Polymer bearings as turn table main bearings.

[Conrad Hoffman]

Since my last post I've done some controlled tests on thrust bearings. More details are over at Vinyl Engine. The results are on my web site at ConradHoffman.com Basically, if you have a soft spindle shaft where the radius is cut and polished into the end, you want something that won't damage the radius over time. There are very few things that will do that. Teflon is good, but it lubricates by shedding layers of itself, and will eventually wear out. It also flows and I'm not a big fan of the stuff. I had high hopes for expensive high-tech polymers like graphite and Teflon filled Vespel (very expensive) and similarly lubricant loaded PEEK, but they didn't treat the radius as nicely as you'd think. For soft spindles, a small polished disk of Lignum Vitae can't be beat. It's harder than Teflon and will likely outlive both you and the turntable with no change in performance over time. It has to be the real stuff, not Argentinian. Run it in oil. I bear against the end grain because it's a bit harder and tends to save material when fabricating, but either way works fine. If you can't get that, vacuum impregnate a piece of rock hard maple or cherry with a good synthetic oil or possibly petroleum wax. My theory is that the grain structure gets lubricant right to the point of maximum pressure, which the other materials can't quite do.

If you have a replaceable ball, get a hard ceramic one like silicon nitride. That eliminates the wear problem on the ball. Then choose whatever thrust surface suits your fancy. I haven't done controlled tests on this, but my guess is hardened tool steel may be a good choice.

Why tables with soft spindles and integral radi even exist, I don't know, but there are a lot of them out there, including both of mine.

The journal section of the bearing is, I think, even more important than the thrust surface. More on that later if anybody's interested.

Best,
Conrad

[jeff spall]

The Lignum Vitae is a very interesting idea Conrad. I have had a small piece of it around for years and never used it. I believe it was used for clock bearings at least 200 years ago, mainly for it's self-lubricating qualities.

I think I may try a little disc of it in place of the acetal thrust pad on my Teres. Thanks!

[Conrad Hoffman]

Not to mention shaft bearings for submarines and destroyers, plus water turbines. When you sand the disk, be careful not to embed abrasive particles in the surface. I usually sand on 500 grit paper, then finish polish on 12 micron metallurgical paper. It's getting rare, but there's lots of reclaimed wood available. I figure one old policemans night stick would yield enough Lignum Vitae disks for hundreds of turntables, so I don't worry too much about the environmental issues. Heck, an old Lignum bowling ball would probably supply a disk for every vinyl player in the world who wanted one!

On the journal bearings, IMO there isn't a bearing made that can compete with an oil film in terms of noise. That means that the material isn't very important, but the geometry is. IMO, Oilite is probably not a good choice. It wears well but I'm not sure about the noise. I wouldn't waste my time with polymers of any type. I'd want a honed bronze bore with perfect geometry (reaming isn't good enough) and a highly finished shaft (needs to be external honed or superfinished- grinding and soft polishing isn't good enough) running with a couple tenths clearance, lubricated with a good synthetic oil. Anything that isn't floating on a film of oil will create rubbing noises that get transmitted to the platter. FWIW, I've tried Lignum sleeve bearings and they work extremely well, but you can't beat an oil film. Very few bearings achieve the necessary float, either because they aren't made to sufficient accuracy, or because they didn't put enough thought into how the oil reservoir would work. My Thor-ject, after some mods, achieves a good float, but only if I pay close attention to the oiling.

[SY]

I had high hopes for expensive high-tech polymers like graphite and Teflon filled Vespel (very expensive) and similarly lubricant loaded PEEK, but they didn't treat the radius as nicely as you'd think.

What you want is something like PEEK or UHMWPE heavily loaded with tungsten disulfide. The nano fullerene stuff from ApNano would be ideal.

[brianco]

Originally Posted by jeff spall

The Lignum Vitae is a very interesting idea Conrad.............
.............I think I may try a little disc of it in place of the acetal thrust pad on my Teres. Thanks!

For those in the UK old bowling woods() are a good source of Lignum Vitae.

[tinitus]

Originally Posted by brianco

For those in the UK old bowling woods() are a good source of Lignum Vitae.

Man, I would like one of those

I think that hardwood is called "pukkenholt" here

But maybe its "puckenholt", or "puckenhol"

Anyway, I dont think the major issue with a bearing is wear, but more the problem with "rumble" noise
And maybe friction
Which made me think about air supported bearing, back then
I was close to trying it, but didnt
I hated those airpumps

[Conrad Hoffman]

Well, IMO whatever wonderful performance one can get when the parts are perfect, degrades as they wear. That's another thing about oil films and air bearings- they don't wear. Does anybody actually get rumble anymore? I associate that with the little rolling bearing rings used in cheap changers. A decent point contact system shouldn't rumble, but the journals can certainly generate a scratching noise that gets transmitted to the platter. Motor noise is another issue. The plinth mounted motor in my Thor-ject is easily audible if you remove the belt, rest the stylus on a record, listen with headphones, then turn it on and off. There's nothing "wrong" other than the motor should have been better isolated.