The BUG is essentially the mechanic father of the paddle and can be compared to a paddle like an electronic keyboard can be compared to a piano. The sound of a Bug is unique, as unique is the conception of this key:  this mechanical device allows speed up to 50 WPM without killing your muscles (Glass Arm).


A Bug is essentially an horizontal pendulum, (ARM), kept together by a mainframe (A) and controlled by a Damper (G).
The operator pushes the dot contact (E) and a spring counterreacts with an ad-hoc force, which in conjunction with a weight on the arm produces mechanically a series of dots. Dashes are made manually by the operator using the (B) contact.



Here is the procedure I use (thanks to Claudio IK0XCB, also):

1. Clean contacts B, E.
2. Put some oil on the pivot points between (ARM) and mainframe (A).
3. Loosen the H spring and register C.
4. Tighten spring H of  a couple of turns.
   
5. Tighten register D so the arm touches slightly the damper G.
6. Tighten of one turn and an half the spring H,  check the arm to slightly touch the damper.
7. Comparing with a paddle and an electronic  keyer, tune-up contacts C and E until the bug produces a series of dot which are identical in duration and spacing.
   
8. Tune register B until you obtain the desired distance.
9. Tune the dash spring J so you are able to produce a series of distinct dashes
   

To purchase a Bug search on  eBay
This film (195KB, needs Apple Quicktime) shows an example of manipulation.

When manipulating a bug, try to stay as close as possible to the 3:1 ratio dash/dot.