Preparing And Cleaning Bare Fiber >By William Graham

Before you can terminate bare fiber, you must remove all outer materials from the fiber until just the fiber, with its core and cladding, is exposed.ince you don't want to cut through the loose tube and damage the unprotected fibers inside, you must remove the loose tube from the buffered fibers with care and knowledge of the materials you're working with. But remember, you don't want to overbend

Before you can terminate bare fiber, you must remove all outer materials from the fiber until just the fiber, with its core and cladding, is exposed.

ince you don't want to cut through the loose tube and damage the unprotected fibers inside, you must remove the loose tube from the buffered fibers with care and knowledge of the materials you're working with. But remember, you don't want to overbend the loose tube; it's made of hard plastic and will kink and break the fibers if overbent. But, the material is softer on the outside than the inside. Thus, you should cut part way through the tube and then snap it.

Here's how to get to the bare fiber.

Step 1: Using a small coaxial cable cutter, put a circular cut around the tube. Make sure you don't expose the blade too much and cut through the tube.

Step 2: Grasp the tube on each side of the cut with the thumb and forefinger of each hand. Then, carefully bend the tube back and forth until it snaps. Continue this until you have removed the desired amount of loose tube.

Once you've removed the tube, you should see the fiber(s) embedded in a gel filling. If there are more than 12 fibers in the loose tube, you might find the groups separated from each other by small colored strings. These strings identify each group.

Step 3: Clean the fibers. You should use a wipe soaked in the same cleaner used to remove the gel filling on the loose tube cable.

Step 4: Give the fibers a final cleaning with alcohol. This will remove the residue from the fibers and your hands.

Buffered and tight buffered construction. Step 1: Remove the plastic or PVC jacket. If there's only one buffered fiber (as in a buffered cable), you can use any one of several tools to remove it. For example, you can use a regular "T" stripper, carried by any electrical distributor, or a specific jacket-removing tool. It makes little difference which one you use; just don't damage the buffered fiber. With either of these tools, you should use a cut-and-pull forward motion rather than the circular motion used in stripping copper cable. You'll probably find a 14 AWG or 16 AWG cutter does the task well. Some use larger spring type wire strippers for outer jacket removal; however, most professionals shun them because of the possibility of cable damage. NECA 301 deals with these tools in some detail.

Because of the larger cable diameter in a tight buffered cable, you have a choice of larger cutters for jacket removal. Generally, you'll need to remove as much as several feet of jacketing. So, first remove a small piece and then use the rip cord to cut through the rest of the jacket. This will save time and reduce the risk of damage to the buffered fiber.

Step 2: Remove the Kevlar or aramid yarn strength member. Some manufacturers produce cutters specifically for cutting Kevlar. Some makes of high-quality stainless steel scissors or ceramic scissors will also do the job. Side cutters and "T" strippers will not cut the Kevlar.

Step 3: Remove the buffer coating. You'll have a 900 micron buffer coating to remove. This coating consists of more than one layer. Generally, there'll be a 250 micron layer and 650 micron layer. It's best to remove the coating in 1/4- to 1/2-in. increments.

First, you have to decide how much to remove. Then, use a small marker pen to mark the buffer. Caution: Don't use a pencil or ballpoint pen; they don't make a clear mark and can damage the fiber.

With a core-and-cladding diameter of 125 microns, a 250 micron first layer of buffer, and a 650 micron second layer, you'll need a cutter with a hole size somewhere between 125 microns and 250 microns in diameter. This writer sometimes uses the "30 AWG" cutter on a "T" stripper for this. It often works well, depending upon how tightly the layers of buffer adhere to each other. At times, the "T" stripper may leave the 250 micron layer on the fiber; then you'll have to use one of several other tools designed specifically for this operation.

A more popular tool for this is the "No-Nik" tool. When you close the tool on the fiber, you should hear a slight click. Then, pull forward in the direction of the arrow. If you're left-handed, the arrow will be out of sight.

While this tool has specific part numbers designating cutting diameter, it's also denoted by the color of the tool's handles. For example, a mustard color handle has a minimum cutter diameter of 175 microns; a red handled tool has a minimum cutter diameter of 203 microns. These two sizes will remove the buffer coating quite nicely, although you may find the red handled cutters slightly better. Other choices, such as the gold handled cutter (152 micron cutting diameter) or light blue handled cutter (254 micron cutting diameter) may be too small and break the fiber or too big and not remove all the buffer coatings.

Even though you're using the right size cutter, the fiber may still break; this is because of small specks of dirt in the cutter. As such, you must clean the tool after every cut you make by flicking the plastic covers. If the dirt is stubborn, you may have to swish the cutters around in some alcohol. (This is a good practice to do with all tools periodically.)

Removing the 250 micron coating can be a problem. A suggestion: Dip the buffered fiber in acetone for a minute or so, depending on the strength of the solution. Then, remove the fiber, wipe it with a wipe saturated with alcohol, and the coating will come off in one piece. Finally, take another clean lint-free wipe and clean it again with 99% isopropyl alcohol to remove any residue.

This is a good method when you have a large number of fibers to strip and want to avoid breakage or when you have to strip off several inches of coating. Once you remove the buffer, only the core and cladding are left. I like to refer to this as the "working part" of the fiber. The next thing is to clean the fiber with 99% isopropyl alcohol and a clean low-lint wipe. Clean part of your work area if you haven't already done so with a wipe and alcohol. Sometimes you might have a holder to hold the bare fiber while you do other things. If not, use a clean low-lint wipe to lay it on.

Remember, while we might not be able to see a piece of lint, it might be as big as the fiber itself.

Stripping bare fiber is not without risks. First, there's the danger from using chemicals. Gel removers, alcohol, acetone, and any other chemicals can affect your skin. Therefore, always wear gloves. As with any chemical, safety eyewear and adequate ventilation are also musts. And, be aware of the flammable and explosive properties of the chemicals you're using.

Second, you can't be too cautious with bare fibers. At 125 microns in diameter, they're about the diameter of a human hair. A skin prick can lead to infection, and a broken piece of fiber can possibly get in the blood stream and cause serious damage. Of course, the biggest concern is getting small pieces in the eye. Sure, you should wear eye protection, but you should also "manage your fibers." In other words, make sure you dispose of every piece of bare fiber in a safe disposal unit.

Precautions should include a sticky pad to catch the fibers, safe disposal unit to hold them, and a pair of nonmetallic-end tweezers to pull the fiber out of the skin.

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