Myth busted.
Very good when a myth falls apart, especially if it contradicts our common sense; but even more I like to understand things personally (numquam jurare in verba magistris, was taught in our schools). So I was trying to retrace your calculations.
Question: to calculate the inertia it's used the average acceleration during the whole cycle, or the maximum one (for v near 0 of the harmonic motion)? Things seem very different.
thanks carlo
to understand your last post it will take me years: really i can't figure out the connection between resonances (are you talking about that at 0.55 hz?) and stylus bending.
Very good when a myth falls apart, especially if it contradicts our common sense; but even more I like to understand things personally (numquam jurare in verba magistris, was taught in our schools). So I was trying to retrace your calculations.
Question: to calculate the inertia it's used the average acceleration during the whole cycle, or the maximum one (for v near 0 of the harmonic motion)? Things seem very different.
thanks carlo
to understand your last post it will take me years: really i can't figure out the connection between resonances (are you talking about that at 0.55 hz?) and stylus bending.
Hi Niffy,
One thing I agree that all the forces are though the contact of the groove wall and stylus. However, my analysis is highly conceptual.
For example, I assume that friction is zero. A 50 g arm may need a minimum 1mN to overcome the gravity to move the carriage. However, for the cartridge, its cantilever may be deflected at .8mN. Therefore, I can say the carriage is too high in mass. In other words, it is too heavy.
Another example. Ideally, when a cartridge is tracking, its base, i.e., the carriage should be as stable as possible. Any small movements at the base will degrade the bass performance. Let’s assume that if a carriage is 20 g arm and it is too light, so when the cartridge tracking the waveform, it may introduce small movements at the base. It will degrade the bass performance. We all know that heavy arm usually has better bass performance than light arm.
In my mind, a good arm is a balanced arrangement of all interacting forces. Although there is one direct interaction of the groove wall and stylus, we can break the force down conceptually.
Jim
One thing I agree that all the forces are though the contact of the groove wall and stylus. However, my analysis is highly conceptual.
For example, I assume that friction is zero. A 50 g arm may need a minimum 1mN to overcome the gravity to move the carriage. However, for the cartridge, its cantilever may be deflected at .8mN. Therefore, I can say the carriage is too high in mass. In other words, it is too heavy.
Another example. Ideally, when a cartridge is tracking, its base, i.e., the carriage should be as stable as possible. Any small movements at the base will degrade the bass performance. Let’s assume that if a carriage is 20 g arm and it is too light, so when the cartridge tracking the waveform, it may introduce small movements at the base. It will degrade the bass performance. We all know that heavy arm usually has better bass performance than light arm.
In my mind, a good arm is a balanced arrangement of all interacting forces. Although there is one direct interaction of the groove wall and stylus, we can break the force down conceptually.
Jim
Hi Jim,
You wrote
"For example, I assume that friction is zero. A 50 g arm may need a minimum 1mN to overcome the gravity to move the carriage. However, for the cartridge, its cantilever may be deflected at .8mN. Therefore, I can say the carriage is too high in mass. In other words, it is too heavy."
If friction is zero then an infinitesimal force will result in an infinitesimal acceleration. There isn't a minimum force required, any force will cause an acceleration. You only need a force to overcome gravity if the carriage is moved vertically. If there is friction then a force will be required to overcome the static friction before the carriage will move.
"Another example. Ideally, when a cartridge is tracking, its base, i.e., the carriage should be as stable as possible. Any small movements at the base will degrade the bass performance. Let’s assume that if a carriage is 20 g arm and it is too light, so when the cartridge tracking the waveform, it may introduce small movements at the base. It will degrade the bass performance. We all know that heavy arm usually has better bass performance than light arm."
A lightweight carriage with move more than a heavyweight carriage. There isn't a mass where the carriage suddenly won't move. Its just the more mass the less it will move, double the mass half the movement. You don't want to add too much mass or you might tune the lateral compliance resonance so low in frequency that it is excited by the frequency of eccentricity 0.55hz.
Niffy
You wrote
"For example, I assume that friction is zero. A 50 g arm may need a minimum 1mN to overcome the gravity to move the carriage. However, for the cartridge, its cantilever may be deflected at .8mN. Therefore, I can say the carriage is too high in mass. In other words, it is too heavy."
If friction is zero then an infinitesimal force will result in an infinitesimal acceleration. There isn't a minimum force required, any force will cause an acceleration. You only need a force to overcome gravity if the carriage is moved vertically. If there is friction then a force will be required to overcome the static friction before the carriage will move.
"Another example. Ideally, when a cartridge is tracking, its base, i.e., the carriage should be as stable as possible. Any small movements at the base will degrade the bass performance. Let’s assume that if a carriage is 20 g arm and it is too light, so when the cartridge tracking the waveform, it may introduce small movements at the base. It will degrade the bass performance. We all know that heavy arm usually has better bass performance than light arm."
A lightweight carriage with move more than a heavyweight carriage. There isn't a mass where the carriage suddenly won't move. Its just the more mass the less it will move, double the mass half the movement. You don't want to add too much mass or you might tune the lateral compliance resonance so low in frequency that it is excited by the frequency of eccentricity 0.55hz.
Niffy
Hi Jim,
You wrote
"For example, I assume that friction is zero. A 50 g arm may need a minimum 1mN to overcome the gravity to move the carriage. However, for the cartridge, its cantilever may be deflected at .8mN. Therefore, I can say the carriage is too high in mass. In other words, it is too heavy."
If friction is zero then an infinitesimal force will result in an infinitesimal acceleration and an infinitesimal displacement of the cantilever. There isn't a minimum force required, any force will cause an acceleration. You only need a force to overcome gravity if the carriage is moved vertically. If there is friction then a force will be required to overcome the static friction before the carriage will move.
"Another example. Ideally, when a cartridge is tracking, its base, i.e., the carriage should be as stable as possible. Any small movements at the base will degrade the bass performance. Let’s assume that if a carriage is 20 g arm and it is too light, so when the cartridge tracking the waveform, it may introduce small movements at the base. It will degrade the bass performance. We all know that heavy arm usually has better bass performance than light arm."
A lightweight carriage with move more than a heavyweight carriage. There isn't a mass where the carriage suddenly won't move. Its just the more mass the less it will move, double the mass half the movement. You don't want to add too much mass or you might tune the lateral compliance resonance so low in frequency that it is excited by the frequency of eccentricity 0.55hz.
Niffy
You wrote
"For example, I assume that friction is zero. A 50 g arm may need a minimum 1mN to overcome the gravity to move the carriage. However, for the cartridge, its cantilever may be deflected at .8mN. Therefore, I can say the carriage is too high in mass. In other words, it is too heavy."
If friction is zero then an infinitesimal force will result in an infinitesimal acceleration and an infinitesimal displacement of the cantilever. There isn't a minimum force required, any force will cause an acceleration. You only need a force to overcome gravity if the carriage is moved vertically. If there is friction then a force will be required to overcome the static friction before the carriage will move.
"Another example. Ideally, when a cartridge is tracking, its base, i.e., the carriage should be as stable as possible. Any small movements at the base will degrade the bass performance. Let’s assume that if a carriage is 20 g arm and it is too light, so when the cartridge tracking the waveform, it may introduce small movements at the base. It will degrade the bass performance. We all know that heavy arm usually has better bass performance than light arm."
A lightweight carriage with move more than a heavyweight carriage. There isn't a mass where the carriage suddenly won't move. Its just the more mass the less it will move, double the mass half the movement. You don't want to add too much mass or you might tune the lateral compliance resonance so low in frequency that it is excited by the frequency of eccentricity 0.55hz.
Niffy
Abec 9 bearings came today. Some of you have open bearings and I'm wondering
if you have rinsed them out after opening them ? And if so, with what ?
Any special low friction lubricant ?
Definitely run them dry. No lubrication. If they are supplied prelubed then you will need to wash the lubricant out. I think acetone will work. An overnight soak will probably help.
Niffy
myth busting
I did my #3301 homework, salvaging vague high school memories with some help from the web
Moto circolare uniforme e Moto armonico – GeoGebra - (sorry, in italian, but the graph speaks for itself)
The calculations were in MKS, but the data are converted in quantities more suitable to our topic, so please check calculations and results, since I get often confused with too many zero
If the disc is centered the stylus travels <86 mm in approximately 1800"- the speed is 0.047 mm/s, practically unnoticeable to the eye. The motion can be considered uniform (minimal variations due to the variable pitch) = 0 acceleration. So we need only the amount of the side force to overcome the friction of the carriage - let's take 50 gr * 0.002 mu (an excellent carriage) = 1 mN at the rail level**.
Unfortunately the disc is never centered - even RIAA admits a runout of +- 0.4 mm - so we will always have to deal with small or large eccentricities; my "crash test" video shows extreme conditions (runout = +- 1.5 mm. = 3 times RIAA) to highlight at best the behavior of the carriage.
The stylus travels 3mm in one turn = 1.8 "- its average speed s/T = 1.66 mm/s, 34 times the uniform motion, and perfectly observable; its average acceleration will be delta v/delta T = 0.92 mm/s^2. The average inertia of our carriage would be m * a = 50gr * 0.92 mm/s^2 = 0.046 mN: a completely irrelevant force.
But: here we don't have a constant speed and acceleration, we have instead an harmonic motion: the speed starts from zero at the turning point to reach the maximum at the center (sin theta function) while the acceleration does the opposite (cos theta function): maximum at the turning point, zero in the center.
Now, using harmonic motion formulas to calculate their maximum value
ω = 2π f (f = 0.55 hz)
then in our test conditions
v (t) max = ω * r = 5.18 mm/s (> 3 times the average speed)
a (t) max = −ω^2 * r = 17.9 mm/s^2 ( > 22.5 times the average acceleration)
applied to our 50 gr carriage --- inertia = 0.89 mN
Damn, this value is small but not irrelevant, it's equivalent to our friction**; and their sum brings also the needed SF near to a dangerous zone - And it also explain better why, at the turning point, the cantilever is bending to build up the side force necessary to move the carriage.
The dogs's tail myth is a myth, this tries simply to understand how it was born
carlo
and Nessie? will it be appropriate to investigate further?
I did my #3301 homework, salvaging vague high school memories with some help from the web
Moto circolare uniforme e Moto armonico – GeoGebra - (sorry, in italian, but the graph speaks for itself)
The calculations were in MKS, but the data are converted in quantities more suitable to our topic, so please check calculations and results, since I get often confused with too many zero
If the disc is centered the stylus travels <86 mm in approximately 1800"- the speed is 0.047 mm/s, practically unnoticeable to the eye. The motion can be considered uniform (minimal variations due to the variable pitch) = 0 acceleration. So we need only the amount of the side force to overcome the friction of the carriage - let's take 50 gr * 0.002 mu (an excellent carriage) = 1 mN at the rail level**.
Unfortunately the disc is never centered - even RIAA admits a runout of +- 0.4 mm - so we will always have to deal with small or large eccentricities; my "crash test" video shows extreme conditions (runout = +- 1.5 mm. = 3 times RIAA) to highlight at best the behavior of the carriage.
The stylus travels 3mm in one turn = 1.8 "- its average speed s/T = 1.66 mm/s, 34 times the uniform motion, and perfectly observable; its average acceleration will be delta v/delta T = 0.92 mm/s^2. The average inertia of our carriage would be m * a = 50gr * 0.92 mm/s^2 = 0.046 mN: a completely irrelevant force.
But: here we don't have a constant speed and acceleration, we have instead an harmonic motion: the speed starts from zero at the turning point to reach the maximum at the center (sin theta function) while the acceleration does the opposite (cos theta function): maximum at the turning point, zero in the center.
Now, using harmonic motion formulas to calculate their maximum value
ω = 2π f (f = 0.55 hz)
then in our test conditions
v (t) max = ω * r = 5.18 mm/s (> 3 times the average speed)
a (t) max = −ω^2 * r = 17.9 mm/s^2 ( > 22.5 times the average acceleration)
applied to our 50 gr carriage --- inertia = 0.89 mN
Damn, this value is small but not irrelevant, it's equivalent to our friction**; and their sum brings also the needed SF near to a dangerous zone - And it also explain better why, at the turning point, the cantilever is bending to build up the side force necessary to move the carriage.
The dogs's tail myth is a myth, this tries simply to understand how it was born
carlo
and Nessie? will it be appropriate to investigate further?
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Hi Carlo,
I fear you may have made a couple of mistakes in your analysis but the general methodology is exactly what I am using for my estimations.
You said "The stylus travels 3mm in one turn = 1.8 "- its average speed s/T = 1.66 mm/s". This was referring to an extreme eccentricity of 1.5mm. The stylus actually travels 6mm. 3mm to the left then 3mm to the right. This would give an average speed of 3.33mm/s.
You calculated a maximum velocity of 5.18mm/s whereas I calculated it as
v (t) max = ω * r
ω = 3.49rad/s (0.55hz)
r = 1.5mm
v (t) max = 5.236mm/s
Similarly for acceleration
a (t) max = −ω^2 * r
a (t) max = 18.27mm/s^2
With a 50g carriage the maximum force will be 0.91mN.
If we assume that cartridge compliance is equal to the manufacturers specs at 0.55hz then we can estimate the maximum deflection of the stylus due to inertia. (this is a little bit of a stretch as most cartridges' compliance vary with frequency but should give a rough estimate). If my cartridge, 22um/mN, were used for this estimate the deflection would be
0.91 x 22 = 20um.
My cartridge has a 5mm long cantilever so we can determine that the resultant maximum angular displacement of the cantilever will be approximately 0.23°
The average force acting on the stylus will be the maximum divided by root2.
0.91 / 1.414 = 0.64mN
From this we can estimate that the average angular displacement will be 0.16° for a 22um/mN cartridge.
This is of course still using the record with the 1.5mm eccentricity. With any normal record the displacements will be much lower than this.
Niffy
I fear you may have made a couple of mistakes in your analysis but the general methodology is exactly what I am using for my estimations.
You said "The stylus travels 3mm in one turn = 1.8 "- its average speed s/T = 1.66 mm/s". This was referring to an extreme eccentricity of 1.5mm. The stylus actually travels 6mm. 3mm to the left then 3mm to the right. This would give an average speed of 3.33mm/s.
You calculated a maximum velocity of 5.18mm/s whereas I calculated it as
v (t) max = ω * r
ω = 3.49rad/s (0.55hz)
r = 1.5mm
v (t) max = 5.236mm/s
Similarly for acceleration
a (t) max = −ω^2 * r
a (t) max = 18.27mm/s^2
With a 50g carriage the maximum force will be 0.91mN.
If we assume that cartridge compliance is equal to the manufacturers specs at 0.55hz then we can estimate the maximum deflection of the stylus due to inertia. (this is a little bit of a stretch as most cartridges' compliance vary with frequency but should give a rough estimate). If my cartridge, 22um/mN, were used for this estimate the deflection would be
0.91 x 22 = 20um.
My cartridge has a 5mm long cantilever so we can determine that the resultant maximum angular displacement of the cantilever will be approximately 0.23°
The average force acting on the stylus will be the maximum divided by root2.
0.91 / 1.414 = 0.64mN
From this we can estimate that the average angular displacement will be 0.16° for a 22um/mN cartridge.
This is of course still using the record with the 1.5mm eccentricity. With any normal record the displacements will be much lower than this.
Niffy
I fear you may have made a couple of mistakes in your analysis ...
You're absolutely right, I had considered only the half-period - so i should divide instead by 0.9 "
Average speed: not my 1.66 mm/s, 3.33mm/s = 68 times the uniform motion.
max speed: your 5.236 mm/s vs my 5.18 mm/s and max acceleration: your 18.27mm/s^2 vs my 17.9 mm/s^2
inertia your 0.91mN. vs my 0.89 mN
I'm glad, the differences seems very small - during the calculations perhaps I exaggerated to rounding the decimals on the pocket calculator.
But I see that you also attribute a little less than 1 mN to inertia - since it is the similar to what you reported for your cart's friction, and being added to that, it is not so irrelevant.
Normally it is for tracking error, but with less good carts than yours, at the turning point it can be the classic drop that brings to skipping, as often happens to see on these arms. Maybe is what gave heavy carriages a bad name.
carlo
thanxs for attention, and again congrats for the stylus behavior in the video
You're absolutely right, I had considered only the half-period - so i should divide instead by 0.9 "
Average speed: not my 1.66 mm/s, 3.33mm/s = 68 times the uniform motion.
max speed: your 5.236 mm/s vs my 5.18 mm/s and max acceleration: your 18.27mm/s^2 vs my 17.9 mm/s^2
inertia your 0.91mN. vs my 0.89 mN
I'm glad, the differences seems very small - during the calculations perhaps I exaggerated to rounding the decimals on the pocket calculator.
But I see that you also attribute a little less than 1 mN to inertia - since it is the similar to what you reported for your cart's friction, and being added to that, it is not so irrelevant.
Normally it is for tracking error, but with less good carts than yours, at the turning point it can be the classic drop that brings to skipping, as often happens to see on these arms. Maybe is what gave heavy carriages a bad name.
carlo
thanxs for attention, and again congrats for the stylus behavior in the video
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Hi Carlo,
"But I see that you also attribute a little less than 1 mN to inertia - since it is the similar to what you reported for your cart's friction, and being added to that, it is not so irrelevant."
Don't forget that this is with an enormous amount of eccentricity. Even a badly eccentric record is unlikely to have even a third of this. An average record is probably going to be more like a tenth with the resultant force also being a tenth. The level of bearing friction is not affected by the level of eccentricity.
Niffy
"But I see that you also attribute a little less than 1 mN to inertia - since it is the similar to what you reported for your cart's friction, and being added to that, it is not so irrelevant."
Don't forget that this is with an enormous amount of eccentricity. Even a badly eccentric record is unlikely to have even a third of this. An average record is probably going to be more like a tenth with the resultant force also being a tenth. The level of bearing friction is not affected by the level of eccentricity.
Niffy
quote this too for sure, Niffy.
This debate on the carriages, introduced by Warren, made me understand the importance of the refinement work that you and Jim have been doing for years, comparing to the ideas that led me to design the Lil Casey, with a radial rail to eliminate the negative lever of the arm.
On a LT if we could have zero frictions the point of application of the force would be irrelevant, while if it were locked we would have a torque on the bearings, multiplied by r*cos alpha.
Between these two extremes live the real tonearms: it is as if the friction behaves as a servo brake: more side force to overcome friction increases the torque on the bearings loaded laterally, which increase the friction and so on.
It's like a trap: if you are very careful you can safely eat the cheese, but when pushing too much, just adding some shake (eccentricities, small scratches, some dust) the game is over = an intolerable bending or even skipping.
With the reverse pendulum I had seen that by exceeding 2mN (and 200 mg resistsnce -all included- are very few) begin the real problems, so staying below that threshold working on every little detail, is absolutely vital: as shown by jim's and your LTs, and very few others around.
Of course Lil Casey has to deal with very similar problems, but the advantage is that any resistance (carriage friction, inertia, cables etc) is applied axially with a progressive deterioration, not a servo brake effect.
In short, it tolerates a less sophisticated construction maintaining really interesting results: at least according to the comments of the Ukrainian friends who have built some different versions.
carlo
..."The level of bearing friction is not affected by the level of eccentricity"....
this makes me think about Ray's stiction hypothesis at turning points...
This debate on the carriages, introduced by Warren, made me understand the importance of the refinement work that you and Jim have been doing for years, comparing to the ideas that led me to design the Lil Casey, with a radial rail to eliminate the negative lever of the arm.
On a LT if we could have zero frictions the point of application of the force would be irrelevant, while if it were locked we would have a torque on the bearings, multiplied by r*cos alpha.
Between these two extremes live the real tonearms: it is as if the friction behaves as a servo brake: more side force to overcome friction increases the torque on the bearings loaded laterally, which increase the friction and so on.
It's like a trap: if you are very careful you can safely eat the cheese, but when pushing too much, just adding some shake (eccentricities, small scratches, some dust) the game is over = an intolerable bending or even skipping.
With the reverse pendulum I had seen that by exceeding 2mN (and 200 mg resistsnce -all included- are very few) begin the real problems, so staying below that threshold working on every little detail, is absolutely vital: as shown by jim's and your LTs, and very few others around.
Of course Lil Casey has to deal with very similar problems, but the advantage is that any resistance (carriage friction, inertia, cables etc) is applied axially with a progressive deterioration, not a servo brake effect.
In short, it tolerates a less sophisticated construction maintaining really interesting results: at least according to the comments of the Ukrainian friends who have built some different versions.
carlo
..."The level of bearing friction is not affected by the level of eccentricity"....
this makes me think about Ray's stiction hypothesis at turning points...
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Hi all,
I've been reexamining the videos that I made of the movement of the cantilever on eccentric records.
YouTube 0. 3mm eccentricity.
YouTube 1.5mm eccentricity.
The deflections of the cantilever just didn't look as large as I had thought. The level of relative movement is very difficult to clearly see as it is at the limit of resolution of the video. This would tend to suggest that my calculations for how much deflection I would expect were also in error. I double checked all of my work. The calculations for the deflection due to inertia were all good. The deflection due to friction had been calculated using the wrong coefficient of friction. I had accidentally used the level of friction from my handmade steel pin bearings and steel wheels.
The calculated deflection of the cantilever using correct coefficient of friction for the jewel bearing and tungsten carbide wheels made quite a difference.
The 0.3mm eccentricity (0.6mm movement) would cause a maximum total tracking error of 0.29° (rather than the 0.42° I had previously calculated). The average tracking error would be approximately 0.23°. The average tracking error for a record with this level of eccentricity would be about 0.15° due to the misalignment of the groove. The maximum tracking error due to groove angle, which occurs at the innermost groove, would be 0.28° for this record.
The 1.6mm eccentricity (3.2mm movement) would cause a total tracking error of 0.49° (rather than the 0.65° I had previously calculated). The average tracking error would be approximately 0.37°. The average tracking error for a record with this level of eccentricity would be about 0.75° due to the misalignment of the groove with a maximum of nearly 1.5°.
The point of maximum error due to friction and inertia luckily occurs at 90° of record rotation to that of maximum groove angle error. This means that you don't get the two maximums adding. Even with the care I've taken in the design of my bearings bearing friction is still the main source of LTA error unless the eccentricity of the record is greater than 0.5mm. The groove angle due to eccentricity is the second greatest source. Inertia is responsible for only a small proportion.
With an average record maximum tracking error is unlikely to be greater than 0.3°.
Hi Carlo,
I love the ingenuity of the lil casey. In most tonearms the most influential component is the armtube. By eliminating the armtube you have also eliminated its negative effects. I believe that this is the main reason for the lil casey magic.
Niffy
I've been reexamining the videos that I made of the movement of the cantilever on eccentric records.
YouTube 0. 3mm eccentricity.
YouTube 1.5mm eccentricity.
The deflections of the cantilever just didn't look as large as I had thought. The level of relative movement is very difficult to clearly see as it is at the limit of resolution of the video. This would tend to suggest that my calculations for how much deflection I would expect were also in error. I double checked all of my work. The calculations for the deflection due to inertia were all good. The deflection due to friction had been calculated using the wrong coefficient of friction. I had accidentally used the level of friction from my handmade steel pin bearings and steel wheels.
The calculated deflection of the cantilever using correct coefficient of friction for the jewel bearing and tungsten carbide wheels made quite a difference.
The 0.3mm eccentricity (0.6mm movement) would cause a maximum total tracking error of 0.29° (rather than the 0.42° I had previously calculated). The average tracking error would be approximately 0.23°. The average tracking error for a record with this level of eccentricity would be about 0.15° due to the misalignment of the groove. The maximum tracking error due to groove angle, which occurs at the innermost groove, would be 0.28° for this record.
The 1.6mm eccentricity (3.2mm movement) would cause a total tracking error of 0.49° (rather than the 0.65° I had previously calculated). The average tracking error would be approximately 0.37°. The average tracking error for a record with this level of eccentricity would be about 0.75° due to the misalignment of the groove with a maximum of nearly 1.5°.
The point of maximum error due to friction and inertia luckily occurs at 90° of record rotation to that of maximum groove angle error. This means that you don't get the two maximums adding. Even with the care I've taken in the design of my bearings bearing friction is still the main source of LTA error unless the eccentricity of the record is greater than 0.5mm. The groove angle due to eccentricity is the second greatest source. Inertia is responsible for only a small proportion.
With an average record maximum tracking error is unlikely to be greater than 0.3°.
Hi Carlo,
I love the ingenuity of the lil casey. In most tonearms the most influential component is the armtube. By eliminating the armtube you have also eliminated its negative effects. I believe that this is the main reason for the lil casey magic.
Niffy
Sapphire Vees and Pivots
Hi again Niffy,
I found some Vees and Pivots on a US site. Your comments good or bad would be appreciated. My existing LTA with Boca bearings on glass rods does suffer from Static friction making the stylus wiggle a little. Attempting to do better with the next one.
https://www.swissjewel.com/ offers Vees and Pivots. I ordered VS-100 threaded jewels at just under $7 ea and N-7D pivots at $5.00 US ea.
The radius of the pivot ends is about 0.001" or 0.0254mm (differing from your Carbide tipped ones). Swissjewel recommended Vees at 3x the radius and that's pretty much what they have.
It'll be a while before I get to test these for friction. So I may keep an eye out for Vees like yours in case I'm going Carbide tips later.
Hugh
Hi again Niffy,
I found some Vees and Pivots on a US site. Your comments good or bad would be appreciated. My existing LTA with Boca bearings on glass rods does suffer from Static friction making the stylus wiggle a little. Attempting to do better with the next one.
https://www.swissjewel.com/ offers Vees and Pivots. I ordered VS-100 threaded jewels at just under $7 ea and N-7D pivots at $5.00 US ea.
The radius of the pivot ends is about 0.001" or 0.0254mm (differing from your Carbide tipped ones). Swissjewel recommended Vees at 3x the radius and that's pretty much what they have.
It'll be a while before I get to test these for friction. So I may keep an eye out for Vees like yours in case I'm going Carbide tips later.
Hugh
Practically perfect results, space age materials and tolerances to bust long seasoned myths (too heavy masses, too short arms, etc.): top class, Niffy
Arm length --- the radial rail was born from simple physical-trigonometric considerations, but then the inverse pendulum showed some surprising behavior.
An usual carriage with normal friction (>3 mN) is very sensitive to the length of the arm, up to the mousetrap effect of which I spoke. --completely as predicted.
But when frictions become minimal, this becomes much less significant. Attaching a stick to the Lil casey carriage (1.4 mN) I was astonished to see how few it changed shifting the application point of the force. Up to 30 - 40 mm of leverage there was just a small variation, until carriage lock up close to 100 mm. Surely going down under 1mN things may go even better.
Now I'm trying to better understand the bearings: it struck me to calculate the uniform speed of the carriage (0.047 mm/s) and to think that a common 22mm bearing does just <1,5 revolution (always near stiction?).
Perhaps -on a non-recirculating- using small balls can be an advantage (>10 turns, on friction?).
Perhaps the use of tight tolerances ball bearings may be another myth to bust
carlo
Arm length --- the radial rail was born from simple physical-trigonometric considerations, but then the inverse pendulum showed some surprising behavior.
An usual carriage with normal friction (>3 mN) is very sensitive to the length of the arm, up to the mousetrap effect of which I spoke. --completely as predicted.
But when frictions become minimal, this becomes much less significant. Attaching a stick to the Lil casey carriage (1.4 mN) I was astonished to see how few it changed shifting the application point of the force. Up to 30 - 40 mm of leverage there was just a small variation, until carriage lock up close to 100 mm. Surely going down under 1mN things may go even better.
Now I'm trying to better understand the bearings: it struck me to calculate the uniform speed of the carriage (0.047 mm/s) and to think that a common 22mm bearing does just <1,5 revolution (always near stiction?).
Perhaps -on a non-recirculating- using small balls can be an advantage (>10 turns, on friction?).
Perhaps the use of tight tolerances ball bearings may be another myth to bust
carlo
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Hi Hugh,
The prices for vees and pivots seem really good. The radius of the pivots are only a fifth of those that I use. I went with the larger diameter pivots and vees only twice the ratio (rather than 3x) in order to reduce the stress on the materials and to make a more robust bearing. The smaller radius components should result in even lower friction than I have achieved but will probably require a lighter mass carriage and very careful handling during record changing and queuing. The smaller radius and larger size ratio will result in a much smaller contact point which might improve mechanical grounding.
Niffy
The prices for vees and pivots seem really good. The radius of the pivots are only a fifth of those that I use. I went with the larger diameter pivots and vees only twice the ratio (rather than 3x) in order to reduce the stress on the materials and to make a more robust bearing. The smaller radius components should result in even lower friction than I have achieved but will probably require a lighter mass carriage and very careful handling during record changing and queuing. The smaller radius and larger size ratio will result in a much smaller contact point which might improve mechanical grounding.
Niffy