Bob, you're misunderstanding the situation. I admit things may be a little
confusing here as we've been talking about two unrelated subjects in the
same threads. There are two significant masses and two significant
resonances that we've been talking about. The mass of the complete
reproducer is significant in that it, combined with the effective end mass
of the tonearm constitutes a resonant system with its spring constant
determined by the compliance of the needle, needle bar, and diaphragm. The
goal is to have this resonance be a very low frequency so that it is not
excited by record modulation. In other words, we DO NOT want the reproducer
and tonearm to vibrate with the needle. To do so robs some of the groove
energy from being directed into the horn and lowers the volume at those
frequencies where the tonearm is vibrating. Extreme vibrations of the
tonearm can also cause the needle to skip out of the groove. This resonance
can be lowered by either increasing the mass of the complete reproducer or
by increasing the compliance of the diaphragm.
But the more difficult resonance to control is that which is dependent
on the effective tip mass at the needle point which we DO WANT to vibrate -
that is we DO want the needle, needle bar, and diaphragm to vibrate while
not allowing the complete reproducer and tonearm to vibrate. The effective
tip mass here with regard to this resonance is determined by the mass of the
needle, needle bar, and diaphragm. These are relatively low masses compared
with the mass of the complete reproducer. Any part of this mass which is
spaced at a large distance from the needle bar pivot will increase its
inertia around that pivot and cause the EFFECTIVE mass as seen at the needle
tip to be larger than if that mass was located closer to the needle bar
pivot. You will note that the needle chuck itself and the needle screw
constitute a significant amount of the above total mass. That is why we are
not engaged in mere mental diddling to be concerned with this mass. A
lower mass here allows the diaphragm compliance to be increased to produce
the same resonance. Lowering this mass and increasing the compliance allows
the groove to do less work because it doesn't have to move so much mass
around. Placing the resonance at a higher, yet still midrange frequency is
necessary to retain efficiency (loudness) from the reproducer. A slightly
higher, well damped resonance together with a higher compliance also allows
better treble AND bass response to be obtained from the system with no loss
of loudness. It's all a delicate balance of masses and compliances to get
the most blood out of the turnip that can be squeezed.
So, the mass of the needle thumbscrew itself is only part of the problem
with the typical needle chuck system. The thumbscrew has to screw into
something rather substantial in order to produce a tight grip on the needle.
That something is the needle chuck which is, itself, rather massive because
it has to have enough "meat" in it to provide several threads in a fairly
hard material that the needle screw can bind into. Eliminating the entire
needle chuck and screw would be desirable as a way of lowering the moving
mass of the needle system. Which is what we've been talking about.
Greg Bogantz
----- Original Message -----
From: "Bob" <rvuill at comcast.net>
To: "Antique Phonograph List" <phono-l at oldcrank.org>
Sent: Thursday, February 14, 2008 8:49 AM
Subject: Re: [Phono-L] threaded needles
> Hi Greg,
> I've read this whole discussion with interest. As I understand it the
> goal of this exercise in "mental masturbation" is to reduce the mass of
> the reproducer by the weight of the thumb screw. I do not have accurate
> measuring tools to weigh a standard thumb screw and don't remember the
> weight of your custom aluminum reproducer but emphericly I don't think the
> thumbscrew makes up a significant proportion of the total mass which is
> why I made the comment about mental masturbation. That being said, I do
> have a practical solution to eliminate most of the mass of the thumbscrew.
> I would think the majority of the mass of the thumbscrew is in the knurled
> disk at the end used for tightening it against the needle. This section
> and a good portion of the threaded shaft could be eliminated if you
> machined a hex or a flat on the end that is left sticking out of the
> needle bar after the needle is inserted and tightened. You would use
> either a small pair of pliers or a custom hex wrench to tighten the
> threaded piece.
> RMV
> ----- Original Message -----
> From: "Greg Bogantz" <gbogantz1 at charter.net>
> To: "Antique Phonograph List" <phono-l at oldcrank.org>
> Sent: Wednesday, February 13, 2008 4:33 PM
> Subject: Re: [Phono-L] threaded needles
>
>
>> Thatcher,
>>
>> That's essentially what I am now doing. The present design is a press
>> fit of the needle shank into the hole (deep well, actually) in the needle
>> bar. But the fit must be tight to prevent rattling. This makes the
>> machining difficult, but more significantly, it makes the needle exchange
>> difficult because you must use pliers, tweezers, or some similar tool to
>> hold both the needle bar and the needle shank for both insertion and
>> removal. Not user-friendly. Specialized tools and/or jigs could be
>> furnished to make the job easier, but it's still a tedious task. A
>> friend of mine has experimented with a similar design. His solution is
>> to glue the needle shank into the needle bar. That works, but getting
>> the worn needle out of the needle bar is a b*tch. He gets around this by
>> using the "semi-permanant" osmium Pfanstiehl needles that were popular in
>> the 1940s and can last for several playings. I don't agree with this
>> because these needles are too hard, as I've commented before, and must be
>> worn in over several playings on junk records to form their flats. He
>> removes the needle by heating the glue with a soldering iron to cause it
>> to flow. Still, very tedious.
>>
>> Greg Bogantz
>>
>>
>>
>> ----- Original Message -----
>> From: "Thatcher Graham" <thatcher at mediaguide.com>
>> To: "Antique Phonograph List" <phono-l at oldcrank.org>
>> Sent: Wednesday, February 13, 2008 3:16 PM
>> Subject: Re: [Phono-L] threaded needles
>>
>>
>>>
>>> As an engineer I could not help but to fixate on this "threaded needle
>>> idea". I agree that threading needles solves the mass issue hence the
>>> instinctive appeal, but the difficult manufacture is equally
>>> discouraging. As an alternative, have you considered a sabot?
>>>
>>> -Thatcher
>>>
>>>
>>>
>>> Jon Noring wrote:
>>>> Greg wrote:
>>>>
>>>>
>>>>> Threading the needle shank and having it screw into the needle bar
>>>>> is an
>>>>> option. I hadn't considered that before, but it would pretty well
>>>>> solve the
>>>>> extra mass problem. But it would make the needles pretty involved to
>>>>> manufacture. I'll keep it in mind.
>>>>>
>>>>
>>>> Yes, it would be involved if all the needles are threaded by hand or
>>>> in small numbers, especially at the diameter being considered.
>>>>
>>>> It is intriguing to consider using a very fine threaded rod, if even
>>>> manufactured in the desired material(s). One would have to grind and
>>>> polish to create the tip geometry.
>>>>
>>>> Which brings up the idea that if a needle is to be especially
>>>> manufactured, one could consider tipping it with a different material
>>>> that can be specially shaped (such as spherical or elliptical with
>>>> no sharp edges at all. It is my understanding that most damage to
>>>> grooves is due to a tip which is no longer smooth. Maybe the tip could
>>>> be made from a material of the same hardness as the "grit" used in
>>>> shellac discs (is it corundum?) to wear down the needle.
>>>>
>>>> Just thinking outside the box...
>>>>
>>>> Jon
>>>>
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>>>>
>>>
>>>
>>>
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>>
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