[CAUT] Renner back action

[Jon Page]

When reworking the back action I am not concerned about the Magic Line.

My concern lies with the elevation of the pivot, meaning that I want the key
to lift the underlever parallel to the key bed. The slots worn in the 
key end felt
are caused by the underlever being at too much of a downwards angle at rest.
Meaning that the pivot is too high.

This scrubbing is friction. Lifting beyond parallel is also counter productive
because the underlever would scrub against the rear end of the lifter felt.

I also move the pivot to be in line with the flange centers. Bearing 
in mind the
fore and aft placement of the top flange.

Recently, I chiseled off the end blocks on the tray and glued in a spacer
underneath them to get a good area for the new pin location. That combined
with replacing the pitman with a section of pedal rod made the pedal depression
easier (was too hard). And now there is no discrepancy regarding the 
upstop rail
between key lift and pedal lift.

When installing new flanges and end blocks, hold a flange and block in place
on a scrap piece of rail and tap the center with a hammer, this will index the
tray pivot hole.

For the support block holes, measure the top flange center distance 
from the belly rail.
This is easily done on the bench. Measure the distance from the top flange
center to the lever flange center. If the t/f/c is 6" and the center 
spread is 3.5",
the new pivot is drilled 2.5" from the belly. This maintains the 
position of the t/f.
And if the key lifts to 1 3/4", bottom of lever to flange center is 3/8",
that makes the new pivot height 2 1/8".    So, 2.5" out, 2 1/8" up.
Simple. It makes for a nicer feel to the touch.

Sometimes I make new pivot support blocks but usually simply place a
spacer behind them to get surface area for the new forward pin location.
If the new location is too close to the old hole, I'll drill out a 
1/4" plug from
the lower corner of the block and plug the old hole (how's that for recycling).


To ascertain to what degree, if any, dampers are scrubbing; measure the height
of the end felt with the key depressed. Lift the underlever to that 
height and look
at its angle with the keybed. If it is still at a downwards angle 
then it is not optimum.
More angle means more friction.
-- 

Regards,

Jon Page