types of synthetic fibres used currently: nylon, polyester and dacron. In terms of durability, and stretch, dacron is the best choice, followed by polyesther, and lastly nylon. Nylon is not a good choice for rope strops because of it's tendency stretch and be very eleastic. The biggest concern with polyesther is that it breaks down with the UV rays. In our rope stropes, we chose high grade synthetic manilla. 
 
If you would like to use traditional hemp, we suggest: Hemp Traders who sell hemp by the yard at a reasonable price.
 
In order to make the strop, unwind a single strand from a three strand rope. Be careful to unwind the three strands gently. The goal is to preserve the twist of each strand.  To maintain the tight twist of each strand's individual fibers, allow the strand to twirl while unwinding it from the original rope.  Do not grab a strand and pull it like shucking corn, the fibers will seperate.  Each strand needs to be unwound from the main rope rather than pulled apart.
 
It will require a length that is three times the circumference of the desired grommet, plus six times the circumference of the rope. In determining the size of the grommet, put the thimble and block one on top of the other, allowing a space about the width of the rope between the two. then wrap a string or rope around the whole outside circumference, and you'll have a general idea for the size of the strop. In general, you want it very snug, but not too tight, as you will need to cinch it closed with a tight lashing.
 
So tor example, a 3/8" thick rope grommet six inches in diameter requires a single strand of rope that is approximately 64 inches long. 
 
When unwound, each strand maintains the "memory" of its winding from the original rope. It is these corkscrew undulations, or wind Intervals that will provide the guide for re-winding the strand onto itself.
 
rope grommet
Make the grommet by bringing one end around to form a ring,  then simply cross the strand work
it around the ring as in fig. 2. Then form a third circuit, leaving the ends of the strand A & B.
 
Bring one end around to form a ring the desired diamter and cross the strand as shown in figure 1. Now pass aloing the long or working end about itself one complete circuit of the grommet as in figure 2.
 
Each wrap should fall in place with the original wind shape and the strand should intertwine naturally with the original Wind Interval as a twisted pair.
 
Keep working the strand  it all the way around the ring until one complete circuit.
 
In the grooves remaining make a third circuit around the ring, as in figure 3. At this time you should be left with the ends A & B. You are now faced with the problem of disposing the two strand ends, in such a manner tas o tuck them in so as to increase the diameter of the rope as little as possible.
 
There are many ways to do this, but by using this method of splicing it is very simple and practical.
 
Split the rope ends A and B into two pairs; so you should have end A split into strands 1 and 2; and end B split into strands 3 and 4.
 
 
split into 4 pairs
Split the two ends into four strands: 1,2,3 and 4.
 
Next, create a left-hand knot by passing the end of of strand 4 under strands 1 and 2, and the end of strand 2 under strands 3 and 4 as shown below. Tighten them together, rolling the grommet as you make the tucks to help keep its form. 
 
splicing grommet together 2
Make a left hand knot with the strand ends,
tucking strand 2 under 3 and 4; strand 4 tucked  under 1 and 2.
 
Now, temporarily leave strands 1 & 3, but begin tucking strands 2 and 4 such that you tuck over one and under two, over one and under two in that pattern, basically 
strand 2 over stands 3 and 4, and the under two strands, over one, and so on until you reach the end of the strand. Then do the same for strand 4, over strands 1 and 2,under two, ober one, and so on. It should then look like the figure below: 
 
tuck splice
Leave strands 1 and 3, and tuck strands 2 and 4 in a pattern of over one, under two etc...
 
Complete the same pattern with strands 1 and 3, whereby where strand 2 is over one, strand 1 is under two, continue rolling the grommet and following the over one and under two pattern until about three repitions are completed.Finally, pull all the strands snug, rolling in your fingers or whacking lightly with a mallet to maintain a consistant shape and uniformity, then cut the ends and tuck the ends in, and your grommet is now completed.
 
Now, as a final step you may want to whip over the splice whith tarred marline, to help hold in the frays, as well as, keep the rope from fraying on the thimble. 
 
how to whip a line
How to whip a line: 1. Make a loop, wrap the line around the loop, 
2. Pass the end through the loop, 3. Pull the ends tight.
 
grummet
A completed rope grummet with a tarred marline whipping

 
8. Assemble & seize the grommet
 
 
Now it is time to assemble everything together, and finally seize the grommet around the block. with tarred hemp marline which is commerical available (although expensive)via mail order from most marine supply stores.
 
 
Alternatively, you could use hemp twine and tar it yourself, we used this route and made a tar mixture using imported genuine Stockholm Tar which you can get from a variety of sources including:
American Rope and Tar
Auson - Imprex Pine Tar
 
Ancient Pine Tar Recipie
Combine equal parts of Genuine Pine Tar and Boiled or double boiled linseed oil.
Heat to 80 degrees F and mix thoroughly.
Apply warm if possible.
 
We used 20 lbs (20#) hemp twine from Global Hemp. You can also obtain reasonably priced hemp twine from Hemp Traders , from them you can also order "waxed" hemp which is similar to soaking it in beeswax.
 
With untreated hemp, take the roll of twin and simply soak it in the pine tar mixture. When it dries it will become tacky to the touch.
 
Lastly, you could use a synthetic twine such as a no.15 mason line from a place like Home Depot, and soak it in beeswax, which can be found for candle making in craft stores at about $10 a pound or a traditional pine tar mixture. The beeswax will be hard at room temparature and it  needs to be made into a creamy "tar" like mixture.
 
To make a beeswax tar,  crumple about 1/2 ounce of beeswax into a small amount of turpentine, and stir the mixture until it has the consistancy of a hand-cream in a small jar or tupperware container.
 
Then submerge and swirl a loosely coiled length of twine in the beeswax cream until the twine is saturated. Then, remove the twine and set it aside to allow the turpentine to evaporate leaving the twine stiff and tacky with no loose fibers.
 
The hemp marline or beeswax nylon line will add a surprising amount of strength, and stiffness to the strop. Closing the grommet around the shell of the block is done by with a seizing. Place the rope around the shell and start the seizing about two rope diameters above the top of the block - the seizing is worked towards the block, drawing the rope together and pinching the shell in place.
 
There are a few different methods that can be used to close and seize the grommet. The first thing is that most seizings are generally started with an eye. Of course, this can be a little troublesome, as marline and twine are very fine things. The easiest way to makean eye is by using a method known as the tucked eye. Basically, just twist the twine in the opposite direction of the lay to "unwind" it a little, form a loop and then tuck in the loose ends between the strands in the lay. Leave the end rather long, and if the tucks and the end are buried under the first few turns of the seizing it will become very secure.
 
Another method is to create a spliced eye, which is a bit more involved, but neater and more secure. It is basically formed in the same method as the tucked eyed, but then the end strands are opened up and then woven through the remaining strands in an over and under fashion, like a typical eye splice.
 
eye spices
A figure showing how to make a proper eye in marline for seizing
 
Howeverm the most basic way to seize (close) the eye is to simply seize the grommet using a knot and frapping procedure known as throat seizing, this method does not require the use of an eye, and is shown below:
 
sezing
 
Note:If you are having trouble getting the grommet to close, in order to get it really tight you may need to use  a spanish windlass to draw the ropes together, and make it easier to work the seizing.
 
spanish windlass
 
The round seizing is probably the most used and practical of all the seizings. In this version you draw the two parts together by using the looped marline. This type of seizing works very well with the spanish windlass, shown above. Once you have drawn it together put on ten to twelve turns working upwards towards the thimble, until you are slightly longer than the rope is wide, then at the top, finish off with a single hitch. Then working downward apply a second layer of turns over the frist, but two less in number. These are called riding turns.
 
Finally, pass the end of the marline through the tucked or spliced eye, between the two parts of the rope to the back, and around the riding turns three or four times. These turns are called crossing or frapping turns, and are hauled as tight as possible and then secured with a single hitch. Then simply trim, and tuck end of the line under the wrappings.
 
round seizing
The round seizing is one of the most common, easy and practical methods.
 
Another style of seizing is called racking seizing and was originally designed for wire rigging.  In a racking sezing you begin with a tucked or spliced eye the end of the marline, the loose end is passed through the eye like a round seizing, and the two parts of the rope are drawn tight, then the twine is wrapped in a figure eight pattern, over and under, around each of the two parts of the rope and with each turn of the twine the seizing is drawn tight before the next turn is put in.
 
racking seizing
 
Once the top is reached, then the twine is run down the seizing, by simply wrapping a second layer of twine over the first, with each turn sitting in the groove between turns on the first layer. Unlike the racking turns, these 'riding turns' do not weave in and out between the two ropes. Instead, they are simply wrapped round the whole bundle. They do not need to be hauled as tight as the racking turns - hand tight is fine. Ideally the finished seizing should be about at least as long or slightly longer than it is wide.
 
racking
 
With the racking and riding turns in place, a several frapping turns are taken around the seizing, between the ropes. To finish off, the start and end of the twine can be square knotted together. and the ends trimmed and buried or if you prefer simply leading the end of the twine around the frapping in a half-hitch, and then drawing all tight before cutting off the tail.
 
racking 3
 
Once you have finsihed yor seizings VOILA! A finished rope stropped block!
 
rope stropped block