Hi Robert. Intriguing problem, and I think I may be able to shed a little 
light. My supposition could be wrong, but if you look at the physics of the 
thing, it could point to not one issue (“…obviously the contact point between 
the leather nib…”), but more likely two issues. You have to raise your 
perception above where the symptom’s cause would appear to originate, and look 
at the whole picture. 

The key to solving your mystery may be directly related to something you 
conveyed very precisely, that the issue occurs over an extremely narrow band of 
speeds. So, it appears that we have a primary cause (vibration source at the 
leather and flywheel), exacerbated or amplified by a secondary condition, which 
I will assume is marginal wear in the holes that the leather pad arm’s arbor 
passes through (the first of the two axles), in possible combination with the 
holes that the speed indicator needle’s arbor passes through, in the indicator 
frame. Given that the steel arm that the leather pad mounts to is supported on 
a smaller arbor, and given that this arbor is first in line and thus closer to 
the governor flywheel where the vibration originates, it’s likely that wear 
would be more present at those holes and possibly the associated arbor as well, 
than at the larger holes and arbor of the indicator needle. The same wear on 
smaller parts will occupy a larger percentage of area, thus having a more 
noticeable effect.

The wear I describe would be very subtle. If for example, the holes that the 
indicator arbor passes through are normally three-thousandths of an inch larger 
in diameter than the arbor (just guessing on this — I have not measured it), 
and it’s known that the arbor touches only a specific portion of the wall of 
those holes at a specific speed, then you may find that the holes and/or the 
arbor itself have worn -slightly- out of round. It would be hard to see, but if 
the holes are normally for example .003” larger than the arbor, and now they’re 
subtly egg-shaped and .005” in only one direction (out of round), then any 
vibration whatsoever at the contact point (leather pad & flywheel) would cause 
the arbor to vibrate in a unidirectional orientation, within its holes. 

Wear would naturally occur on the associated parts only in the specific areas 
of the arbors and holes that would be in constant contact when the machine is 
set to run the correct speed, assuming that for most of the machine’s life it 
was set to run at the correct speed, thus causing the wear at those limited 

Keep in mind that even though the holes may appear to be a very close fit to 
the arbors and thus touching them all around, the reality is that the contact 
point between arbors and holes can only be over a specific small part of the ID 
of the holes. For them to touch all around, the holes would have to be the same 
size as the arbors, which would be a zero clearance, zero tolerance hole — 
almost a press fit. The holes are larger than the arbors to provide freedom of 
movement. Freedom of movement when constrained within certain engineered limits 
is a good thing. Freedom of movement outside of those limits can either cause 
problems or allow problems originating elsewhere to come to light.

Chances are that this machine has lived with a slight vibration at the governor 
most of its working life, and this has in effect caused more wear to occur in a 
very narrow and specific way. ANY vibration will lead to greater wear on 
associated parts than the same arrangement with no discernible vibration. There 
are multiple causes of vibration at the governor and pad, which could be 
explored as part of another investigation.

To correct your immediate problem, and assuming nothing is done to correct the 
vibration, then you might approach where the visible effects of this vibration 
manifest, by sourcing a different indicator frame and arbor. While the 
indicator needle serves to show the turntable speed, it also makes a marvelous 
vibration indicator!

All of the above supposition is based on imagining all of the related parts 
working in the mind, in the absence of physical inspection, and therefore 
remains in the realm of theory. To check to see if the arbor holes are worn 
slightly out of round, a clockmaker would insert a "smoothing broach" into the 
holes (tapered steel tool of round cross section), until the tool gently seats 
in the hole. Then they would hold the indicator frame and broach up to a light 
source and hunt for a slim, crescent moon shaped irregularity showing at the 
hole, around the broach. If present, this would prove a worn hole. The test 
would be repeated for each hole. Wear would likely be greater at the hole 
closest to the steel arm and hairspring that supports the pad, than at the 
opposite end of the same arbor. You should also inspect the arbors themselves, 
where they touch the holes. I would expect to see that a narrow portion of 
their OD would at minimum appear more polished, indicating a history of 
(normal) rubbing. They could still be in tolerance  however unless they measure 
out of round with a caliper.

All this conjecture about worn holes is based solely on your comments about the 
problem manifesting only across a narrow portion of the speed range. For a 
condition where vibration of the needle is present across the entire speed 
spectrum, I would focus on resolving the source of the vibration, which could 
be as simple as refreshing the mounting pads between the motor housing and 
motor board. Vibration transferred to the motor board from the motor, could 
result in sympathetic vibration from the motor board to the indicator frame 
mounted under it, even if there is no wear at the indicator frame holes and 
arbors. In this case, you can ignore nearly all of the above. Ultimately, if 
the inidcator assembly is worn and replacements weren’t readily available, they 
could be restored to their factory tolerances.

Best and good luck. Keep me posted on what you learn,
Andrew Baron
Santa Fe, NM

> On Sep 12, 2019, at 7:47 AM, Robert Wright via Phono-L <phono-l@oldcrank.org> 
> wrote:
> Hello to all! I hope someone can help me with this incredibly annoying 
> problem: the speed indicator mech of one of my Credenza X's chatters at 78rpm 
> It's fine at 80, it's fine at 90 (I have a Hughes adapter I use for Pathé 
> verticals), and it's fine below 77. But right at 78 to 79rpm, it chatters. 
> It's pretty obviously the contact point between the leather nib and the 
> governor disc -- once it's up to speed, it bounces instead of riding smoothly 
> against the surface. I've cleaned the disc and even held some 2400 sandpaper 
> against it, I've replaced the leather nib with fresh leather shoestring of 
> two different gauges (one which was sold specifically as material for 
> phonograph brakes), I've soaked the nibs in oil, I've slathered them with 
> lithium grease… Nothing helps. I can get a few plays without chatter if I 
> apply more grease, or clean off the grease that's there (same result -- 
> "disturbing" that contact point in either way helps for a few plays). 
> Anyone else ever had to deal with this? 
> Thanks in advance,
> Robert
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