I need to produce a complex lever with offsets in all three dimensions to restore sostenuto (middle pedal) operation to my grand piano with modern player unit.
Travel is low (<1½ cm max). Required operation force cannot be more than 100 grams with travel at the actual force bearing point < ¾ cm. While reasonably compact in the 3-D sense the full developed length if straightened will easily exceed 40 cm. One end has an operator; the opposite a very and long pivot with the point of operating force > ¾ of the developed length away from the operating end which unfortunately results in magnified bending stress at the operation point.
To have proper operation befitting an excellent instrument I must limit the mass of the lever as much as possible with practically zero deflection during operation or over time.
Am I correct that carbon fiber reinforced PETG with 100% infill is my best chance to produce a properly functioning part?
Don’t use 100% infill.
Yes petg-cf for being cheap is strong. Make sure the forces aren’t plying layers apart, z is the weakest axis.
Infill is not where strength is, walls are. If you want a thing as rock solid as FDM is able to produce, I use 6 walls 6 tops 6 bottoms 50% infill of a noncrossing variant
I have no idea of the thing you are describing, but a diagram of the mechanism sounds like it would help more.
Be wary of using CF or GF filament for parts which rub against one another - they are abrasive. These materials will help your stiffness though, GF tends to be maximum stiffness.
@Bullocks: Thanks for the reply and suggestions!
Here’s a image that gives you something of an idea of what’s going on:
This comes from the installation manual of a different player system as mine offers no suggestions for restoring manual operation of the sostenuto system. In the illustrated case the job is relatively easy with the pieces made to fit from plywood and solid wood. This is due to the very low profile of the solenoid unit the large cover of which is indicated by the yellow arrow.
In my application the solenoid unit profile is far (about 3x) thicker because all of the solenoids are installed completely below the structure supporting the action (keyboard). This necessitates deep “U” offsets in each end of the lever. The actual design of mine will vary rather considerably but this is reasonably close. The pivot at the rear will involve stainless steel dowels and sintered bronze bushings so under no circumstance will the CF impregnated object “rub” against something causing friction. The lever will interlock with the pivot member via a sliding dovetail joint. Fortunately there is no need to handle stress from over-travel as the lift rod that fits into a recess at the rear of the foot pedal has a restricted, finite and short length of travel.
@Krellboy:
Thanks for your comment. I’ve had some experiences with PETG that make me understand exactly why it lacks strength in the “Z” direction. The size and offsets of the main lever will find it positioned and supported at a goofy angle in order to fit within the build volume. I’ll keep this in mind when determining the final position to avoid stresses directly in the “Z” axis as much as possible. Both aesthetics and available space limit my options for stiffening members but I [should] be able to somewhat reinforce the most stress-prone areas.
The sostenuto system of a grand piano is pretty much the final refinement of the modern instrument. It’s related to the sustain pedal that keeps the dampers from falling back to the strings and ending the note. When properly operated–and it is rather tricky to do–any damper that is above a specific level when the pedal is pressed is trapped at a higher-than-normal level sustaining the affected notes. Meanwhile the remaining dampers and pedals operate normally until the sostenuto pedal is released to drop the trapped dampers. Exceptionally precise adjustment is required for the system to operate properly as is effectively perfect consistency of pedal and linkage function.
If you want to hear sostenuto in operation and understand why it is utterly critical to some music, listen to “Piano Man” by Billy Joel. The long-sustaining bass chords are only possible using sostenuto and allow a skilled pianist to somewhat mimic the sound/effect of double-bass violin backing.
Those shapes look really good for 3d printing. Your use case of needing it thicker is a benefit as well.
I’m still unsure if this is the bit someone could stomp on, so I’m hesitant to suggest materials, but abs-gf in a thick layer height will probably be as stiff as a rock and a good first choice. Maybe upgrading to a nylon-(any)fiber if breaking to shock load is a concern.
