Compact Clock 16 Friction Clutch
Having fun tweaking Compact Clock #16.
My first-ever 3D print is coming along nicely as I fix and upgrade the first print -- which admittedly was rough. Eventually, it will be finsihed. Right now the clock is ticking along nicely. However, the hands are running at about half speed.
Data:
In Compact Clock 16 that means the middle arbor is not turning normally.
Middle arbor is driven by Gear 4 (which is driven the Gear 5 and the weight shell.) Gear 4 is friction clutched to the middle arbor. It is escapement controlled to 1 R/Hour.
Gear 4b is set screw attached to the middle arbor so both 4 and 4b turn at 1R/H.
If I understand the schematic, the entire "hands" gear set is drive through the friction clutch of Gear 4.
As I interpret the schematic the only driven arbor is the middle arbor. THe only two attachements are Gear 4 friction clutch and Gear 4b, with a set screw. All the gears on Arbor 1 are free spinning. Gear 5, the drive gear is its own Gear/Arbor structure.
Problem: Middle Arbor is turning at about 2/3 normal speed. THe clock is ticking at the normal pendulum rate of 80bpm.
Guess:
Friction Clutch Gear 4 is slipping.
Test: 1. The minutes hand turns easily and the hour hand follows properly.
Reaching around the side of the clokc I can rotate Gear 4b -- and the downstream gears respond properly and the hands turn properly.
Binding: THe motions are all smooth and requiire little pressure for either test. No binding. (I had a bow in the back frame from first build. I use a home-crafted frame straightener (wife's hair drying) and got the frame flat. (<1mm lift.)
Since both hands are equally slow the prime suspect is a slipping clutch that affects both hands. have not discovered a test for the clutch.
BTW. Since most gears are free-spinning and because binding was a problem, I loosened all the spacers and let them float on their arbors. Also, I sliced a layer or two off several spacers. The net result is a gain on 2 or 3 mm extra space on the two ware arbors. The gears are wide enough to allow a mm shifting fore and aft.
Ideas and suggestions are welcome.
This diagram shows the gear topology in the clock.
There is a long unbroken chain of gears between the winding drum and the escapement. If the pendulum is swinging properly then gear 4 must be rotating at close to once per hour. The rate is determined by the pendulum length and it cannot run at 2/3 speed. Therefore, the issue must be between the friction clutch and the hour hand.
The friction clutch adds a loose connection between gear 4 and gear 4b to allow changing the time without affecting the pendulum. It does not need to be very strong. It only needs to be strong enough to overcome any downstream friction. Music wire (also known as spring steel or piano wire) creates enough pressure against the M3 arbor. Soft steel or brass wire might not apply enough pressure.
Gear 6 is the primary gear to check for friction. The printed gear 6 arbor must pass through the dial without binding. Also gear 6 must not be pressed against the back of the dial. Push and pull on the hour hand to make sure gear 6 has some end shake. Look for end shake in gear 5 as well.
One more thing to check is the gear 4b set screw. The friction clutch is circled below in green in the exploded diagram below. It loosely presses against the M3 arbor. Gear 4b tightly connects to the M3 arbor using a set screw, also circled below in green. Move the minute hand and make sure gear 4b moves at the same rate. There should be a slight resistance felt by the friction clutch.
Hopefully, this will give you some ideas to check. Please report back if you find the cause.