The problem with a shaft with radius/half dome end is that the contact point with the thrust pad never falls on axis (imagine the thrust pad is never perpendicular to the axis of the shaft). So the contact point wanders on a circle when the platter rotates. This circle may have very small radius, but it is never zero. And there is a friction noise of the contact point wandering (sliding) around.
Its impossible to centre any bearing perfectly when its positioned/created by a device with a single linear axis of operation. Fortunately measuring the run out at the platter edge can show you that the tolerances that can be achieved are sufficient that we needn't worry about it causing bearing precession, and as far as noise goes it'll polish itself smooth and quiet soon enough. If Linn can achieve -72db A weighted bearing rumble it seems to me like the issue is well handled, even if the manufacture is not perfected.
NO bearing is perfect and must have some clearance or it will not work. Even NASA has a tolerance / clearance spec. Since I used a reamer .0005" over the shaft size and a little spring back from the Vespel, I figure there a .00025" tp .0003" clearance total as near as I can measure. My platter uses a mag-lev system consisting of a 4"OD x 3"ID X 1/2" thick neo ring magnet which can lift / float 134 lbs.The carbide shaft can be raised or lowered with fine adjustment in a locking collet type mechanism so I can regulate the amount of force on the thrust pad even though it can take enormous weight. I have the 55 lb plater with approx 4 lbs. of pressure on the thrust pad, and it works just fine. I also made use of MU metal in the magnet well to keep stray magnetic fields (if any) away from the top of the platter / cartridge. The friction difference between the bronze bearings I made and the Vespel bearing is substantial to say the least !!!! Hope this info helps.
audistar,
This turntable is a work in progress but is near completion. I made the turntable using a 15" Le blond lathe / Bridgeport milling machine etc. Plinth is made out of 3" thick granite with 1/2" stainless steel plate epoxied to the bottom. The granite / stainless plinth was made on a water jet machine by the son of one of our audio club members. I was done as an experiment and didn't cost me anything !!!! The plinth is 18" x 22" and weighs 131.8 pounds naked, Five holes were also water jetted, a 2" hole in the center for the bearing and four 1.25" holes in each corner for the 4 feet and arm stanchions. There is also a 7" diameter x 3.5" in from the center on the left side ( creating a half moon shape ) making a well for the motor. The top and bottom parts ( feet / arm stanchions ) are made from bronze and the feet are made from 2" diameter copper shaped to a cone 1 1/2" long. Before turning the copper I epoxied a 1" diameter Nylatron rod 1" long into each copper foot so the Nylatron will protrude about 5/8'. I suck with computers and posting pictures but will have friend help me soon. I live in Brooklyn N.Y. so anybody in the area would be welcome to look at this project and listen to my 4 way horn system using some field coil drivers and 845 SET mono blocks.
This turntable is a work in progress but is near completion. I made the turntable using a 15" Le blond lathe / Bridgeport milling machine etc. Plinth is made out of 3" thick granite with 1/2" stainless steel plate epoxied to the bottom. The granite / stainless plinth was made on a water jet machine by the son of one of our audio club members. I was done as an experiment and didn't cost me anything !!!! The plinth is 18" x 22" and weighs 131.8 pounds naked, Five holes were also water jetted, a 2" hole in the center for the bearing and four 1.25" holes in each corner for the 4 feet and arm stanchions. There is also a 7" diameter x 3.5" in from the center on the left side ( creating a half moon shape ) making a well for the motor. The top and bottom parts ( feet / arm stanchions ) are made from bronze and the feet are made from 2" diameter copper shaped to a cone 1 1/2" long. Before turning the copper I epoxied a 1" diameter Nylatron rod 1" long into each copper foot so the Nylatron will protrude about 5/8'. I suck with computers and posting pictures but will have friend help me soon. I live in Brooklyn N.Y. so anybody in the area would be welcome to look at this project and listen to my 4 way horn system using some field coil drivers and 845 SET mono blocks.
RE: central point of thrust bearing being exactly on center of shaft. Interesting how many ways there are to skin a cat! If you go back to Bill Firebaugh's descriptions of his original WellTempered turntable you will find him describing exactly why he chose to make the contact point off center. I am not agreeing or disagreeing with either approach. I chose to keep the thrust bearing on centers when I built my bearing. As far as longevity of polymer bearings vs solid metal bearings goes, I used "bearing Nylon" given me by the head machinist at my work place. The ball is a highly polished ruby jewel. That was 10 years ago about one year ago I inspected the bearing's condition and didn't find any trace of wear. I have yet to hear any noise from it. The thrust pad is the same nylon. As the saying goes, your mileage may vary.
Regards to all, I really enjoy following this forum.
BillG
Regards to all, I really enjoy following this forum.
BillG
audiostar,
I have to concentrate on building the turntable first but I do have most of the parts to start on a linear tonearm ala "Niffy" from the DIY linear tracking tonearm thread. I sent niffy a pair of 3mm tungsten carbide rods so he could build that fabulous arm !!! Niffy did the lions share of the work and research so sending him those rods was my small contribution to move the ball forward. So, the linear tracking tonearm is on my short list to build.
bgruhn,
Depending on the weight of your platter (about 12lbs - 15lbs) you can probably get away using Delrin / Nylatron etc. but when you get 50lb+ you start running into problems. I tried Nylatron, (graphite loaded) Vesconite, (look it up) Bronze, (worked fine) with Vespel being by far the best. Since I don't have research equipment, I could only do certain tests so what I did with all the bearings was to spin the platter with a .0005" dial indicator riding on the top edge of the platter and pushing down with a firm pressure at the platter edge and check for deflection. The bronze bearing deflected about .003" and then came back to within .002", the Nylatron bearing deflected .009" and only bounced back about .002 which means to me this material took a "set". I pushed down several more times and got similar measurements but the deflection varied too much for my liking. The Vesconite I thought held the most promise (extreme low friction, self lubricating etc.) but turned out to have more deflection (.014+) then the Nylatron and more varied bounce back. The Vespel (graphite loaded) was much harder / rigid then the other two polymers and performed much like the bronze bearing. The Vespel has extreme low friction, self lubricating with even lower friction when oil is used, machines beautifully with a nice finish. Now, this deflection is not readily visible by eye so use a dial indicator to check your bearing. Also, the Nylatron, Vesconite needed a larger clearance (.0015 or so over shaft size) to spin free. The Vespel only needed .0005 over shaft size to spin free. There is much less friction with Vespel and is more rugged then the other polymers tried. There are different grades of Vespel--you want SP-22 or SP-211 which has graphite and or moly disulphide mixed in. The cost of Vespel is extremely high but worth it to me. This has been my experience making turntable bearings but yours may vary. Hope this info helps.
I have to concentrate on building the turntable first but I do have most of the parts to start on a linear tonearm ala "Niffy" from the DIY linear tracking tonearm thread. I sent niffy a pair of 3mm tungsten carbide rods so he could build that fabulous arm !!! Niffy did the lions share of the work and research so sending him those rods was my small contribution to move the ball forward. So, the linear tracking tonearm is on my short list to build.
bgruhn,
Depending on the weight of your platter (about 12lbs - 15lbs) you can probably get away using Delrin / Nylatron etc. but when you get 50lb+ you start running into problems. I tried Nylatron, (graphite loaded) Vesconite, (look it up) Bronze, (worked fine) with Vespel being by far the best. Since I don't have research equipment, I could only do certain tests so what I did with all the bearings was to spin the platter with a .0005" dial indicator riding on the top edge of the platter and pushing down with a firm pressure at the platter edge and check for deflection. The bronze bearing deflected about .003" and then came back to within .002", the Nylatron bearing deflected .009" and only bounced back about .002 which means to me this material took a "set". I pushed down several more times and got similar measurements but the deflection varied too much for my liking. The Vesconite I thought held the most promise (extreme low friction, self lubricating etc.) but turned out to have more deflection (.014+) then the Nylatron and more varied bounce back. The Vespel (graphite loaded) was much harder / rigid then the other two polymers and performed much like the bronze bearing. The Vespel has extreme low friction, self lubricating with even lower friction when oil is used, machines beautifully with a nice finish. Now, this deflection is not readily visible by eye so use a dial indicator to check your bearing. Also, the Nylatron, Vesconite needed a larger clearance (.0015 or so over shaft size) to spin free. The Vespel only needed .0005 over shaft size to spin free. There is much less friction with Vespel and is more rugged then the other polymers tried. There are different grades of Vespel--you want SP-22 or SP-211 which has graphite and or moly disulphide mixed in. The cost of Vespel is extremely high but worth it to me. This has been my experience making turntable bearings but yours may vary. Hope this info helps.
bgruhn,
Depending on the weight of your platter (about 12lbs - 15lbs) you can probably get away using Delrin / Nylatron etc. but when you get 50lb+ you start running into problems. I tried Nylatron, (graphite loaded) Vesconite, (look it up) Bronze, (worked fine) with Vespel being by far the best. Since I don't have research equipment, I could only do certain tests so what I did with all the bearings was to spin the platter with a .0005" dial indicator riding on the top edge of the platter and pushing down with a firm pressure at the platter edge and check for deflection. The bronze bearing deflected about .003" and then came back to within .002", the Nylatron bearing deflected .009" and only bounced back about .002 which means to me this material took a "set". I pushed down several more times and got similar measurements but the deflection varied too much for my liking. The Vesconite I thought held the most promise (extreme low friction, self lubricating etc.) but turned out to have more deflection (.014+) then the Nylatron and more varied bounce back. The Vespel (graphite loaded) was much harder / rigid then the other two polymers and performed much like the bronze bearing. The Vespel has extreme low friction, self lubricating with even lower friction when oil is used, machines beautifully with a nice finish. Now, this deflection is not readily visible by eye so use a dial indicator to check your bearing. Also, the Nylatron, Vesconite needed a larger clearance (.0015 or so over shaft size) to spin free. The Vespel only needed .0005 over shaft size to spin free. There is much less friction with Vespel and is more rugged then the other polymers tried. There are different grades of Vespel--you want SP-22 or SP-211 which has graphite and or moly disulphide mixed in. The cost of Vespel is extremely high but worth it to me. This has been my experience making turntable bearings but yours may vary. Hope this info helps.[/QUOTE]
Hi Hottatoo,
Thanks for the information. Good Stuff! My platter is inch thick 12" dia CORIAN. Clearly way under 50 lbs. So yes I can get away with it. At the time I built the TT it was way heavier than all the commercial TTs on the market. In fact it works so well for my needs and ability to discern further improvement that I will never try building a 55 pound platter. BTW it helps to see where you are coming from. It puts some of the issues you feel strongly about in proper perspective. THANKS!
BGRUHN
Depending on the weight of your platter (about 12lbs - 15lbs) you can probably get away using Delrin / Nylatron etc. but when you get 50lb+ you start running into problems. I tried Nylatron, (graphite loaded) Vesconite, (look it up) Bronze, (worked fine) with Vespel being by far the best. Since I don't have research equipment, I could only do certain tests so what I did with all the bearings was to spin the platter with a .0005" dial indicator riding on the top edge of the platter and pushing down with a firm pressure at the platter edge and check for deflection. The bronze bearing deflected about .003" and then came back to within .002", the Nylatron bearing deflected .009" and only bounced back about .002 which means to me this material took a "set". I pushed down several more times and got similar measurements but the deflection varied too much for my liking. The Vesconite I thought held the most promise (extreme low friction, self lubricating etc.) but turned out to have more deflection (.014+) then the Nylatron and more varied bounce back. The Vespel (graphite loaded) was much harder / rigid then the other two polymers and performed much like the bronze bearing. The Vespel has extreme low friction, self lubricating with even lower friction when oil is used, machines beautifully with a nice finish. Now, this deflection is not readily visible by eye so use a dial indicator to check your bearing. Also, the Nylatron, Vesconite needed a larger clearance (.0015 or so over shaft size) to spin free. The Vespel only needed .0005 over shaft size to spin free. There is much less friction with Vespel and is more rugged then the other polymers tried. There are different grades of Vespel--you want SP-22 or SP-211 which has graphite and or moly disulphide mixed in. The cost of Vespel is extremely high but worth it to me. This has been my experience making turntable bearings but yours may vary. Hope this info helps.[/QUOTE]
Hi Hottatoo,
Thanks for the information. Good Stuff! My platter is inch thick 12" dia CORIAN. Clearly way under 50 lbs. So yes I can get away with it. At the time I built the TT it was way heavier than all the commercial TTs on the market. In fact it works so well for my needs and ability to discern further improvement that I will never try building a 55 pound platter. BTW it helps to see where you are coming from. It puts some of the issues you feel strongly about in proper perspective. THANKS!
BGRUHN
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When essentially using flat washers, or an expensive version of that, I have found that three together works much better than a single.
I would tend towards a phenolic or just ground and polished steel with some lubricant and a square cross section, light rubber seal around the perimeter. Often a phenolic with steel on each side works too.
For the radial load, a nice ceramic bearing would be my choice.
Nylon absorbs water, and as you have found, takes a set like that. Torlon is pretty cool stuff, I wonder how it would work for trust washers?
I would tend towards a phenolic or just ground and polished steel with some lubricant and a square cross section, light rubber seal around the perimeter. Often a phenolic with steel on each side works too.
For the radial load, a nice ceramic bearing would be my choice.
Nylon absorbs water, and as you have found, takes a set like that. Torlon is pretty cool stuff, I wonder how it would work for trust washers?
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