Focuser has a point at which it binds

I am using a 2.7" ap focuser on my homebuilt 6" refractor. The focuser has been a joy. However, the focuser has just recently started to bind about 1 1/2 inches from being fully racked in. Once past that point, it is perfectly smooth. The teeth on the tube look perfect.
Has anyone else experienced this? If so I would appreciate your suggestions on how to fix this. thank you, Bill

Bill,

I have reworked several AP focusers for the same problem. Old grease can be part of the cause however, I have found the main problem is the relationship of the rack to the pinion gear. The focuser has 4 screws which include a spacer and a spring for allowing some movement between the pinion and the rack. Any loosness in the focuser which allows the pinion to change its relationship to the rack such that the mesh angle of the gears is no longer perfectly perpendicular, causes binding. Clamping the screws down tight will cause the focuser to jam.

The best solution I have found is to shim the focuser pinion out from the rack using thin plastic or paper shims placed between each set of screws, on each side of the focuser. Shim both sides evenly and tighten down the screws carefully, adding shims until the focuser screws can be snugged down and the focuser moves freely. I have gotten good results doing this especially on my Stowaways.

I would also completely remove all of the old grease and replace it with a small amount of non-outgassing optical grease.

Clear Skys,

Mike Mandall