Inconsistent touch is something that bothers many pianists and, while there are a multitude of things that can be done to improve the feel of playing, one I often go straight to is the friction within the mechanism particularly at the balance rail. As the name suggests the balance rail is the fulcrum point for the key and is often enough the centre of the problem.
A nearly 20 year old Yamaha 6-footer recently crossed my path and I did my standard check to see if the friction had been looked at. This involves gently pulling the keyfronts up and seeing if they fall back down.
More than half the keys stayed up so I knew that the balance rail pin and the key hole connections were not moving smoothly. The piano owner had moved from dry Northern BC down here to the wet coast a few years ago, and the piano was in storage for a while. The different humidity had caused everything to swell slightly and start to bind.
The fit for the balance pin and the key is critical as the slightest friction can add several grams to the weight needed to set the hammer in motion. If you really want to delve into touchweight this fellow has done a lot of work on the subject. Stanwood Piano
Remove the keys from the frame, turn on the compressor and get rid of the dust bunnies and shoot a blast through the key balance rail hole since it gathers down the cavity and will cause further problems if it continues to grind between the pin and the wood for another few years.
A little lubrication for the balance and front rail pins and that will often fix many of the sticky ones, but a further test of removing each key and letting it sit on the pin reveals a deeper problem. On the theory that a picture is worth a thousand words, here’s some pictures.
(It’s a video; hover over the image if you don’t see the controls to play it.)
This relatively inexpensive procedure can result in a substantially smoother piano to play generally serving to even up touchweight across the keyboard.