Cleaving optical fibers without secrets – blade adjustment.

Proper preparation of the ends of optical fibers is the basis for successful fiber splicing. Even the best and most expensive splicing machine will not be able to properly connect dirty or improperly cleft fibers. For this reason, care for the cleanliness of fiber optic tools is extremely important.
A good, clean and well-adjusted fiber optic cleaver guarantees correct and precise cleaving of fibers. In the event of cleaving problems, installers usually send their cleavers for servicing. The fact that the whole service procedure can take several days often forces them to buy spare tools, to continue their work. Of course, it is not a bad approach, but it is worth having an uncomplicated knowledge about diagnosing such problems and the adjusting procedure. With a bit of patience, each installer will be able to correct the dysregulated blade on their own.
There may be various reasons for dysregulation of the blade. Most often this is the result of either exploitation or a fall. Whatever the reason, the procedure is the same.
Construction of a fiber optic cleaver. The circles with numbers mark the subsequent screws to be manipulated during the adjustment process:

(1) – screw fixing the blade,
(2), (3) – screws stabilizing the blade carriage in the horizontal axis,
(4) – screw stabilizing the blade carriage in the vertical axis,
(5) – blade height adjustment screw.

The first step when encountering problems with proper cleaving should be thorough cleaning of the entire tool. First of all it applies to grooves in which fibers are laid and rubber linings responsible for supporting the fiber in the cleaving operation. Contamination of these elements causes the fiber to raise, which in turn results in the inability to cut it (the blade does not reach the fiber). If, after careful cleaning, the fibers are still not properly cleft, it is necessary to manually adjust the position of the blade (instructions provided later in the article).
Improper quality of cleaving may result from a blunt blade. The blades in most expensive tools can make up to 50,000 operations, in cheaper ones about 10,000–15,000. It should be remembered that these numbers are the sums of all operations that can be performed in all blade positions. The number of positions is usually 16, and each of them ensures at least 500–800 correct cleaving operations. In the case of a crooked face of the cleft fiber, the position of the blade should be changed to the next number. It is necessary to loosen the screw number 1, turn the blade to the desired position (preferably the next one), and then tighten the screw.
For manipulating the screws, it is recommended to use the hex (Allen) wrenches supplied with the cleaver. The use of popular screwdrivers with interchangeable bits is not a good solution because of frequent looseness in such tools. When adjusting the blade (especially its height), a far-reaching precision is needed.
If, despite cleaning the tool and changing the position of the blade, there are still problems with correct cleaving of fibers, the next step is to change the height of the blade. Before doing this, however, it is good to have a preliminary idea whether the blade in the tool is set too high or too low. The following figures are real photos taken from a fiber optic splicing machine.
An example of a bad result caused by too low blade position –
the fiber is not cleft throughout the entire cross-section

An example of an improper result caused by a little too low blade position –
the fiber is not cleft throughout the entire cross-section (visible a "tooth")

An example of a bad result caused by a too high blade position – the fiber end face is jagged.
A characteristic feature of fibers cleft with a blade set too high is damage to the fiber core (in the bright area).

An example of an improper result caused by a little too high blade position –
the fiber end face is partially irregular and not at a right angle

Of course, it may happen that initially the installer will not be able to assess whether the blade is too high or too low. Then, a good practice is to deliberately lower or raise the blade to obtain effects similar to those presented above. After reaching one of the extreme positions, the optimum position can be approached gradually by successively lowering/raising the blade.
Operations needed to change the height of the blade: loosen the screws (2), (3) and (4). Use the screw (5) to lower (turning left) or raise (turning right) the blade of the knife. After changing the height, tighten the screw (4), then the screws (2) and (3).
The effect of each change in height must be verified on the screen of a splicer. It is important to do it for two ends of the fiber, as it happens that one end looks correct, while the other - not.
It is also important to tighten all the stabilizing screws after changing the height - they also have a slight effect on the position of the blade.
It is not advisable to manipulate the height adjustment screw by more than 90 degrees, and the closer to the optimal blade position, the more the angle of adjustment must be narrowed.
In the final phase of the adjustment of the height, the ultimate cleaving quality depends on turning the screw (5) even by several degrees – so it is necessary to be precise and patient!
A well-set blade should cleave fibers at right angles, with flat faces, without any damage.