Adjusting Straight Keys 
(Adapted from N1FN at mtechnologies.com)
 
The available adjustments are:

Arm Tension, the force needed to move the lever up and down. It's usually exerted by a coil spring between the arm and the base.

Bearing Tension, the setting of the pivot bearings on which the arm rotates. It is controlled by the pressure on the bearing surfaces, and there is one bearing (and one adjustment) on each side of the pivot arm.

Contact Spacing, the space between the two electrical contacts when the key arm is not depressed (unkeyed). The contacts are located beneath the arm, toward the front of the key. The adjustment is at the back end of the arm.

The two screws at the back of the key, on either side are the binding posts for connecting the key to the transmitter.

Here are the four steps you will need to "set up" your key:

1. UN-adjust the key. That's right- we need to loosen everything up and get to a common starting point, because each of the adjustments has some impact on the others. Loosen the spring tension on the arm until no resistance is felt when you depress the knob. Open the contact spacing as far as you can without removing the adjustment screw from the arm. Loosen the bearing tension screws until the arm wobbles loosely.

2. Adjust the bearing tension. Choose one of the two bearings and tighten its adjustment screw (A) until you can just barely feel a bit of friction as you move the arm up and down. Now back the screw off until just the point at which the arm moves freely again- usually it's just a fraction of a degree of screw rotation, or about as fine an adjustment as you can make. Repeat with the other bearing tension adjustment screw. Setting the second bearing is likely to have had some effect on the first, so readjust the first bearing and then finally the second bearing. At this point the arm should move up and down perfectly freely, with no sideways play or "slop."
(When adjusting the bearings, ensure that you don't move the arm off the center line of the key. In other words, ensure that the contacts are still directly above one another. -mk)

3. Adjust the contact spacing. The contact spacing determines the amount of vertical movement when you depress the arm. It's entirely a matter of taste, but if you haven't used a key before and haven't developed your own preferences, start with a sixteenth of an inch or about the thickness of a penny. Adjust the screw until you have the desired spacing between the contacts.

4. Adjust the arm tension. Tighten the arm tension adjustment screw to a comfortable level of tension on the arm. Again, this is a matter of preference, but it is possible to suggest a good rule of thumb if you haven't developed preferences- set it for the minimum amount of tension that will allow you to feel that you are in control of the key.
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From "The Art and Skill of Radiotelegraphy, CHAPTER 9:
The key should be located far enough back from the edge of the operating table (about 18 inches) that the elbow is just off the edge of the table.  The operator's arm rests lightly on the table with his wrist off the table and more or less "flat".  His first finger rests on the top of the key knob and his second finger generally on top near the edge. His thumb may rest lightly against the other edge of the knob, or not touch it at all.  (The student should find his own most comfortable way.)  Downward movement of the knob to close the key and upward movement to open it are by rocking the hand, pivoting it from the wrist: the finger end moving down while the wrist moves slightly upward, and vice-versa, without any accompanying independent finger motion.  The upward key knob movement is produced by the built-in spring in the key, but may be helped by the thumb.

Walter Candler's advice to professional telegraphers in training (to avoid developing a painful "glass arm") was:-

    Hold the knob between the thumb and first two fingers much as you would hold a pencil.  Hold it firmly, but do not squeeze it or let go of it while sending.
    The wrist -- not the fingers or the whole arm -- does the work as the key goes down and up.  Keep the wrist off the table.
    Take care of the sending arm -- the forearm muscle carries the weight of the arm.  Otherwise, keep the arm itself relaxed and at ease as you move the key down and up.  -- Immediately below the elbow on the lower side of the arm there is a nerve which comes close to the surface.  If that nerve presses against the table it may begin to make the the arm cramp and produce telegrapher's paralysis ("glass arm" or writer's cramp).   If this happens, put a soft pad under it there to relieve this condition.
    There is no need to waste energy on springs.  The key return spring does not need to be stiff -- just enough to keep the contacts apart.
    Contacts should be spaced only wide enough apart to be easily opened and closed.  A key is obviously a highly personal object.  Every one who has gotten his own key adjusted till it feels just right will be uncomfortable and fail to send as well if he uses a different key, even though it looks exactly like his own.  If you set up two different keys of identical design, with the same tension, and gaps, they will nevertheless "feel" different.  They are as individual as violins.
