I just completed an reconditioning job on a Bluthner grand with a patent action. I've worked on several of these pianos and I really love them; they have a completely unique sound and when they are regulated properly they perform as well as the modern Erard action.
It's very important to get the hammer blow distance a consistent 45mm in each section, but since the shanks must rest on the hammer rail felt in a patent action, the thickness of the cloth is crucial. Moths had taken their toll on this action and I replaced almost every single piece of cloth and felt. I replaced the underlying cloth and the blue felt that you see in the photo at the client home so I could be sure I had the correct distance with the new hammers installed. I brought the remainder of the hot hide glue I had used a few days before for the backrail cloth, key bushings, and new backcheck leather strips with me and reheated it onsite, and it worked great!
The abstracts are the parts dangling from the hammer shanks, and they function in a similar manner to a vertical hammer butt. They were in amazing condition and the pinning in both the abstracts and hammers was almost perfect as-is. New parts are available but they aren't inexpensive and the client wanted to preserve as much of the original action as possible. I did polish all of the metal guide pins and the springs that control the amount of drop with Flitz and this greatly improved the feel and the ease of regulation.
The balance rail punchings were basically gone from moth damage, and the keypins were greasy, grimy, and felt like they had been coated with sugary cola and smoke. Probably the dirtiest keypins I've ever polished. Note the secondary felt punching on top of the front rail cloth punchings. These are very important in the patent action because you want to have a "squishy" feel with the keydip, as there really isn't any aftertouch.
In the photo above you can see the new leather key bushings (I used the leather Jurgen sells and wow is that stuff nice!) It was my first time rebushing keys with leather and it is so easy to use; I'm thinking of using it on other key bushing jobs in the future. I also discovered that the key easing iron and brass cauls work perfectly on leather (using a dial-temp of course!). The balance rail pins on this action were .156 so I had Bill Spurlock make me a custom set. Another thing I learned is that since leather thickness is highly variable, more easing is required, and even easing on the balance rail mortises, which is rare when using cloth and Spurlock cauls.
You can also see the rocker capstans and the bent wires that control the amount of hammer drop. The Hart spring tool works perfectly on these.
Some of you probably already know this trick but I bought a $5 no-slip rug runner at Lowe's so that the action and hammer hanging jig stay put without clamps. Also note the hammer extractor pliers I just purchased from Jurgen. They are simply the best tool for the job that I've ever seen. I bought two new shanks as backups but didn't need either of them! No breaks, no problems at all...
If anyone out there has experience with replacing the stack on the keyframe - without first having to remove all the individual hammers - I'd love to hear what your trick is!