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I am square dab in the middle of rebuilding a friends SL1200 main bearing with a ceramic ball interfacing a mirror polished, super hard surface.
Here is a picture of the worn down stock machined steel surface Technics runs on the business end of the main platter bearing. This probably represents about 25 years of happy spinning time.
The thrust surface is an interesting material. I am not sure if it is a tough graphite impregnated plastic, a sintered metal piece, or some yet to be disclosed gem of Technics engineering.
What I can tell you is that this old bearing is shot! The ball is flat and the thrust plate is worn down a great deal. There is so much friction on this thing there is no way you can hear deep dark backgrounds or low level details. These are all masked by resonance.
More to follow....I might not be able to get this done for a while. I have to order and process the parts. Then I have to arrange some lathe time. I doubt I can get to this until after Muzikmikes Ribfest.
Here is a look at the bearing assemby. The plate with the worn disk interfaces to this bearing piece and the other side is the spindle and platter engagement.
When done it should be able to deliver a good deal of the deep dark backgrounds and inner detail my Rek O Kut bearings achieve.
I would like to do 4 or 5 of these for a trial just to see how they effect SL1200 tables in different asylum inmate's systems.
Cheers!
"Music Matters" Help support our schools music programs.
Follow Ups:
I also have the one tapped by KAB to hold his clamp. I am interested in this mod to my old bearing for proof of concept depending on pricing. I would consider a later upgrade of the KAB bearing if everything doesn't go down in a blaze of glory during the guinee pig stage and assuming that it does bring a notable improvement.
I have seen where the outboard power supply company inthe UK is working on an upgrade. With your friends, if it has 25 years of heavy use more might be worn also.
Good luck on your upgrade project. I think a better bearing would improve playback. But I bought a new one from KAB for 29.95.
George
It is generally a mistake to increase the hardness of the thrust surface, especially if you have also increased the hardness of the spherical contact.The relavant calculation is the Hertzian contact pressure for spherical point contact, an online version of which can be found in the link
Note that the default stress (4.2 MPa) is the standard ISO stress for ball bearing races and should not be used for TT bearing calculations. If you do not know the allowable shear stress limit for the material you are using you can substitute the 0.2% yield stress.
Edit: The 0.2% yield stress obviously only applies to ductile materials.
Mark Kelly
Edits: 05/18/09
"Note that the default stress (4.2 MPa) is the standard ISO stress for ball bearing races and should not be used for TT bearing calculations."
I'd like to understand why this is true but not being a mechanical expert don't even know whhere to begin looking. Can you point me in a direction to help me understand this statement?
As I understand it, 4.2 GPa is the standard used to calculate bearing loads according to ISO 281 of 2007 "Rolling bearings — Dynamic load ratings and rating life". This is for standard ball bearings with steel balls and races at a very high hardness and is calculated to give 90% survival at 1 million revolutions. That may sound like a lot but translating it into turntable terms that's a 10% chance of failure after 500 hours.
If you used the same material for your thrust pad and were prepared to accept that failure rate you could use that same stress in your calculation. If you use less highly hardened steel to improve the toughness of the bearing you would use a lower stress - I believe 1.8GPa is typical. If you used bronze you would use an even lower stress dpending on the type - ordinary bearing bronze is as low as 400MPa.
Mark Kelly
I need to think about that for a while.
If you make the bearing from stiffer materials the contact area is reduced (because the stiffer material bends less). This increases the contact pressure because the same weight is being borne by a smaller area.If you are not careful the resulting pressure will be so high that the material will fail. It will fail in shear because there's a large difference in the compression immediately under the contact point and a point just outside the contact area. One is being pushed down, the other is not so they are effectively being torn apart.
Edit: the actual mechanism is more complex than this and has to do with Poisson's ratio but I'm trying to keep this non-technical.
Further edit: I changed "harder" to "stiffer" to remove potential confusion
Mark Kelly
Edits: 05/18/09 05/20/09
"If you make the bearing from harder materials the contact area is reduced (because the harder material bends less). This increases the contact pressure because the same weight is being borne by a smaller area."mark: big fan, but this sentence is patently false.
hardness: resistance to plasticity (permanent deformation)
elastic modulus: resistance to elastic (non-permanent deformation)Typically these scale together... most ceramics have both higher hardness and higher modulus than metals, but definitely not always. Iridium is my favorite "low cost" example.
I believe we had a very similar discussion to this on diyaudio some time back regarding bearing and thrust plate materials. Not sure if there was ever any sort of consensus though. What is needed is something that can hold the weight of the platter for high cycle fatigue, and has very little friction. I personally feel that having a hard thrust plate and a "disposable" ball is a reasonable option. In which case a hardened steel ball and a sapphire thrust plate would yield excellent results. For a "light weight" platter, the ball could easily last 2 or 3 thousand hours. Take it out, degrease the bearing, blow it out, regrease, insert new ball and go.
Edits: 05/20/09
I was trying to explain things in terms even T4 would understand. I thought the gloss was permissible given that with the ceramic materials he was talking about hardness and modulus generally scale together.I have edited the post to remove the potential confusion.
Mark Kelly
Edits: 05/20/09
Mark,
Two years ago you said that an SiNi ball would potentially destroy a polished steel thrust surface.
After more than a year of continuous use there is no more than a polish mark where the SiNi ball engages the steel. There is no shearing, no material transfer, and no damaged materials. The bearing performs with a reduced noise floor, it exhibits improved micro dynamics, clarity, and focus. Even untrained ears can hear the improvement in the sonics.
Regarding the current project, I have engaged the expertise of engineers who work with bearings, materials applications and hardened surfaces. I have discussed my goals, the application as it pertains to the Technics table and the underlying issues regarding what I perceive to be the current failing in bearing performance.
My research has led to a consensus. I expect higher performance. I am happy to provide you with samples of the bearing thrust surface materials for you to test first hand.
You were wrong two years ago Mark. Can you admit you are wrong?
Are you willing to actually test your opinions or do you prefer to simply attack me personally?
Mark, you pulled the original material because it did not apply to mirror polished thrust surface. That is the reality. That is what I clearly understand.
"Music Matters" Help support our schools music programs.
"Two years ago you said that an SiNi ball would potentially destroy a polished steel thrust surface."
It really depends on the applied load. SiNi WILL destroy a polished steel thrust plate given enough load or cycles.
"After more than a year of continuous use there is no more than a polish mark where the SiNi ball engages the steel. There is no shearing, no material transfer, and no damaged materials. The bearing performs with a reduced noise floor, it exhibits improved micro dynamics, clarity, and focus. Even untrained ears can hear the improvement in the sonics."
Unless you left your turntable on for the entire year you'll come nowhere near the point on the S-N curve where you're going to do damage.
BUT. When you reach that point, make sure you're using a bearing system that you don't care about. I'd actually be more worried about the bearing shaft, as that part is usually not easily replaced. A SiNi ball will destroy your polished steel (polishing really has very little effect on wear). It is a complicated system that depends highly on bearing diameter, loading, and number of cycles.
No one can get around physics.
"You were wrong two years ago Mark. Can you admit you are wrong?"
Two years is a very short time for a bearing of this type. Leave that player on continuously for 1 or 2 million cycles and take another look.
"Are you willing to actually test your opinions or do you prefer to simply attack me personally?"
Most of this stuff was worked out well before I was born. I don't think anyone is personally attacking anyone else.
"Mark, you pulled the original material because it did not apply to mirror polished thrust surface. That is the reality. That is what I clearly understand."
Polishing has a miniscule effect on hardness, although a measurable effect on wear. It may increase component lifetime by 50% or so, but once again. It is not the thrust plate that I'm necessarily concerned about. It is the bearing shaft. This may be easily, and cheaply, replaceable on the 1200, but is not on most other players.
I appreciate the mature discussion points.
In my application the mirror polishing is not intended to improve longevity of the bearing. However I fully expect this finish preparation to achieve this result as well as achieve my intended goal.
For discussion, here is a picture of one of the worse wear marks I have encountered while refurbishing, restoring, or modifying a Rek O Kut turntable. The chrome surface had actually worn away from the ball (probably ran dry) and the ball and steel showed signs of rust.
This was a 30+ year old table when I refurbished it. This damage was created by pressure, friction and time. You are not kidding when you say time will be the nemesis of a ball riding against a thrust surface.
I have been asked to take my own improved bearing concept and build it into some of my friend's turntables.
In my opinion, in order to do this both professionally and responsibly requires a two piece assembly process. One piece will be installing the appropriate ceramic ball at the optimal height to engage the thrust surface. This might require machining for some platter bearings but this is pretty standard stuff for any competent machine shop.
The second and most important step is creating a removeable/replaceable mirror polished thrust surface that is durable, will resist Brinnelling, and achieve noise floors equal to or better than I have accomplished to date.
I completely agree that 1 year or more spin time is inadequate to test for wear and bearing performance.
Regaring the future of turntable bearings, looking at the space age plastics and ceramics we are dealing with today, I doubt a high quality turntable bearing manufactured 10 years from today will look anything at all like the bearings manufactured 20 years ago.
Thanks for your input. I highly value your experience and your opinions. This will be a fun and interesting process.
Cheers!
"Music Matters" Help support our schools music programs.
With certain ceramic materials the bearing surface exhibits self lubricating qualities. I simply need a thrust material which will not crack under force as ruby or saphire are likely to do.
The material I am selecting will be mirror polished, and it has less susceptibility to failure under stress than other materials I have investigated.
I have talked to several physical application engineers about this improved bearing concept and every one is on board regarding the materials, their finish grading and the overall expected results.
I am happy to discuss this with you off line. My personal email address is jim_howard_pdx@yahoo.com.
"Music Matters" Help support our schools music programs.
I urge you to review the calculations. The shear strength of the material is the limiting factor no matter what surface finish you achieve.
If you exceed the maximal stress the material will either crack or deform by plastic flow. Assuming you avoid the first, the second will mould the thrust plate to the contact ball and your advantage will be lost.
Mark Kelly
That's pretty cool...thanks for the pics!
It's too bad that the bearing replacement isn't just swap in a new ball and bolt in a new thrust plate. From the looks of it, you've got some machining to do to get the old parts out of the way and figure out how to mount the new ones?
If it was bolt in, I'd be in with my SL1210
I'd love to see the progress as you continue with the project.
But since I don't have many hours on it (and thus don't have a good "feel" for it yet) I wouldn't be able to give you any useful feedback.
See you at Mike's!
Jim
Ribs...yummn I am getting hungry already.
I am bringing some toys with me. Cheers!
"Music Matters" Help support our schools music programs.
a silicon carbide ball? I was shocked at the difference between the SS ball and the SC...the accumulative effects of separating the motor from the chassis, changing out the thrust bearing's ball, big spikes as "feet" and the 12.7 pivot point on the JMW 10 created a table I'd put up against anything out there. It is incredible!
I'm looking forward to "showing you do its THANG!" Of course, you're bringing something that I'll cry about...but the stock Piccolo ain't no slouch, either.
There is no such thing as too many records.
There is just too little room for them!
The receipe will be a mystery for a while. I really need to get some alpha site bearings out to folks that have a good reading on their SL1200 turntables.
Good, bad or ugly the SL1200 bearing is a weak link. Improving it will be an interesting follow up post.
I don't have a table of my own to evaluate, so I really need about 5 inmates to let me know how the results sound in their systems.
Luckily this is not an irreversible modification. I can always return this to a chrome steel ball and sintered metal thrust plate. This would be a slight improvement over the stock machined surface.
Cheers!
"Music Matters" Help support our schools music programs.
Your statement that replacing the machined surface with a chrome steel ball would be an improvement is quite wrong.
If you look at the bearing you will see that it is machined as an oblate hemispheroid to increase the effective radius at the contact point, thereby decreasing the load stress and increasing the toughness of the bearing. If the machining is done the right way the apparent surface roughness is not very important as the apparent roughness is orthogonal to the direction of motion.
Bottom line: Technics engineers really know what they are doing. It is important to understand why they made a particular decision before reversing it.
Mark Kelly
Regarding the bearing materials, machining quality and design criteria, this bearing is built to be a nearly indestructable piece perfect for high utility studio and DJ applications.
This bearing provides lower opportunity for Brinnelling given the rubber damped vinyl sub plinth which communicates a lot more pounding than a suspended platter assembly. The SL1200/SL1210 was designed for easy and trouble free mobility which is perfect for a studio or DJ.
Replacement bearings are sold between 75-100 dollars and are available from Technics. They are very simple, very plain, and easy to replace.
Nothing I do in my trials could in any way impact the overall value of the table to its owner. The modified bearing could be tossed out and replaced with a factory bearing if the alpha user does not like the results.
If the modification is successful, I could easily machine plain steel, stainless steel or even a silicone nitride ball to the same geometry of a stock Technics bearing if the table is going to be used in high mobility applications.
I could even use graphite impregnated space age plastics as a thrust surface that would be superior to the stock Technics bearing.
If you want a sample of the thrust surface material I plan to evaluate, I am happy to provide one or several to you for your own testing. I will do so at my own expense. I have no agenda with this test. I am looking for ways to achieve quieter noise floors for my friends spinning an SL1200 turntable.
I have CDR test recordings of similarly improved bearings if you want to hear the results in your own system. My own turntable bearings show no sign of wear after more than a year of daily spinning and I am using a platter at least twice as heavy.
"Music Matters" Help support our schools music programs.
I'd take a sample. I do friction and wear testing for a living. Heck, send me some of the technics stuff and I'll test that too.
I've gotten so much through various forums, that I really would like the opportunity to give back.
If you have not done so, email me at jim_howard_pdx@yahoo.com. I am happy to send you several pieces for your evaluation. I can outline my project, the desired results and some additional details that can make this more fun from a testing/performance perspective.
"Music Matters" Help support our schools music programs.
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