First Kundo - ideas about pendulum weight and "precision"

[PrimarchBentley]

First time owner, recently picked this up from a local thrift store ($15). According to what I can discern from "the bible," it's a 1371AA plate. The main spring still had some charge, so when I brought her home, a spin of the pendulum and she started to tick away.

She runs and lost about 19 min over the first 72 hours from "off the thrift store shelf" (and on a cheap Ikea table in a traffic area prone to vibration), so she seems good enough to look at for an overhaul and trying to tune her in.

One of the pendulum weight screws was missing, so I bought a new pendulum that looked to visually match off of ebay. This is where I'm at today (haven't been able to find a replacement foot yet though):

Now that I have a total of 7 pendulum weights and 6 cap screws to work with (the last pair won't budge from the spare - I feel like I'll break the post if I try to force it any more), I've been chasing down the rabbit hole of trying to select the best combinations of weight+cap to get uniformity. I've gotten 3 pairs that are within .05g from highest to lowest, but the fourth "best fit" pair is .13g lighter than the lightest of those three. I have some ideas on how to try adding a touch more weight to it (hence the nail polish, seeing how much weight I could add by using some clear nail polish on the inside of the brass shell - drying loses half the mass, so it's not looking as promising now), but during a break I had an epiphany.

So this is where I pause and ask people with more experience than I: "Am I trying too hard"? At what point are the gains no longer worth the effort, when it comes to the variations between pendulum weights?

I still plan on other work (cleaning/oiling the main spring and other innards, replacing the torsion spring, checking pendulum rotation arcs) but I figure that can wait until I get the pendulum squared up.

 

[Schatznut]

Welcome to the world of 400-day clocks! You've got a good "starter clock" there. Don't overthink it - it will drive you plenty nuts later. Put together the best set of pendulum parts you have, set the rating nut so the pendulum is in the middle of the adjustment range, get it onto a stable platform and let it run for a couple of days and report your findings back to the forum. We'll help you from there. But first you need to get a good baseline.

 

[PrimarchBentley]

Don't overthink it - it will drive you plenty nuts later.

Sounds about right. I can always get more into the weeds later...

She's up and running on the mantle, shimmed with some thin cardboard since I don't have all three feet for adjustment. Gives me a chance to have her near the Jefferson Golden Hour to figure out how I'll wind up arranging them long term...

Thanks for the response, will be interesting to see how this new rabbit hole goes

 

[Schatznut]

I've got one just like it on the shelf waiting its turn for an overhaul. You'll find they can become addictive like salted peanuts.

 

[PrimarchBentley]

Okay. After 50 hours so far up on the more stable mantle, I've lost 82 min with the pendulum adjustment in the middle (this is moved up from where it started, so it makes sense that it got slower). I'll post ~3 days and ~4 days if a longer period would be more helpful for baseline.

 

[MartinM]

If you post a good pic of one of the feet, I'm sure I can provide a replacement.
There were a few variants across the years. Some had plastic surface protectors (of various colors in the beige to black range) and some just had a polished brass button.

 

[Schatznut]

OK, you've got the information you need. 82 minutes in 50 hours indicates it's running about 2.73% slow, or put another way, it's taking 61.6 seconds to make eight beats. it should make 8 beats in exactly 60 seconds.

You can coarsely and fairly quickly set the rating by running the stopwatch function on your phone and observing how long it takes for eight beats to occur. Then turn the rating nut in the correct direction, restart the pendulum, wait a couple of minutes for it to stabilize, and check the timing again. This will get you close. The final adjustment can be made by letting the clock run exactly 24 hours and tweaking the rating nut appropriately. Keep in mind that these clocks are not great timekeepers, but patience and a healthy clock will allow yours to keep pretty good time.

It has been suggested by some on these forums that one should always start with the clock running fast and adjusting it to slow it down. This uses gravity to mitigate the effect of mechanical backlash in the pendulum mechanism.