On my EMT 930 ST i replaced the Steelball with a Sapphire of same diameter.
Sapphire was choosen because the manufacturer had better roundness specs therefor than for his tungstencarbide version of same diameter.
I found the friction is lower now, since the platter had befora around 240 sec to come down from 78 rpm to zero rpm , ( specified by EMT is minimum 180), now it has 300 second.
Listening on the bearing with stethoscope gave very small to no real difference, listening music i believe it has a little bit more details..
But for sure i can see that the bearing still looks like new after 2 years of use.
Price for the sapphire ( Radius 6mm) was 200 $, and the manufacturer demands minimal order of 350$, so i have the tungstencarbide ball still on stock.
BTW. The manufacturer says they make really very round balls, for gyroscopes, surface measuring systems and some other hitec apps where it is really critical to have lowest tolerances and friction.
Sapphire was choosen because the manufacturer had better roundness specs therefor than for his tungstencarbide version of same diameter.
I found the friction is lower now, since the platter had befora around 240 sec to come down from 78 rpm to zero rpm , ( specified by EMT is minimum 180), now it has 300 second.
Listening on the bearing with stethoscope gave very small to no real difference, listening music i believe it has a little bit more details..
But for sure i can see that the bearing still looks like new after 2 years of use.
Price for the sapphire ( Radius 6mm) was 200 $, and the manufacturer demands minimal order of 350$, so i have the tungstencarbide ball still on stock.
BTW. The manufacturer says they make really very round balls, for gyroscopes, surface measuring systems and some other hitec apps where it is really critical to have lowest tolerances and friction.
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That's just in the US...I'm thinking larger than that.
I could rule the world if only I had the right plug!!
jn
I seem to remember a discussion awhile back on this forum, where a machinist recommended, that to properly install sintered-bronze, not to machine afterward. A special fitting needed to be made, to fit around the ID of the bushing. When pressed in, the bushing would then compress around the fitting, and conform to the proper size.
Maybe this would be a better way to refit the bearing, rather than trying to home or machine afterwards?
Maybe this would be a better way to refit the bearing, rather than trying to home or machine afterwards?
The problem with oil impregnated bearings is that lubrication takes place because rotation of the shaft generates friction and hence heat - the heat draws the oil out of the bearing and lubricates the surface - and a turntable bearing does not rotate anything like quickly enough to generate this process.
Hmmmm... do you have a reference for that? One of the ones I cited said that the bearings were good down to 10F, so I'm not sure how much heat would be generated at that low temperature if what you said is true. They also don't seem to specify a minimum speed and load for the bearings.
I do agree that jewel bearings are probably better for this application.
Sintered bearings operate pretty much like unsintered bearings, but they supply their own lube. Heat doesn't seem to be an issue in making them work. The issue, IMO, is that tt speeds are way below what you find in any of the tables that give the minimums to avoid metal to metal contact between the parts. IMO again, the solution is extreme control over surface finishes, geometry and clearance.
OK, so jeweled bearings are most likely the best for a turntable then. Some of the gears in a watch or clock turn very slowly.
I'm not sure about jewels, but they do offer an expense and coolness factor! IMO, the first question is to decide what the important parameters are, and then rank bearing methods and materials based on those parameters. My guess is you won't get perfect agreement on what to put at the top of the list. There's also the execution factor. Excellent execution of a possibly second rate choice might well outperform sloppy execution of something that might otherwise be at the top of the heap.
Keep an open mind. I remember reading about a method that involved pushing pieces of rubber against the spindle, running with oil. Everybody likes super hard point contact thrust bearings except me. I find a piece of Lignum Vitae wood gives the least damage to the typical rounded spindle, far better than the usual Delrin, Teflon and such. Too bad it's endangered, but there's lots of used and recycled Lignum around.
Keep an open mind. I remember reading about a method that involved pushing pieces of rubber against the spindle, running with oil. Everybody likes super hard point contact thrust bearings except me. I find a piece of Lignum Vitae wood gives the least damage to the typical rounded spindle, far better than the usual Delrin, Teflon and such. Too bad it's endangered, but there's lots of used and recycled Lignum around.
John Harrison used Lignum Vitae for his turntable bearings..
H1, H2, and H3.
jn
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We are here far off topic of the OP's problem, but as it seems this is quite usual and accepted in this forum I'm not too much ashamed to add my 2cts.
I'm with you, Conrad, regarding super hard point contacts. However I have to state that my little bit of experience is with Lenco tts, and these have a very powerful motor and don't need a super easy going bearing. Patience, I'm just coming to the gist of my scribblings here.
I experimented with Lignum Vitae thrust plates and ball-less spindles from hardened steel with a large radius on the end. To my surprise these spindles were quite severely scratched after about 50 hours. Even a hard chromed spindle got such scratches! So I ruefully went back to Delrin, which works a treat. Btw. I consider Teflon not suitable, because it creeps under a constant load. YMMV, as some say...
It seems that a ceramic ball on L.V. is not so much influenced, but had no opportunity to check this.
As soon as time permits and I can work on a couple more bearings, I will try a stuff called Turcite. It's normal use is for coating slideways on machine tools. As it's a liquid (paste rather), it can form a little bowl with the exact radius as the spindle end. Then this bowl also serves for sideways guiding (stabilizing) the lower spindle end. Hope you are still with me...
Greetings, Hansrudolf
the BIG advantage of lignum vitae is that there is no need for lubricant. And thus nothing to gum up the works.John Harrison used Lignum Vitae for his turntable bearings..
H1, H2, and H3.
H3 was so much smaller than H1 and H2, that he went for small and hard bearings/pallets and had to use lubricant for these.
So much smaller is a relative term.
The pic I provided was not H3, I'm not sure what it was, they didn't have a Placard describing it.
Here is a picture I took of the H3 at the Greenwich Observatory. I can't see close enough on it to see if they he used rollers. It does appear that he used Lignum vitae for the bushings he mounted the brass gears to however. Looks like wood consistent with LV.
jn
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Love those clocks! Way OT here, but not all Lignum is equal. The modern stuff you can get isn't really Lignum at all. Then you have the choice of using end grain or not. The tests I did with Lignum were combined with a bit of light mineral oil and even a soft spindle nose had no damage at all, unlike most every other "engineering" plastic. Agree, Teflon has too many downsides, usually flaking onto the spindle. Good results were also had with cherry and maple, vacuum impregnated with oil. One trick- you can't sand the wood! That embeds particles that will scratch. You have to scrape or machine it only. Wood only seems good for thrust; haven't found a way to do a stable accurate bearing with it.
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This discussion is NOT OT!!! It's about bearings and bearing surfaces as they apply to the topic of the OP.
My biggest concerns with wood is actually the rate of moisture movement and it's impact on geometric stability. When I make an 8 inch clock gear, I do multiple cutting passes on the pin router, the last pass is the final tooth profile cut, where I remove about 1/32 inch, 30 mils. That is to relieve all the build in stresses of the grains. When done, I do 3 to 5 coats of a good sealer to stop moisture movement into or out of the work. The goal is to keep the radius accurate to under 5 mils over time. Otherwise, tight clearance gears can lock.
Using wood for bearing surfaces entails the exact same problems, showing in a different fashion. Pressure and friction will eventually bring out the grain pattern, oil penetrating over time can change dimension. That's why I do not recommend LV for high pressure contact/bearing.
Teflon creeps too much.
I really like extreme hardness contact with low contact area, it just requires quench and polish. Ruby by nature does it.
I assume others have already made tonearm bearings using watch style jewel techniques?
jn
My biggest concerns with wood is actually the rate of moisture movement and it's impact on geometric stability. When I make an 8 inch clock gear, I do multiple cutting passes on the pin router, the last pass is the final tooth profile cut, where I remove about 1/32 inch, 30 mils. That is to relieve all the build in stresses of the grains. When done, I do 3 to 5 coats of a good sealer to stop moisture movement into or out of the work. The goal is to keep the radius accurate to under 5 mils over time. Otherwise, tight clearance gears can lock.
Using wood for bearing surfaces entails the exact same problems, showing in a different fashion. Pressure and friction will eventually bring out the grain pattern, oil penetrating over time can change dimension. That's why I do not recommend LV for high pressure contact/bearing.
Teflon creeps too much.
I really like extreme hardness contact with low contact area, it just requires quench and polish. Ruby by nature does it.
I assume others have already made tonearm bearings using watch style jewel techniques?
jn
This one uses ballbearings and jewelbearings, assembled and adjusted by a skilled watchmaker. No lubrication there.
THALES - Simplicity
THALES - Simplicity
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