Bill and Crack, you are right. I mixed up forged and cast. Forged and machined to size is king is what I meant.
English is not my first language.
English is not my first language.
Not deviating from the options on bearing servicing or modifying one, which has benefits, if carried out using certain disciplines.
The subject of producing a Chassis from a Metal, will be worthwhile countering, with the suggestion of using Densified Wood as the material of choice over a metal.
The subject of producing a Chassis from a Metal, will be worthwhile countering, with the suggestion of using Densified Wood as the material of choice over a metal.
Could we get back on topic? To the question of sourcing the turntable bearing ball, and therefore the subsidiary questions of what that ball should be made of and what qualities it should have?
Various posters have commented on the effects of poor lubrication. Others have pointed out that although a bearing needs a hard material and a soft material in contact to minimize wear, the soft material must wear. Which brings me to the ball and its lubrication. Turntable platter bearings traditionally take the thrust on a single centrally placed ball bearing. The ball then bears on a thrust pad. If the ball and thrust pad were infinitely hard/strong, there would be no deformation and the contact area would be zero. That would mean infinite pressure, squeezing out any lubrication. The bearing runs dry. Not a problem, because we said that the bearing and thrust pad were infinitely hard/strong. But real bearings and thrust pads aren't infinitely hard/strong. So we see wear. That seems to suggest that the thrust pad should be sufficiently soft to increase the area of contact to something that reduces the pressure so that either the bearing runs perfectly well dry, or to such a pressure that lubrication is not expelled. If that argument is true, then it suggests that we need the ball to be as perfectly round as possible because larger radii of the ball will be scraping the soft material and we want a uniform contact that doesn't create noise.
Turning to the thrust pad, PTFE has been mentioned. Wonderful stuff and easily available. But it creeps. I put a PTFE thrust pad under a synchronous motor and it worked beautifully for reducing a previously felt grumble as the rotor rotated. But the rotor and its pulley must have weighed, oooh, 10g? I think PTFE isn't really going to be practical for a platter bearing where 3kg or more is to be supported. I'm wondering about a nice accurately round ball on a lignum vitae thrust pad. Perhaps with some opposing magnets to reduce the thrust on the bearing because reduced thrust should reduce deformation and reduced deformation will reduce the radius of the contact area, reducing noise. Discuss.
By the way, this is not a rhetorical question; I'm working up to making a turntable from scratch. I've been improving my machining skills and improving my lathes ready for the task.
Various posters have commented on the effects of poor lubrication. Others have pointed out that although a bearing needs a hard material and a soft material in contact to minimize wear, the soft material must wear. Which brings me to the ball and its lubrication. Turntable platter bearings traditionally take the thrust on a single centrally placed ball bearing. The ball then bears on a thrust pad. If the ball and thrust pad were infinitely hard/strong, there would be no deformation and the contact area would be zero. That would mean infinite pressure, squeezing out any lubrication. The bearing runs dry. Not a problem, because we said that the bearing and thrust pad were infinitely hard/strong. But real bearings and thrust pads aren't infinitely hard/strong. So we see wear. That seems to suggest that the thrust pad should be sufficiently soft to increase the area of contact to something that reduces the pressure so that either the bearing runs perfectly well dry, or to such a pressure that lubrication is not expelled. If that argument is true, then it suggests that we need the ball to be as perfectly round as possible because larger radii of the ball will be scraping the soft material and we want a uniform contact that doesn't create noise.
Turning to the thrust pad, PTFE has been mentioned. Wonderful stuff and easily available. But it creeps. I put a PTFE thrust pad under a synchronous motor and it worked beautifully for reducing a previously felt grumble as the rotor rotated. But the rotor and its pulley must have weighed, oooh, 10g? I think PTFE isn't really going to be practical for a platter bearing where 3kg or more is to be supported. I'm wondering about a nice accurately round ball on a lignum vitae thrust pad. Perhaps with some opposing magnets to reduce the thrust on the bearing because reduced thrust should reduce deformation and reduced deformation will reduce the radius of the contact area, reducing noise. Discuss.
By the way, this is not a rhetorical question; I'm working up to making a turntable from scratch. I've been improving my machining skills and improving my lathes ready for the task.
A design I have read up on recently, is a air bearing with a magnet design to lift the platter, reducing the contact force on the ball.
Lubrication will not be a concern if the design is correct. The necessary Magnet type is potentially costly.
Engineering out Precession down to low microns, is a challenge.
Lubrication will not be a concern if the design is correct. The necessary Magnet type is potentially costly.
Engineering out Precession down to low microns, is a challenge.
Does the thrust pad have to be perfectly flat? How about if it is "cupped"? That will do two things:
(1) Keep the ball bearing centered in the shaft. So the spindle doesn't slide on the thrust pad.
(2) Increase the surface between the thrust pad and bearing, thus lowering the pressure and allowing the lubricating oil to create a layer.
I just had the Karousel upgrade on my LP12. The machining of the parts looked fantastic (stainless steel) and they sound even more fantastic... it is an eye opener how much of a difference a new bearing assembly will do.
I now have the old parts, bearing and subplatter in the box... still working great.... Interestingly... the trust pad did not looked "cupped".. but then, it was hard to see looking down the shaft. I might be a slight cupping?
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But, how do you keep the magnetic field supporting the platter from affecting the cartridge?
A 60 deg dead centre has worked well on ultra precision cylindrical grinders, but to my knowledge, never tried on record players. If I were to make my own turntable, that's where I'd start.
Neodymium magnets are surprisingly cheap (and small). I paid about £10 each for a pair of magnets each having an attractive force of 2kg, so put them opposing and really close and they'll lift a 3kg platter off its thrust pad. Adjusting gap between them will adjust residual force on thrust pad. You need them to be concentric, suggesting that they need to be interference fits into accurately machined sleeves. I don't see that as a great problem, but it will depend on how accurately (physical dimensions) the magnets were made. As for inducing currents into the cartridge, one magnet is rotating, but about its magnetic axis, so I don't see it inducing a change of flux in the cartridge.
I think we'll have a cupped thrust pad whether we like it or not. I think the important thing is that the ball should be centred on the shaft. That needs some careful machining, but should be possible. I had in mind a nylon cap on the end of the shaft to locate the ball. I suspect in the end it comes down to how concentric the shaft is in the lathe when machined to accept the cup. With a lot of patience (and a lever-type dial test indicator) it's possible to get it to better than 2um using a four-jaw chuck.
But I'm lost on the suggestion of a 60 degree dead centre.
I think we'll have a cupped thrust pad whether we like it or not. I think the important thing is that the ball should be centred on the shaft. That needs some careful machining, but should be possible. I had in mind a nylon cap on the end of the shaft to locate the ball. I suspect in the end it comes down to how concentric the shaft is in the lathe when machined to accept the cup. With a lot of patience (and a lever-type dial test indicator) it's possible to get it to better than 2um using a four-jaw chuck.
But I'm lost on the suggestion of a 60 degree dead centre.
noisy.
FWIW, I've been using a small tungsten ball against a 0.750" 5211 ball for over 30 years without issue.
FWIW, I've been using a small tungsten ball against a 0.750" 5211 ball for over 30 years without issue.
Ball can never be considered without the mating thrust surface. IMO, the main requirements are that it wear forever and not be fragile. If the contact area is small, friction will be low, but if the contact area is too small, it will degrade. Look up Hertzian contact. There are a couple free apps for that. My preference is not crazy hard against crazy hard because damage is almost certain. A plain steel ball (52100) of any decent quality is fine. I like a somewhat compliant thrust surface, though most of the common engineering plastics perform poorly. Teflon creeps and flakes. Others will actually damage the ball. Brief test results on on my website somewhere. One of the IGUS materials is much better, like P210. I've also had good luck with Lignum Vitae discs as long as you never sand them. They have to be cut or they retain grit.
Because the surface speeds of TT bearings are very slow, you need close clearances to prevent metal-to-metal contact. As a result, you don't want a cupped bearing seat as it will probably put side forces on the spindle. Getting things to run true at the precision required is near impossible, so make the design tolerant of imperfection. Low noise comes from parts having perfect geometry and good surface finish. The only way I know to get that is honing, both external and internal. You can do it by hand with the right tools and techniques.
See eighth item down- http://www.conradhoffman.com/chsw.htm
This is really good- https://www.vinksda.com/toolkit-mechanical-calculations/hertz-contact-stress-calculations/
Because the surface speeds of TT bearings are very slow, you need close clearances to prevent metal-to-metal contact. As a result, you don't want a cupped bearing seat as it will probably put side forces on the spindle. Getting things to run true at the precision required is near impossible, so make the design tolerant of imperfection. Low noise comes from parts having perfect geometry and good surface finish. The only way I know to get that is honing, both external and internal. You can do it by hand with the right tools and techniques.
See eighth item down- http://www.conradhoffman.com/chsw.htm
This is really good- https://www.vinksda.com/toolkit-mechanical-calculations/hertz-contact-stress-calculations/
Because the speed of TT bearing thrust surfaces is very slow, it is doubtful that you will be able to maintain any sort of lubricant film there, and contact of the thrust surfaces is inevitable. The rationale for using dissimilar materials for the thrust surfaces (tungsten and 52100 steel) is to vastly reduce the galling that would occur if similar materials were used. This concept is commonly used in ball bearings which operate under conditions of poor or no lubrication, where micro asperity welding would cause them to quickly self destruct. It also seems to the rationale for the old Sota Sapphire turntable which used sapphire as one of its thrust surfaces.
Yes, the hertzian stresses there are great, and permanent deformation of one of the surfaces (52100) is inevitable.
But there are may ways to skin a cat.
Yes, the hertzian stresses there are great, and permanent deformation of one of the surfaces (52100) is inevitable.
But there are may ways to skin a cat.
Thought I'd add my 2cents.
I've recently machined an inverted bearing motor modification for an SP10mk2. The platter is 13kg sitting on a 5mm SI3N4 ball running on a Vesconite Hilube thrust pad. I ran this in the lathe at 300rpm with well over 13kg of pressure and there is only a very small divot in the thrust pad. This was done to check longevity. I also machined the journal sleeves from Vesconite Hilube and placing the platter upside down with a mass on the motor so it spins for a while and there is ZERO audible bearing noise in the platter using a stethoscope.
Lignum Vitae is unavailable in most parts of the world as it's illegal to import/export from the USA and a lot of other countries. Vesconite Hilube was specifically formulated for journal sleeves and thrust bearings in harsh environments and has been tested extensively in axle components on rolling stock (trains). Vesconite Hilube has lower coefficient of friction of almost all the bearing grade thermoplastics, it's very close to PTFE with the dimensional stability of POMH.
Regarding magnetic lev. I tested this to use on my SP10mk2, the results were an unacceptable level of stray magnetic flux on the top of the platter 70mm away from the magnets. As the magnetic field is rotating there is a high probability this will have some unknown effect on the cartridge.
I've recently machined an inverted bearing motor modification for an SP10mk2. The platter is 13kg sitting on a 5mm SI3N4 ball running on a Vesconite Hilube thrust pad. I ran this in the lathe at 300rpm with well over 13kg of pressure and there is only a very small divot in the thrust pad. This was done to check longevity. I also machined the journal sleeves from Vesconite Hilube and placing the platter upside down with a mass on the motor so it spins for a while and there is ZERO audible bearing noise in the platter using a stethoscope.
Lignum Vitae is unavailable in most parts of the world as it's illegal to import/export from the USA and a lot of other countries. Vesconite Hilube was specifically formulated for journal sleeves and thrust bearings in harsh environments and has been tested extensively in axle components on rolling stock (trains). Vesconite Hilube has lower coefficient of friction of almost all the bearing grade thermoplastics, it's very close to PTFE with the dimensional stability of POMH.
Regarding magnetic lev. I tested this to use on my SP10mk2, the results were an unacceptable level of stray magnetic flux on the top of the platter 70mm away from the magnets. As the magnetic field is rotating there is a high probability this will have some unknown effect on the cartridge.
That Vesconite sounds like very interesting stuff. It's not well known here in the USA- I've never seen it promoted.
Lignum Vitae is typically available only as existing and reclaimed material, usually from things like policeman's nightsticks and bocce balls. A small piece will make a lifetime supply of TT thrust pads.
It's true that the slow surface speeds make maintaining a lube film difficult. That's where perfect geometry and surface finish come into play. It can be done, but only with small clearances and honed parts. Surface speed goes up if the shaft is large, but that also increases the risk of noise should the film not be maintained.
Lignum Vitae is typically available only as existing and reclaimed material, usually from things like policeman's nightsticks and bocce balls. A small piece will make a lifetime supply of TT thrust pads.
It's true that the slow surface speeds make maintaining a lube film difficult. That's where perfect geometry and surface finish come into play. It can be done, but only with small clearances and honed parts. Surface speed goes up if the shaft is large, but that also increases the risk of noise should the film not be maintained.
Lots of interesting comments. Vesconite Hilube indeed looks interesting. Agreed, lignum vitae is an internationally protected species. Note sure what a bocce ball is, but in the UK, old lignum vitae lawn bowls (4"-4.5" diameter) typically go for about £10 each. I've fitted all the hand wheels on both my lathes with rotating handles made from lignum vitae. Much nicer to use. Sadly, I've discovered a practical point that although a piece of lignum vitae might look fine from outside, once you start cutting, you may discover internal voids. One large handle took three attempts before I had a voidless part (using up a lot of wood). And the wastage cutting from a sphere tends to be high. So it doesn't always go as far as you might have hoped. On the positive side, the stuff machines beautifully with a fresh non-ferrous insert.
Looks like I need to look up honing by hand.
I don't see an unchanging magnetic field around the cartridge as a huge problem. Admittedly, as a warp is traversed, a current will be induced, but the rate of change of flux and therefore voltage will be very low compared to the audio. It's really about choosing the right compromise. If magnetic levitation can reduce the force between ball and pad to a point that low noise is produced, then a little extra warp signal is fine.
Looks like the consensus is that practical turntable bearings actually run dry, despite the presence of lubricant.
Looks like I need to look up honing by hand.
I don't see an unchanging magnetic field around the cartridge as a huge problem. Admittedly, as a warp is traversed, a current will be induced, but the rate of change of flux and therefore voltage will be very low compared to the audio. It's really about choosing the right compromise. If magnetic levitation can reduce the force between ball and pad to a point that low noise is produced, then a little extra warp signal is fine.
Looks like the consensus is that practical turntable bearings actually run dry, despite the presence of lubricant.
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I looked into importing LV balls from the USA but was unable to because of the restrictions on shipping them. This is why I started investigating other materials, Vespel is prohibitively expensive and Vesconite ticked all the boxes. I run the bearing with only a light coating of oil, no oil bath.
Vesconite machines nicely. I use PCD tooling which gives the smoothest surface finish.
There are ball hones available for honing engine cylinders and valve guides, These can be used in a had drill.
1st pic is a Vesconite Hilube thrust pad I made for a stock SP10mk2 motor, 2nd is a Vesconite top sleeve in an SP10mk2 motor housing.
Vesconite machines nicely. I use PCD tooling which gives the smoothest surface finish.
There are ball hones available for honing engine cylinders and valve guides, These can be used in a had drill.
1st pic is a Vesconite Hilube thrust pad I made for a stock SP10mk2 motor, 2nd is a Vesconite top sleeve in an SP10mk2 motor housing.
I have lignum vitae and I don't have Vesconite (and it would probably be expensive to import some), so it looks like that decision is made. And a valve guide is the right diameter. I was intending to use Altmann's suggestion of an engine valve as the shaft because it is a hardened part intended for use as a bearing. I'll look up ball hones.
Well, am I surprised! That wasn't what I expected a ball hone to be. A loo brush with abrasive balls on the end. But they're for cylinders. Do you have a link for something suitable for valves?
Well, am I surprised! That wasn't what I expected a ball hone to be. A loo brush with abrasive balls on the end. But they're for cylinders. Do you have a link for something suitable for valves?
First is an empty SP10mk2 motor (no stator and rotor) fitted with Vesconite sleeves. Second is a stock SP10 bearing where the metal to metal contact is clearly audible, (this motor bearing has been cleaned and new oil added. I have attached a contact microphone on the bearing housing and the record level is at maximum. For comparison is a Linn Cirkus bearing I found on the web (not my recording)
A ball hone won't help you because it doesn't correct geometry. See https://www.americanlap.com/ for some inexpensive lapping tools. I was going to do more with TT bearings but never got a round tuit. This is my Sunnen- http://www.conradhoffman.com/honetech.htm
Don't fret about Vespel. Not only is it expensive, it doesn't make a very good thrust pad. Ditto Torlon and many other fancy engineering plastics. Oddly, regular black Delrin, not even the fancier AF stuff, is quite good. But not as good as IGUS and probably the Vesconite stuff.
Don't fret about Vespel. Not only is it expensive, it doesn't make a very good thrust pad. Ditto Torlon and many other fancy engineering plastics. Oddly, regular black Delrin, not even the fancier AF stuff, is quite good. But not as good as IGUS and probably the Vesconite stuff.
warrjon: I've just watched/listened to the Utoob videos. This is a rare thing for me as they are usually tedious. OK, so noticeable grumbling on the Linn and I couldn't hear anything on the Technics. I didn't turn the sound right up for fear of a stupid advert. You've made your point. And that's superb run out shown on the DTI.
Conrad Hoffman: I will follow up your links. Thank you.
In with the Utoob videos was Dan Gelbert's lathe. Not really that difficult to make? Not if you already have an extremely well-equipped workshop (way better than mine). Wonderful stuff. And I note he has a serious electronics lab too.
Conrad Hoffman: I will follow up your links. Thank you.
In with the Utoob videos was Dan Gelbert's lathe. Not really that difficult to make? Not if you already have an extremely well-equipped workshop (way better than mine). Wonderful stuff. And I note he has a serious electronics lab too.