Assemble Your Own Compression Terminals
Do-it-yourself sailors have long been attracted to the concept of swageless rigging terminals, also known as compression terminals. Unlike swaged terminals, which require expensive dedicated machinery to create, compression fittings can be assembled with simple hand tools. They can also be reopened and inspected periodically, and their proponents claim they can be reused. In fact, once a terminal has been well and truly loaded, it can be difficult to take apart.
Assembling the terminals is fairly easy. The first time may seem difficult, but a little practice makes it routine. At present there are three different types of terminals available, each of which goes together differently. The most common types by far are the Norseman and Sta-Lok terminals, which are very similar. More recently, Suncor has introduced Quick Attach terminals, from Denmark, and Petersen, from the U.K., has offered its Hi-Mod terminals on the U.S. market.
A couple of tips apply to all these types: First, make sure you get a clean cut at the end of the wire to which you want to fit your terminal. Cable cutters work quickest, but usually yield a lopsided cut that can make putting the terminal on the wire much harder. It is best to cut the wire with a hacksaw (be sure to use a fresh blade) or with a grinding disk so you get a clean, square cut. Second, be sure you are using the right size terminal and appropriate parts for the type and size of wire you are working with.
Be sure to tape stainless wire before cutting it with a hacksaw. Or try clamping the wire between two blocks of soft pine in a vise, and mark the wood where you need to cut. The wood will adapt to the wire's shape and stop the ends from unlaying while you're cutting.
This is a Sta-Lok terminal disassembled. Sta-Loks are very similar to Norseman terminals. In a Norseman terminal, however, the forming cup (center) is an integral part of the terminal body (left). Otherwise, the two go together in much the same way.
Slip the terminal head onto the wire nose first, then carefully unlay the outer strands of the wire with a small screwdriver. The hands doing the job here belong to Loric Weymouth, of Lyman Morse Boatbuilding, and you can see he's quite good at doing it neatly. Keep a firm grip on the wire a couple of inches down to keep it from unlaying more than you want. Also, be sure you are using wire with a left-hand lay.
Next, slip the slotted cone over the wire core, narrow end first. You'll probably need to tap it a bit with a hammer to get it to slide up the core. When you've got the cone all the way on, there should be about 2mm of core sticking out the end, like this. It's not a bad idea to measure to be sure.
Now re-lay the outer wire strands around the cone, and then slide the terminal head down the wire over the cone. The key here is to make very sure that none of the wire strands fall into the slot on the cone. The slot must stay open so the cone can compress around the wire core.
Note that it is possible to get the cone on the core without unlaying the wire. If you cut the wire very cleanly, you should be able to carefully work the leading edge of the cone's narrow end between the core and the outer strands. Then you can slip the cone up the core. Again, you need 2mm of core sticking out the end, and no strands should fall in the slot on the cone.
Next, dress the threads on the terminal head with some Loctite, which helps to prevent galling. If the threads gall, the terminal will be ruined and you'll have to start over again with a new one. With a Sta-Lok terminal, you must also remember to drop the forming cup into the terminal body before threading it onto the head.
Now carefully tighten up the terminal with a wrench (or two wrenches if you can't use a vise). If you feel any hint of galling, immediately stop, open the terminal, and add more Loctite.
After you've tightened up the terminal all the way, immediately open it again to check that the outer strands of wire have properly formed around the base of the cone, as shown. Again, be sure no strands have fallen in the slot. Here you also see why you must use wire with a left-hand lay–the outer strands must lay around the cone in the same direction as the terminal body screws on the head.
The final step is to drop a marble-size dab of sealant into the terminal body. Then screw the body back on the head, tighten it all up nice and snug, and you're done. Do not tighten it up as hard as you can! Overtightening the terminal will damage the wire and cone inside.
This is a Hi-Mod terminal, with a threaded rigging stud instead of an eye. It has a slotted cone, like a Sta-Lok, but the cone has thin twin slots instead of one big one, so you don't have to worry about strands of wire getting caught in them. Note the toothed crown ring (center), which captures the wire strands when the terminal is assembled.
Unlike the Sta-Lok, the main body of the terminal with female threads is the part you slip over the wire first. Then, as with the Sta-Lok, you unlay the outer strands of the wire and slip the cone over the core, as shown. Unlike the Sta-Lok, the leading edge of the cone is beveled outward rather than inward. This means it isn't possible to take the shortcut of working the end of the cone onto the core without unlaying the wire.
The terminal's end fitting with male threads has a recessed cup into which the end of the wire core fits. After you slide the cone up the core, slip on the crown ring, then mate the end fitting over the core. The recessed cup makes it unnecessary to measure the protruding bit of core.
The tricky part of assembling a Hi-Mod terminal is re-laying the outer strands of wire so that the ends of each bit of wire fit into their respective slots in the crown ring. We found a third hand was helpful here. Keeping all the bits in place while re-laying the wire is a little fiddly. The advantage of the crown ring is that you can use either right- or left-hand-lay wire with the terminal.
The finished terminal, after the end fitting has been screwed into the body. You'll need Loctite on the threads, but Hi-Mod claims sealant is not necessary because the crown ring keeps the wire strands separated enough that moisture cannot get trapped in the terminal.
This is a Suncor Quick-Attach terminal disassembled. Of the three terminals we worked with, this one was by far the easiest to assemble.
The key component in a Quick-Attach terminal is this three-piece gripping jaw, which has serrated teeth on the inside and a small rubber O-ring on the end holding the three pieces together.
To assemble the Quick-Attach, all you do is slip the terminal body, gripping jaw, and pressure ring over the entire wire. There is no need to unlay the wire or otherwise separate the core from the outer strands. You do need to measure to make sure the proper amount of wire (5mm) is sticking out the end, but then you just screw the end fitting into the body.
The finished terminal. These Quick-Attach terminals have performed well in tests with static steady loads, but Suncor's competitors question whether the teeth in the gripping jaw will stand up to dynamic cyclical loads, as are experienced in working sailboat rigs. Suncor believes this is not a problem and claims there are no reports of any of these terminals failing in service. Because they are so easy to assemble, the terminals are ideal to use in temporary jury-rigging situations.