Troubleshooting of Common Faults in the Coarse Focusing Assembly of Microscopes
The main faults of the coarse focusing mechanism are automatic slipping and inconsistent tightness during lifting. Automatic slipping refers to the phenomenon in which the tube, arm or stage slowly descends under its own weight without any adjustment when it stays at a fixed position. It occurs when the gravitational force of the tube, arm or stage exceeds the static friction force. The solution is to increase the static friction so that it exceeds the weight of the tube or arm.
For the coarse focusing mechanism of inclined-tube and most binocular microscopes, if the arm slips downward, grip the anti-slip wheels inside the coarse focusing handwheels with both hands, and tighten them clockwise firmly to stop slipping. If this method fails, the microscope should be repaired by a professional technician.
Automatic slipping of the tube often causes misunderstanding that the gear and rack meshing is too loose. Some operators therefore add shims under the rack. Although slipping may be stopped temporarily, this places the gear and rack in an abnormal meshing condition. Continuous movement will deform both components. If the shim is unevenly placed, the rack will deform more severely, resulting in uneven meshing: tight in some sections and loose in others. Hence this method is not recommended.
In addition, if the coarse focusing mechanism lacks maintenance for a long time and the lubricating oil dries up, the lifting operation will feel stiff, and friction noise between parts may even be heard. In this case, the mechanical assembly can be disassembled, cleaned, greased and reassembled.
