Renner Back Action (May 2023)

This is a tribute to all my mentors from North Bennet Street School, Mr. David Betts who contributed his life to this trade and his beloved apprentices. Today is Mother's Day. Best wishes and lots of love to Debbie and Emily, my caring mentors who support us from the beginning and there seems to be no end for it.

This process is taken from two backaction replications. Personally, it is still a new skill to be refined. Compare to WNG Aluminum backaction, we found Renner's wooden system more consistent and with less flaws.  

Lay out the parts, check if anything is missing from the box, and read assembly process from manufacture. First, determine location for the first underlever. On old damper tray, measure distance from the bass end to center of note 1 underlever, transfer measurement onto new damper tray. Again, on old tray, measure distance from bass end to bass side of note 1 underlever, transfer on to new tray. Position new underlever flange onto new tray, determine the most accurate position according to the two marks, then mark it down. The new damper tray comes with the screw line grooved. Use a pencil to mark along the groove to make it more visible for easy working process.

Place scale stick taken from action. Pay attention to place note 1 right on the mark, triple check with the old backaction. Once the drilling process starts, it can not be undone. Mark for underlever screws, capstans, and springs.

The new damper tray is provided extra long. There is room to test drill bits and parts before official drilling process. Test on underlever screw holes, capstans holes, and spring holes. Make sure the drill bits are selected perfectly. After drilling screw holes and capstan holes, counter sink them for easy installation. Spring holes don't need counter sinks.

To make slot for sostenuto monkey, the tray is clamped onto table saw. Roll the saw blade all the way down, turn on machine, slowly raise the blade to make the cut. The top opening for the monkey is made with belt sender. The new slot is smaller than the original backaction but there is surely enough room for monkey to pass through. Next time, there will be a better idea to machine it, one would hope...

Use a forstner bit, cut a hole for damper pitman under damper tray. Cut tray spring hole as well. Bush the spring hole with leather. ​The hole locations are taken from the old tray. 

Transfer the treble end measurement from old backaction to new, cut to length on a chop saw. The first two pictures were taken early on. I found chopping the tray before installing any parts is a much better idea.

Install capstans with a drill and capstan hook. Turn them down to the same height. Here is our fancy height jig, a ruler. There will be capstan screw bottom tips sticking out through the tray, sand them down flush on a large belt sander.

Lay out underlevers by number of leads, heaviest (with most number of leads) at bass, lightest (with no lead) at treble. Wax screws and install parts. 

The supplier provides felt to glue on underlever. So when capstans push up the underlevers thus dampers, no noise is made. At section ends, on the bottom of underlevers, mark capstan contact point, place felt, center of felt covers the mark. Use strips of tape to mark where to glue for all felt. Glue on felt, the glue squeeze out will be caught by the tape for a clean finish. We use Roo Glue, no clamping is needed. According to the glue manufacture, "... just in case you were worried, no kangaroos are used in the making of our products!"

The springs are only installed at bass for the heavier touch for pianists. The coil part of springs should not touch wood surface which may cause noise. Insert spring, use a ruler to jack coil up while driving tooth pick in. The springs are fastened by pressure fit with tooth picks. After installation, simply snap off the tooth picks.

It is important that the damper wires move freely in the wire holes. Remove damper wire set screws on the posts, find a drill bit slightly larger than the wire, set drilling depth above sostenuto tap center pin, ream the holes, test with damper wires, then replace set screws. 

The end blocks and pivot pins will be installed by the shop owner later on. We are still trying to figure out the best rotation point for the damper tray with less force on the pivot pin, less damper noise, and ease on the pianist's performing experience. Here she is, a new backaction, actually two, a couple months apart, under strings. at the back of keyboard. Next time, better process and work efficiency, hopefully.