Upon asking few friends, I came to realize that we (young ones) have inherited a system of work from experienced guys without understanding. We often walk to the machine and give it so many shots from/with a grease gun. What determine the amount of lubrication one should apply on each size of a motor? How do I work it out so I can know and measure so as to avoid too little or too much of lubrication on a motor?
The amount should accomplish flushing all old grease out and leaving fresh behind, without overfilling. Therefore best to do while equipment is running to assist in expelling old grease. Bearings such as deep groove ball beatings with steel cage need most due to the space therein while cylindrical roller bearings need least. The recommendation of the bearing company should be followed regarding volume or weight of grease. Take your standard grease gun and determine by weight typically the amount discharged by one normal stroke of gun. You now have defined the relubrication quantity in terms of the equipment used.
The ideal system would be and I have designed some just like this in a 2 MW wind turbine application as follows: Auto lub package replenishing hourly a small precise quantity. Reservoir holds enough grease for 2 bearings for one year. A container to catch expelled old grease and empty annually. Flinger disc on outboard of bearing to expel old grease so no blockages and on inboard side a labyrinth seal to stop grease leaking into windings and a sheet metal shute to direct old grease into container. It also had an alarm system if no grease was being delivered and if reservoir was empty for any reason. Still a bit of time to check it out. Separation of oil and soaps prevented by slow stirring in reservoir. Grease fed into inboard side of bearing. Bearings used were deep groove ball and SKF Carb. Worked a treat, running now for 9 years. (Carb to eliminate fretting corrosion where bearing slides in housing for thermal expansion.)
How often? This is a function of grease life, which is a function of time naturally, due to exposure, separation of oils & soaps, but also a factor of service duty cycle. The duty may be benign or rough. Best to go with the equipment recommendations as the expertise SHOULD lie therein. BUT question everything? The ignorance of some companies sometimes beggers belief? It is also a factor of running hours. (One running one standby for example.)